LM35 Temperature Sensor Calibration
Initially it was intended that the LM35s themselves would be submerged in boiling water and then ice water in order to calibrate the top and bottom end of the temperature spectrum against two fixed ‘known’ values. Unfortunately, it was noticed that steam softened the araldite - used to seal the sensors - to an unacceptable level and therefore submerging them in boiling water for a prolonged period presented too high a risk of damaging the sensor. For example: water ingress from steam exposure to T6 causing temporary malfunction.
Because of this, the accuracy of a thermocouple was measured in this manner instead and then the LM35s were calibrated against the thermocouple at room temperature. In an attempt to ensure uniform air temperature across all ten sensors and the thermocouple, the sensors were bunched together and suspended in air in a sealed box.
Readings were then recorded for each sensor, as well as the thermocouple, and the signals arithmetically adjusted in LabVIEW such that they all agreed with the thermocouple. The table below lists the readings and errors. Full details of the temperature sensor calibrations can be found within the calibration excel documnent linked here.
HIH Humidity Sensor Calibration
The issue with calibration of the humidity sensor was identifying a manner of getting both 0% RH (relative humidity) and 100% RH. Since this could not be easily and accurately achieved it was decided to calibrate the sensor against an instrument of known accuracy. The instrument of choice was part of a thermal comfort kit provided by Dr. Paul Strachan. The sensors were isolated in a sealed container in a similar manner to the temperature sensors to ensure uniform conditions. The table lists the readings taken and error noted as part of this exercise.
