This is a controller with only 2 switching states, that is, the output signal is switched ON and OFF depending on whether the process variable goes below or above a preset limit or setpoint.
An example of a discontinuous controller is a resistance thermometer (Pt 100), whose electronic circuitry switches heating on if the temperature falls below a certain value.
A discontinuous controller with two outputs can be considered as a combination of two discontinuous controllers, each with one output, but linked together, one below the other. They can be used for heating, for instance, when below the setpoint and for cooling when above the setpoint. They may also be applied in a climatic cabinet for humidification and dehumidification. Each output of the controller is assigned a manipulating variable; for instance, first controller output being used for heating and the second output for cooling.
Also read: What is Sequential Control System?
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