Hi,
I am having an issue with a 4-wire RTD measurement I am trying to make. Basically, I have an RTD (100 ohm PT) two wires on a 5 mA excitation source (from an adjustable LM317, I have an exact current) and the other wires two at an analog input. I am getting a stable response from the RTD but the problem is the RTD is measuring a little higher resistance than expected (It's about 10 ohms (10%) higher than expected). What I think I've narrowed it down to is that the analog input isn't high enough impedence and current is leaking and subsequently reading an increased resistance measurement. Does this make sense, or sound familiar as a potential DAQ issue? I used two big resistors to increase the impedence of the analog in loop and that lowers my resistance measurement, but it still is too high and becomes more noisy.
Does anyone have any idea how I can correct for this? If I am off base on this issue I would love to hear any thoughts/experience that anyone has with this.
Thanks.
Ramsey
