Rieter

Open-loop control

Index

A measuring sensor is provided in the region of the infeed for continuous detection of the actual value (volume) – mechanically, optically, pneumatically, or otherwise (Fig. 41). A regulator compares the result with the set reference value, amplifies the difference signal, and feeds it to an adjusting device (actuator), which then finally converts the impulse into a mechanical adjustment.

Control by this chain of steps requires an additional element, namely a storage device. Since the material has to travel a certain distance between the measuring and adjusting points, and therefore arrives at the adjusting point with a time delay, the signal must be held back in the storage device until this instant. This additional requirement represents a second disadvantage of open-loop control in addition to the lack of self-monitoring. There is a third disadvantage, since very exact values of the adjustment are required at all times.

Fig. 41 – The principle of open-loop control; A, measuring sensor; B, store; C, amplifier; D, adjusting device; E, adjustment point; F, set-value input