Humidity measurement control circuit design

As shown in the figure, the control circuit is composed of a reference pulse generator, a humidity sensitive sensing one-shot delay circuit, a pulse width comparison circuit, an integrating circuit, and a measuring head for performing relative humidity measurement.
The humidity sensor head uses a humidity sensitive capacitor Cs, which uses a moisture sensitive polymer film as a dielectric, and uses the film to adsorb the reversibility of water molecules, so that the change of the dielectric coefficient is reflected in the change in capacitance. The humidity sensitive capacitor has strong anti-interference ability and good linearity. IC1 and IC2 use a dual time base circuit 556, half of which is made into an astable multivibrator. The oscillation frequency is determined by R1, RPl, and Cl. The oscillation period of the illustrated parameters is about 130?s, and the duty ratio is 1: 1. IC2 and R3, the humidity sensitive sensing capacitor (Cs) form a one-shot delay circuit.