The magnitude and duration of the error signal then determines the value of the controller’s output or manipulated variable which in turn dictates the corrective efforts applied by the actuator.įor example, a car equipped with a cruise control uses a speedometer to measure and maintain the car’s speed. The controller subtracts the latest measurement of the process variable from the setpoint to generate an error signal. For a continuous process, a feedback loop attempts to maintain a process variable (or controlled variable) at a desired value known as the setpoint. Familiar examples include using a thermostat controlling a furnace to maintain the temperature in a room or cruise control to maintain the speed of a car.Ĭontinuing the analysis, it is clear that all closed-loop operations are not alike. This measure-decide-actuate sequence-known as closed-loop control-repeats as often as necessary until the desired process condition is achieved. In a closed-loop control system, information flows around a feedback loop from the process to the sensor to the transmitter to the controller to the actuator and back to the process. An actuator functioning as the final control element that applies a corrective effort to the process per the controller’s instructions.A controller that reads the transmitter’s signal and decides whether or not the current condition of the process is acceptable, and.A transmitter that converts the measurement into an electronic signal. An instrument with a sensor that measures the condition of the process.It consists of five fundamental elements: Arguably the most ingenious tool of the control engineering profession is the feedback loop shown in the Basic Feedback Loop graphic.
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