[volt-nuts] 732A and Prologix received

[Mike S]

On 8/25/2014 9:54 PM, Don at True-Cal wrote:
> Why?
>
> Let me count the ways.You can never count on any Seebeck voltage to
> be immediately offset, there are far too many variables.
...
 > A set of
> 5440A-7002 (banana plug) cables comes with this calibrator
> (5440A-7003 spade lugs for 5720A)

For those leads, Fluke says they have the advantage of "minimizing the 
emf caused by temperature difference between the ends of the leads." I 
don't have much argument with that - if there's a temperature difference 
between the ends, you won't have an equal thermocouple offset, so 
minimizing such effects makes sense.

But, since those leads use pure copper wiring ("Belden 8262 or 8719 or 
equivalent"), how does having only the contact itself made of tellurium 
copper (TC) make a difference? Shouldn't they be TC end-to-end, with gas 
tight crimped connections? Does the tinning on that copper cable have an 
effect? What's the Seebeck coefficient for a copper to tellurium copper 
connection?

You said that "Tellurium Copper is usually not used for a device's 
terminal posts but used as the lead wire..." But, Fluke does exactly the 
opposite - those Fluke leads use TC connectors and are characterized 
"while engaged in a five-way binding post of Tellurium Copper Alloy 145, 
half hard." Since they use pure copper cabling, I'd think they'd work 
even better with a pure copper binding post, since the offsetting 
thermocouples would be in close proximity, and not at different ends of 
the cable.

You earlier said "Any type of Silver or Gold plating on the terminal or 
wire will introduce the undesirable  dissimilar metal properties, both 
at the plating junction and at the plating metal to DUT terminal." Now 
you emphasize that by saying "If someone used a set of gold-plated 
interconnects for this procedure, they would be laughed out of the lab 
and the calibrator would be useless until recalibrated properly..."

But, the specs for the Fluke 5440A-7003 which you say are appropriate 
for the 5720A state: "Connector materials: Copper space lug with gold 
plating over silver plating." (Both platings!!) Is someone to be laughed 
out of the lab for using the cables they're supposed to use? The 
5440A-7002 specs aren't clear, but if they're not plated, are you 
required to clean them of copper oxide for every use? It seems that 
would be necessary, since a gold-copper thermocouple is ~0.5 uV/C, while 
a copper-copper oxide one is ~1000 uV/C.

You seem to be stating one thing, but then giving evidence which 
contradicts your claim. It seems that Fluke uses TC where there's 
thermal mass, and pure copper where there's little, and uses plating in 
addition.

Please clarify, this isn't making sense to me.