The control variable in a closed-loop system is the specific physical quantity that you are trying to maintain or adjust to a desired value. It's the output of the system that is being monitored and controlled.
In a closed-loop system, the control variable is continuously measured and compared to the desired setpoint. Any difference between the actual value and the setpoint (the error signal) is then used by the controller to adjust the system's input in order to bring the control variable closer to the desired value. This feedback loop allows the system to automatically compensate for disturbances and maintain the desired output.
Here's a breakdown to illustrate:
- Setpoint (s): The desired value of the control variable. This is what you want the system to achieve.
- Control Variable (r): The actual physical quantity that is being measured and controlled.
- Measurement (i): The process of determining the actual value of the control variable.
- Controller: The component that compares the measured value to the setpoint and calculates the necessary adjustments to the system's input.
- Actuator: The component that implements the adjustments calculated by the controller to influence the control variable.
- Error signal: Difference between the Setpoint and the measured value of the Control Variable.
Examples of Control Variables:
| System | Control Variable |
|---|---|
| Home Heating System | Room Temperature |
| Cruise Control System | Vehicle Speed |
| Chemical Reactor | Reactor Temperature |
| Water Tank | Water Level |
In each of these examples, the system continuously monitors the control variable and makes adjustments to maintain it at the desired setpoint. For instance, in a home heating system, the thermostat (controller) monitors the room temperature (control variable) and turns the furnace on or off (adjusting the system's input) to maintain the desired temperature (setpoint).
In essence, the control variable is the heart of the closed-loop system - it's the parameter you are actively managing to achieve a specific outcome.
