Rieter

Measuring, open- and closed-loop control

Index

For better understanding of the subsequent remarks, these three concepts will be defined briefly by using room heating as an example. If a thermometer is provided in a heated room and the temperature is read, then nothing more has happened than the determination of a condition by measuring. If that condition is not satisfactory, then appropriate action would be required. The heating system could, however, also be controlled with the aid of an external thermostat. More or less heat could be supplied depending upon the outside temperature.

As long as the conditions in the room remain constant – if, for example, only one person is present all the time – no problems arise. If the owner of the apartment gives a party for 10-15 people, however, then it will certainly become very warm.  Open-loop systems lack a check upon the effects of a change, even as to whether a change has occurred. The system can be referred to as a control chain. The system is different if a thermostat is provided in the room itself and is set for a specific temperature. There is a continual comparison of the actual and the set conditions, and the temperature is held constant, regardless of what happens in the room. This operation, with constant self-monitoring, can be referred to as a  closed-loop control system. Both open-loop and closed-loop control are used in spinning mills. In every case, the volume of fibers passing through is measured, and adjustment is made by altering the draft. This can be carried out as described below.