Temperature Troubles

Today the team tested the thermistor in conjunction with PWM-controlled Peltier heating. This test acts to validate the thermistor's ability to accurately measure the Peltier's temperature for later closed-loop temperature control. Of course, an external thermocouple was also used to double-check the thermistor's measurements.

Peltier control and temperature measuring circuit

Going into the experiment the team noted several potential issues. Firstly, the thermistor has a settling time of 1.5s, meaning that it may not be able to record temperature swings at a sufficient rate. Secondly, the sphericle shape of the thermistor means that there may not be good thermal contact between the thermistor and the Peltier. This lack of thermal contact is expected to decrease both the rate of change and the magnitude of temperature measurements.

Thermistor dimensions

Upon testing it was discovered that the thermistor temperature measurements lagged behind the thermocouple ones. This resulted in a staggering 7-degree difference toward the maximum allowable Peltier temperature. This difference can be seen in the figure below.

Work will need to be done to improve the thermistor temperature measurements. The team plans on retrying the test with thermal paste to improve the thermistor's thermal contact. The team remains optimistic that this approach will work, however, clearly more testing is needed.