I just realized that all my measurement tolerances are nV not pV. Sorry
about not checking units first.
Charlie
On 8/25/2014 9:50 AM, Charles Black wrote:
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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