The function of a control loop is to restore a controlled variable to its setpoint value whenever it varies from this value and thereby maintain the process in the desired condition. The action by which this is accomplished is referred to as the control mode.
Control modes are divided in to two categories
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Discontinuous control mode
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Continuous modesnous Discontinuous modes include the on/off mode and the floating control mode.
Continuous modes include the proportional,integral and derivative modes.