[time-nuts] HP10811 current versus temperature

Bruce Griffiths bruce.griffiths at xtra.co.nz
Thu Nov 22 18:47:21 EST 2007

Didier Juges wrote:
> Bruce,
> I have some 4 terminal current sense resistors at work, but they are very
> low values (0.1 ohm and lower), so what I may gain at the sensor I may loose
> in the amplifier. Right now, the 1 ohm resistor and OP-27 give a voltage
> that is way out of the noise, as the curve shows. If I can find more
> temperature stable resistors for the instrument amplifier, then I could use
> one of those 4 terminal resistors. I will see what I can get to improve this
> setup. As it is, it may not be extremely accurate in absolute terms, but it
> is precise and probably sufficiently relatively accurate for what I want to
> do.
> What do you think of the 2mA/degree current sensitivity? Is it in the
> ballpark? I need to run the test much longer, and over greater temperature
> variations, but I am still tinkering with it... The engineer's curse :-)
> Didier

Its hard to find temperature stable 4 terminal resistors with tempcos
better than 50ppm/C or resistances greater than 0.1 ohm off the shelf.
The only source of 1 ohm 4 terminal resistors would appear to be used
L&N, JRL, etc 4 terminal (Thomas style) standards which can be expensive
($US2000 or so).
However have found listing for NBS pattern standard resistors at $US165.
Such standard resistors have very low tempcos but are intended for oil
bath operation.

The only current US manufacturer of such standard resistors (including
ones rated for operation in air) appears to be Ohm labs:
http://www.ohm-labs.com <http://www.ohmlabs.com>

Leeds and Northrup and Julie Research labs once made such resistors.

All that can be done to check that the temperature dependence of the
oven current is in the ballpark is compare your results with those in
the HP journal article on the 10811A

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