[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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