How Thermal Type Humidity Sensor Works? Learn with Diagram

Hey, in this article we are going to learn how the thermal type humidity sensor works. The thermal humidity sensor basically measures the absolute humidity which is why it is also called an AH Sensor also. They do it by calculating the conductivity of the dry air and humid air.

First of all, let's see the diagram which shows the internal construction and working concept of the Thermal Type Humidity sensor.

You can see, the main part of the AH sensor is a Thermistor whose resistance or conductivity changes with the temperature and humidity mostly the temperature. There are two thermistors are used and they are negative temperature coefficients. One of them is sealed with dry nitrogen and another one is open to the environment. They are connected in series within a resistive bridge circuit.

When the temperature and humidity change, the resistance of the thermistor also changes so their conductivity also changes. Basically, the conductivity of the open thermostat changes due to the moisturized air, and the conductivity of the sealed thermostat changes due to the dry air. Because dry air and moisturized air have different temperatures.

Now the difference between the resistance or conductance of those two thermistors is related to the absolute humidity. And practically, we can measure the absolute humidity(AH) by measuring the output voltage. To get the proper result, the input voltage must be constant. If the input voltage varies, the output voltage will be varied while the circuit is not in its operation.

The main advantages of the thermal-type humidity sensor are, that it can be used in high-temperature environments and high-corrosive situations, it provides higher resolution than others, and they are very durable.

The main disadvantage of the thermal humidity sensor is that the reading measurement is affected due to the gasses.

Read Also: How Capacitive Humidity Sensor Works? Learn with Diagram

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