The Humidity Transducer - INNOVA MM0037 measures the absolute humidity of air. If the humidity is to be expressed as Relative Humidity (RH), this can easily be calculated when the Air Temperature also is measured with INNOVA MM0034.

The design provides a robust and very stable transducer for field use. The transducer is not affected by chemicals in the air that can cause problems when measuring with other types of humidity transducers. The transducer comprises a Light Emitting Diode (LED), a light sensitive transducer, a mirror, a cooling element and a Pt100 temperature sensor. The mirror is easily accessible for cleaning when necessary, while the other components are maintenance-free.

Measurement Principle

A cooling element is attached to the conical mirror. When the humidity measurements are started, the cooling element is activated and the temperature of the mirror begins to drop. Control of the transducer now moves to the LED and light-sensitive transistor. The LED emits a constant beam of light, which is reflected by the conical mirror. Under normal circumstances, the light-sensitive transistor does not receive any of the light being emitted by the LED, however, as the temperature of the mirror drops condensation forms on the surface. The mirror is reflecting the light now becomes scattered and is detected by the light-sensitive transistor. This transistor now controls the temperature of the mirror so that there is a constant film of dew on the mirror's surface. The Pt100 sensor registers this dew-point temperature. The accuracy with which the humidity can be measured is dependent on the stability of the sensor measuring the mirror's temperature. Therefore a Pt100 sensor with high stability and accuracy is used.