[volt-nuts] 732A and Prologix received
Charles Black
cblack at centurytel.net
Mon Aug 25 15:28:34 EDT 2014
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, acbern at 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.eman at gmail.com>
>>> An: "Discussion of precise voltage measurement" <volt-nuts at febo.com>
>>> Betreff: Re: [volt-nuts] 732A and Prologix received
>>>
>>> On Sun, Aug 24, 2014 at 1:46 PM, Don at True-Cal
>>> <truecalservices at 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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>
>
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