2.4.5 Feedback HandlingFeedback handling can be configured to work withapplications requiring advanced control, such as multiplesetpoints and multiple types of feedback (see Figure 2.16.Three types of control are common:Single zone, single setpointThis control type is a basic feedback configuration.Setpoint 1 is added to any other reference (if any) and thefeedback signal is selected.Multi-zone, single setpointThis control type uses two or three feedback sensors butonly one setpoint. The feedback can be added, subtracted,or averaged. In addition, the maximum or minimum valuecan be used. Setpoint 1 is used exclusively in this configu-ration.Multi-zone, setpoint/feedbackThe setpoint/feedback pair with the largest differencecontrols the speed of the adjustable frequency drive. Themaximum attempts to keep all zones at or below theirrespective setpoints, while minimum attempts to keep allzones at or above their respective setpoints.ExampleA 2-zone, 2-setpoint application. Zone 1 setpoint is 15 barand the feedback is 5.5 bar. Zone 2 setpoint is 4.4 bar andthe feedback is 4.6 bar. If maximum is selected, the zone 1setpoint and feedback are sent to the PID controller, sinceit has the smaller difference (feedback is higher thansetpoint, resulting in a negative difference). If minimum isselected, the zone 2 setpoint and feedback is sent to thePID controller, since it has the larger difference (feedback islower than setpoint, resulting in a positive difference).Figure 2.16 Block Diagram of Feedback Signal ProcessingProduct Overview Design GuideMG20N622 Danfoss A/S © 09/2014 All rights reserved. 252 2
