[time-nuts] HP10811 current versus temperature

Didier Juges didier at cox.net
Thu Nov 22 17:33:33 EST 2007


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

> -----Original Message-----
> From: time-nuts-bounces at febo.com 
> [mailto:time-nuts-bounces at febo.com] On Behalf Of Bruce Griffiths
> Sent: Thursday, November 22, 2007 3:28 PM
> To: Discussion of precise time and frequency measurement
> Subject: Re: [time-nuts] HP10811 current versus temperature
> 
> Ideally you should use a 4 terminal current sensing resistor 
> and a high input impedance instrumentation amplifier.
> A Thomas style 4 terminal resistor in a temperature 
> controlled oil bath would be nice, but failing that a low 
> tempco 4 terminal resistor will suffice.
> 
> Bruce




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