Metal probes, placed on the delivery side of the drying unit, are used for controlling the dried wool moisture content (which must be uniform and predetermined); these probes measure the electrical capacity or resistance fluctuations, which vary according to the quantity of water contained in the fibres. It is however worth remembering that these measures are generally affected by the level of cleanness of the wool and by the possible presence of soluble salts.
The control device shown in Figure 125 (Moisture meter) calculates and determines the average moisture content in the material by means of four electrodes, each one carrying out 600 measurements per second, which determines the electrical resistance of the material when the current drops through the element. The measurement is carried out with a +/- 1% accuracy even when moisture values are very low (approaching zero).

A controller (Figure 1) can be added to the previous control device; the controller generates a signal that is used for checking one of the parameters affecting the process: the energy to be supplied to the dryer (through steam or gas valves) or the quantity of material fed (through the feeding speed).

Fig. 1 - Moisture meter