Introduction and working principle of humidity sensitive capacitor (humicap)

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Introduction and working principle of humidity sensitive capacitor (humicap) [Copy link]

Humidity sensitive capacitors (English name: humicap) are generally made of polymer film capacitors. Commonly used polymer materials include polystyrene, polyimide, cellulose acetate, etc. When the ambient humidity changes, the dielectric constant of the humidity sensitive capacitor changes, causing its capacitance to change as well. The capacitance change is proportional to the relative humidity.

1. Features:

The main advantages of humidity-sensitive capacitors are high sensitivity, good product interchangeability, fast response speed, small humidity hysteresis, easy manufacturing, easy miniaturization and integration, and their accuracy is generally lower than that of humidity-sensitive resistors. The main manufacturers of humidity-sensitive capacitors abroad include Humirel, Philips, Siemens, etc. Taking the SH1100 humidity-sensitive capacitor produced by Humirel as an example, its measurement range is (1%~99%) RH, and the capacitance at 55%RH is 180pF (typical value). When the relative humidity changes from 0 to 100%, the capacitance changes from 163pF to 202pF. The temperature coefficient is 0.04pF/℃, the humidity hysteresis is ±1.5%, and the response time is 5s.

2. Humidity measurement principle

During the measurement process, the capacitive humidity sensor is equivalent to a tiny capacitor. The measurement of capacitance mainly measures its capacitance value C. The humidity sensor is not a pure capacitor. Its equivalent form is shown in the dotted line part of the figure below, which is equivalent to a capacitor and a resistor in parallel.

3. Measurement circuit and schematic diagram

The figure below is the specific measurement circuit of the complex voltage method for capacitive humidity sensors, which includes three parts: a differential circuit, an inverting circuit, and an integral circuit. After the sinusoidal signal Vin generated by the sine wave generator passes through the differential circuit, the signal becomes Vout, and then the output of Vout is divided into two paths. One path directly enters the integral circuit through the electronic switch 1K, and the other path first passes through the inverting circuit to make the output of Vout Vout. After passing through the electronic switch 2K, it also enters the integral circuit. The function of the electronic switches 1K and 2K is to rectify the Vout signal and then measure it through the integral circuit. The above method is used to measure the value of the humidity-sensitive capacitor. The measurement range is between 30pF and 100pF, and the relative error of the measurement can reach ±0.2%

Source: Internet Humidity sensitive capacitors (English name: humicap) are generally made of polymer film capacitors. Commonly used polymer materials include polystyrene, polyimide, cellulose acetate, etc. When the ambient humidity changes, the dielectric constant of the humidity sensitive capacitor changes, causing its capacitance to change as well. The capacitance change is proportional to the relative humidity. 1. Features: The main advantages of humidity-sensitive capacitors are high sensitivity, good product interchangeability, fast response speed, small humidity hysteresis, easy manufacturing, easy miniaturization and integration, and their accuracy is generally lower than that of humidity-sensitive resistors. The main manufacturers of humidity-sensitive capacitors abroad include Humirel, Philips, Siemens, etc. Taking the SH1100 humidity-sensitive capacitor produced by Humirel as an example, its measurement range is (1%~99%) RH, and the capacitance at 55%RH is 180pF (typical value). When the relative humidity changes from 0 to 100%, the capacitance changes from 163pF to 202pF. The temperature coefficient is 0.04pF/℃, the humidity hysteresis is ±1.5%, and the response time is 5s. 2. Humidity measurement principle During the measurement process, the capacitive humidity sensor is equivalent to a tiny capacitor. The measurement of capacitance mainly measures its capacitance value C. The humidity sensor is not a pure capacitor. Its equivalent form is shown in the dotted line part of the figure below, which is equivalent to a capacitor and a resistor in parallel. 3. Measurement circuit and schematic diagram The figure below is the specific measurement circuit of the complex voltage method for capacitive humidity sensors, which includes three parts: a differential circuit, an inverting circuit, and an integral circuit. After the sinusoidal signal Vin generated by the sine wave generator passes through the differential circuit, the signal becomes Vout, and then the output of Vout is divided into two paths. One path directly enters the integral circuit through the electronic switch 1K, and the other path first passes through the inverting circuit to make the output of Vout Vout. After passing through the electronic switch 2K, it also enters the integral circuit. The function of the electronic switches 1K and 2K is to rectify the Vout signal and then measure it through the integral circuit. The above method is used to measure the value of the humidity-sensitive capacitor. The measurement range is between 30pF and 100pF, and the relative error of the measurement can reach ±0.2%