Which statement best defines a process variable in a control loop?

Which statement best defines a process variable in a control loop?

• A. A measurable parameter of the process, such as temperature or pressure.
• B. The desired setpoint value.
• C. The controller output to the actuator.
• D. The power supply voltage.

Answer: (A)

In a control loop, the process variable is the actual, measurable property of the process that the system monitors. It’s what you read from sensors and feed back to the controller—the real-time value you want to control. Examples include temperature, pressure, flow, or level. This value is compared to the setpoint to determine the error the controller acts on. The setpoint is the target value you want the process to reach, while the controller output is the signal sent to an actuator to influence the process. The power supply voltage is simply the electrical power available to drive components and is not a process property being controlled. So the statement describing a measurable parameter of the process, such as temperature or pressure, best defines the process variable.

In a control loop, the process variable is the actual, measurable property of the process that the system monitors. It’s what you read from sensors and feed back to the controller—the real-time value you want to control. Examples include temperature, pressure, flow, or level. This value is compared to the setpoint to determine the error the controller acts on. The setpoint is the target value you want the process to reach, while the controller output is the signal sent to an actuator to influence the process. The power supply voltage is simply the electrical power available to drive components and is not a process property being controlled. So the statement describing a measurable parameter of the process, such as temperature or pressure, best defines the process variable.