This water filter level control system uses an ultrasonic level transmitter to sense the level of water in the filter, and a controller to drive a motor-actuated valve introducing raw water to be filtered:
Assuming a direct-acting level transmitter (increasing filter level = increasing signal), and a signal-toopen control valve (increasing controller output signal = wider open valve), determine whether the level controller needs to be configured for direct-action or reverse-action, and explain your reasoning. Annotate the diagram with “+” and “−” symbols next to the PV and SP controller inputs to show more explicitly the relationships between the controller inputs and output.
Next, determine the response of the controller to the following situations. In other words, determine what the controller’s output signal will do when this water level control system is affected in the following ways:
More Questions :
This controller needs to be reverse-acting:
This re-drawing of the control system uses an opamp symbol in place of the ISA-standard circle used to represent a loop controller:
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