MATHEMATICAL MODEL OF A PARAMETRIC HUMIDTRANSDUCER WITH A FREQUENCY OUTPUT

Abstract

A mathematical model of a frequency parametric humidity transducer with capacitive elements based on: NaCl+polymer, NaCl; BaCl2+polymer, BaCl2, as well as capacitive elements based on complex compounds. A parametric humidity transducer with a frequency output is developed on the basis of a bipolar transistor structure, which forms an active inductance with dynamic negative resistance, which forms an oscillatory circuit of the transducer with a humidity-sensitive capacitor. Mathematical modeling and experimental studies have shown that in the range of relative humidity from 30 % to 100 %, the range of capacitance change for a humidity sensitive element based on NaCl is from 0.030·10-8 F to 3.9·10-8 F, and for a two-layer structure based on NaCl+polymer - from 0.125·10-8 F to 3.9 ·10-8 F. For a moisture sensitive element based on BaCl2 − the range of capacitance change is from 0.060·10-8 F to 3.9·10-8 F, and for a two-layer structure based on BaCl2+polymer - from 0.130·10-8 F to 3.9·10-8 F. On the basis of experimental studies it was found that the composition of complex compounds affects the sensitivity of the sensor, namely, the sensitive in the humidity range from 7 % to 27 % is a capacitive element, which is made on the basis of a hetero-metallic complex compound II, contains two antimony atoms. The sensitivity of such a capacitive element is 285 pF/%. The capacitance versus relative humidity in the range from 30 % to 75 % is almost linear, and the sensitivity is 135 pF/%. In the range of 75...95 %, there is a sharp increase in sensitivity up to 450 pF/% for all capacitive elements based on hetero-metallic complex compounds I − IV. On the basis of mathematical modeling, graphical dependences of the conversion function and sensitivity of the frequency parametric humidity transducer are obtained. The highest sensitivity of the frequency parametric humidity transducer from changes in the ambient humidity is 62 ... 107 kHz/%.