Structure of a control loop
A control loop is a fundamental principle of automated process control that ensures that certain physical variables (such as pressure, temperature, flow) in a system are kept constant or controlled according to a specified setpoint. The control loop operates continuously by detecting deviations from a specified setpoint and adjusting the system accordingly.
Structure of a control loop
A typical control loop consists of the following main components:
- Control variable (actual value): This is the physical variable to be monitored and controlled, e.g., pressure, temperature, or flow.
- Sensor (measuring element): The sensor measures the current value (actual value) of the controlled variable and transmits it to the controller.
- Controller: The controller compares the measured actual value with the desired setpoint. In the event of deviations, it calculates a control signal that is sent to the actuator to correct the deviation.
- Actuator (e.g., control valve): The actuator receives the control signal from the controller and adjusts the process, e.g., by increasing or decreasing the flow of a medium through a control valve to reach the setpoint.
- Disturbance variables: Unavoidable external influences that affect the process, such as temperature fluctuations or pressure changes in the system. The control loop must compensate for these in order to maintain the setpoint.
How a control loop works
A control loop works on the principle of feedback. The sensor continuously measures the actual value, and the controller compares this with the setpoint. In the event of deviations, the controller generates a correction signal that activates the actuator. The actuator keeps the controlled variable within the desired range.
Example: In a heating system, the temperature sensor (actual value) measures the room temperature. The controller compares this with the desired temperature (setpoint) and, in the event of deviations, controls the heating valve (actuator) to increase or reduce the heating output.
Conclusion
In industrial processes, a control loop ensures the accurate and continuous adjustment of physical variables to specified setpoints. The interaction of sensors, controllers, and actuators achieves precise control and regulation, which is indispensable for the smooth and efficient operation of modern plants.