PT100 probe issues

[UpTheToon]

I completed 4 brews on my new one pot BIAB rig without issue but at the start of the 5th the temp was being measured at -20 odd at the start then I got errors from the sestos PID.

I've done 2 brews just measuring the temp by hand and have now managed to borrow a multimeter to try and find the source of the issue. When I measure the resistance of the white and red wire in the 3 wire (Mr Lard) PT100 probe (or any 2 of the three wires for that matter) the multimeter is fluctuating wildly.

Does anyone have any idea what could cause that?!

[sparky Paul]

2 of the wires should be connected together at the probe, so there should only be the resistance of the wiring there and back. The other wire is connected to the other end of the PRT element. With a sensitive multimeter, should read around 108Ω at ambient temperature.

Make sure all connections are good, dry, and that nothing is shorting to metalwork. If you still have problems, PRT could be kaput, or contaminated with moisture.

[UpTheToon]

Thanks for the detailed response.

Something seems to be wrong, if I hold the multimeter it starts to settle close to 108 but jumps around to 0, 160, 108, 140, 0 etc.

Connections all seem sound and the rest of it is encased in plastic or metal. Might be a goner...

[sparky Paul]

All it needs is a dry joint onto the element or summat, and you've had it.