Humidity Sensor, digital and analog to measure air and soil moisture
To measure the rel. humidity by means of a special prepared hairstring element, with direct indication of rel. humidity and electrical transmission. The temperature range is from -60 to +70°C and the humidity range is from 5% to 100%.
Measuring the relative humidity is based on the fact that hygroscopic materials will change their dimensions depending on the ambient humidity. Selected and pre-treated human hair as well "PERNIX"-elements, which are manufactured by a special process, in are such hygroscopic materials. They are particularly suited for measuring purposes because their longitudinal expansion and contraction is very large, and also because of the consistency of the measured values and their independence of changes in temperature. The sensor contains a number of "PERNIC"-elements, combined in bundles and framed in three sections in order to increase the displacement force. The upper end of the measuring elements is connected through a lever to the axle of the pointer so that changes in length of the elements will cause the pointer to turn. The relative humidity may this way be read on the dial which is scaled 0...100 %. If e.g. the pointer indicates a value of 60 % -this means that the ambient air contains 60 % of the - at this temperature - max. possible amount of water vapour (in relation to the saturation pressure).
The transmission of the measured data is achieved by converting the variations in length elements into resistance values. For this purpose the instrument is equipped with a potentiometer having its wiper connected to the pointer axle. The wiper divides the winding of the potentiometer into two branches whose resistances change with the position of the wiper, i.e. with the rel. humidity.
The sensor 3112 has a linearized potentiometer output. This model is especially used for the automatic data acquisition. It has a potentiometer winding by which a linear correlation of the resistance values between A and R and between E and R in relation to the relative humidity is achieved. The local scale thereby retains a characteristic for hygrometers almost logarithmic division. Humidity sensors with a linear resistance output are specially calibrated to unit values. Hereby the replacement of the measuring elements or the receiving equipment is possible without additional re-calibration.
The total range from 0...100 % relative humidity results in a resistance variation of 100 W. Every
10 %-variation in humidity therefore yields a change in resistance of + or - 10 W in each branch of the potentiometer.
The winding of the potentiometer and the wiper are made of gold alloys. By this a corrosion-resisting quality is obtained. The potentiometer may receive an electric load of up to 0.5 W with the wiper drawing a max. current of 60 mA (DC).