Calibration of special relative humidity and temperature (RHT) sensors and evaluation and expression of uncertainty in the measurement

This paper reports the calibration of special type of relative humidity and temperature sensor, which gives the output in terms Of millivolts, measured by precision digital multimeter (DMM) to further estimation of relative humidity in,the range of 25 %RH to 95 %RH. The sensor has been calibrated against the standard aspirated psychrometer having a pair of matched dry and wet bulb quartz thermometers. The temperature of wet bulb thermometer is effectively depressed when a ventilated airflow is maintained at a speed more than 3 metre/second. The relative humidity of reference standard psychrometer is computed using psychrometric equation to relate with the output of the RH indicator under comparison. The paper also describes the details of estimation and expression of expanded uncertainty in the calibration of the sensor at measured relative humidity. A sufficient number of data were undertaken to evaluate the uncertainty at a confidence-level of approximately 95% for a normal probability distribution.