Feedback conversionIn some applications, it is useful to convert the feedback signal. One example is using a pressure signal to provide flowfeedback. Since the square root of pressure is proportional to flow, the square root of the pressure signal yields a valueproportional to the flow, see Illustration 11.5.130BF834.10Reference signalDesired flowReferenceFB conversionFB signalPFlowFBPFlowPIDPParameter CL-01Parameter CL-04Parameter CL-07Illustration 11.5 Feedback Conversion11.2.4 Control Structure OverviewThe control structure is a software process that controls the motor based on user-defined references (for example, RPM) andwhether feedback is used/not used (closed loop/open loop). The operator defines the control in parameter 1-00 Configu-ration Mode.The control structures are as follows:Open-loop control structure• Speed (RPM)• Torque (Nm)Closed-loop control structure• Speed (RPM)• Torque (Nm)• Process (user-defined units, for example, feet, lpm, psi, %, bar)11.2.5 Open-loop Control StructureIn open-loop mode, the drive uses 1 or more references (local or remote) to control the speed or torque of the motor. Thereare 2 types of open-loop control:• Speed control. No feedback from the motor.• Torque control. Used in VVC+ mode. The function is used in mechanically robust applications, but its accuracy islimited. Open-loop torque function works only in 1 speed direction. The torque is calculated based on currentmeasurement within the drive. See chapter 12 Application Examples.Basic Operating Principles ... Design GuideMG22B102 Danfoss A/S © 05/2017 All rights reserved. 10311 11
