RTD excitation current

[mark294]

Hi,
I have a question regarding the SCC-RTD01 temperature module.  I connected a RTD to the module, ran the LabView example, and set the excitation current (external) to the recommended 1mA.  I was happy to see a value of 25 deg C.  I figured since I hadn't really calibrated anything being off by 2 degrees was no big deal.  At one point I decided to try reducing the excitation current to 0.9mA and got a temperature reading of 56 deg C.  Is this normal for the excitation current to change the measurement so drastically?
Thanks,
Mark

[AlanArmstead]

Mark,
I've got a couple things to mention.  First, you should be selecting "Internal" for the excitation source and 1mA for the value, since the excitation is provided by the SCC-RTD01 module. 

Secondly, changing the excitation level by 10% could certainly drastically effect the temperature measurement.  So, I don't think that is a problem at all. 

-Alan A.

[Henrik_Volkers]

Yes that is normal

As already recommended, try to use the internal current source, than you can expect the given spec.

U=R*I  and the R of your RTD is only small but well known changing with temperature.

If you need precision with low thermal masses or low thermal conduction you might look at self heating of you RTD.