I am planning to build a series of Arduino-controlled temperature-reporting units for a room full of "Ultracold" -80°C freezers. (I ultimately want to convert the signal to a serial stream that will interface with my existing system.)
So far I have only found one-wire and other sensors that are only rated to -55C. In my application they would spend most of their time around -80C. I only need about 0.5 to 1 degree accuracy at those temperatures.
Does anyone know a source for a low-temperature sensor that would be arduino-compatible, reliable, and be able to be placed at the end of a wire (to be passed into the freezer through a small port)?
Small update below.
Best Answer
The forward voltage (\$V_f\$) of a diode at a small constant current is often used to measure low (cryogenic) temperatures. Silicon diodes have a \$V_f\$ which is nearly a linear function of temperature over a wide range, with slope approximately -2 mV/K. There are even specially-built diodes standardized to specific \$V_f\$ vs. T curves. If you're willing to do a two or three point calibration yourself, then you can use an ordinary signal diode. Even a 1N4148 can accurately measure liquid nitrogen temperatures if you calibrate it.
You can improve accuracy by: