Sensor purge is also an automatic procedure that minimizes the drift at the wet end readings of the dew point measurement. Sensor purge is performed once a week or when the power is switched on. The sensor is heated for several minutes, which will then evaporate all excess molecules out of the sensor polymer. This, together with the auto-calibration, results in a very small drift. The measurement output of the transmitter is frozen to the last measured value for the duration of the sensor purge.