Humidity sensitive resistor type1

The appearance of the humidity sensitive resistor is the resistance type, also belong to the semiconductor components. Humidity sensitive resistor is the use of humidity-sensitive material absorbs moisture from the air and cause itself resistance change of this principle. Today engineering mainly to introduce the types of humidity sensitive resistor, hope I can help you know more about the application of humidity sensitive resistor.

1, semiconductor ceramic moisture sensor

- chromic acid magnesium Titanium dioxide ceramic moisture sensor is more commonly used a humidity sensor, it is by the MgCr2O4 - TiO2 porous semiconductor ceramic composed of solid solution. This kind of material surface resistance value can be in a very wide range smaller with the increase of humidity, even under the condition of high humidity, for repeated heat cleaning, performance is still not changed. The device adopted MgCr2O4 - TiO2 porous ceramics, electrode material of ruthenium dioxide by silk screen printing to both sides of the ceramic chip, formed under high temperature sintering porous electrode. Around the ceramic chip device has a resistance wire winding heater, 450, 1 min on ceramic surface heat cleaning. The resistance of the humidity sensitive resistor - Relative humidity characteristic curve is shown in figure 1.

figure 1 - resistance Moisture characteristic curve of the

figure 2 humidity-sensitive resistance measurement circuit block diagram

figure 2 is the wet a measuring circuit of sensor applications. Diagram for humidity sensitive resistor R, with a thermistor for temperature compensation. In order to make the testing the sensitivity of the humidity, the largest R =. At this time of the sensor output voltage through the follower and the rectifier and filter, on the one hand into the comparator 1 compared with reference voltage U1, the output signal to control a certain humidity; On the other hand to the comparator 2 compared with reference voltage U2, the output signal to control the heating circuit, so that in a certain time heating to clean.

2, lithium chloride humidity sensitive resistor

figure 3 is lithium chloride humidity sensitive resistance of the structure. It is made a comb on the polycarbonate substrate gold electrode, and then dip coating soluble in lithium chloride colloidal solution of polyvinyl alcohol, its surface coated with a layer of porous coating again. Lithium chloride is deliquescence salts, the electrolyte solution can form the membrane as the change of water vapor in the air and moisture absorption or dehydrated. Sense of wet film resistance changes over the air relative humidity, when the air humidity increases, the sense of lower concentration of salt in wet film.

figure 3 lithium chloride humidity sensitive resistor structure

figure 4 is a relatively hygrometer electrical principle diagram. Measuring probe composed of lithium chloride humidity sensitive resistor and thermistor, and through the three wire cable connect to the bridge. Thermal resistor as temperature compensation, was used to measure the temperature compensation of indicating device first appropriate correction, will bridge correction to zero, can be read out directly from the dial relative humidity value. Two arm bridge is composed of partial pressure resistance, in addition, and, or and the other two arms. A bridge by the oscillator supply voltage. The output of the bridge after amplifier amplification, through the rectifier circuit for ammeter indication.

3, organic polymer membrane humidity sensitive resistor

organic polymer membrane humidity sensitive resistor is set on alumina ceramic substrates such as type of comb electrodes, and then on its surface coated with a sense of wet performance, and conductive polymer film, the performance of Shanghai juji another layer of porous polymer film covering layer. This moisture sensor is the use of steam wet membrane attached to the sense, resistance and relative humidity corresponding to the nature. Due to the use of the win molecular material, so is suitable for the wet cell in high temperature gas measurement.

figure 5 is ferric oxide - Polyethylene glycol (peg) polymer membrane structure and properties of humidity sensitive resistor.

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key words: thermal resistance, thermocouple, thermal resistance, platinum resistance, PT100, PT1000, pressure sensor and digital temperature sensor