Two states of a controller?

• A. Start and Stop
• B. Auto and Off
• C. Automatic and Manual
• D. Run and Idle

Answer: (C)

The thing this item tests is the operating modes a controller can be in. In process control, a controller typically has two fundamental states: automatic and manual. In automatic mode, the controller uses its built-in algorithm to calculate the manipulated variable and drive the process toward the setpoint automatically. In manual mode, the operator can directly set the manipulated variable, bypassing the automatic control action, which is useful during start-up, tuning, or if the loop is being adjusted or trouble-shooted. This automatic/manual distinction is the standard way controllers are described and operated.

The other pairings describe different concepts. Start/Stop are about turning the system on or off, not the ongoing control mode. Auto and Off could imply an off state, but the common, practical two-state model for controllers is automatic versus manual. Run/Idle speaks to the overall process or equipment status, not specifically the controller’s control mode.