CTC Heated Bed Thermistor

[bug2k22]

I've just picked up a Duet2 Ethernet to replace the original mightyboard that came with the CTC. I also ordered the thermocouple daughter board for the extruder thermocouple (I removed the second extruder some time ago).
From what I've read the heated bed has a 100k thermistor with a resistor in series, will this work with the Duet2?

[Phaedrux]

Yes it should work. Do you have an idea what the B value might be? Is it a common 100k 3950?

[bug2k22]

@phaedrux I'm not too sure on this ctc, but it's pretty much a clone of the original makerbot replicator which looking at the wiki says "Thermistor 100K 1206 1%, most probable the NTHS1206N01N1003FE, B value 3964 K"

It has a 4pin connector which has the pins +5v/gnd/gnd/Signal.

[Phaedrux]

I don't think I've ever seen a 4 wire thermistor

[dc42]

I suggest you connect the thermistor GND/PAD1 connection to the VSSA pin of a thermistor input on the Duet and SIG_PAD1 or PAD5 to the other pin of the thermistor input. Leave VCC-PAD6 not connected.

[bug2k22]

@dc42 That seems to have worked fine, both the extruder thermocouple and the heated bed thermistor are working. I think the temperature readings are out, the bed shows ~31degC at idle whereas the extruder seems to show ~16degC which is probably about right for ambient.
I do think the extruder is under reading at working temps as printing at a reported 198 seems quite a bit higher than needed to print pla. I don't have a ir thermometer to check at the moment.