Improvements in the measurement and control of moisture

951,942. Measuring electrically. BRADFORD DYERS' ASSOCIATION Ltd. June 16,1961 [June 21, 1960], No. 21744/60. Heading G1N. The moisture content of a material is determined, for the purpose of controlling that content, by measuring the relative humidity of air in moisture equilibrium with the material by means of electrical wet and dry thermometers which give a single signal, and modifying the signal in accordance with the temperature by means of a second electrical dry thermometer. Applications are in the control of the moisture content of continuous lengths of textile materials, bales of cotton, wool, tobacco, hay and silage. Air is drawn from the vicinity of a continuous sample 1 of textile material after it leaves a drying apparatus (not shown) and passes over a dry thermistor 3 and a wet thermistor 4, kept moist by wick 5 dipping into water reservoir 6. Further dry thermistor 9 compensates for the temperature of the airstream. Thermistors 3, 4 are fed with two equal antiphase outputs from a balanced transformer and the resulting output is amplified and fed to a non-linear amplifier, whose gain is controlled by thermistor 9. The output is rectified and fed to a meter giving a relative humidity reading indicative of the moisture content of the material, and to a control unit which alters the speed and/or temperature of the drying apparatus. The percentage moisture content by weight may be calculated for a given material. Electric resistance thermometers or thermocouples may be used instead of thermistors.