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: [EMAIL PROTECTED] > [mailto:[EMAIL PROTECTED] 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 _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
