Brigadoon - An Occasional Corner on the Internet
Calibrate Ground Temperature Sensor
Designed by Mark Little
Four things are required to calibrate the temperature sensor. The first is a stable ambient temperature, to ensure that the sensor is measuring a constant temperature during calibration. The second is a +5V power supply to power the sensor. Next, an accurate digital thermometer is required to measure the ambient temperature close to the sensor; and lastly, an accurate digital multimeter to measure the output of the sensor. Ideally, the voltmeter and the thermometer should be calibrated, but this is unlikely in most domestic situations.
Once the power has been connected to the sensor and the voltmeter connected between the sensor output and the earth lead, take measurements of the ambient temperature to ensure that it is steady. When this is the case, measure the output of the sensor with the voltmeter.
The output voltage of the sensor is set to 10mV/°K. Since the temperature in Kelvin is the temperature in Celsius plus 273.15, at 25°C, the digital voltmeter should be reading 2.9815V.
Calculate the voltage reading expected for the measured ambient temperature.
Adjust the Trimpot so that the voltage read matches the calculated voltage.
Come back in 15 minutes and monitor readings for 15 minutes to confirm that the voltage being read matches the ambient temperature.
When you are satisfied that the calibration is done, place a dab of nail polish or similar around the trimmer screw to ensure that it remains in this position. Nail polish is brittle and will break away if you need to recalibrate.
If you do not have an accurate digital thermometer, the bottom of this page on the Australian Bureau of Meteorology (BOM) website shows how to get an accurate temperature of 0°C for calibration purposes. If you use this method, make sure that the sensor is an a plastic bag that will not leak during the calilbration process.