Temperature sensors and temperature controller

I switched the two diodes between the channels. Now, the good diode is working correctly and following the set point at a fixed ramp rate; the second diode, which was not sensing the temperature correctly, also following the ramp rate but showing around 15 K temperature more than the set point. I guess the issue is in the wiring of the second diode.

When I measure the resistance between the diodes using a multimeter, it shows around 26-27 mega Ohm resistance between I+ and V-, and when reversing the polarity of the probes, it shows an open circuit.

I would like to clarify the problem. I have two DT-670 diode sensors; one is on the sample mount (sensor A, which is the control sensor for heater output), and another is on the sample holder (sensor B). Sensor A and B were connected to temperature controller input A and B, respectively, and were working fine (the only thing is sensor B always used to show 2-3 K lower temperature than sensor A or setpoint. Since both the sensors were following the ramp rate so this small difference was not a problem to us.) Suddenly, Both the sensors stopped to follow the ramp rate according to the given command. When I cooled the sensors using some external source, sensor B did not sense the temperature properly; it sensed the temperature decrease around 290K and then again started to raise the temperature. While sensor A showed the temperature decrease properly as we cooled the sensor using an external source. Although both the sensors showed 26-27 mega Ohm resistance and open circuit when polarity was reversed.


When I switched the diode sensors between the input channels as per your suggestion, sensor B, which was not working well previously, is now working well and following the set point at a fixed ramp rate. While sensor A, which was sensing the temperature properly previously, is now not following the ramp rate and showing a higher temperature than the set point while cooling through the program and a lesser temperature during the warming cycle. The difference between sensor A and the setpoint continues to increase as the program runs further.


Sensor A is the control input for heater output, and no manual output percentage is selected.

I am not able to understand what the problem is.

Hello Sir @lake Shore Jeff M

I checked all the connections and tested each sensor as well. Temperature controller settings are also acceptable. I am wondering that a diode that was not sensing the temperature correctly is working fine after switching the controller input channel while the good diode is not working correctly in any channel.

We have a Lakeshore model 336 temperature controller as well. In this controller, also, sensor B is not sensing the temperature correctly. But when we switched the input channel in temperature controller 335, as per your suggestion, sensor B started working fine. How is this possible?