The (T)FG120 is an HVAC relative humidity and temperature transmitter. It has the Polyga® humidity measuring element which is composed of several synthetic fabric bands. Each of these bands have 90 fibres, each with a 3 μm diameter and a molecular structure that is arranged lengthways. In the untreated state, the fibers do not attract and hold water molecules.
The hygroscopic properties are obtained through a process which makes the synthetic fibers take in moisture. When water is taken up, the molecule chains of the threads alter and this leads to a change in length. A loss of water results in an opposite effect. The length of the fiber in equilibrium with the air humidity is the gauge for the relative humidity.