Glossary · Automation fundamentals, platforms and components
Manipulated variable
Also known as: Controller output, Control variable
German: Stellgröße
In closed-loop control, the manipulated variable is the quantity that the controller changes to influence the controlled variable, such as a valve position, heater power or motor speed setpoint.
- Automation components
- Standards
In one sentence
The manipulated variable is what a controller changes, such as valve position or heater power, to influence the controlled variable.
Example
The temperature controller outputs 65 % as manipulated variable, which opens the steam valve to 65 %.
How it applies
- Engineering: Manipulated variables are limited by the actuator's range; when the output saturates, anti-windup measures prevent overshoot.
- Operation: In manual mode, operators set the manipulated variable directly; in automatic mode, the controller does.
- Documentation: Loop descriptions should state the manipulated variable, its range and fail behavior. Be careful with abbreviations: "MV" means manipulated variable in most process control literature, but vendors vary.
- Commissioning: Output limits and the direction of action (direct or reverse) are checked before the loop is switched to automatic.
Manipulated variable vs. controlled variable
The Controlled variable is what should stay at the setpoint; the manipulated variable is the lever used to get there. A tank level (controlled) is held by changing the inlet valve position (manipulated).