Schmidt humidity sensor

Schmidt humidity sensor

Humidity reflects the degree of dryness and humidity of the atmosphere. Measuring environmental humidity
is very important for industrial production, weather forecasting, food processing, etc.
Humidity-sensitive sensors are elements that are sensitive to the relative humidity conversion of the environment.
Components, usually composed of wetted layers, metal electrodes, leads and substrate substrates
.
    The figure shows a Schmidt humidity sensor , a
Schmidt circuit composed of three-plate tubes VT1 and rr2 . When the ambient
humidity is small, the resistance value of the humidity-sensitive resistor RS is larger, and the input end of the Schmidt
circuit is at low voltage. In flat state, VT1 is cut off, VT2
conduction is at low level, and the red LED lights up; when
the humidity increases, the RS resistance value decreases, the VT1 base current increases, v, ri collector current increases, and the load resistor Rl The voltage drop increases,
causing the base voltage of VT2 to decrease and the collector current of VI2 to decrease. Due to the positive feedback of the circuit, VT1 is saturated and turned on, VT2 is cut off, making
the collector of VI2 close to the power supply voltage, and the red light-emitting diode goes out. By the same token, when the humidity decreases, another positive feedback process occurs, and
the Jingmit circuit quickly flips to the VT1 cutoff. VT2 is in the saturated conduction state, and the red LED changes from off to on.