The moisture sensor is a capacitor whose dielectric is formed of a polymer hygroscopic. Since the relative dielectric constant of the water is about 80, a large variation in capacity is obtained as the moisture content increases this polymer varies. The particular advantages of this type of sensor are good linearity, insensitivity to temperature variations, short response time and a long time. The sensor may momentarily lose its accuracy if there is any condensation on its surface (the transmitted value will be higher than the actual value because of an increase in effective capacity). The temperature sensor is Platinum thermal resistance (Pt100Ω @ 0 ° C). The resistance variation Pt100 is transformed into a current signal or linear voltage in temperature.
SIGNAL TRANSMISSION
The electronic circuit is designed so that the signal increases linearly at as humidity and temperature increase.
In the presence of cables transmitting strong currents or provoking machines electromagnetic disturbances, it is necessary to arrange the cables for connection of the transmitter in a separate channel or at a distance from to protect them from disturbances. For model connections with output voltage (HD9009TR) It is recommended to use a shielded cable.
INSTALLATION AND ASSEMBLY
Figures 1 and 2 show the connection diagram of the two models. The symbols RH and ° C indicate the current input of any device inserted into the loop 4 ... 20mA, ie: an indicator, a controller, a data logger or a collector.
In Figure 2 the symbols Vin% RH and Vin ° C refer to the same definition.