Temperature Dewpoint Sensor
The Temperature/Dewpoint Sensor (hygrothermometer) measures the temperature and dewpoint of the ambient air.
Dewpoint is the temperature to which a given parcel of air must be cooled at constant pressure and constant water-vapor content in order for saturation to occur (and condensation to occur).
Hygrothermometer is an instrument that is used to obtain ambient temperature and dewpoint from remote sensors. The readouts are usually located inside the weather office
The sensor uses a chilled mirror method to measure dewpoint. In this method, a mirror is cooled to the point where a fine film of condensate is present on the mirror's surface. The temperature of the mirror at this condition is equal to the dewpoint temperature. The presence of condensation is detected by the reflection of an infrared light off the surface of the mirror. Internal circuits refrigerate a small mirror, and by using an optical feedback loop, maintain the mirror at exactly the temperature at which the mirror surface is slightly clouded with condensed water vapor from the sampled air. A thermal sensor embedded in the mirror measures the temperature. A similar thermal sensor in a sample of the ambient air measures the ambient air temperature.
The measured temperatures are transmitted to the Data Collection Package (DCP) using a power cable and two fiber optic cables.