Open loop and Closed loop control system

Open loop control system:

the process in the system where one or several input variables affect other output variables as a result of the law affecting each other from a system.

Control is characterized by an “open-loop” sequence of actions or control chains. The system is the contents of the box itself. The input variable action on the system is connected in a box and exits as an output variable. The output variable currently exists in the energy flow or period to be controlled.


control system

The controlled system can be divided into more detailed signals, control elements, actuators and working elements. Besides that, the signal flow goes according to the control signal and actuator to the working element.

Controls are often separated between the signal and power parts. The part of the signal uses a voltage and pressure that is smaller than that used by the power section, in this connection then called the control unit and the power unit. This is especially useful for large working elements and long cable control.

Signal elements can be stored in a row because of their small dimensions, but the actuator must be adjusted to the characteristics of the work element. In pneumatics, electro-pneumatic or electro-hydraulic controls, the actuator also has an interface function between signal and power supply, because the output signal generated from a combination of input signal logic is passed from a signal in the electrical part.

Closed Loop Control or Automatic control:

automatic control is the process by which a controlled variable (controlled variable) is continuously measured and compared with other variables, command variables, the process will be affected according to the results of this comparison by modifying it to match the command variable. The action sequence of this form is called a closed loop control.


The purpose of a closed loop control is to adjust the value of the controlled variable to the value specified by the command variable. Controlled systems are influenced by comparisons between controlled system outputs (ie controlled variables) and certain command variables (set values/setting points.


The automatic control to maintain the temperature in the oven during production automation, this cannot be realized with open loop control. Output variables in the form of temperature must be continuously controlled and during the process, an intervention is made to the occurrence of deviations from the nominal value (too cold – heating is turned on, and when it reaches the upper limit temperature – the heater is turned off).

The output temperature is adjusted by adjusting the set point in the process, and the actual value, so this is said to be an automatic control (setting). Automatic control is the process by which the magnitude of the control variable is continuously detected and compared with the reference variable, and corrected until the same results are obtained. The automatic control indicator is the closed action flow, and the control variable in the loop control action path itself is continuously affected.

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