I need to build a control panel for a freeze-dryer I already own. One aspect of the device will be monitoring the temperatures in the freezing chamber and the condensing chamber. Both of these can reach as low as -50 degrees.
The gadgeteer-compatible temperature/humidity module won’t work for me - it won’t fit. I need something with a separate thermistor that I can jam up into the already-existing housing.
My questions:
Will the temperature e-block work with the Spider and/or Hydra?
Can I replace the temperature sensor with one that works in my temperature range (-50-40 degrees Celcius)?
What electrical characteristics should I look for when selecting a replacement thermistor? The one I am considering is the Vishay NTCACAPE3C90066 → http://www.vishay.com/docs/29095/ntcacap.pdf
Will the temperature e-block work with the Spider and/or Hydra?
Yes, it will, but I would be surprised if it was spec’d to work at -50C. As an alternative, you could wire your own thermistor very easily with the extender module or my MakeBread Module (see wiki community offers). A thermistor is just a resistor that varies an analog signal as temp changes. There are plenty of analog input pins on several socket types.
Can I replace the temperature sensor with one that works in my temperature range (-50-40 degrees Celcius)?
Replace the sensor on the eBlock? Yes, but you might as well do what I suggest in (1) and save your eBlock.
What electrical characteristics should I look for when selecting a replacement thermistor?
Not exactly sure what you’re looking for here. As long as the thermistor is rated to measure the range of temperatures you need, you should be fine.
the only thing I can think of about “electrical characteristics” is that an analog output needs to be less than 3.3v so that you don’t saturate the analog input.
You could also look at other higher accuracy devices if that made sense (maybe thermocouples are better, i don’t know?!)
Thermocouples would be suitable… they have a WIDE temperature range (-270°C to +1372°C, though the insulator materials are almost always less than that…).
They need an extra amplifier IC to work with, and they’re definitely more expensive than a DS18B20 or a thermistor.
For that matter, if you’re really only dealing with -50C and up, a DS18B20 is small, cheap, and works from -55°C to +125°C. They’re easy to interface, and you can interface both of them on the same pin, if you want.