9. Sensor systems

Placed on the top of a tank or silo, this device comprises a drum, a ribbon and a feeler designed to contact the product during periodic vertical sweeps back and forth, controlled automatically or manually (figure 33 ). When contact is made, the ribbon is released, causing the motor driving the drum to reverse direction and the feeler to move upwards. As with a servo-controlled level gauge, pulses are generated, the number of which depends on the length of ribbon unwound, and enables the dip to be assessed. The periodic information thus collected is processed by a local indicator, or remotely by remote transmission. The fundamental difference with a servo-controlled gauge is precisely the absence of servo-control, which means that this information is not delivered on a continuous basis....