rtd reading 50 degrees low

I have a copper coil through my HLT to use as a HERMS with an RTD probe on the output side of the copper coil. The RTD is reading about 50 degrees low. The controller (Ascon x1) seems to be operating properly... when I compensate for the temp difference it sends a switch signal to the SSR that's controls the (120v) heating element in the HLT at appropriate times.
I am using an Ebay RTD probe with 3 wires out of the probe- could a mis-wiring from the probe to the PID account for the bad temp reading, or do I have a bad probe?

If you have a meter, check the resistance of the RTD & refer to the reference tables for that particular unit and see how close you are. If I remember correctly, 2 of the wires are connected together on one side of the RTD so those should read very close to 0 ohms and between either of those and the third wire is the resistance that changes with temperature.

quite right- 2 conductors connect to one terminal in the PID. Checking resistance between the three makes a lot of sense- beats rolling the dice like I did. Thanks!

There's more than one kind of rtd as well maybe you have the settings on the pid wrong for the type of rtd you have. I think one rtd is pt100 and the other is a Cu50, at least that's what my auber manual has listed as supporting different rtd sensors.