How inaccurate should I expect an SCC-RTD01 to become over time?

[Ellen_Ward]

Hi,
I have already had one SCC-RTD01 totally die on me, and I am trying to make sure the same isn't happening again. I've had the module for less than 5 months, and it is now reading a temperature almost 25% above actual. (reading approx 20degC when the temp is known to be 16degC) At greater temperatures the difference is not as pronounced, but somewhere closer to 10%.

Do I just need to adjust my software to account for this innaccuracy? Or is this, as I personally feel, just a little too large to be a calibration issue?

Any help you can offer will be greatfully recieved.

Many thanks

Ellen

[SimonS]

Hi Ellen

I think this sounds like quite a large temperature offset. Could you supply details about your RTD please?What is the variation in resistance per degree for your RTD?

It seems strange, the properties of your system have varied. How are you testing the accuracy of the RTD measurements? Have any changes to the system set-up been made recently? Try checking the excitation source on the RTD01, is it still 1mA?

Regards

[Ellen_Ward]

I'm using a standard bullet pt100 RTDs, class B (from RS, I can supply the stock number if you require it). I have to confess to not knowing the variation in resistance per degree, however the tollerance is, apparently, within .5 of a degree.

The system itself seems to be the same as it was when I first put it together. If I attach a new SCC-RTD01 into the place of the one giving me problems, the temperatures given are what other, external, temperature probes suggest they should be, however when I reconnect the 'problem' module, the temperature drift still exists.

No changes were made prior to this problem being noticed.

I have not checked the excitation source, however I will do this as soon as I can open it up again.

Many thanks for your h
elp

Kind regards
Ellen

[Ellen_Ward]

Hi Simon,

Thanks again for taking the time to respond to my query, however now the module appears to be in need of return as the temperature is no longer 'drifting', and has now pretty much died. The excitation current is 1.4mA, and the temperature reading is five times what it should be.

Again, thank you for your time and your assistance.

Regards

Ellen