Connecting PT100 to Bed Temp

Sculpt Fabricator

We currently have a self contained high voltage bed heater that uses a TCN4 that controls and displays bed temperature and does not connect to our duet wifi board. We had originally drilled a thermistor into the side of the bed and hooked to the Bed Temp input on the duet wifi board to be able to get some visual on the computer that the bed was on and working, but the temperature is not close to being correct.
The TCN4 uses a PT100 to read the bed temperature. We hoped we could connect to this at the TCN4 input and hook to the Bed Temp input of the duet wifi board and get an accurate reading, but we are getting around 540C reading when off and the ambient is around 23C
After some research I see that the PT100 needs an adapter board like we have on our two extruder PT100's but not sure how one would plug into the Bed Temp location, if this is even the issue, or maybe just a setting, any help would be much appreciated.

We are running Duet WiFi 1.02 or later + DueX5 version 2.05 (2019-12-13b1)

M305 P0 T100000 ; Set thermistor + ADC parameters for bed heat

Sorry, I tried to upload some pictures of what we had but keep getting an error !

dc42

@sculpt-fabricator if the PT100 sensor is connected to the TCN4 then connecting it to the Duet as well is not going to work. Possible solutions:

Disconnect the heater and the PT100 from the TCN4 and control them from the Duet instead. You will need a PT100 daughter board and a solid state relay.
Continue to use the TCN4 but add a second temperature sensor to the bed to connect to the Duet.

Sculpt Fabricator

@dc42 Thank you