[volt-nuts] Agilent 3458A Issues

[Randy Evans]

I just received an Agilent 3458A that has a problem with noise and a
drifting voltage measurements.  I am using two Fluke 732As to compare
absolute voltage measurements over time against the Agilent and an HP
3458A.  The HP unit has a new A3 ADC card and seems to be very stable and
low noise, so is being used for comparison.  I have been doing simultaneous
absolute voltage measurements and DC Cal Constant measurements several
times a day and then calculating the drift rates of the two units using the
HP Service Note 18 procedure.



The results indicate the Cal Constant drift rate of both units is very
similar and within spec per Service Note 18.  However, the absolute value
measurements show the Agilent unit changing 1.1 ppm over a day whereas the
HP unit is within a tenth of a ppm over a day.  In my way of thinking the
Cal Constant procedure assumes the voltage reference board in the 3458A is
stable, hence the absolute value reading should remain essentially constant
after each ACAL DCV, which is the case with the HP unit.  Since the Agilent
unit shows a steady drift in the absolute reading, this would indicate to
me that the voltage reference board is likely the cause of the problem, and
is also likely the cause of the noisy readings.  If so, this is a
“relatively” easy fix (I have several 3458A voltage reference boards, one
of which has been continuously powered up for several years).



The issue is that I have to make a decision to keep or return the Agilent.
It has a cal seal on it and if I open the unit up to change the voltage
reference board, I own it and can’t return it.  I would appreciate an
opinion from the members of the group as to what they think the odds are
that the voltage reference board is the source of the problems with the
Agilent 3458A.



Thanks,



Randy Evans


HP-3458A Calibration drift rate 2017-11-17A.xlsx
Description: MS-Excel 2007 spreadsheet
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Re: [volt-nuts] Neon bulbs for HP 3420B or 419A chopper

[Charles Steinmetz]

george wrote:


Farnell (UK) list NE-2U neon lamps.


Note that the NE-2U is a "high brightness" lamp with a 135vDC (max) 
strike voltage.  Standard brightness lamps strike at 90vDC (max).  The 
Farnell site available to me here in the US lists the CML (Chicago 
Miniature Lamp) A3C, which CML list with NE-2U as the "Old Reference 
Number."


Farnell do not seem to carry the CML standard brightness lamps with 
reduced dark effect.  According to the CML datasheet, there are four 
part numbers with that combination:  A1D, A1D-T, A2B, and A2B-T.  "T" 
indicates tinned leads.  The design current of the A1 parts is 300uA, 
and of the A2 parts it is 700uA.  Check the schematic and you should be 
able to calculate the neon operating current of the circuit, and choose 
A1 or A2 accordingly.


Dave, perhaps Farnell will special order one of these part numbers for 
you.  If Farnell can't get you the right part, I believe both Mouser and 
Digi-Key operate in the UK and both have A1D(-T) and A2B(-T) parts in 
stock (in the UK, I think).


Cheers,

Charles


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Re: [volt-nuts] Neon bulbs for HP 3420B or 419A chopper

[george]

Hi Dave

Farnell (UK) list NE-2U neon lamps.

73 George G6HIG
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Re: [volt-nuts] Neon bulbs for HP 3420B or 419A chopper circuit

[Jeremy Nichols]

Thank you, Charles, for the excellent summary and references.

Jeremy
N6WFO


On Fri, Nov 17, 2017 at 6:23 AM Charles Steinmetz 
wrote:

> David wrote:
>
> >> to buy NEW bulbs from a reputable manufacturer who provides specs
> >
> > Any recommendations - I can't find a source in UK.   I know Philips used
> to make them, but where I'd buy a few &deity only knows.
>
> Google is your friend.  neon, bulb, lamp, radioactive, and "dark effect"
> are good search terms.  Here's what I found in about 5 minutes (all
> US-centric):
>
> Mouser and Digi-Key both have quite a variety of neon bulbs available,
> including bulbs with wire leads from VCC, JKL, and Lumex.  You would
> need to review datasheets and contact the manufacturers to inquire about
> radioactive additives:
> <
> https://www.mouser.com/Optoelectronics/Lamps-Holders/Lamps/_/N-5g6r?Keyword=neon&FS=True
> >\
>
> Other large distributors probably have similar selections.
>
> This catalog from  VCClite indicates that some of their bulbs have
> reduced dark effect, including the A1D-T and A2B, both of which Mouser
> and Digi-Key carry:
> <
> https://vcclite.com/wp-content/uploads/wpallimport/files/files/NeonIndicatorLamps.pdf
> >
>
> You will probably still want to find out for sure if the dark effect
> reduction is due to a radioactive additive.
>
> Here's some general information on glow lamps:
>
> 25 pages of glow lamp specifications from GE back in the day.  Quite a
> few of them are listed as having a "mild radioactive additive" to reduce
> the dark effect:
> <
> https://static1.squarespace.com/static/57ae25c75016e1690c41b053/t/57ae2fd003596ed24fa8f54c/1471033297306/Glow+Lamp+Specifications.pdf
> >
>
> The 1966 edition of the GE glow lamp manual can be found here:
> <
> http://www.ko4bb.com/getsimple/index.php?id=download&file=06_Misc_Test_Equipment/GE/General_Electric_Glow_Lamp_Datasheet_1966.pdf
> >
>
> Best regards,
>
> Charles
>
>
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Re: [volt-nuts] Neon bulbs for HP 3420B or 419A chopper circuit

[Charles Steinmetz]

David wrote:


to buy NEW bulbs from a reputable manufacturer who provides specs


Any recommendations - I can't find a source in UK.   I know Philips used to make 
them, but where I'd buy a few &deity only knows.


Google is your friend.  neon, bulb, lamp, radioactive, and "dark effect" 
are good search terms.  Here's what I found in about 5 minutes (all 
US-centric):


Mouser and Digi-Key both have quite a variety of neon bulbs available, 
including bulbs with wire leads from VCC, JKL, and Lumex.  You would 
need to review datasheets and contact the manufacturers to inquire about 
radioactive additives:

\

Other large distributors probably have similar selections.

This catalog from  VCClite indicates that some of their bulbs have 
reduced dark effect, including the A1D-T and A2B, both of which Mouser 
and Digi-Key carry:



You will probably still want to find out for sure if the dark effect 
reduction is due to a radioactive additive.


Here's some general information on glow lamps:

25 pages of glow lamp specifications from GE back in the day.  Quite a 
few of them are listed as having a "mild radioactive additive" to reduce 
the dark effect:



The 1966 edition of the GE glow lamp manual can be found here:


Best regards,

Charles


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Re: [volt-nuts] Neon bulbs for HP 3420B or 419A chopper circuit

[David C. Partridge]

> to buy NEW bulbs from a reputable manufacturer who provides specs

Any recommendations - I can't find a source in UK.   I know Philips used to 
make them, but where I'd buy a few &deity only knows.

Thanks
Dave

-Original Message-
From: volt-nuts [mailto:volt-nuts-boun...@febo.com] On Behalf Of Charles 
Steinmetz
Sent: 17 November 2017 08:12
To: volt-nuts@febo.com
Subject: Re: [volt-nuts] Neon bulbs for HP 3420B or 419A chopper circuit

Pete wrote:

> I've seen 95V but nothing as high as 125V.
> The high brightness ones are usually 95V

Neon gas at the typical pressures used in small lamps ignites somewhere near 
200vDC.  For this reason, commercial neon bulbs use a mixture of Neon and 
Argon, which lowers the strike voltage to the 70-100v region (again, depending 
on pressure).  By this means, the original NE-2 was designed to strike at 
around 70v (DC or peak AC), while the NE-2H was designed to strike at around 
120v (DC or peak AC).

BUT:  You never know what the heck you might get from many sources today.  If 
you need a controlled strike voltage, the best bet is to buy NEW bulbs from a 
reputable manufacturer who provides specs. Most such bulbs have designations 
other than "NE-", although some are also identified with an original type on 
the datasheet.

Note also that common neon lamps (e.g., NE-2) depend on some ambient light to 
promote ionization due to the "dark effect."  This is particularly true for 
striking (many neons will not strike at all in total darkness), but affects 
continuing operation as well.  For this reason, some variants had radioactive 
material added inside the envelope to promote ionization.  These were often 
identified as "dark effect reduced" bulbs.  The NE-2U, NE-2J, and NE-2H5 were 
among these.

Originally, Thorium was used for this purpose, but before long Krypton
85 became the standard additive.  Being a gas, it was much easier to 
incorporate.  NOTE that the half-life of 85Kr is less than 11 years. 
This explains most failures of neons in chopper and LDR applications today.

Radioactive enhancement is very important for chopper operation, since the 
chopper assembly necessarily keeps the lamps in total darkness.  It also means 
that you probably do not want to buy/use surplus neon bulbs to repair choppers 
and LDRs (for two reasons -- you never know if they really had radioactive 
enhancement to begin with, and if they are old enough that you can be sure, 
they were made at least two half-lives ago and probably more like four, so they 
are all pooped out before you even install them).

I managed to source some brand-new NE-2U equivalents in small quantities a few 
years ago, but I can't remember where I got them.  (No problem if you want 10k 
of them -- several manufacturers will be happy to oblige.)

Whatever you get, test them with a beta-sensitive detector to make sure they 
are reasonably active.  The indication should be unmistakably strong -- if it's 
a case of, "Well, I think there may be some indication," they will not do.

Best regards,

Charles


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Re: [volt-nuts] Neon bulbs for HP 3420B or 419A chopper circuit

[Charles Steinmetz]

Pete wrote:


I've seen 95V but nothing as high as 125V.
The high brightness ones are usually 95V


Neon gas at the typical pressures used in small lamps ignites somewhere 
near 200vDC.  For this reason, commercial neon bulbs use a mixture of 
Neon and Argon, which lowers the strike voltage to the 70-100v region 
(again, depending on pressure).  By this means, the original NE-2 was 
designed to strike at around 70v (DC or peak AC), while the NE-2H was 
designed to strike at around 120v (DC or peak AC).


BUT:  You never know what the heck you might get from many sources 
today.  If you need a controlled strike voltage, the best bet is to buy 
NEW bulbs from a reputable manufacturer who provides specs. Most such 
bulbs have designations other than "NE-", although some are also 
identified with an original type on the datasheet.


Note also that common neon lamps (e.g., NE-2) depend on some ambient 
light to promote ionization due to the "dark effect."  This is 
particularly true for striking (many neons will not strike at all in 
total darkness), but affects continuing operation as well.  For this 
reason, some variants had radioactive material added inside the envelope 
to promote ionization.  These were often identified as "dark effect 
reduced" bulbs.  The NE-2U, NE-2J, and NE-2H5 were among these.


Originally, Thorium was used for this purpose, but before long Krypton 
85 became the standard additive.  Being a gas, it was much easier to 
incorporate.  NOTE that the half-life of 85Kr is less than 11 years. 
This explains most failures of neons in chopper and LDR applications today.


Radioactive enhancement is very important for chopper operation, since 
the chopper assembly necessarily keeps the lamps in total darkness.  It 
also means that you probably do not want to buy/use surplus neon bulbs 
to repair choppers and LDRs (for two reasons -- you never know if they 
really had radioactive enhancement to begin with, and if they are old 
enough that you can be sure, they were made at least two half-lives ago 
and probably more like four, so they are all pooped out before you even 
install them).


I managed to source some brand-new NE-2U equivalents in small quantities 
a few years ago, but I can't remember where I got them.  (No problem if 
you want 10k of them -- several manufacturers will be happy to oblige.)


Whatever you get, test them with a beta-sensitive detector to make sure 
they are reasonably active.  The indication should be unmistakably 
strong -- if it's a case of, "Well, I think there may be some 
indication," they will not do.


Best regards,

Charles


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