Development and performance of a small relative humidity sensor for indoor microclimate measurements

The development and performance of a small relative humidity sensor is described, capable of distinguishing humidities over distances only millimetres apart, allowing humidities to be measured in the microenvironments of biocontaminants such as dust mites and mould. The sensor can, for example, distinguish between humidities at the bottom of a carpet pile from humidities at the top, or between closely spaced locations in bedding such as below a sheet and on top of a mattress. Calibration showed that the device was accurate to 1% humidity, had a time constant of the order of 10 seconds, and had low drift. Being cheap it can be used in large numbers.