Which statement best describes the process variable (PV) in a control loop?

Which statement best describes the process variable (PV) in a control loop?

• A. The input the controller can adjust (MV).
• B. The difference between SP and PV (Error).
• C. The desired target value for the PV (Setpoint).
• D. The current measured value of the process.

Answer: (D)

PV is the current measured value of the process, as read by the sensor. In a feedback control loop, you have SP (the target value), PV (what the process is actually at), and MV (the controller’s output that acts on the process). The controller compares SP and PV to form the error (SP minus PV) and then adjusts the MV to move PV toward SP. For example, in a temperature control loop, if SP is 100°C and PV reads 95°C, the error is 5°C, and the controller increases the heater to raise PV toward 100°C. The input the controller can adjust is the manipulated variable, not PV; the difference between SP and PV is the error, not PV; and the desired target value for PV is the setpoint, not PV itself.

PV is the current measured value of the process, as read by the sensor. In a feedback control loop, you have SP (the target value), PV (what the process is actually at), and MV (the controller’s output that acts on the process). The controller compares SP and PV to form the error (SP minus PV) and then adjusts the MV to move PV toward SP. For example, in a temperature control loop, if SP is 100°C and PV reads 95°C, the error is 5°C, and the controller increases the heater to raise PV toward 100°C. The input the controller can adjust is the manipulated variable, not PV; the difference between SP and PV is the error, not PV; and the desired target value for PV is the setpoint, not PV itself.