[volt-nuts] Sn10Pb90

Volker Esper ailer2 at t-online.de
Tue Aug 13 18:04:47 EDT 2013


I agree with Rob. I never heard about special solder from HP.

Bear in mind, it's not the thermal voltage itself, that causes 
measurement error, it's the _difference_ between the two leads. It's 
much more important to keep associated plugs and solder joints at the 
same temperature! So if you solder the plus-joint with your own 
soldering wire, solder the minus-joint, too. That makes sure, thermal 
EMF will be the same at both joints and hence compensate one each other.

As I mentioned before, I compared 24bit streams from two 34401A over 
many days. The DMMs were at their highest sensitivity, one of them was 
fixed by soldering an input relay with usual Sn60Pb40. The curves ran 
absolutely parallel when the room temp changed. If there had been an 
issue with the thermal EMF, the 6.5 digit DMM would have been able to 
measure those voltages with ease.

So either the EMF difference isn't measurable (because temp at both 
relay pins change synchronously), or HP didn't use special solder.

I wouldn't go the way of using special solder, except Fluke would 
recommend it explicitly.

What about asking Fluke itself?

Volker




Am 13.08.2013 21:38, schrieb Rob Klein:
> Op 13-8-2013 20:16, Joseph Gray schreef:
>> I came across a couple of old Fluke differential voltmeters that need 
>> some
>> work. I thought it would be best to use low thermal EMF solder on these.
>>
> I think it would be best *not* to.
>
> As far as I know, Fluke never used any low thermal EMF solder on any 
> of its equipment, even
> the very top-of-the-range stuff. I certainly never seen it mentioned 
> in any service manual
> for e.g. the 720, 845, 750, 752.
>
>
> Rob.
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