ETG - Model SHN - Thermo Hygrometre - Datasheet

The SHN transducer is a multiple sensor containing the transducers for measuring air temperature and humidity. The instrument consists of a “PT100 CI.A” thermistor according to the DIN 43760 standards to measure air temperature. The thermistor is crossed by a constant current, so the change in temperature is brought back to a voltage change at its ends. A capacitive type of sensor to measure relative humidity consists of a membrane of hygroscopic material that forms the dielectric of a capacitor so that the water molecules in the air are absorbed by the dielectric, thus causing a change in the capacitor’s capacity, due to the humidity, to which a change in the oscillation frequency of an electrical circuit connected to a sensor corresponds, which in turn transforms it into a change in direct voltage. The temperature sensor is immersed in a convective current produced by natural ventilation inside an anti-radiation shield. The shield is made up of several concentric and overlapping metal discs painted white, whose particular shape plays the two-fold role of fostering natural ventilation of the sensor and of protecting it from solar radiation (direct and reflected) and from the rain. The paintwork of the discs ensures high reflectivity and low heat retention.