The control loop

Control circuit

Management system on a sensor-based system consists of a loop sensor and controller of the managed device. The relationship between these parts 332 cycle can be electric, pneumatic or mechanical (see Fig. 28.1).

Controller action can have three elements. These proportional, integral, and derivative. This controller is known as three-term controller or PID. Proportional element creates a portion of the output for which the reaction is proportional to the deviation from the setpoint or 'error'. An essential element examines the history of errors and creates a part of production on the basis of the sum of the errors. Differential element creates a part of the output depending on speed of change of the error. Most cooling control uses proportional and integral parts, installation part of the derivative to zero. Experience has shown that the use of a considerable quantity of derivative in a control algorithm leads to instability.

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Control circuit