The working principle of humidity resistance and its application (II)

The principle of humidity resistance:

Humidity-sensitive resistance sensors are mainly composed of a wet sensing layer 3, an electrode 4, and an insulating substrate 2 having a certain mechanical strength, as shown in FIG. The moisture-sensitive layer causes a change in the resistance value between the two electrodes after absorbing the moisture in the environment, thus converting the change in the relative humidity into a change in the resistance value.

Humidity resistance can only be exchanged, and DC will cause moisture-sensitive failure, because the DC electric field will cause the charged particles in the polymer material to be biased toward the two poles. After a certain period of time, the humidity sensitive resistor will fail. Therefore, it is necessary to use AC to maintain its dynamic balance, which is why the resistance of the humidity-sensing resistor must be bridged instead of using an ordinary multimeter.

Water molecules are polar molecules that decompose into H2 and O2 in a DC electric field, affecting measurement, and in terms of humidity

The presence of conductive ions in the sensor, in the case of high humidity, such as the use of direct current will drift, causing conductivity drift, affecting the life of the sensor. RC can be used to charge and discharge, timing method, some chips have RFC function, can also be used, or use IC to directly generate 1KHZ square wave, superimposed on the sampling resistor and humidity sensor, through AD, in the positive cycle can also measure the partial pressure . Or use analog circuits, R/V conversion by logarithmic operations, and AD sampling.