Unfortunately yes, we need the external temp sensor because the perfusion chamber for the electrophysiology recording is not from the same manufacturer and, therefore, it does not have any built-in sensor. We have calibrated the temperature needed at the heating element that gives us 30ºC at the bath using a thermometer, but this will obviously not be accurate anymore once a microscope objective is immersed in the solution and starts conducting heat away, and in this case the thermometer won't fit the chamber for a new calibration. So yeah, we're kinda stuck until we find a probe small enough for the chamber. Whoever bought this should have considered these things, and it would have been better to try and find the additional € than to have something that's not really practical or functional. I guess, based on the info I already got from you, that using a thermistor-based probe is not possible at all?
I'll break the bad news to the person that bought this heating system...
Thanks a lot for your help!
Cheers,
Paulo.