rauol said:
i have to design a temperature controller with +/- 0.1 deg C. accuracy.
Input is PT100 and temperature range is from 30 t0 45 Deg C.
Any referances?
Thanx
There are lots of references out there, but what to do, what to do?
Here are some guidelines for issues to focus on:
1. Use a constant-current source to excite the rtd. Set the current high enough to produce an rtd voltage well above the noise, but not so much as to cause rtd self-heating. Constant current will enable you to run long cables to the rtd without suffering lead-loss degradation.
2. Rather than try to control the current exactly, simply measure it with the adc.
3. Sense the rtd voltage out at the rtd (i.e., "4-wire" circuit) so as to eliminate the cable losses in the current loop. If throughput is not an issue, consider an integrating type adc, which will further help to reduce noise.
4. Convert the measured rtd voltage to temperature units. This can be done to your specified accuracy with a simple lookup table. You don't need a huge table; simply interpolate between table values. You can easily determine the number of table values by simulating on a spreadsheet.