Re: [volt-nuts] Solartron (aka Schlumberger) 7081

[Dr. David Kirkby (Kirkby Microwave Ltd)]

On 27 September 2017 at 11:09, David C. Partridge <
david.partri...@perdrix.co.uk> wrote:

> I assume you've seen my website:  Solartron7081/index.htm>?   The last corporate owner of the Solartron
> brand was Ametek, and their branch in Farnborough did calibrate them up to
> at least the late "noughties".  I don't know if they still do.   The full
> service manual and factory calibration instructions are on my website.
>

FWIW, I received an email from Ametek saying:

"Support on this product has now ceased – but please find attached, copy of
the original brochure / operating manual which may be of use. The company
in the UK which would do a good job is CALMET at Kingston"

Calmet Laboratory Services are a UKAS accredited calibration laboratory.
I've not looked at what their uncertainties are.

I stuck copies of the documents sent to me by Ametek at

http://www.kirkbymicrowave.co.uk/manuals/Solartron/

The MD5 checksums are

drkirkby@hawk:~/km.new/manuals/Solartron$ digest -a md5 *
(7071_7081_brochure.zip) = 26db83139e8a765f1083c972a1a507a7
(7081_Operating_Manual_Part_1.pdf) = 2a396d8653815cf450c215a28513b3c3
(7081_Operating_Manual_Part_2.pdf) = d861d8dc3c4db187e61d27b8fde35eb2

Dave
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Re: [volt-nuts] Best way to measure micro Ohms

[Dr. David Kirkby (Kirkby Microwave Ltd)]

On 28 September 2017 at 19:17, ed breya  wrote:

> Hmm. Alternating the direction of the current repeatedly and processing
> the results - sure seems like that is fundamentally an AC measurement too,
> despite using DC measurement equipment.
>
> Ed


I guess the point is current/voltage can be measured accurately before the
direction is changed, whereas that's less so with AC. But I don't need
great accuracy in trying to sort out if there are contact resistance
problems caused by things such as copper slip, or aluminum oxides. I need
to measure very low resistances, but not with great accuracy.

For me at least, I have no Fluke 5520A, or low resistance meter.  The
Agilent programmable DC power supplies I have are not designed for
precision measurements.

But the lock-in amplifier I already had, and the audio amplifier was cheap.

Sometimes you have to make do with what you have, or can justify buying.

Dave
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Re: [volt-nuts] Best way to measure micro Ohms

[Dr. David Kirkby (Kirkby Microwave Ltd)]

On 27 September 2017 at 22:22, ed breya  wrote:

> I just noticed this discussion recently, so I'm late to the party, but
> that never stops me from adding my one-cent's worth.
>
> David, regardless of the aluminum and other material issues, I think your
> initial idea of using a lock-in analyzer is definitely the way to go. I'm
> very fond of LIAs, although I seldom need or use them, so my opinion is
> somewhat biased. I have five - two Ithaco 391A orange-band, a PAR 5204, an
> SR830 and SR850.
>


Yes, me too. I have used a number over the years, the nicest of which was
the Stanford Research SR830. The EG&G 7260 I own has rather user-hostile
interface. There's not even a power switch on the front, and I'm not sure
if there's even on on the rear.

The following link might interest others who don't know about these
instruments

http://www.thinksrs.com/downloads/PDFs/ApplicationNotes/AboutLIAs.pdf



>
> If you use an audio power amplifier for driving the experiment, you can
> rig it up so that the LIA can be used to measure the drive current as well
> as the resulting voltage drop. Let's say the amplifier is for 8 ohms, so
> you put a few ohms in series with the output, then from there into a
> precision one-ohm sampling resistor, then into the RUT, forming a voltage
> divider. The RUT is expected to be in the micro-ohm region, which is many
> thousands of times smaller than the sampling R, so its tiny voltage drop
> will be negligible, allowing the sample voltage to be a good representation
> of the test current. You could also just treat the whole thing as a voltage
> divider and calculate the "exact" results.
>

I did purchase a Radio Shack 100 W Public address  I will set this up
later.


>
> This could be fun and interesting. There are plenty of pieces and
> variables involved to experiment with to optimize the measurement, and lots
> of other tricks available to enhance it if necessary.
>
> Ed


Yes, with lock-in amplifiers there are an almost infinite set of
possibilities of how to do the actual measurement. I don't know if the
reference output is a sine wave or square wave on this unit. I have the
option of using a Stanford Research DS345 30 MHz function generator to
generate a sine wave if needed. There are almost a million things that one
can change.

Dave
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Re: [volt-nuts] Solartron (aka Schlumberger) 7081

[Dr. David Kirkby (Kirkby Microwave Ltd)]

On 27 September 2017 at 11:09, David C. Partridge <
david.partri...@perdrix.co.uk> wrote:

> I assume you've seen my website:  Solartron7081/index.htm>?


Yes I had. I believe your site has more about the meter than the sum total
of the rest! I was surprised how little information there is about the
meter available.

I downloaded the user manual, but not the service manual. I will give this
some more consideration. I can get the instrument for 600 Euros + shipping
from Germany, so its not a fortune, but the issue of calibration is
concerning me a bit, as is the fact that a few people have sent me emails
to say they are noisy and slow.

I wanted to make some low-resistance measurements the other week, and was
considering getting an Agilent 34420A. I'm wondering if that might be a
better investment.

Of course, it would be nice to have a 3458A and a 34420A, but that is out
of the question due to the cost.


> The last corporate owner of the Solartron brand was Ametek, and their
> branch in Farnborough did calibrate them up to at least the late
> "noughties".  I don't know if they still do.   The full service manual and
> factory calibration instructions are on my website.
>

Someone else sent me a private email, and gave me there name too, so I have
sent an email to them.

>
> Sadly the Commodore PET software to control the calibration process was
> never released (AFAIK)?
>


>
> They are easy to calibrate if you have a good calibrator (I have a 4808
> which is now fully working).  I live in Kenilworth so not too far from  you.
>
> Dave
>

I can't drive as I'm epileptic, so so you are not quite as easy to get to
as you might first appear. I guess it can be shipped easy enough.

Dave
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[volt-nuts] Solartron (aka Schlumberger) 7081

[Dr. David Kirkby (Kirkby Microwave Ltd)]

I've been offered a Solartron 7081 8.5 digit meter, but are having
difficulty finding out much about this. Is there any "official" place where
these can be calibrated? As far as I can see from a search of Companies
House

https://beta.companieshouse.gov.uk/company/02858371

Solartron Instruments Ltd was dissolved in 2013. I don't know if there is
really anybody able to calibrate these things.

Clearly the meter is not in the same league as a 3458A. but I've been
offered it for little more than the cost of a new Keysight  U1282A 4.5
digit handheld meter! I've no idea when it was last calibrated, but I
suspect long ago.




Dr. David Kirkby Ph.D CEng MIET
Kirkby Microwave Ltd
drkir...@kirkbymicrowave.co.uk
http://www.kirkbymicrowave.co.uk/
Tel: 01621-680100 <01621%20680100> / +44 1621-680100 <01621%20680100> (0900
to 2100 UK time)

Registered office: Stokes Hall Lodge, Burnham Rd, Althorne, Essex, CM3 6DT,
UK.
Registered in England and Wales, company number 08914892.
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Re: [volt-nuts] Power consumption of 3458A reference board / fitting one in a 3457A

[Dr. David Kirkby (Kirkby Microwave Ltd)]

On 23 September 2017 at 18:03, Tom Knox  wrote:

> If you want I will send you a few to play with for a few months.
>

Thank you very much. I'd like to have a play. I sent you a private email.

Someone suggested using the DCV:DCV ratio mode to look at two references,
but I don't see this facility on the 3457A. I think the only way to compare
two of them would be to put them in series, but back-to-back to subtract
the voltages, and look at the difference on the 3457A.


>
> Thomas Knox
>

It's odd there's someone selling LTZ1000A chips on eBay at $50 each.

http://www.ebay.com/itm/1x-LTZ1000ACH-Ultra-Precision-Reference-LTZ1000A-/111325506311

It looks like they have been removed from PCBs with a sledge hammer - they
are heavily scratched and/or dented. The sellers seems to have sold quite a
few, yet the chips are only marginally more expensive if bought new from
the manufacturer.

Dave
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Re: [volt-nuts] Power consumption of 3458A reference board / fittingone in a 3457A

[Dr. David Kirkby (Kirkby Microwave Ltd)]

On 24 September 2017 at 08:52, Bill Gold  wrote:

> David:
>
> Your answer to question #1.  I have a spare reference board setup to be
> powered up on the bench.
>
> I measure around 36 ma when it starts cold and then around 30 ma when
> it
> warms up to operating temp.  This is at 18 volts.
>
> Of course this is in an enclosed, insulated box.  If the LTZ 1000
> starts
> to cool off then the current goes up again.
>
> Bill
>


Thank you. That's interesting. Ignoring the warmup time, which would be a
small fraction of 48 hours, if one assumes 30 mA for 48 hours, that's 1440
mA hr. So 15 x 1.2 V Nickel Metal Hydride  AA cells would easily do that,
as they are available up to about 2400 mA hr.  It means it is practical put
a 3458A reference board in a box, and ship it to someone else for measuring
whilst keeping is powered up in transit.

Dave
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[volt-nuts] Power consumption of 3458A reference board / fitting one in a 3457A

[Dr. David Kirkby (Kirkby Microwave Ltd)]

I've got two different, but not totally unrelated questions.

1) Does anyone know what is the power consumption of the 3458A reference
board? I was thinking of getting one, boxing it up with a battery, that
allowed it to keep running without mains power. I would like to know the
energy storage the batteries would need to keep it running for 2 days.

2) Would there be any point fitting a similar board, with an LTZ1000A in a
3457A 6.5 digit meter? Would it be practical? I wonder if the drift on the
3457A's reference is significant, and so a LTZ1000A would be a worthwhile
upgrade. Or is the main drift not the voltage reference, and so such an
"upgrade" would be a total waste of time/money?

Dave
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Re: [volt-nuts] Best way to measure micro Ohms

[Dr. David Kirkby (Kirkby Microwave Ltd)]

On 19 September 2017 at 20:32, Charles Steinmetz 
wrote:

Looking at the pix, there appear to be lots of aluminum joints due to the
> "built-up" construction, maximizing the potential for the sort of troubles
> you are having.  I would re-make the piece in brass, doing everything
> possible to use as few pieces as possible (for example, by milling recesses
> into one piece rather than building up a compound piece from more easily
> machined sub-parts).
>

A practical problem is the tools available to me. The U-channel was
machined by someone in my radio club, and the rest I made myself using
nothing more than a drill and hand tools. It would be nice to make more out
of one piece, but it would require better tools than I have readily
available. There are certainly engineering companies that could do a better
job, but it would be quite costly.


>
> I would also plate everything in silver.


Yes, I was thinking that.

I contacted one local plating company, and asked them about silver plating.
The lady said they did not do brass, but did aluminum. This struck me as
odd, as they had plated brass for me before -  but that was gold, not
silver. From what I read, aluminum is a lot more tricky to plate than
brass. I sent them a drawing some time ago, but got no response. I will
have to chase them up.

The conductivity of aluminum is better than brass, and since I am mainly
interested in low frequencies (1.8 to 28 MHz), the skin depth will be
deeper than it is possible to silver plate. So the "RF resistance" might
well be set by the material its constructed from, rather than any plating.
Of course, if the plating stops an oxide building up, that should cut the
losses.

But certainly something is not quite right, as the RF losses are higher
than expected. I was keen to see if any of those could be explained by DC /
low frequency losses.

Best regards,

Charles


Dave, G8WRB
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Re: [volt-nuts] Best way to measure micro Ohms

[Dr. David Kirkby (Kirkby Microwave Ltd)]

On 18 September 2017 at 23:28, george  wrote:

> The reason that DC is used commercially to measure resistance is simple,
> if you use AC you may well get the reactive component as well as the
> resistance coming into play.
>

That may not be an an issue with a dual-phase lock-in amplifier, as the
phase angle of the voltage can be resolved. In fact, it hints at something
I have long thought about - using a lock-in amplifier as an LCR meter. I do
however have a decent HP 4284A LCR meter, but it can't read very low
impedances in the micro ohm range.

I've put a couple of offers in on micro-ohm meters, but also bought a 150 W
public-address (PA) audio amplifier for £25 (around $35). With that, and
the lock-in amplifier, I should be able to make measurements, although I
accept the uncertainty will be higher than a dedicated micro ohm meter.


>
> Such low resistance measurements commercially are normally only made on
> high current power distribution networks as part of a periodic test regime
> where you need to determine the quality/resistance of such things as bus
> bar joints/connections and loop resistance.
>
> It is not a good idea to use copperslip around aluminium, there is an
> aluminium based version that should be used, but, be warned, just like
> copperslip it is an insulator, try putting your meter probes, set for
> resistance, into a tub of both, I have.  I do not know just why but the
> aluminium version is just like sand, it gets everywhere when you use it.
>

So does Coperslip! It sure is messy, but I was given it free, and it
stopped a leak.


>
> To check your joint I would use a four wire Kelvin set up using say 10
> Amps from my constant current bench supply and then use my Keithly 616
> digital  electrometer to measure the voltage/s present across the joint, a
> simple application of Ohms law will then give the resistance.
>

I don't have such an instrument, whereas the audio amplifier cost me very
little, and I already have the lock-in amplifier. I did buy a lower powered
(15 W, $5) amplifier from China, but thought by the time I box it up with a
PSU, it would cost more than a PA amplifier with a built in mains supply.
The PA amp, being in the UK, should also arrive a lot quicker than the
units from China.


>
> 73 George G6HIG
>

Dave, G8WRB
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Re: [volt-nuts] Best way to measure micro Ohms

[Dr. David Kirkby (Kirkby Microwave Ltd)]

On 18 September 2017 at 18:36, Todd Micallef  wrote:

> Dave,
>
> Another meter is the Cambridge LOM-510A. I am not sure if it is in your
> budget but there has been a review made on EEVBlog. There is one currently
> on eBay with a current amplifier that I have never seen before today. It
> may be worth reviewing if it meets your needs.
>
> Todd
>


Hi Todd,
Something struck me as odd about the *model* number LOM-510A.

When I google the Keithley 580, I see a *paid advert* for an IET Labs
LOM-510A.

http://www.ietlabs.com/lom-510.html?gclid=CjwKEAjw3f3NBRDP_NHS9fq53n4SJACKIfEYZT_jyIk_TKn0gqEkzvfxwKASIpIZTcDFJfJlMwvnRRoCZYHw_wcB

But it looks nothing like the Cambridge LOM-510A on eBay

http://www.ebay.com/itm/Cambridge-510A-Micro-Ohmmeter-DLRO-Includes-NEW-leads-NIST-Calibrated-LOM-510A-/291956733548

It seems a bit odd for two manufacturers (IET Labs and Cambridge
Instruments) to both have the exact same model number (LOM-510A) for an
instrument with identical functionality (micro ohms). Yet photographs of
the two instruments show they look similar, but are not identical. The IET
Labs one appears to have a couple of extra switches.

Just to make something appear even more odd, the IET Labs has a link to a
review on EEVblog.

http://www.eevblog.com/forum/testgear/ie/30/

but the picture shows Cambridge Instruments, but the title shows IET Labs.



Dave
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Re: [volt-nuts] Best way to measure micro Ohms

[Dr. David Kirkby (Kirkby Microwave Ltd)]

On 17 September 2017 at 21:58, Mitch Van Ochten <
mi...@vincentelectronics.com> wrote:

> The Keithley 2002 uses DC but automatically takes a reading of any offset
> voltage and subtracts it (offset compensation).  Rated accuracy on the 20
> ohm range (2 years) is +/- 26 ppm, and with 10 averages it has a resolution
> of 0.1 microohms.
>
>
> Best regards,
>
> mitch
>

Also very pricy!

I've made an offer on a Keithley 580 micro ohm meter, and ordered a couple
of $3 audio amplifier boards. I will try one with the lock-in amplifier. It
it does not work, or works poorly, it will not have broken the bank.

Dave
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Re: [volt-nuts] Best way to measure micro Ohms

[Dr. David Kirkby (Kirkby Microwave Ltd)]

On 17 September 2017 at 20:12,  wrote:

> The question is what accuracy you need.
>

No a lot. I just want to find out if there's any voltage drops that are
significantly higher than I would expect. The unit makes an RF transmission
line, and the loss at RF is significantly higher than predicted by a
computer model, which takes into account the skin depth of the materials.
I'm wondering if there's something odd going on. I suspect the problem is
the current in the aluminum is not being computed properly due to the oxide
on the surface. But I just wanted to make sure there was no unexpected DC
resistance. I don't think there will be, but I want to climate that
possibility.


> The classical way to do that (achieving high accuracy) is to apply a known
> accurate current (say 10A) and measure the voltage drop accross the rod
> with a nanovoltmeter.
> As the piece of aluminum is isothermal you should not expect a big
> thermovoltage. You could also compensate for this by reversing the current
> and take the average, also by nulling the voltage reading prior to applying
> any current. Generating precisely known AC currents (low uncertainty) is
> difficult (i.e. measuring it precisely), therefore DC currents are ususaly
> used also in metrology for this.
> If you do some internet search you will find metrology reports about this.
> If you do not have a nanovoltmeter you could build a measurement amplifier
> with not that much of an effort (based on chopper amp or low drif precision
> opamp)
>

The only nV meter I have is the lock-in amplifier, which has a full-scale
sensitivity of 2 nV to 1 V in a 1-2-5 sequence.

The only instrument I have able to measure > 3 A of current is a handheld
multimeter. One of my power supplies can supply 35 A, and has an ammeter in
it. I don't have any particularly accurate means of measuring DC current
outside the limited of the 3457A.

In terms of simplicity, getting a $10 audio amplifier from China and using
the lock-in amplifier is the way to go, but I accept a metrologist would
not like that idea!

Dave
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[volt-nuts] Best way to measure micro Ohms

[Dr. David Kirkby (Kirkby Microwave Ltd)]

I want to measure the resistance between two bits of aluminum. Each are 40
x 30 mm across. One is 250 mm long, the other is 8 mm long. I'm wondering
is surface oxides are on the faces, so despite being held together with
bolts, the resistance is perhaps not as long as I would expect. There's
also a layer of "copperslip" between these, to provide a waterproof joint.
That might be adding unnecessary resistance.

What sort of instrument is (if any) capable of measuring this? I have a 6.5
digits HP 3457A with a 30 Ohm 4-wire mode, but the uncertainty is 0.0065% +
20315 counts. Those 20315 counts are a lot!

I can't seem to see much in the way of commercial instruments for very low
resistance measurements. I would have thought an AC source was needed, yet
they all seem to use DC. Why?

I've thought of hooking a signal generator up to an audio amplifier capable
of driving a few amps, passing that through the joint, then using an EG&G
7260 lock-in amplifier to measure an AC voltage across the joint.

Any better suggestions?

Can anyone explain why commercial instruments use DC, despite that small DC
voltages will be developed by unwanted thermocouples? I would have thought
that using AC was a no-brainer no very low resistance measurements, but
commercial instruments don't use to use AC.


Dr. David Kirkby Ph.D CEng MIET
Kirkby Microwave Ltd
drkir...@kirkbymicrowave.co.uk
http://www.kirkbymicrowave.co.uk/
Tel: 01621-680100 / +44 1621-680100 (0900 to 2100 UK time)

Registered office: Stokes Hall Lodge, Burnham Rd, Althorne, Essex, CM3 6DT,
UK.
Registered in England and Wales, company number 08914892.
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Re: [volt-nuts] Screws in bottom of 3457A

[Dr. David Kirkby (Kirkby Microwave Ltd)]

On 11 June 2017 at 08:19, John Phillips  wrote:

> If you are sending it in you could just tape the cases halves together and
> let them replace the screws. You may want to check with them about it but I
> would be more surprised than not if they charged you for it.
>

I don't want to push my luck. From what I understand, if something goes
into Keysight for "repair", the repair is performed before any measurements
are taken of the instrument. When my 4284A LCR meter was sent to Keysight,
I did not get any information about the state it was sent, as a software
upgrade (support for 2 m and 4 m cables) was added before the instrument
was calibrated. The upgrade was free.

So they would seem to be doing me a favor by checking the meter, then
changing the battery, then checking calibrating it. This is not normal
practice, so I'm not keen to send the 3457A in bits, if I can put it back
together. M4 screws are very easy to obtain in the UK, I will see if I have
some 45 / 50 mm ones, but if not, will order some.

Dave
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[volt-nuts] Screws in bottom of 3457A

[Dr. David Kirkby (Kirkby Microwave Ltd)]

I've done something rather stupid with my 3457A. I took it apart to replace
the battery, and then seem to have mislaid the screws that hold the thing
together. As far as I can see, there are 4 screws in the base. The problem
is, I don't know what type they are. Could anyone with a 3457A tell me the
type - a photo with dimensions on emailed to me would be great. I'm
guessing these will be an American thread of some sort. I can get these in
the UK, although not quite as readily as metric. But of course its
difficult if you don't know what you want.

FWIW, I decided not to change the battery. Having visited Keysight in
February, their cal lab manager said if I asked for it, they would check
the calibration of the instrument before replacing the battery, then
replace the battery at zero cost*, then calibrate it. So I would get before
and after data anyway.

* This assumes the battery is not very expensive. If the battery was
expensive, I'd have to pay for the battery.

My 3457A has not seen a cal lab in a couple of decades, so I think it
deserves a check over.

Dave
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Re: [volt-nuts] Anyone got a photo of a 3458A with "new volt" printed on it?

[Dr. David Kirkby (Kirkby Microwave Ltd)]

On 31 May 2017 at 20:57, Frank Stellmach  wrote:

> >> I was chatting to someone from my radio club in the pub last night, and
> somehow we got onto the definition of a volt.
> >> I'd like to try to research this, and perhaps give a talk at our radio
> club on it.
>
> David, there was very good Swiss metrology school in 2007, Les Houches,
> where Blaise Jeanneret published a concise presentation about the Volt, its
> definition and history. Unfortunately, this is nowhere online anymore.
>
> I could send it to you, if you were interested.
>
>
> Frank
>

Sure Frank, that would be good. I  assume you have a PDF, but if not I can
pay postage/copying costs. The email address you see I'm sending from is
valid, and can accept attachments.

If you can email it, I can stick it on a web server, and let others find
it, as I doubt I'm the only one interested on volt-nuts.


Dave
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[volt-nuts] Anyone got a photo of a 3458A with "new volt" printed on it?

[Dr. David Kirkby (Kirkby Microwave Ltd)]

IIRC, there are reports of 3458A's being sent to Agilent, and having a
sticker to say the "new" standard volt was used - I assume the last time
the volt was redefined.

I was chatting to someone from my radio club in the pub last night, and
somehow we got onto the definition of a volt. I'd like to try to research
this, and perhaps give a talk at our radio club on it. I'd like to get a
picture of a 3458A with such a sticker if I could.

Dave


Dr. David Kirkby Ph.D CEng MIET
Kirkby Microwave Ltd
Registered office: Stokes Hall Lodge, Burnham Rd, Althorne, Essex, CM3 6DT,
UK.
Registered in England and Wales, company number 08914892.
http://www.kirkbymicrowave.co.uk/
Tel: 07910 441670 / +44 7910 441670 (0900 to 2100 GMT only please)
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Re: [volt-nuts] Short term "standard" cell?

[Dr. David Kirkby (Kirkby Microwave Ltd)]

On Sun, 12 Mar 2017 at 17:03, Frank Stellmach 
wrote:

> Hi Chris,
>
>
>
> Therefore,  instead of poking around with these mediocre 10V
> "references", I'd look for a possibility to get access to a 3458A, maybe
> there's a friendly volt-nuts nearby.
>
> Frank
>

There are a number of reference boards supposedly removed from 3458As on
eBay. Assuming they are non counterfeit (not necessarily a valid assumption
for items on eBay), how easy would they be to integrate into a box to make
a stable reference?

The LTZ1000A chip is about $50 new, but to make a stable reference you need
quite expensive resistors, so a used 3458A reference is attractive. But I
don't know if problems making low thermal EMF joints might totally ruin the
potential performance.




-- 
Dr. David Kirkby Ph.D CEng MIET
Kirkby Microwave Ltd
Registered office: Stokes Hall Lodge, Burnham Rd, Althorne, Essex, CM3 6DT,
UK.
Registered in England and Wales, company number 08914892.
http://www.kirkbymicrowave.co.uk/
Tel: 07910 441670 / +44 7910 441670 (0900 to 2100 GMT only please)
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[volt-nuts] Don't bother changing a 3457A battery if sending to Keysight for calibration.

[Dr. David Kirkby (Kirkby Microwave Ltd)]

Today I went to Keysight in Winnersh in the UK for a seminar on RF material
measurements.

We were given the opportunity to go for a 20 minute tour of the repair and
calibration labs. Needless to say I took up the opportunity.

There are 3 areas at Keysight in the UK.

* Repair
* Main calibration area
* Metrology (which we didn't go into in order not to change the
temperature, but one can see a lot as its surrounded by glass)

I asked whether a 8.5 digit 3458A can be calibrated there,  since somewhere
I had heard that a 3458A could not be calibrated in the UK.  I was told a
3458A can be calibrated there.

I asked about calibration of a 6.5 digit 3457A, and wherever I should send
it for cal having just removed the battery, which loses the calibration
data, or hotwire it to save the calibration data. I was told that if the
battery is available,  and not more than £30~£40, then they would change
the battery free.

I mentioned that I was a little disappointed that when I sent an 4284A LCR
meter for a free software upgrade and calibration,  no data was provided
about the instruments state before the calibration.  I was told that if an
instrument is repaired or upgraded,  even if just a software upgrad, the
repair would normally happen in the repair section, before being moved to
the calibration area, so one will not get any data about the status when it
was received.

However,  if one asks for data before an item to serviced, they will
provide that, then service it,  then calibrate it and provide that data
too. Apparently there would be no extra cost.

I don't know how policies might vary at other Keysight cal labs, but I got
the feeling that at Winnersh in the UK,  they are quite flexible.

So I am going to send my 3457A for calibration,  but ask for

1) Data on condition as received.

2) The battery to be changed.

3) Condition after it's been calibrated.

I got the business card of the individual who said that this can all be
done for no extra charge.

Obviously Keysight is not the cheapest place to get a 6.5 digit 3457A
calibrated,  but it seems that you get quite a bit for your money.

Dave.
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Re: [volt-nuts] PCB Artist

[Dr. David Kirkby (Kirkby Microwave Ltd)]

On 14 Dec 2016 14:14, "Dan Kemppainen"  wrote:
> If it's a one off board, with a handful of components anything should
work. You can always redraw it later in something else. If you have 500
components, differential signals, and controlled impedance stuff that's a
different story.

A handful of surface mount components can easily exceed 500!

But like you,  I find the idea of using an open source program much more
attractive.

Someone mentioned earlier about making PCBs on a milling machine. That
needs a different approach than to etching.  To reduce tool wear one should
leave as much copper on the board as possible,  removing only that which is
essential to keep.

Thinking of it logically,  leaving as much copper on the board as possible
will preserve the useful life of the etchant, but most people leave remove
as much copper as possible, except for RF boards.

Dave.
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Re: [volt-nuts] [time-nuts] OT: ExpressPCB (cross-post from volts-nuts)

[Dr. David Kirkby (Kirkby Microwave Ltd)]

On 9 December 2016 at 19:58, BIll Ezell  wrote:
> Sorry if I'm behind the times, just did a new project that required a pcb,
> and ExpressPCB is my go-to vendor for one-off boards. I just noticed they
> now provide the low-cost boards (fixed size, 3x5, quantity 3) that I've
> always ordered with silk screen and solder mask for $71. I got my latest
> boards that way and they're beautiful. No relationship to them, just a happy
> customer. You can still get the barebones boards for $51.

You also lock yourself into one vendor. There's other free software,
like Kicad, where you can export files that many PCB manufacturers
use. So you avoid vendor lock-in.

https://en.wikipedia.org/wiki/Vendor_lock-in

If the company goes belly up, where are you going to get any more
boards made, without starting from scratch?

Anyway, it is a bit off topic.

Dave
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Re: [volt-nuts] Availability of 3458A in Europe after the end of 2016.

[Dr. David Kirkby (Kirkby Microwave Ltd)]

On 13 November 2016 at 14:17, Chuck Harris  wrote:

> RoHS does not apply to test equipment.
>

Where do you get that from? When I was looking briefly the other day, there
did not seem to be a lot of exemptions.

I'm sure Keysight must be a bit more on the ball than to put that notice,
if RoHS did not apply to test equipment.

There's a similar notice about a power supply I have - 6674A (70 V @ 30 A
PSU).

Dave
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Re: [volt-nuts] Availability of 3458A in Europe after the end of 2016.

[Dr. David Kirkby (Kirkby Microwave Ltd)]

On 13 November 2016 at 09:19, Alessandro Saporetti 
wrote:

> Hi all
> Just got back from Electronica in Munich where i did have a small
> conversation with keysight people about 3458A Rohs issue, they have a vague
> idea about when it will kick-in , but where sure about availability of the
> meter in the future.
> Probably they have some kind of workaround to avoid shortage on the
> market. (not that a beast like 3458A goes by the millions)
>

The problem might be a bit more complicated than just the lead in solder -
see for example the recent discussion about low-EMF from solder with
cadmium in.

As an EU member myself and maker/seller of electronics equipment shall I
> say that EU regulation are at least byzantine and usually you can read it
> from left to right and reverse , so let’s see what happens.
>

I feel one advantage of the UK leaving the European Union. The regulations
we introduce will not have to have such a large committee for approval, and
don't need to be translated in numerous different languages.

Of course, the other advantage, is I will be able to buy a 3458A if I want
to !!

Dr. David Kirkby Ph.D CEng MIET
Kirkby Microwave Ltd
Registered office: Stokes Hall Lodge, Burnham Rd, Althorne, Essex, CM3 6DT,
UK.
Registered in England and Wales, company number 08914892.
http://www.kirkbymicrowave.co.uk/
Tel: 07910 441670 / +44 7910 441670 (0900 to 2100 GMT only please)
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[volt-nuts] Availability of 3458A in Europe after the end of 2016.

[Dr. David Kirkby (Kirkby Microwave Ltd)]

The 3458A page on the Keysight website is interesting.

"Notice for European Union Customers: This product is not updated to EU
RoHS compliance and can be ordered via Keysight directly or Keysight
Authorized Distributors until 31 December 2016. Beyond this date, the
product can still be purchased from Keysight Authorized Distributors.
Please contact Keysight Authorized Distributors or your local Keysight
sales representative for quotation and ordering."

It seems you can't buy it from Keysight, but you can from their
distributors. But most times I've contacted Keysight about buying things,
they tell me to get them from their distributors anyway.

If I interpret


https://www.gov.uk/guidance/rohs-compliance-and-guidance

correctly, nobody should be stick non-compliant things in the EU market.

I can't be bothered to read in detail the

"DIRECTIVE 2011/65/EU OF THE EUROPEAN PARLIAMENT AND OF THE COUNCIL of 8
June 2011 on the restriction of the use of certain hazardous substances in
electrical and electronic equipment (recast)"

http://eur-lex.europa.eu/LexUriServ/LexUriServ.do?uri=OJ:L:2011:174:0088:0110:EN:PDF

as I some paint I want to watch dry. But a cursory glance shows exceptions,
but none seem relevant to a 3458A.

Dave
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Re: [volt-nuts] low emf solder

[Dr. David Kirkby (Kirkby Microwave Ltd)]

On 29 October 2016 at 14:51, NeonJohn  wrote:

>
>
> On 10/28/2016 08:39 PM, Dr. David Kirkby (Kirkby Microwave Ltd) wrote:
>
> > I wonder how practical it is to weld test leads, so there's no solder or
> > thermal EMF.
> >
> > I know that this will sound crazy, and probably is, but could one weld
> > components to a PCB?
>
> Yes indeed.  About 20 years ago I had a machine that made circuit board
> by routing tiny wires and spot welding them to the connection.  I can't
> for the life of me remember that process name.
>
> Only problem is, if you weld two different metals together, even copper
> with different compositions, you've still made a very rugged and durable
> thermocouple.
>
> John
>

But if one could use copper as the bond wire, rather than gold which is
quite common, then it would give you very little thermal EMF

I would have thought any impurities in copper wire, would be quite small,
as it would reduce the electrical conductivity. Whilst I accept one is not
going to get 100.00 % pure copper, I would have thought
the effect of any impurities at least an order of magnitude less than using
solder. I'm only postulating this - I have no evidence to back it up, and
have never studied the subject.

Perhaps the person who was making the measurements on the solder, could try
making a thermocouple by welding two bits of wire taken from different
sources. I guess the problem would be preventing any impurities entering
the weld. A quick Google suggests one needs argon gas when welding copper.

Dave
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Re: [volt-nuts] low emf solder

[Dr. David Kirkby (Kirkby Microwave Ltd)]

On 28 Oct 2016 15:25, "Juris L"  wrote:
>
> Found reference to optimal emf solder composition cadmium/tin alloy
> (70 %/30 %) in JJ array measurement article page 12.

I wonder how practical it is to weld test leads, so there's no solder or
thermal EMF.

I know that this will sound crazy, and probably is, but could one weld
components to a PCB?

I don't even have the excuse of been drunk or taking drugs,  but I will
risk ridicule for making the above comment!  Sometimes thinking out of the
box is useful.

Dave.
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Re: [volt-nuts] Is there a "standard" much better than a LTZ1000, but much cheaper than a Josephson Junction Array?

[Dr. David Kirkby (Kirkby Microwave Ltd)]

On 20 October 2016 at 00:08, Poul-Henning Kamp  wrote:

> 
> In message  g...@mail.gmail.com>
> , "Dr. David Kirkby (Kirkby Microwave Ltd)" writes:
>
> >The question about the Josephson Junction Array got me thinking. I wonder
> >if there are any sort of technologies that can produce a voltage with much
> >better stability than the LTZ1000, but without the cost of a Josephson
> >Junction Array. A sort of half-way house.
>
> As far as I know there are only two steps between the LTZ1000 and JJAs:
>
> 1. Specially cared for LTZ1000's (See: Fluke)
>

Do you have a specific reference?  A google found lots of kits on Fluke and
LTZ1000,  but none of the pages were from Fluke.


> 2. Lots of LTZ1000's to get sqrt(N) reductions.
>


> --
> Poul-Henning Kamp   | UNIX since Zilog Zeus 3.20
>


But that assumes the drifts are completely uncorrelated, which I doubt is
the case - especially if they are all from the same batch. But there are a
limited number of resistors of the quality needed (Vishay is the only one I
can think of), and PCB materials are likely to be the same. It seems to me
that you would not gain sqrt(N) unless N is quite small. How small, is
anyone's guess.

Dave
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[volt-nuts] Is there a "standard" much better than a LTZ1000, but much cheaper than a Josephson Junction Array?

[Dr. David Kirkby (Kirkby Microwave Ltd)]

The question about the Josephson Junction Array got me thinking. I wonder
if there are any sort of technologies that can produce a voltage with much
better stability than the LTZ1000, but without the cost of a Josephson
Junction Array. A sort of half-way house.

BTW, I see some rather battered up LTZ1000A's on eBay,

http://www.ebay.com/itm/1x-LTZ1000ACH-Ultra-Precision-Reference-LTZ1000A-/111325506311

that have dents in them. They are more expensive than buying the chip new
from the Linear Technology website.

http://www.linear.com/purchase/LTZ1000

Yet people seem to buy them. Now I know the stability of those improve with
age, but when they have dents in them, its clear they have not been exactly
cared for. Maybe I will buy some new LTZ1000As and stick them on eBay for
$100 and see how many I sell !!

It seems the real cost of an LTZ1000A standard is not the chip, but the
resistors you need.
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Re: [volt-nuts] Low-cost Josephson Junction Array

[Dr. David Kirkby (Kirkby Microwave Ltd)]

On 19 October 2016 at 20:15, Ken Peek  wrote:

> Well, I already have a 3458A,


OK, quite an expensive multimeter. Otuside my budget for something I don't
really need, but would like!


  $400K is *WAY* out of my budget.  I was looking more for
> something on the surplus market-- or some "cast away" JJA that someone is
> getting ready to throw into the dumpster-- something that nobody wants
> anymore that I can get working on a _very_limited_ budget...


It might be worth mentioning how much money you are willing to spend on it,
as it may give people ideas about what could possibly be done yourself, and
what is just not going to be practical.

You may well find getting liquid helium impossible. Here in the UK it is
very difficult to get chemicals dangerous chemical if you are not on an
industrial site. I very much doubt British Oxygen Company (BOC) would
delivery liquid helium to my house.


Stage 1 would be to see what you would need in order to get the He
delivered. Without that you are not going to get anywhere, and I doubt you
will get that delivered unless you have vessels that have been properly
maintained.

I would imagine that just getting the stuff delivered would be next to
impossible without spending a lot of money, especially in the USA.
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Re: [volt-nuts] Calibration of 34401A

[Dr. David Kirkby (Kirkby Microwave Ltd)]

On 12 Oct 2016 10:31, "Poul-Henning Kamp"  wrote:
>
> 
> In message <120112818.2234439.1476263954...@mail.yahoo.com>, Bruce
Griffiths wr
> ites:
>
> >Does anybody know if a 34401A can be adjusted by a competent 3rd party
lab,
> >or are the details of how to adjust the meter not available outside of
> >Keysight?
>
> The service manual has the calibration procedure, and it is all software.
>
> --
> Poul-Henning Kamp   |

Cheers.  It seems that the lab is incompetent then, as none of the values
appeared to be in a massive difference
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[volt-nuts] Calibration of 34401A

[Dr. David Kirkby (Kirkby Microwave Ltd)]

I have a 'friend" (actually a person who I have never met, but is a pain in
the ***).

He sold a Agilent 34401A multimeter which the customer said is out of
specification and can not be adjusted.

Quickly scanning the measurent results,  the  meter is not showing results
with any huge errors  (say 1%), but which (if any) range it is out of
specification I don't know. Unlike the Keysight calibration certificates I
have seen, the measurement results doesn't show the upper and lower limits
for the specification of the meter,  so one can not tell from a quick
glance if the meter is out of specification. One would need to study the
detailed specification.

*IF* I understand correctly, (and the data is in Spanish which I don't
speak),  with an input of 9,0 V, the meter reads 9,99899 which  the
data  indicates is an error of  -91 uV/V with an uncertainty of 7.7 uV/V.

The lab said the meter can not be adjusted.  I don't know if they mean

1) This lab has no ability to adjust the meter.

OR

2) It is too far off to adjust.

Does anybody know if a 34401A can be adjusted by a competent 3rd party lab,
or are the details of how to adjust the meter not available outside of
Keysight?

Dave
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Re: [volt-nuts] Keysight 3458A vs Keithley 2002 8.5 digit multimeters.

[Dr. David Kirkby (Kirkby Microwave Ltd)]

On 18 Jul 2016 17:34, "John Phillips"  wrote:
>
> Most labs never turn 3458As off. The longer they are on the lower the
drift
> rate. I would rather have an 20 year old meter with new batteries than a
> new meter.

If one buys a used meter, one has no idea if it has been switched on very
occasionally or on 24/7.

Do you keep your meter powered up during the transit between your lab and
the cal lab? I would think that quite difficult if you used a courier,  but
not a problem if it was taken in a car.

Dave.
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[volt-nuts] Keysight 3458A vs Keithley 2002 8.5 digit multimeters.

[Dr. David Kirkby (Kirkby Microwave Ltd)]

I am interested to hear people's view on the relative merits  of the
HP/Agilent/ Keysight 3458A vs the Keithley 2002.

I noticed that when I recently visit the standard lab for voltage at NPL,
the place was littered with Agilent 3458As, but I did not notice a single
Keithley 2002. But maybe NPL get better discounts from HP/Agilent Keysight
than Keithley/Tektronix.

I notice that the used prices of 3458A is higher than 2002s.

Also, are there any things ons should be looking out for when buying a
3458A or 2002? I have in the past thought an Agilent front panel was a
better than an HP one, as it would not be as old, but this is not always
true - see my comment later.

What S/N are best avoided? Does anyone have a record of S/Ns of Keighley
meters with time?

Very recently I had a somewhat scruffy HP 6674A PSU with a damaged LCD. It
cost me $50 or so to pick up a clean Agilent front panel with a new
display.  The display actually turned out to be unsuitable,  yet my Agilent
badged 6674A is actually a fairly old HP unit.  So white my intention was
not to rebadge the PSU, that happened as a result of a legitimate reason to
get it working. So this really indicates how an old HP 3457A could be made
to look a newer Agilent one.

Dave.
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Re: [volt-nuts] Keithley 2001 - do you need to open it to calibrate it?

[Dr. David Kirkby (Kirkby Microwave Ltd)]

On 26 June 2016 at 20:46, Todd Micallef  wrote:

> David,
>
> I have found that many sellers like to remove any calibration stickers or
> tamper evident stickers. Not sure why they do that as a sticker does not
> mean the item is calibrated.
>

The sticker on the front has been removed, but the one underdeath, which
covers a screw, is still there, but the screw has clearly been undone, so
the seal is "broken". I'm interested to know if it is necessary to undo the
case to calibrate the 2001, or whether it can all be done from the front
panel, probably removing that sticker on the front.

There are a few things I am not happy about this - the front panel appear
to move far more than I would expect. Depressing one key seems to make
several keys nearby go retreat towards the back of the unit, although it
appears to function.

I was a bit surprised when I put it on the 2 A range, with no leads
connected, the current is showing as high as 6 mA at times. This seems odd
given the current is obviously zero. I realize leaving the leads open on
voltage is going to lead to undefined results, but I would have expected on
current for the meter to read very close to zero.

If I put it on "auto", on DC current, with no leads, the reading is going
as high as 20 nA - there's noise on the last 3 digits. I don't know if that
makes any sense. The update rate is very fast, so perhaps that's to be
expected unless one increases the integration time.

But there are a few things making me think this meter might have issues. A
rather strange smell was initially evident, but that seems to have cleared.
The movement of the keys seems very odd. I will almost certainly return
this.


>
> If you have 14 days, run it through the paces and perform self-tests. There
> are some test scripts here https://xdevs.com/article/dmm_noise/ to see if
> the meter is measuring close to others.
>

Thanks, I will take a look.

My computer that has the GPIB board in is is rather sick at the minute. I
need to sort out what is wrong with it, as its the only convenient computer
to have a controller card in.

Dave
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Re: [volt-nuts] Thermal EMF of common solder

[Dr. David Kirkby (Kirkby Microwave Ltd)]

On 26 June 2016 at 15:12, Andrea Baldoni  wrote:

> Hello All.
>
> I measured the thermal EMF of two common solder, the lead free
> Sn96.5/Ag3/Cu0.5 and the old Sn60/Pb40.
>

Please excuse my ignorance, but how do you mean the thermal EMF of solder?
Do you not need another metal, such as copper to make a junction? If so,
you are measuring the emf

Dave
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[volt-nuts] Keithley 2001 - do you need to open it to calibrate it?

[Dr. David Kirkby (Kirkby Microwave Ltd)]

I got the 2001 that I ordered yesterday. There are a few things that make
me feel uneasy about it, so I will probably return it.

The calibration seal is missing off the front, which is obvious from the
eBay photo, but also one at the bottom which looks as though one needs to
open in order to get inside the unit. That had a seal, but has been broken.
I'm wondering if that would be a normal part of the calibration routine, or
if someone has opened this up after it was calibrated.

The cal was due "Jan/12/10", which I assume means the 12th of January 2010.

Also, although when I see the pictures on eBay I never noticed it, a closer
inspection of the photos .

http://www.ebay.co.uk/itm/KEITHLEY-2001-DMM-/152113460174

does show that the hole on the front where a calibration seal would be
placed, has at one time in the past had a device too large pushed into the
hole. The hole is no longer round as I would expect it to be.
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[volt-nuts] Keithley 2001 vs HP 3457A multimeters / Any problems to watch out for on Keithley 2001?

[Dr. David Kirkby (Kirkby Microwave Ltd)]

I've got an HP 3457A (6.5 digit multimeter) which has served me well.  But
I see a Keithley 2001 7.5 digit meter on eBay

http://www.ebay.co.uk/itm/152113460174

which sort of tempted me as

1) It has an extra digit, I have not looked to see how much that extra
digit gains one. It would be nice to think the uncertainty is only 10% of
the 6.5 digit 3457A, but I very much doubt that's the case. I have not
looked at the specs closely.

2) I see it was a current model at Farnell selling at £4150 + 20% VAT =
£4980, so quite a bit of money. The 2001 is not a cheap meter.

3) It was £650 or "best offer".

4) The 3457A is a great meter, but is much older.

Anyway, my offer of £380 (GBP), was accepted, which is 7.6% of the current
cost of this new from Farnell. As I write, this is around $520 (USD), but
with the UK just voted to exit the EU, and the pound fallen quite a bit,
that US price may not be very representative. But it seems fairly cheap. I
can't see any Keithley 2001's sell for that low on eBay, unless they have
had faults.

Having made an offer, it been accepted, and me paid for it, now I decide to
see if it was a good or bad idea! I think one is compare the meters first,
then make a decision to buy or not, but I have done this the other way
around!

I'm interested in hearing any onions on

1) What's the 2001 like in general?

2) How does it compare to the 3457A? Have I made  big mistake in paying
£380 (GBP) to buy a 2001, when I already have a HP 3457A?

3) Are there any specific advantages of the 3457A which would make it
desirable to keep both units, rather than sell the 3457A, which is my
intention?

4) I assume the "Revision A06" refers to some hardware/firmware releases.
Does that give any idea of how old this is?

5) I note from a Google there are some revision B07's, which I am assuming
are later. Does anyone know if there are any significant issues on an A06,
or whether it can be upgraded - is it just firmware?

*6) Most importantly, are there any specific faults that occur on the 2001,
which I might be able to spot doing procedures X, Y and Z, but which are
not blindingly obvious? *

Obviously when this arrives, I will attempt to do any self-tests I can find
in the manual. I don't have any "standard" good enough to check the
accuracy, but a comparison with the 3457A should show up any really bad
faults - or at least leave me wondering what meter to trust! I will be like
the man with two clocks! The 3457A has not bee calibrated for ages.

I will get a quote from Tektronix for calibration. Hopefully that will show
up any faults.

BTW, it does seem the 8.5 digit meters (Agilent 3458A, Keithley 2002) hold
their value far more than the 7.5 digit ones. I guess the cheaper 7.5 digit
ones are sold in much larger quantities.


Dave
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Re: [volt-nuts] LTZ1000 project build

[Dr. David Kirkby (Kirkby Microwave Ltd)]

On 4 Jun 2016 20:44, "Poul-Henning Kamp"  wrote:
>
> 
> In message <57527f8a.6070...@yandex.com>, Charles Steinmetz writes:
>
> >As I have mentioned before, for many years I have put precision circuits
> >that may be sensitive to humidity into gasketed metal boxes with fresh
> >silica gel packets.

> Only thing to remember is that it also reduces air circulation in the
> box and therefore increases thermal gradients.

I don't know how practical they are, but I have see humidity calibration
standards (e.g 50%). These  use a chemical reaction to keep a volume at a
constant humidity.  That might be a way of keeping the humidity constant,
without introducing increasing thermal gradients.

They might introduce a whole host of other problems,  so such a method
would need researching.

If a new PCB was designed,  it would be nice if there were pads to take the
expensive Vishay foil resistors,  in addition to a cheaper choice.

Dave
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Re: [volt-nuts] LTZ1000 project build

[Dr. David Kirkby (Kirkby Microwave Ltd)]

On 25 May 2016 at 19:24, Russ Ramirez  wrote:

> A lot of great information Eric, thanks for sharing the link.
>
> Due to my ignorance in general on the subject of Metrology, I have the
> following question for the list.
>
> If one built a project with the LTZ1000, like the one described on xDevs
> and could set it to a value of 7.1500v at the NIST lab, and observed
> stability to 7 1/2 digits, would using that device to calibrate your own 7
> 1/2 digit DMM be considered NIST traceable? Let's say your device is well
> insulated and battery powered, and your calibration was done at the same
> altitude and room temperature as at NIST, plus anything I left out that
> would make the conditions ideal.
>
> The above was not meant to be a trick question, and I may have asked it
> incorrectly, but I view the answers as instructive - or I hope they are.
>
> Russ
>

As far as I can determine, as long as you can work out the uncertainties,
no matter how large they might b,  the measurement is traceable. If you use
a 3.5 digit multimeter that is NIST traceable to calibrate a 7.5 digit
multimeter, the calibration is still NIST traceable. The calibration will
be pretty useless, and you may not be accredited, but it is still NIST
traceable.

Or if you want to be accredited, get your mate down the local pub (bar) to
accredit you!

On a more serious note, if people felt that design was good, and wanted to
produce the PCBs. and/or make parts available, I'd be interested. I only
have a 6.5 digit meter, but feel sure I could find someone with a 3458A in
the UK who could measure the voltage for me.

Dave 
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[volt-nuts] Suggestions for 10 milli Ohm 0.04 % 100 W resistor

[Dr. David Kirkby (Kirkby Microwave Ltd)]

I have an HP 6674A power supply with option J06,  which means that the PSU
is 70 V @ 30 A rather than the standard 60 V @ 35 A .

I've replaced a couple of bits in this and will need to replace some more,
so it would be prudent to get this calibrated.

The service manual calls for a 8.5 digit 3458A, which seems a bit over the
top given the displays for voltage and current are only 4 digits. I think
my 6.5 digit 3457A will be good enough. This is a 2.1 kW PSU, not a
precision measuring instrument. But I don't have any ammeter that can read
30 A, so I can not just use an external ammeter if I want to know the
current.

The service manual also calls for a 0.010 Ohm 0.04 % 100 W resistor, with a
recommended resistor of a Guildline 9230/100. I am wondering how practical
it is to make such a resistor and verify its performance on the 3457A.
Some versions of this PSU have a lower output voltage (56 V) but higher
current (42 A). With the 30 A PSU I have,  the maximum power that could be
dissipated in a 0.01 Ohm resistor is obviously 9 W.

Any suggestions about what I can use that will not cost a fortune?

Looking on eBay, Guildline resistors are several hundred USD each. I can't
justify that given the cost of a Keysight calibration of the PSU is $199 in
the USA.

I much admit that I have never really much attention to calibration of a
PSU. It seems a bit of a waste of money when you can use a decent
multimeter if you really want to know the voltage or current. But with a
PSU of this size, I don't have an ammeter good enough.

The other tricky bit about calibration of this PSU is the need for loading
it to full power (2.1 kW) then dropping the load to 50% and measuring the
recovery time. It should recover to within 100 mV in 900 us. Likewise it
should recover the same if switched from 50%  of load to 100 %. The manual
calls for an electronic load,  but I suspect a FET switch and some big
resistors in water will do. I don't see any need for such resistors needing
to be very high precision, but obviously something decent is needed to
calibrate the ammeter.

Dave.
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Re: [volt-nuts] Just back from cal

[Dr. David Kirkby (Kirkby Microwave Ltd)]

On 8 Apr 2016 04:21, "Joseph Gray"  wrote:
>
> In February, I sent my HP 3457A in for cal. In late March, I sent my
> EDC VS330 DC Voltage Reference in for cal. Today, I just got the VS330
> back and thought I'd compare the two instruments.

Did you send them to the manufacturers or a third party lab? I am
personally VERY skeptical of the competence of a number of so-called
calibration labs. A few months back there wss a 40 GHz vector network
analyser on eBay for auction which included a cal certificate.  The
certificate listed the items used for the calibration.  The calibration kit
used was a 6 GHz economy type N kit made by HP. The N connector will not
work properly at 40 GHz, but even if it did,  the use of a calibration kit
is insufficient to calibrate a VNA.

I have seen countless examples of this sort of thing. I would not
personally consider getting any of my HP kit calibrated by anyone other
than Keysight.

> Both instruments have been on for a couple of hours. It is about 25 C
> in the room.

That is quite warm.  Are both specified at that temperature?

> Setting 10.0 on the VS330, I measure 9.99891 VDC on the 3457A.

I would try to find a local volt-nut with a 3458A.

I would also keep a log of the differences between your voltage standard
and multimeter.  If the difference is changing significantly over time, it
would tend to indicate one or both are unstable.  If however the difference
remains very similar then I would be more suspicious that one is
incorrectly calibrated.

> The report on the 3457A, dated 16 Feb says the 30 VDC range read
> 29.9991 VDC. The report on the VS330, dated 31 Mar says 10 VDC read
> 10.0001 VDC. Both instruments required adjustment.

I have heard several reports of 3457As being in spec many years after they
were last calibrated.  The fact your unit required adjustment seems a
little unusual.

If the VS330 was out by 1  on the last digit,  that suggests to me it
didn't require adjustment.

> These numbers would lead me to believe that I should be getting a lot
> closer agreement to 10 VDC for both of these instruments. Am I
> expecting too much?

I have not checked your numbers,  but would agree if both units have been
recently calibrated,  the agreement between the two should not be just
inside the limits if you take the worst case of each. I would expect much
closer agreement.

If the two appear to be drifting with respect to each other the the
purchase of another 3457A, even if uncalibrated,  would probably allow you
to determine what one of your

> Joe Gray
> W5JG

Dave, G8WRB.
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Re: [volt-nuts] volt-nuts Digest, Vol 77, Issue 15

[Dr. David Kirkby (Kirkby Microwave Ltd)]

UOn 31 Jan 2016 19:56, "new"  wrote:
>
> I'm thinking of doing non-commercial 'calibrations' for
> folks like us volt-nuts.
>
>  Since I have three 3458s, three 732As, a 732b, a 4214,
> an sr104, a 4210, all NIST cal'ed and I could do front-panel
> adjustments for the 3457.



>  Probably best to do it on fleabay to protect everyone
> involved.

eBay would not provide any real protection to either party.  In the event
one party was dishonest,  the most eBay would provide in compensation to
the other  would be the amount paid for the calibration.  That is likely to
be considerably less than the value of a high-end DMM.

Dave.
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Re: [volt-nuts] 3457A - should I preserve SRAM contents, or purposely corrupt them by removing power?

[Dr. David Kirkby (Kirkby Microwave Ltd)]

On 25 January 2016 at 11:12, Dr. David Kirkby (Kirkby Microwave Ltd) <
drkir...@kirkbymicrowave.co.uk> wrote:

> As noted in another thread, I want to replace a battery in a 3457A that
> has not been replaced in at least 11 years. The instrument has not been
> calibrated in that time either. At the time it was purchased from a dealer,
> I was told it was within specification, but if I wanted it calibrated I
> would need to pay. I never did have it calibrated, so have no historical
> data about this. I've no idea when it was calibrated, and have no cal
> certificate, so have no idea of the errors at the time of calibration.
>
> I now want to change the battery, *and* send it to Keysight for
> calibration - I have a healthy skepticism of 3rd party labs, so would
> rather pay more and get the job done by Keysight.
>
> I'm wondering if I would be better purposely removing the battery, and
> putting a short across the SRAM so I ensure the contents are definitely
> lost. My logic is that
>
> 1) If I send it to Keysight and the cal data is corrupt, they will set the
> meter correct.
>
> 2) If sent to Keysight, with the cal data in tact, then if its within
> specification they will not adjust it. So if the limit on some parameter is
> 1%, and the error is 0.5%, then it will not be adjusted. But if the SRAM is
> corrupted, the error will be huge (if it will read at all), so it would
> force Keysight to adjust it to the correct value.
>



> At that point the error should be effectively zero
>


> Thoughts?
>

Someone sent me a private email, saying that if by purposely removed the
power from the SRAM  caused the 3457A to fail its self-tests, which is may
well do, then Keysight may consider the 3457A needs repair, and so offer a
fixed-price repair. Hence my "trick" to get this calibrated as accurately
as possible would have backfired, and I'd be out of pocket. In fact, on a
3457A, the fixed-price-repair would probably cost more than the instrument
is worth, as these are not worth a lot now.

Hence I would not do this before getting clarification from Keysight. It
might be possible to get them to set it right, even if within spec, but I
think their calibration routines are very automated, so its probably not so
easy to get a special calibration, whilst paying for their cheapest
calibration service.

Dave
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Re: [volt-nuts] Wanted - UK source of a replacement battery (type LX 1634) for HP 3457A 6.5 digit multimeter

[Dr. David Kirkby (Kirkby Microwave Ltd)]

On 25 January 2016 at 15:23, Andrea Baldoni  wrote:

> On Sun, Jan 24, 2016 at 07:54:34PM +0000, Dr. David Kirkby (Kirkby
> Microwave Ltd) wrote:
>
> > I've got a HP 3457A 6.5 digit multimeter - S/N 2703A04579. It's working
> > fine, but I'm aware the battery must be at least 11 years old, as I first
> > bought the meter 11 years ago. I suspect its due for a change.  I'm
> trying
> > to find a *reputable* source for a replacement. I want to avoid eBay, due
> > to the number of fakes on there.
>
> Hello David.
> If the Panasonic replacement is good, you can buy the equivalent Varta
> 06127201301 from RS (their code is 240-9437).
>
> http://uk.rs-online.com/web/
>
> Best regards,
>  Andrea Baldoni
>


It is the same general type, but the pinout is wrong. Mine has two radial
pins, not 3. That will not fit.

Dave
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Re: [volt-nuts] 3457A - should I preserve SRAM contents, or purposely corrupt them by removing power?

[Dr. David Kirkby (Kirkby Microwave Ltd)]

On 25 January 2016 at 15:40, Poul-Henning Kamp  wrote:

> 
> In message <
> canx10halwjxt+8ev8lywdqy9eez+anawihgqeyrzntsy80v...@mail.gmail.com>
> , "Dr. David Kirkby (Kirkby Microwave Ltd)" writes:
>
> >I'm wondering if I would be better purposely removing the battery, and
> >putting a short across the SRAM so I ensure the contents are definitely
> >lost. My logic is that
>
> I would save the content before doing that, so that I could compare it
> to whatever I got back from calibration.
>
> My experience so far says that there probably is a GPIB command which
> can read out the memory, but of course you still need to know the
> address-space layout.
>

I've not looked myself, but I did see a note on the web there was no
documented command to do read out the cal data on a 3457A. But in any case,
unless I know how to interpret those values, a bunch of meaningless 0's and
1's is not going to be a lot of use. Of course, if I could save them I
would, then in the event someone ever figures out what the numbers mean, I
could do a comparison.

It would be nice to know if the meter is in/out of spec, but to me, I think
having it put as close as possible to correct is more worthwhile, even
though a metrologist who gets their meter calibrated regularly would no
doubt see it different.


Dave
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[volt-nuts] 3457A - should I preserve SRAM contents, or purposely corrupt them by removing power?

[Dr. David Kirkby (Kirkby Microwave Ltd)]

As noted in another thread, I want to replace a battery in a 3457A that has
not been replaced in at least 11 years. The instrument has not been
calibrated in that time either. At the time it was purchased from a dealer,
I was told it was within specification, but if I wanted it calibrated I
would need to pay. I never did have it calibrated, so have no historical
data about this. I've no idea when it was calibrated, and have no cal
certificate, so have no idea of the errors at the time of calibration.

I now want to change the battery, *and* send it to Keysight for calibration
- I have a healthy skepticism of 3rd party labs, so would rather pay more
and get the job done by Keysight.

I'm wondering if I would be better purposely removing the battery, and
putting a short across the SRAM so I ensure the contents are definitely
lost. My logic is that

1) If I send it to Keysight and the cal data is corrupt, they will set the
meter correct.

2) If sent to Keysight, with the cal data in tact, then if its within
specification they will not adjust it. So if the limit on some parameter is
1%, and the error is 0.5%, then it will not be adjusted. But if the SRAM is
corrupted, the error will be huge (if it will read at all), so it would
force Keysight to adjust it to the correct value. At that point the error
should be effectively zero given its a 6.5 digit multimeter, which means
the uncertainly in Keysight's measurements should be much lower than the
uncertainty of my meter.  So by corrupting the SRAM, I should get a meter
returned to me that is more accurately calibrated than if I take the
trouble to preserve the SRAM contents.

3) The adjustments are I believe software, so there's no risk that
adjusting potentiometers will cause drift to increase.

4) I don't have any historical data from cal certificates, so even if I a
range is in error by 0.5%, I can't make any attempt to estimate the drift
over time. Clearly if I had cal certificates over a period of years, I
maybe able to get some idea of how the instrument is drifting, so possibly
correct for that, if it is drifting in one direction.

Thoughts?

Dr. David Kirkby Ph.D CEng MIET
Kirkby Microwave Ltd
Registered office: Stokes Hall Lodge, Burnham Rd, Althorne, Essex, CM3 6DT,
UK.
Registered in England and Wales, company number 08914892.
http://www.kirkbymicrowave.co.uk/
Tel: 07910 441670 / +44 7910 441670 (0900 to 2100 GMT only please)
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Re: [volt-nuts] Fall of SRAM voltage in a 3457A without external power

[Dr. David Kirkby (Kirkby Microwave Ltd)]

On 25 January 2016 at 11:50, Poul-Henning Kamp  wrote:

> 
> In message <
> canx10hcamahhhxqiao9bdzu03c2bbt787mr10rmnywk3oa8...@mail.gmail.com>
> , "Dr. David Kirkby (Kirkby Microwave Ltd)" writes:
>
> >ESD and leakage of the human body would probably make screw this up, so
> I'm
> >not suggesting replacing the battery that way if you want to preserve the
> >contents of the SRAM, but there's a fairly good chance the contents would
> >remain in RAM if one was reasonably quick, especially if you topped the
> >voltage up from the mains just before removing it from the chassis.
>
> I usually hook up a separate battery while doing such surgery.
>


Yes, it is the logical thing to do, but there's a reasonable chance one
could get away with it, but obviously if its important to keep the data,
one would use an external supply. I'm tempted to purposely let the data
become corrupted for the reasons I gave in another thread.

Dave
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[volt-nuts] Fall of SRAM voltage in a 3457A without external power

[Dr. David Kirkby (Kirkby Microwave Ltd)]

I decided to try a little experiment on my 3457A, When on mains the SRAM
gets 4.8 ~ 5 V. This does not seem to be well regulated, so I assume
depends on mains voltage. Once power is removed, the voltage on the SRAM
stays well above the battery voltage for some considerable time, which I
assume is due to a decoupling capacitor. My 10 M Ohm input Z multimeter is
loading the circuit too much to continuously monitor the voltage, but a few
checks indicated the voltage across the SRAM is falling quite slowly.
Starting at 4.8 V from mains power, after 23 minutes of no mains power, the
voltage on the SRAM was at 3.4V, which is above the battery voltage (3.03
V). and well above the 2.0 V needed to hold the SRAM contents. Assuming the
SRAM takes a constant current one would expect the voltage to fall linearly
with time. If so, it would take 46 minutes to fall to 2.0 V even without
battery power.

ESD and leakage of the human body would probably make screw this up, so I'm
not suggesting replacing the battery that way if you want to preserve the
contents of the SRAM, but there's a fairly good chance the contents would
remain in RAM if one was reasonably quick, especially if you topped the
voltage up from the mains just before removing it from the chassis.

Dr. David Kirkby Ph.D CEng MIET
Kirkby Microwave Ltd
Registered office: Stokes Hall Lodge, Burnham Rd, Althorne, Essex, CM3 6DT,
UK.
Registered in England and Wales, company number 08914892.
http://www.kirkbymicrowave.co.uk/
Tel: 07910 441670 / +44 7910 441670 (0900 to 2100 GMT only please)
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Re: [volt-nuts] Wanted - UK source of a replacement battery (type LX 1634) for HP 3457A 6.5 digit multimeter

[Dr. David Kirkby (Kirkby Microwave Ltd)]

On 25 Jan 2016 03:51, "Tom Miller"  wrote:
>
> Looking through the service manual I don't see a connection from the
battery to the NVRAM. I am sure I measured battery voltage on pin28 so I
suspect a schematic error. Can someone that has one open verify that? My
3457 is in cal and I prefer not to break the seals.

NVRAM (non-volatile random access memory), an example of which is flash
ram, doesn't need any power source to hold the data.  The 3457A has SRAM
(static random access memory), which does.

Using my old Tektronix 4.5 digit multimeter I definitely measured a voltage
on positive voltage on pin 28 which was around 200 mV less than the
battery.  I believe it must be via a high impedance path as my meter, which
I assume is 10 M Ohm input impedance,  is loading the circuit and so one
sees the voltage drop slowly although the battery voltage doesn't change.

When I put the mains power on, the voltage on the SRAM rose to about 4.8 V.
When the mains power is removed the voltage stays well over 4 V but
gradually drops in voltage.  I assume that a decoupling capacitor has been
charged to 4.8 V, so the voltages across the SRAM doesn't immediately fall
back to 2.8 V. Without having acess to an electrometer or other very high
input Z multimeter I could not say for sure, but I suspect that if one was
fairly quick (of the order of minute or two) one could probably just cut
the old battery out, solder a new one in, without loosing the contents of
the SRAM. But one would not want to take that chance if one considered it
was important to keep the data.

I am actually thinking whether it is better for *me* to actually purposely
let the SRAM contents be lost, but my reasons for this world form another
thread.

Dave.
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Re: [volt-nuts] Wanted - UK source of a replacement battery (type LX 1634) for HP 3457A 6.5 digit multimeter

[Dr. David Kirkby (Kirkby Microwave Ltd)]

On 24 January 2016 at 22:46, Poul-Henning Kamp  wrote:

> 
> In message  t305g+...@mail.gmail.com>
> , "Dr. David Kirkby (Kirkby Microwave Ltd)" writes:
>
> >Thank you. That is certainly important if that's the case. I can't seem to
> >find a data sheet on the exact SRAM in my 3457A (Toshiba TC5564PL-15), so
> >difficult to know.
>
> This one ?
>
> www.cryptomuseum.com/spy/fs5000/files/TC5564.pdf
>
> That looks like vanilla CMOS RAM, and it has a wide range of
> retention VCC, so you should be fine.
>


No. I had already found that data sheet. My SRAM does not have that extra
"A" in the model - it is a TC5564PL-15 not an TC5564APL-15.  I suspect they
are similar, but I don't have any hard evidence to support that assumption.

Dave
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Re: [volt-nuts] Wanted - UK source of a replacement battery (type LX 1634) for HP 3457A 6.5 digit multimeter

[Dr. David Kirkby (Kirkby Microwave Ltd)]

On 24 January 2016 at 22:16, Poul-Henning Kamp  wrote:

> 
> In message <
> canx10hcknsnxczjx8gccd2-t0j-jom7ybmncgdvis9ic3yv...@mail.gmail.com>
> , "Dr. David Kirkby (Kirkby Microwave Ltd)" writes:
>
> >The SRAM actually gets about 4.8 V
> >when on mains, so even a fresh Lithium Thionyl Chloride cell, which would
> >be more than 3.6 V off load, would not be too much for the SRAM. So I
> think
> >I am safe for now, but given the cell is at least 11 years old (probably
> >much older), it is living on borrowed time.
>
> The one footnote to that is that some SRAMs go into a special "hibernate"
> state when VCC drops below a certain threshold.  If this SRAM has that,
> you want to make sure the threshold is above the battery voltage.
>

Thank you. That is certainly important if that's the case. I can't seem to
find a data sheet on the exact SRAM in my 3457A (Toshiba TC5564PL-15), so
difficult to know.

Dave
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Re: [volt-nuts] Wanted - UK source of a replacement battery (type LX 1634) for HP 3457A 6.5 digit multimeter

[Dr. David Kirkby (Kirkby Microwave Ltd)]

On 24 January 2016 at 21:24, Poul-Henning Kamp  wrote:

> 
> In message <
> canx10hadbw1u9ejc8_zgsk94k8az8vzg4ose+xngfwrali0...@mail.gmail.com>
> , "Dr. David Kirkby (Kirkby Microwave Ltd)" writes:
>
> >Opening the meter up, I see the PCB shows "BT 601". There's no name on the
> >battery I can see, but the type number of LX 1634. The voltage measured on
> >my 4.5 digit handheld DVM is 3.03 V. Googling around
>
> My guess is that this is a 3.6V Lithium-Thionyl battery, and if it is
> only 3.03V now, you're very likely tethering right on the brink.
>
> The most reputable vendor in this space is Tadiran, and they charge
> accordingly.
>


The post by Glenn (WB4UIV) in the link

https://groups.yahoo.com/neo/groups/hp_agilent_equipment/conversations/topics/48964

does say that it is Lithium-manganese dioxide (Li-MnO2). That information
was apparently taken from the battery manufacturer's web site. So I don't
think it is a Lithium Thionyl Chloride cell, although I'm very tempted to
fit one, as I can get one easy enough and I can't see the extra voltage
would do any harm given the SRAM is 5 V. The SRAM actually gets about 4.8 V
when on mains, so even a fresh Lithium Thionyl Chloride cell, which would
be more than 3.6 V off load, would not be too much for the SRAM. So I think
I am safe for now, but given the cell is at least 11 years old (probably
much older), it is living on borrowed time.

Dave
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[volt-nuts] Wanted - UK source of a replacement battery (type LX 1634) for HP 3457A 6.5 digit multimeter

[Dr. David Kirkby (Kirkby Microwave Ltd)]

I've got a HP 3457A 6.5 digit multimeter - S/N 2703A04579. It's working
fine, but I'm aware the battery must be at least 11 years old, as I first
bought the meter 11 years ago. I suspect its due for a change.  I'm trying
to find a *reputable* source for a replacement. I want to avoid eBay, due
to the number of fakes on there.

Opening the meter up, I see the PCB shows "BT 601". There's no name on the
battery I can see, but the type number of LX 1634. The voltage measured on
my 4.5 digit handheld DVM is 3.03 V. Googling around

https://groups.yahoo.com/neo/groups/hp_agilent_equipment/conversations/topics/48964

would suggest the battery was made by Saft and is a Lithium-manganese
dioxide (Li-MnO2). The size appears to be known as 2/3A. One source
suggests a replacment is the Panasonic BR-2/3AE2SP

Mouser's uk site
http://www.mouser.co.uk/
says shipping is restricted, so only available in the USA.

The nearest I've found to anything remotely suitable is actually a 3.6 V
battery

"CROMPTON ETERNACELL  T32/8AA8F  Battery, Single Cell, Lithium Thionyl
Chloride, 2100 mAh, 3.6 V, 2/3A, Axial Leaded, 16.3 mm"

http://uk.farnell.com/crompton-eternacell/t32-8aa8f/battery-lithium-2-3aa-axial-lead/dp/774017

I'd rather not fit a higher voltage battery, although given it provides
power to some 5 V static RAM, I would not expect it to be a problem. That
said, I believe when on mains power this battery is not needed, so there
may be some circuitry that would not like a 3.7 V battery. When power is on
the unit, there is 4.88 V across the static RAM. As mains is reduced, so
the voltage drops to about 2.8 V. I think there must be a Schottky diode
that stops the battery being drained when the mains power is on.

The battery needs to have either very thin pins or wire-ended. Some I have
seen have tags a 2~3 mm wide, which will not fit in the PCB. Others have 3
terminals, which stops you putting it in the wrong way around, but they
will not fit properly on the PCB.

In applications like the 3457A, when the SRAM needs to be kept alive when
power is off, I wish HP would have put two batteries in holders and diode
-OR'ed them. If they had done that, one could just pull out a battery from
holder A, and put a new one in B. Then when B gets old, put one in A.

My first problem though is finding a suitable battery. Next problem is
changing it without losing the RAM contents, but I don't think that's a big
deal.

The 3.6 V Lithium Thionyl Chloride is very tempting, as it has a higher
capacity than the Lithium-manganese dioxide and they have a very low
self-discharge (1%/year). I'm just not overly happy about fitting a higher
voltage battery than it is supposed to have, but phyysically it fits, and I
can get one easy enough from Farnell in the UK.

Dr. David Kirkby Ph.D CEng MIET
Kirkby Microwave Ltd
Registered office: Stokes Hall Lodge, Burnham Rd, Althorne, Essex, CM3 6DT,
UK.
Registered in England and Wales, company number 08914892.
http://www.kirkbymicrowave.co.uk/
Tel: 07910 441670 / +44 7910 441670 (0900 to 2100 GMT only please)
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Re: [volt-nuts] Low-cost voltage reference questions

[Dr. David Kirkby (Kirkby Microwave Ltd)]

On 29 November 2015 at 10:53, Charles Steinmetz 
wrote:

Dave wrote:
>
> As regards humidity, I wonder if an reasonable attempt at sealing a package
>> combined with silica gel inside would give an internal humidity that keeps
>> fairly stable.
>>
>
> That is exactly what I do.  I typically package references in small, cast
> aluminum boxes, and include as large a dessicant packet as will fit in the
> unused space.  Without any special precautions as to sealing, I have never
> seen one of the dessicant packs more than slightly used, even after a
> decade or more and even if there was a hole in the box wall to allow for a
> potentiometer adjustment.  With precautions (using a gasket or sealing the
> seam with RTV after final testing, and sealing any adjustment holes), I
> think you'd be good for a lifetime.
>
> Best regards,
>
> Charles


Are you, or anyone else, aware of any reasons silica gel should not be used
in electronic enclosures?

A friend and I were thinking of developing antennas, which would be used
outside, but enclosed in a fibreglass or similar tube.  I suggested
flushing the antenna with nitrogen, then putting silica gel inside.

He was of the opinion that silica gel was not a good idea. Instead he
reckoned on pressuring the inside with nitrogen above ambient pressure,
and having gas-tight seals would be better. I'm personally of the opinion
that's a bit over the top, as then you need valves to get the nitrogen in.
His idea stuck me as a bit of a sledgehammer to crack a walnut, but he has
better mechanical engineering skills than me.

The difference with the antennas compared to a voltage standard is antennas
would be used in a more hostile environment than a laboratory. So perhaps
whats reasonable in a lab, is not so sensible for an antenna exposed to
wind, rain, ice etc.

Dave
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Re: [volt-nuts] Low-cost voltage reference questions

[Dr. David Kirkby (Kirkby Microwave Ltd)]

On 25 Nov 2015 11:18, "Charles Steinmetz"  wrote:
>

> I'm curious why you think the AD587/586 are better than other
hermetically packaged references with better drift and noise specifications
-- in particular,
>
> MAX6350MJA
> AD588KQ
> LTC6655CHLS8
> LTC6655BHLS8
> REF102CM
>
> (see attached table).

Your table mentions at the bottom the LTZ1000, but you don't have that
device listed in the table.  I assume that is an oversight,  but perhaps it
was intensional.

As regards humidity, I wonder if an reasonable attempt at sealing a package
combined with silica gel inside would give an internal humidity that keeps
fairly stable.

I recall seeing a mix of chemicals on eBay that were a calibration standard
for humidity.

I assume that if one got some hermetically sealed feedthrough caps, it
would not be hard to put a PCB inside a tinplate box that's soldered along
each edge to form a hermetically sealed container. Then one would have a
sealed environment. I can imagine it would be desirable to flush out all
solder fumes before making a final seal. Maybe the flux residuals that I
expect outgas over time would cause more problems than it solves.

Note that I have never worked on anything requiring such sealing,  so I
would not be surprised if someone who has worked on such products would
laugh at my suggestions!

I note that Schott appear to produce hermetically sealed enclosures.

I would have thought it practical to build electronics at home where
changes of humidity over time could be virtually eliminated. But I have no
experience in this subject.

Dave.
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Re: [volt-nuts] Making a Reference IC

[Dr. David Kirkby (Kirkby Microwave Ltd)]

On 13 Sep 2015 09:15, "M K"  wrote:
> There has been some of those references available second hand from ebay,
mostly pulled, but some may be counterfeit, so look for sellers with
pictures showing it as old..

Several sellers have more than 1, but with one photo, so you would have a
hard time arguing that your board is a fake just because it looks newer
than the photo. I believe it is standard practice to photograph a genuine
article but to ship a fake.

In any case, it is probably possible to make a board look older.

A used 3458A fetches several thousand USD, so I find it hard to believe
that many would be broken for parts. But even if there is a reason 3458As
are being broken up, why are other parts not showing up as often as  the
voltage references?

I just looked on ebay for "3458A board" There are 10, of which 6 are the
voltage reference and the other 4 being various other 3458A boards.
Looking for "3458A PCB" changes it to 6 references and 2 two other PCBs. It
seems a bit suspicious to me that the one board that has wider usage than
the others is available in roughly 2~3 times the quantity of all other
boards put together.

We why don't we see 3458A front panels, power supplies etc,  showing up
much - why all the voltage references?

The fact that there seems to be a market for 3458A reference boards
suggests to me that there would be a market for a voltage reference board
based on the same chip, but designed as a stand alone board.

I can think of a few improvements over a 3458A board.

1) Option to run from batteries to keep it as stable as possible when there
are power failures.

It should also make it possible to ship a board to another volt-nut,
keeping it powered in transit.

I don't know the power consumption of the reference,  and I am aware that
there are some issues shipping batteries,  but these seem much more relaxed
if the battery is inside equipment.

2) Option to run chip at a lower temperature than in a 3458A, as some have
claimed is better.

3) Temperature sensor that recorded min and max temperatures during
shipping.

4) Ability to read time board has been powered on.

I for one would buy such a board, if someone produced one, either as a
blank PCB or populated with components & adjusted. Specialist components
would be more readily available is there was a number wanted.

Dave
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[volt-nuts] Could you fall an HP 4-wire LCR meter into thinking you have a negative resistor?

[Dr. David Kirkby (Kirkby Microwave Ltd)]

I just sent an email by mistake, failing to finish it before hitting
"send".

The recent discussion about creating inductor standards from a capacitor
and two resistors got me thinking. I suspect if you connected up an HP (or
similar) LCR meter in a way not intended, you could make it appear you have
made a negative resistor. I've not tried it, and some care would be needed,
as it has the potential to damage a meter if one did not use a bit of
common sense.

If you connect the current wires (Lcur and Hcur) to the primary of a
transformer, and measure the voltage at the secondary with Lpot and Hpot,
then one could probably get the meter to indicate a negative resistance. If
the wires to the secondary are are of  the correct phase (just revese them
if not), then the voltage measured on the meter would be out of 180 degrees
out of phase with the current injected. So one could appear to make a
negative resistor. Of course it is not really a negative resistor, and if
measured on a normal multimeter would would just measure the DC resistance
of the transformer.

One could need a bit of care to make sure the meter is not damaged, as one
has the possibility to develop a high voltage on the secondary of the
transformer.

Of course such a negative resistor would have no practical use, but I see
it an obvious extension of making inductors out of capacitors. Unlike the
synthesized inductor, this should be indicate something fairly close to a
pure negative resistor, rather than a very low Q inductor.

Dave
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Re: [volt-nuts] Anyone know how to make stable inductors?

[Dr. David Kirkby (Kirkby Microwave Ltd)]

On 20 August 2015 at 02:38, Todd Micallef  wrote:

> Here is a DIY guide to making some lab standards. It is detailed with some
> component values.
>
>
> http://nopr.niscair.res.in/bitstream/123456789/4848/1/JSIR%2065%286%29%20510-513.pdf
>


As I wrote before, I think this is of dubious use, as you are not making an
inductor, but just making the meter indicate there's a low Q inductor, by
using the 4-wires in an incorre

>
> On Wed, Aug 19, 2015 at 8:48 PM, Dave M  wrote:
>
> > Here's a paragraph from IETLab's web site on how their inductance
> > standards are made:
> >
> > "Each standard inductor is a uniformly wound toroid on a ceramic core. It
> > has a negligible external magnetic field and hence essentially no pickup
> > from external fields. The inductor is resiliently supported in a mixture
> of
> > ground cork and silica gel, after which the whole assembly is cast with a
> > poƫting compound into a cubical aluminum case."
> >
> > Sounds like their objective is to isolate the winding from as many
> > external influences as possible.  Of course, the same couild be said of
> any
> > physical or electrical standard.
> >
> > Cheers,
> > Dave M
> >
> >
> >
> >
> > Dr. David Kirkby (Kirkby Microwave Ltd) wrote:
> >
> >> I was looking to make some inductors that I can use as a sanity check
> >> for
> >> my HP 4284A LCR meter. I don't too much care what their values are,
> >> but I want them to be stable with time. Any suggestions about the
> >> best way to
> >> make or buy them? I'd like values in the range of 1 nH to 100 mH.
> >>
> >> The LCR meter has 4 terminal Kelvin connections, with 4 x BNC sockets
> >> on a 22 mm pitch.
> >>
> >> The meter is at Keysight at the moment being calibrated, along with a
> >> free software upgrade they are kindly providing. So I'd like to
> >> measure some inductors when it comes back, and track their values
> >> over time, to see if the meter is drifting.
> >>
> >> The meter covers 20 Hz to 1 MHz, and has a basic uncertainty of
> >> 0.05%, so ideally I'd like to keep inductor changes to less than
> >> 0.005% over a year, so the inductor is an order of magnitude better
> >> than the meter. Maybe that is not practical. As I say, the absolute
> >> value is not important, since I only want a comparison.
> >>
> >> The calibration costs on this meter are not too bad (£207 GBP), but
> >> the calibration interval is 6 months, which is a bit annoying. I'd
> >> rather not
> >> be sending it off every 6 months if I can satisfy to myself it has not
> >> drifted too much. Luckily I don't need to satisfy anyone else.
> >>
> >> Dr. David Kirkby Ph.D CEng MIET
> >> Kirkby Microwave Ltd
> >> Registered office: Stokes Hall Lodge, Burnham Rd, Althorne, Essex,
> >> CM3 6DT, UK.
> >> Registered in England and Wales, company number 08914892.
> >> http://www.kirkbymicrowave.co.uk/
> >> Tel: 07910 441670 / +44 7910 441670 (0900 to 2100 GMT only please)
> >>
> >
> >
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> > and follow the instructions there.
> >
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Re: [volt-nuts] Anyone know how to make stable inductors?

[Dr. David Kirkby (Kirkby Microwave Ltd)]

On 20 August 2015 at 02:38, Todd Micallef  wrote:

> Here is a DIY guide to making some lab standards. It is detailed with some
> component values.
>
>
> http://nopr.niscair.res.in/bitstream/123456789/4848/1/JSIR%2065%286%29%20510-513.pdf
>

OK, I tried this.


I was hoping to use a box I had with the connectors on already, but that
shorted all 4 shields, so was no use. I cobbled together 2 x 1000 Ohm
resistors, and a 100 pF cap. I had components mounted on leads, and leads
about 600 mm long, and the return point about the same length, so I could
not expect much accuracy, but I was not going to waste much time on this.

Between 1 kHz and 100 kHz, I was getting values around the 75-100 uH
inductance. I had a self-resonance at a few hundred kHz, so obviously it
went wrong there. Also below a few hundred Hz, the inductance started going
negative too. Given how poor my setup was, I am not going to give the
actual values I measured. I am inclined to believe their basic method works
(of sorts).

But having looked at it in more detail, the paper is *exceeding* poor, so I
am *firmly* in agreement with Brooke Clarke that it is pseudoscience.

The first paragraph says that inductors wound on a coil have unwanted
parasitic components, such as coil resistance and distributed capacitance.
OK, we all know that is true, but using the component values they give in
table 1, make for an inductor with an exceeding high series resistance

* 10 uH is 200 Ohms
* 100 uH is 632 Ohms
* 1000 uH is 2000 Ohms

I bought some 33 mH inductors a week or two ago and they had a series
resistance of under 200 Ohms, so I think 200 Ohms for 10 uH is rather
excessive!

I think most engineers, if presented with a component in a black box with
two terminals and asked to guess what it is, they would assume it a wire
wound resistor rather than an inductor.

Also on the first page, the authors mention it uses the 4 terminal pair
(4TP) system, and describes the advantages of the 4TP system. They
conveniently fail to mention their inductors (resistors?) rely on this.

So overall, a totally useless paper IMHO, perhaps befitting of the April
Fools joke I first thought of, but certainly not a credible scientific
paper.

Dave
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Re: [volt-nuts] Anyone know how to make stable inductors?

[Dr. David Kirkby (Kirkby Microwave Ltd)]

On 20 August 2015 at 19:11, Brooke Clarke  wrote:

> Hi Dave:
>
> I'd classify this article more like pseudoscience than April's fool.  To
> get an idea of the quality of the paper just check out the publisher.
>

Yes, the publisher does seem dubious. If Wikipedia is to be believed, they
were willing to publish a paper written by a random word generator. I did
not try looking very hard, but I can't see anything at indicate the authors
attributed with being at NPL are actually there.

But as Ed Breya points out, the circuit is not actually making an inductor.
Whereas with an LCR meter, or resistance meter one normally injects current
and measured the voltage at approximately the same place, using Kelvin
leads, the authors of that paper (if indeed they are the authors),
purposely inject the current at one place, and measure the voltage across a
quite different place.

I guess whether you consider it good  or pseudoscience depends on ones
perspective. It is certainly "interesting" - if it works at all. Tomorrow I
will get the soldering iron out!!

I got my 4284A LCR meter back from Keysight today, so tomorrow I will knock
one of those up and test the idea out. But I don't believe it will actually
be of any use in the calibration of an LCR meter, or even if verifying if
it drifts. Ultimately it is going to be limited by the drift in the
capacitance.

FWIW, if you did not see my earlier note, I stuck the cal certificate from
the LCR meter that came back from Keysight here.

http://www.kirkbymicrowave.co.uk/cal_certificates/Keysight-standard-calibration-with-uncertainties-for-4284A-precison-LCR-meter-18-08-2015.pdf

No inductors were used to verify the performance - only resistors and
capacitors.

There's a trick one can do with capacitors and a transformer, to "fake"
other values, for want of a better expression. But they are available from
reputable sources like IET labs.

Dave
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[volt-nuts] LCR meter calibration certificate

[Dr. David Kirkby (Kirkby Microwave Ltd)]

I just got my LCR meter back from Keysight today.

For anyone interested in looking at the cal certificate, which includes the
uncertainties, a copy may be found here,

http://www.kirkbymicrowave.co.uk/cal_certificates/Keysight-standard-calibration-with-uncertainties-for-4284A-precison-LCR-meter-18-08-2015.pdf

It's not entirely sure if it was adjusted or not, as the instrument was
upgraded, although I'm not convinced that the upgrade really would have
required any adjustments. I suspect only a verification it was working, as
it was purely a software upgrade. Though perhaps it allows other hardware
in the meter to be used.

It lists

As received condition: "Not applicable, as this calibration certificate
applies to the initial calibration of a new, refurbished or upgraded
equipment."
Action taken: "The equipment was upgraded."

So nothing specifically mentioned about it being adjusted, but nothing to
indicate if it was in spec when received either.

There's a few things rather puzzling about this.

1) Why did Keysight use two 3458A multimeters to calibrate it?

2) Why did Keysight use two 53132A frequency counters to calibrate it?

3) It's not clear to me what the actual values of the devices they used to
calibrate it with are. They used a range of resistors (100 Ohms and 1000
Ohms), and capacitors (10 pF to 1 uF in decade steps), but no inductors.
The nominal value is given (e.g. 10 pF, 100 pF), and the uncertainty. But I
assume those capacitors are not perfect, and so they would be calibrated
periodically. Would they not use the actual value to determine if an
instrument meets is spec, rather than the nominal value?

One line is this:

min=9.9605 pF measured=9.9941 pF max=10.0409 pF uncertainty = 0.0014 pF

If you average the minimum and maximum values, you don't get 10. pF,
but 10.0007 pF. Does that mean the actual value of the capacitor they used
is 10.0007 pF, within their uncertainty of 0.0014 pF?

4) Strangest of all, and I'm sure some time-nuts might think is odd, is the
uncertainty on the measurement of the "Test Frequency Accuracy".  It is
measured at various frequency, and Keysight's uncertainty ranges from 7.6
mHz when measuring 1 kHz to 7.6 Hz when measuring the 1 MHz. I'm puzzled
why the uncertainty should be so high.A half-reasonable frequency counter
that has not been calibrated for a decade should do better than that!

Anyway, I thought it might interest some.


It does show, as someone else indicated earlier, that inductors are not
needed to calibrate LCR meters.
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Re: [volt-nuts] Anyone know how to make stable inductors?

[Dr. David Kirkby (Kirkby Microwave Ltd)]

On 20 August 2015 at 02:38, Todd Micallef  wrote:

> Here is a DIY guide to making some lab standards. It is detailed with some
> component values.
>
>
> http://nopr.niscair.res.in/bitstream/123456789/4848/1/JSIR%2065%286%29%20510-513.pdf
>
>

If this was April the first, I would be convinced that paper was an April
Fools Joke!

I can't imagine how you can make high Q (low loss) inductors, by using a
capacitor and two resistors. It just makes no sense to me, but I will read
the maths later. The mere fact there is resistance makes me think it must
be lossy, so low Q. Also the equations seems to come out with convenient
numbers - R in Ohms, C in pF and H in Henries.

But if the paper is real, it is very close to what I want, although it
still leaves the position of finding stable capacitors. I thought inductors
would be easier than capacitors, but maybe not.

Dave
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[volt-nuts] Anyone know how to make stable inductors?

[Dr. David Kirkby (Kirkby Microwave Ltd)]

I was looking to make some inductors that I can use as a sanity check for
my HP 4284A LCR meter. I don't too much care what their values are, but I
want them to be stable with time. Any suggestions about the best way to
make or buy them? I'd like values in the range of 1 nH to 100 mH.

The LCR meter has 4 terminal Kelvin connections, with 4 x BNC sockets on a
22 mm pitch.

The meter is at Keysight at the moment being calibrated, along with a free
software upgrade they are kindly providing. So I'd like to measure some
inductors when it comes back, and track their values over time, to see if
the meter is drifting.

The meter covers 20 Hz to 1 MHz, and has a basic uncertainty of 0.05%, so
ideally I'd like to keep inductor changes to less than 0.005% over a year,
so the inductor is an order of magnitude better than the meter. Maybe that
is not practical. As I say, the absolute value is not important, since I
only want a comparison.

The calibration costs on this meter are not too bad (£207 GBP), but the
calibration interval is 6 months, which is a bit annoying. I'd rather not
be sending it off every 6 months if I can satisfy to myself it has not
drifted too much. Luckily I don't need to satisfy anyone else.

Dr. David Kirkby Ph.D CEng MIET
Kirkby Microwave Ltd
Registered office: Stokes Hall Lodge, Burnham Rd, Althorne, Essex, CM3 6DT,
UK.
Registered in England and Wales, company number 08914892.
http://www.kirkbymicrowave.co.uk/
Tel: 07910 441670 / +44 7910 441670 (0900 to 2100 GMT only please)
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[volt-nuts] Stabilising resistors

[Dr. David Kirkby (Kirkby Microwave Ltd)]

I have bought some resistors of 0.1, 1.0, 10, 100, 1k, 10k & 100k Ohms.
These are in little boxes with 4 BNC connectors spaced 22 mm apart.

This sort of thing

http://m.ebay.co.uk/itm/231460477406

although I paid a *lot* less.

They are designed for use verifying the performance of LCR meters. I don't
know what the uncertainty of *impedance* on these are, but they are
probably optimised for use to 1 or more MHz rather than DC resistance
standards. At least one I bought is supplied with a 120 MHz LCR meter, but
the others are possibly designed for a lower frequency. Getting
specifications on these is not easy.

My HP 4284A LCR meter is at Keysight being calibrated.  My aim is to use
these resistors as a way of tracking drift in the meter which would
indicate it needs calibration.  The basic uncertainty of the HP 4284A meter
is 0.05%, although it is higher at very low and very high impedances.

Is there realistically anything I can do to stabilise these resistors? I
don't want to go to the expense of adding Peltier temperature controllers
to them.

I suspect the fact that they are several years old means that they are as
stable as they are going to be, but I just wanted to check if there is any
improvement that I could make. I expect thermally cycling these in an oven
and fridge would do more harm than good,  but perhaps I am wrong.

I do have a 3457A 6.5 digit multimeter which has not been in a calibration
lab for at least 15 years, although I have measured some 0.005% resistors
as a check for gross errors.  It would be worth tracking these HP resistors
with that too.

It is not worth paying commercial rates for calibration of the resistors as
getting the LCR meter calibrated at Keysight is not that expensive (£207
GBP). Keysight also agreed to provide me a software option 006 (support for
2 m & 4 m cables), so getting the meter calibrated was especially good
value.

Dave
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[volt-nuts] Keysight seminar of possible interest to those in the UK

[Dr. David Kirkby (Kirkby Microwave Ltd)]

This might interest those with an interest in metrology in the UK. It
is run by Keysight on the 16th and 18th June

http://www.keysight.com/main/eventDetail.jspx?cc=US&lc=eng&ckey=2553856&nid=-33166.920244.08&id=2553856&cmpid=1-6830540895

The annoying this is Keysight are running something else that
interests me on the 17th June

http://www.keysight.com/main/eventDetail.jspx?cc=US&lc=eng&ckey=2548118&nid=-33166.920244.08&id=2548118&cmpid=1-6830540895

with the two locations more than 200 miles apart. It makes it just
about impractical to attend both


Dr. David Kirkby Ph.D CEng MIET
Kirkby Microwave Ltd
Registered office: Stokes Hall Lodge, Burnham Rd, Althorne, Essex, CM3 6DT, UK.
Registered in England and Wales, company number 08914892.
http://www.kirkbymicrowave.co.uk/
Tel: 07910 441670 / +44 7910 441670 (0900 to 2100 GMT only please)
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[volt-nuts] Seminar: Fundamentals of Low Current and Ultra-High Resistance Measurement

[Dr. David Kirkby (Kirkby Microwave Ltd)]

Google that and you should find a seminar sponsored by Keysight,
scheduled for Tuesday, April 14, 2015 1:00pm ET / 10:00am PT (I'll
convert to GMT later)

Trouble is, it is streamed in a Windows format.

Dr. David Kirkby Ph.D CEng MIET
Kirkby Microwave Ltd
Registered office: Stokes Hall Lodge, Burnham Rd, Althorne, Essex, CM3 6DT, UK.
Registered in England and Wales, company number 08914892.
http://www.kirkbymicrowave.co.uk/
Tel: 07910 441670 / +44 7910 441670 (0900 to 2100 GMT only please)
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[volt-nuts] Checking an LCR meter

[Dr. David Kirkby (Kirkby Microwave Ltd)]

I have bought an HP 4284A precision LCR meter. This is an old model with a
basic accuracy of 0.05% and covers 20 Hz to 1 MHz.

Converting the specifications into determining the uncertainty of a
measurement is nontrivial, but I think it reasonable to assume the
uncertainty will always be >0.05%.

Surprisingly the current precision LCR meter from Kesight, the E4980A (20
Hz to 2 MHz) offers the same basic accuracy. So while fairly old, the 4284A
doesn't seem to be miles behind the current crop  LCR meters from the top
manufacturers.

The recommended calibration period on the 4284A is 6 months, which would
get rather expensive - on the current E4980A the calibration period is a
more respectable 12 months.

I am looking for suggestions on how I can get "reasonable" confidence in
the instrument at "reasonable" cost, without returning it to Keysight every
6 months.

I have a 3457A DVM, but mot much else in the way of precision low frequency
equipment.

It has 4 BNC connectors for Kelvin probes.

I suspect that getting precision resistors and keeping them for a house
standard might be worthwhile,  but are looking for suggestions on the best
approach.

I will send it to Keysight once when it arrives to ensure that there are no
faults on it, but I don't currently feel I can justify getting it
calibrated every 6 months.

Maybe I can make some stable "standards", then measure them soon after the
LCR meter calibrated been calibrated and periodically measure their values.
Any suggestions about how to approach that?

Dave
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Re: [volt-nuts] 3458A reference boards on ebay

[Dr. David Kirkby (Kirkby Microwave Ltd)]

On 30 January 2015 at 12:25, Will  wrote:
> The boards are factory rejects.

I doubt all boards on eBay are in this category. Some are probably
quite genuine, some may be rejects, and it would never surprise me if
some are counterfeit. The problem is, I have no idea what ones are
what.

I don't know what the problems sourcing the parts for making a
reference would be, but if a number of people wanted to make one from
parts, perhaps someone could produce a PCB and people contribute
towards the cost of it. Maybe leave people to get their own reference
chip, as there are different grades of that. But things like the
precision resistors may be easier to buy in a quantity of 10 rather
than 1.

I would certainly not mind buying one if a PCB was available. Even if
it works out costing a bit more than a 3458A reference from eBay, I'd
feel a bit happier.

Dave
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Re: [volt-nuts] 3458A reference boards on ebay

[Dr. David Kirkby (Kirkby Microwave Ltd)]

On 27 Jan 2015 09:47, "Orin Eman"  wrote:
>
> There is a seller letting a slow trickle of them out there... they seem to
> be going for about $165.  The current batch of two is around $100, but
will
> probably be bid up.

I am puzzled why there are so many reference boards that are supposed to
come from 3458As on the used market. It makes me wonder if they are
genuine.

One seller,  with the two high stability reference boards at $750, claims
that they come from working and recently calibrated 3458As. Why would
anyone wreck a working and recently calibrated 3458A?

It is not beyond the bounds of possibility that a 3458A might be worth more
in parts than as a complete unit. I know this is true for some HP items,
but I doubt that is the case with a 3458A.

Another seller,  who has them at $395 "or offer", has sold 17 and has 11
left.

Although expensive,  having two and monitoring the difference between them
would probably allow their stability to be measured with a DVM of modest
specification.

There are lots of counterfeit components around,  and I fear that it could
be some of these boards could fall into that category.  This makes the
building a board from new components more attractive.  In the short term it
is likely to be less stable than an old reference,  but at least one would
know the history of it. If the components were sourced from reliable
sources, it would get around the  potential counterfeit problem.

Dave.
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Re: [volt-nuts] plastic caps on 3458A reference board

[Dr. David Kirkby (Kirkby Microwave Ltd)]

On 28 January 2015 at 18:56, Charles Steinmetz  wrote:

> The problem is that an LTZ1000 (or LM399) runs hot enough that most plastics
> you find lying around won't stand up to it for very long (some of them melt
> almost immediately when you power it up).  This is true even of
> polycarbonate, which is one of the most durable common plastics, and is why
> the original caps were made from polysulfone.
>
> Unfortunately, it also means that replacements may be hard to make by 3D
> "printing," since the process depends on melting the base material.
>
> Best regards,
>
> Charles

Is there any reason this cap is not made of metal? If its purpose is
to restrict airflow by convection, metal will do. Copper sheet can
easily be soldered to make something that would restrict airflow and s

If you want thermal insulation, then PTFE rivited to a metal shield
would provide a plastic that will not melt, and the metal would keep
it in place, as its hard to form a box out of PTFE. It is not an easy
material to glue, but nuts/bolts/rivits will work.

Dave
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Re: [volt-nuts] 3458A reference boards on ebay

[Dr. David Kirkby (Kirkby Microwave Ltd)]

On 27 January 2015 at 09:16, Orin Eman  wrote:
> There is a seller letting a slow trickle of them out there... they seem to
> be going for about $165.  The current batch of two is around $100, but will
> probably be bid up.
>
> I just received one that I won.  Seems to be working fine after a quick
> breadboard lashup.  I'll be making an enclosure for it next.
>
> A little expensive IMO, but given the trouble getting the precision
> resistors to DIY with the LTZ1000A, probably worth it.
>
> Orin

Orin,

What do you intend doing with it?

I was thinking about getting one of those, with a view to putting it
in a box with a couple of terminals to have something to compare with
my 6.5 digit 3457A.  But what put me off is a lack of knowledge in
knowing how to convert a 3458A reference board into a boxed unit with
a known output voltage at the terminals. How would I avoid / control
thermal EMFs?

I'd be interested to hear what your plans are for it, and how you
intend tackling those issues.

Do you know what the difference in the reference is between a standard
3458A (8 ppm) and the high stability option 002 (4 ppm) model? I'm
guessing the chips for the option 002 might be the top performing
ones. I wonder if there's any way to tell from your board if it came
from a standard 3458A or a 3458A with option 002.

Dave
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Re: [volt-nuts] Design Spark PCB Design Package

[Dr. David Kirkby (Kirkby Microwave Ltd)]

On 5 Jan 2015 15:36, "Randy Evans"  wrote:
>
> This is indirectly pertinent to the group since I am designing a PCB for
> the HP-419A and Fluke 845A modifications.  Does anyone have any
> experience/comments on the Design Spark PCB design package?  Is is a
viable
> package for hobbyist use?
>
> thanks,
>
> Randy Evans

I have not used it.

Have you looked at Kicad? It is used by both professionals and hobbyists,
and being open source, is not reliant on RS to update it.

Now there is a decent open source PCB layout program,  I would not suggest
anyone learn a new proprietary package unless there were very good
reasons,  such as an employer says you must use a particular program.

Dave
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Re: [volt-nuts] "averaging reference" / "Perfect Volt"

[Dr. David Kirkby (Kirkby Microwave Ltd)]

On 22 Dec 2014 08:51, "Joel Setton"  wrote:
>
> Frank (and all!),
>
> These are all very valid questions.
>
> The context is a hobby activity, and the purpose of the reference voltage
is to have something which is good enough to calibrate, for example, a
30-year old DVM after restoring or repairing it.

What class of DVM? Are you going to be restoring 30 year old 3.5, 4.5, 5.5,
6.5, 7.8 or 8.5 digit DVMs?

> With currently available reference chips, 3 1/2 digits is relatively
easy, 4 1/2 digits is much more difficult, and 5 1/2 digits is almost
completely out of reach.

So you obviously realize that the sort of instrument you restore would
dictate the stability of the reference you need.

> And as with many physical measurements, you may have access to an
external standard at a given point in time (for example with help from a
fellow volt-nuts list member), but after this initial calibration the
stability of your reference over time becomes important since you can't
send it out for recalibration every year.

I don't suppose it would cost too much in postage to do it, and I don't
suppose that you would find it too hard to find willing people.

>From what I have read, the
LM399 &  LTZ1000 are the best devices. So how about this for a suggestion:

1) Build one reference based on the LM399 in one box.

2) Build a second based on an  LTZ1000 based in a second box, using any
critical components, such as resistors from different manufactures.

3) Did *not* perform any sort of averaging in electronic hardware.

4) Wait a few months, to reduce, but not eliminate the "shock" to the
devices of being built.

5) Got the two units measured by volt-nuts.

At this point you should have two pretty darn good references,  with I
believe the LTZ1000 being the better of the two. So you are a man with two
clocks, but both your clocks are good, and you know one is better than the
other. You can also compare them, and would be aware of any significant
differences which indicate a problem with one of them.

At this point you can do any averaging, with greater weight given to the
source expected to be better? Use different calculators to do the averaging
just in case you find a new variation of the "Pentium bug"

The drift, temperature sensitively of each can calibrated. Any drift which
does occur is unlikely to be correlated as the two "house standards" are
built from different components.

Would the weighted average of these two house-standards be good enough to
calibrate the DVMs you want to restore? It really depends on what you want
to restore - 3.5, 4.5 ...8.5 digits.

The fact you have two devices, if the difference between them exceeds some
threshold, you must conclude one of them has drifted too much.

Personally I would have thought that it would offer something useful, but
obviously if you are going to be restoring 3458As, it is not going to be.

A sample of two is not going to be the ultimate in metrology, but it may be
good enough.

You could do the maths by looking at the prices of components, but I would
think that building just two independent references with decent components
is going to work out much cheaper than building a lot from poorer
components and averaging all those.

Someone else can probably think of something better, but it is all going to
come down to cost. But I doubt building a LM399 and  a LTZ1000 reference is
going to break the bank.

Dave
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Re: [volt-nuts] The "averaging reference"

[Dr. David Kirkby (Kirkby Microwave Ltd)]

On 20 Dec 2014 21:18, "Joel Setton"  wrote:
>
> Jan,
>
> Thanks for a good summary f the pros/cons. Of course the LTZ1000 is much
closer to the current state of the art, but the REF102 is far easier to use
and to calibrate. I'm definitely not shooting for sub-ppm performance, if I
can build anything that stays within (say) 20 ppm long-term, that would be
more than adequate as a home standard.
>
> One thing I don't like about the LM199 and LTZ1000 is that although they
are stable, they are sold uncalibrated. As a result, building a 10-V
reference with either of them would require at least two very stable
resistors, one of which must be selected within a range of several percent
to get an accurate 10V output.

I suspect if you built something very stable using an LTZ1000, it would be
possible to get one or more volt-nut with a 3458A or similar to measure it
for you.
You could even average the result from several volt nuts.

Dave.
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Re: [volt-nuts] The "averaging reference"

[Dr. David Kirkby (Kirkby Microwave Ltd)]

On 19 Dec 2014 19:30, "Jan Fredriksson"  wrote:
>
> It's no coincidence that virtually all 8.5 digit DMMs use the LTZ1000.
> It's in a class of it's own.

What do the 8.5 digit meters use if they don't use the LTZ1000?

Dave.
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Re: [volt-nuts] The "averaging reference"

[Dr. David Kirkby (Kirkby Microwave Ltd)]

On 18 Dec 2014 19:06, "Poul-Henning Kamp"  wrote:
>
> 
> In message <5492f59e.8060...@free.fr>, Joel Setton writes:
>
> >In my search for the Perfect Volt, I'm thinking about building a
> >reference voltage generator which would average the voltages generated

> If you want to do it "right", you should average all sorts of
> different (but obviously: good) chips, possibly assigning them
> different weight depending on their qualities.

I was aware of  three 8.5 digit multimeters

* Keysight 3458A
* Fluke 8508A
* Keithley 2002.

But

http://www.eevblog.com/forum/testgear/8-5-digit-dmm/

lists several others - some from manufacturers I have never heard of.

I would assume that they all use a state of the art voltage references. I
wonder if they all use the same method?  If not, perhaps averaging those
would be one approach.

How would you average them? Assuming they are supposed to be the same
voltage, would it be OK to tie N output together with N resistors? Use low
value resistors on the references you trust most, and higher values on
those you trust least.

Dave
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[volt-nuts] Building a box to measure DC resistance of multiple RF loads.

[Dr. David Kirkby (Kirkby Microwave Ltd)]

I am looking to measure as accurately as possible the DC resistance of a
number of types of RF loads - all around 50 Ohms. Types of interest include
SMA, 3.5 mm, N, APC7, 7-16 & BNC. I want to see if the difference between
the actual resistance at DC and 50 Ohms correlates with the performance at
RF as measured on a vector network analyzer. I want to do both sexes, with
the exception of the APC7.

I would expect RF performance to correlate well at low frequencies,  but as
the frequency is increased I would expect it not to correlate.

I am looking for advice on the best way to do this. I have a HP 3457A (6.5
digit DVM with 4-wire resistance capability), but will consider purchasing
a meter designed for low resistance measurements which I believe uses AC to
avoid thermal EMF issues. But if possible I would rather use the 3457A.

I was thinking of a plastic box with the RF connectors & 4 banana plugs. I
suspect running the sense and drive wires back to the banana plugs would
work.  No signicant current would flow into the unterminated connectors as
they would have just the dielectric.

Ideally I would like to measure just the load and contact resistance and
not the resistance of the plug or socket I connect it to. That might be
next to impossible.

Can anyone offer any recommendations of how to wire it up, type of
connector (e.g. banana plug or similar)

PS I once see someone selling a dummy load on eBay with an SO 239 socket
and 47 Ohm wire wound resistor! Apparently the inductance made it 50 Ohms.

Dave
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Re: [volt-nuts] Buying HP-3458A

[Dr. David Kirkby (Kirkby Microwave Ltd)]

On 6 Jul 2014 07:12, "John Phillips"  wrote:
>
> ​They do really offer that service as​ long as you send them a complete
> meter... No missing parts. Well they will take a few missing screws and
> such.

There is also the possibility someone has tried repairing it, but done so
badly.

I assume that there has been some design changes over the years, so not all
boards are identical.  Agilent would probably decline to fix a unit made
from parts from a mixture of revisions.

Buying one and hoping to get it repaired for a fixed fee seems a bit risky
to me.

Dave

My experience with them is they charge the same no mater what need to
> be fixed. Not sure what the price is, there prices are country dependent.
I
> thought it was a little more than $2200 last I checked.
>
>
> On Sat, Jul 5, 2014 at 4:08 PM, Randy Evans 
> wrote:
>
> > I am in the market for a used HP-3458A and, in researching past
messages, I
> > came across an interesting question:
> >
> > *Chris Erickson* ericksonc2 at comcast.net
> >  >
40febo.com?Subject=Re%3A%20%5Bvolt-nuts%5D%203458A%20questions&In-Reply-To=%3C001b01cc7960%24a15d2840%24e41778c0%24%40net%3E
> > >
> > *Thu Sep 22 19:48:41 UTC 2011*
> >
> > If Agilent will fix everything, bring it up to specs, and calibrate it
no
> >
> > matter what's wrong with it for $2200, then why would I spend
$5000-6000 or
> >
> > more for one that is in good shape - even if calibrated? Just grab the
> > first
> >
> > bargain that comes along for $1500-3000, send it straight to Agilent
and be
> >
> > money ahead. Seems the better course of action to me if that price is
> >
> > accurate - do they really offer this service?
> >
> >
> >
> >
> > I could not find an answer to this question but it does beg the
question.
> >  Does nayone have an answer as to why not buy the cheapest unit and
send it
> > in for repair?
> >
> >
> > Thanks,
> >
> >
> > Randy Evans
> > ___
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> > and follow the instructions there.
> >
>
>
>
> --
> John Phillips
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