Hi Adrian,
Although I have not used the Pomona spade lugs or a nano-voltmeter, my
experience is consistent with yours otherwise.
Anyone who has calibrated (CAL 0 anyway) a 3458A has enough information
to deduce that lowest input short voltage is going to be a copper wire
since the meter is set to zero volts during calibration using a heavy
gauge (14 to 16) copper wire to short the top four input terminals. This
is very convenient since it is so easy to duplicate in the field and
makes simple inexpensive test leads best for high precision
measurements. In order for the 3458A to make full accuracy measurements
(8 digit) NPLC must be set to 1000 (according to the User's Guide). If
you use a lower NPLC value there is a table in the User's Guide that can
be used to determine how accurate your measurements are going to be.
Just for fun I ran several shorts for NPLC 1000 on my 3458A. It has been
about a year since I clid my last CAL 0 so it was going to be
interesting at least for me. The first shunt was my test "U' shaped
shunt that I used for my last CAL 0. Note: STP = Shielded Twisted Pair.
Calibration shunt -0.00021mv +/- 10
pV Equilibration time 5 minutes. 14 gauge per Calibration
Manual.
"U" heavy wire -0.00021mv +/-
10pV Equil. time 5 minutes. Used the through holes in the
Input banana posts only.
Copper wire -0.00019mv +/-
10pV NAPA PVC covered automobile wire at same contact
points as CAL shunt
Standard Ground Plate -0.00040mv +/- 10pV Equil. time 5
minutes. Gold plated ground plate from my Datron 4910
Copper wire -0.00019mv +/-
10Pv Equil. time 2 seconds. Used the banana through holes.
STP 2 meter test lead -0.00021mv +/- 10pV
Equil. time 2 seconds. M27500 24 gauge STP Tefzel insulation.
Banana plugs -0.00021mv +/-
30pV Equil. time 20 minutes. My best "Perfect" gold plated
plugs with copper wire.
Charlie
On 8/25/2014 3:36 AM, acb...@gmx.de wrote:
I have used the pomona spades, mainly to interface the low emf pomona banana
cables to binding posts. I have stopped this, reasons being, they are large and
worse, that the pomona spring loaded insulation tube that covers the banana
plug conductor uses such a strong spring that slowly the plug works its way out
of the spade. this btw also happend to me when I used the pomona low emf
binding posts together with the pomona low emf banana cables. overall I m not
happy with these.
so, due to lack of options, I changed to self-made twisted shielded pair of
high grade teflon/kapton silver plated copper cable with gold plated copper
spades (crimped). I use them not only with the 3458a but also with nanovolt
meters. these have higher resolution and accuracy in low level measurements
than the 3458a. emf voltages were never an issue with these cables if properly
used. I have posted some results doing 34420a stabilty measurements on the pmel
forum, and the results are convincing (purpose was actually not to test the
cables but the stability of the 34420a, but the emf issue is a part of this of
course. we use the 34420a to do low voltage precision measurements on thermal
converters where the full scale signal sometimes is 1mV).
that btw also relates to don's statements below, I do not concurr with his
comments about copper telurium as cable and spade material and so on. this
material, as stated here many times, is used because it is machinable, for
copper spades one would not use it. the 34420a factory cable uses copper cable
and copper spades, not telurium-copper. if there was a problem, it would be
worse with the 34420a than with the 3458a because of its low level ranges. and
again, I have not seen any problems in a chain of (output to input):
1.copper-tellurium post from e.g. 8 digit calibrator
2.crimped copper spade, gold plated
3.silver plated tsp copper cable
4a.crimped copper spade to copper-tellurium post or
4b.soldered copper connector(34420)
my consistent results over more than a year using them.
Gesendet: Montag, 25. August 2014 um 06:33 Uhr
Von: "Orin Eman" <orin.e...@gmail.com>
An: "Discussion of precise voltage measurement" <volt-nuts@febo.com>
Betreff: Re: [volt-nuts] 732A and Prologix received
On Sun, Aug 24, 2014 at 1:46 PM, Don@True-Cal <truecalservi...@gmail.com>
wrote:
Randy & all,
You have correctly concluded that some (maybe not all) of your measurement
problem is thermal EMF being added or subtracted in series within your
measurement interconnect. This thermal EMF is generated at the junction of
dissimilar metals when accompanied with thermal gradients between the test
lead and device terminals. You have to eliminate both the dissimilarity of
the metal junctions as well as minimize the thermal differences. The
terminals of the 3458A as well as the 732A are Beryllium Copper so you want
to use the same test lead terminals. Forget the typical Tin plated lugs or
even Gold plated as both are not Beryllium Copper and constitute dissimilar
metals. The best solution (as usually the most expensive) is to use a set
of
Fluke 5440A-7005 (48") cables. I also have just as good results using the
much more flexible Pomona 11174A (lugs end always stay connected to the
732A) or 11058A with more convenient shielded banana plugs. The Fluke cable
has the added Guard built in but be sure to also use a Guard lead with the
Pomona cabled. The Guard lead does not need to be low thermal EMF. DIY
cables is usually not a good idea because the lead wire to terminal also
constitutes just as critical of junction. The above cables use Tellurium
Copper wire which is usually hard to find and hard to crimp properly and
NEVER solder.
11058A and 11174A are discontinued at Keysight. However, Pomona 5295 spade
to banana cables are available (5295-36 at Mouser et al) and claim that
they are designed to minimize thermal EMFs. Datasheet is here:
http://www.mouser.com/ds/2/159/d5295_1_01-51722.pdf Any comments on these
as an alternative?
Orin.
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