In process control, a process variable is defined as which of the following?

• A. The independent input variable.
• B. The dependent variable that is to be controlled.
• C. The ambient environmental condition.
• D. The calibration reference value.

Answer: (B)

In process control, the process variable is the actual measured value of the process parameter you’re trying to regulate. It represents the current state of the system and changes in response to the manipulated variable (the input you adjust) and any disturbances. Because its value depends on how you control the process, it is the dependent variable in the loop. The thing you adjust to influence the process is the manipulated or input variable, not the variable you’re measuring. Ambient environmental condition refers to external factors that can affect the process but are not the target of the control loop. The calibration reference value is the setpoint or target you want the process variable to reach, not the observed process state itself.