PID temp is wrong

[mike11b82]

so i have a simple 1 PID controler and i have used it about 8 time with no problems. the last two times i have brewed the temp probe is reading high. the first bath about 4-5 degrees the next it was 7-8.

Auberins PID
RTD temp probe from them with the cable they sell, i did have to extend the wires to reacn the PID.

any idea what is going on?

 

[atoughram]

You might want to calibrate it in boiling water and then keep a close eye on it for temperature drift. How did you extend the wires? Did you solder them together?

 

[muhteeus]

I know "cold junctions" when you use a thermocouple (any change in wiring, adding TB, new heads, new wire) require a recal.

This could affect RTD performance as well... I doubt you have made any changes. Maybe you have some oscillation or offset on the DC excitation voltage coming from the PID? Have you verified resistance and/or voltage measurements across the probe?

 

[stlbeer]

Did the end of the probe where the connections go get wet at all? What about on the plug end? That has caused me problems in the past. You might have to take it apart and let it try out if that is the case.