Danfoss VLT AQUA Drive FC 202 Design Manual

Also see for VLT AQUA Drive FC 202: Service guide Installation guide Installation guide Operating guide Installation guide

Contents

1155 HPKE IND PWE high PWE low0000 H 0000 H 0000 H130BA094.10Illustration 3.53 Parameter ValueIf the value in 3-41 Ramp 1 Ramp Up Time is 10 s, theresponse from the slave to the master is130BA267.101155 HPKE IND0000 H 0000 H 03E8 HPWE high PWE lowIllustration 3.54 Response from Slave3E8 hex corresponds to 1000 decimal. The conversionindex for 3-41 Ramp 1 Ramp Up Time is -2, i.e. 0.01.3-41 Ramp 1 Ramp Up Time is of the type Unsigned 32.3.8.9 Modbus RTU Protocol3.8.9.1 AssumptionsDanfoss assumes that the installed controller supports theinterfaces in this document, and strictly observes allrequirements and limitations stipulated in the controllerand frequency converter.The built-in Modbus RTU (Remote Terminal Unit) isdesigned to communicate with any controller thatsupports the interfaces defined in this document. It isassumed that the user has full knowledge of thecapabilities and limitations of the controller.3.8.9.2 Modbus RTU OverviewRegardless of the type of physical communicationnetworks, the Modbus RTU overview describes the processa controller uses to request access to another device. Thisprocess includes how the Modbus RTU responds torequests from another device, and how errors are detectedand reported. It also establishes a common format for thelayout and contents of message fields.During communications over a Modbus RTU network, theprotocol:• Determines how each controller learns its deviceaddress.• Recognises a message addressed to it.• Determines which actions to take.• Extracts any data or other information containedin the message.If a reply is required, the controller constructs the replymessage and sends it.Controllers communicate using a master-slave technique inwhich only the master can initiate transactions (calledqueries). Slaves respond by supplying the requested datato the master, or by taking the action requested in thequery.The master can address individual slaves, or initiate abroadcast message to all slaves. Slaves return a responseto queries that are addressed to them individually. Noresponses are returned to broadcast queries from themaster. The Modbus RTU protocol establishes the formatfor the master’s query by providing:• The device (or broadcast) address.• A function code defining the requested action.• Any data to be sent.• An error-checking field.The slave’s response message is also constructed usingModbus protocol. It contains fields confirming the actiontaken, any data to be returned, and an error-checking field.If an error occurs in receipt of the message, or if the slaveis unable to perform the requested action, the slaveconstructs an error message, and send it in response, or atime-out occurs.3.8.9.3 Frequency Converter with ModbusRTUThe frequency converter communicates in Modbus RTUformat over the built-in RS485 interface. Modbus RTUprovides access to the control word and bus reference ofthe frequency converter.The control word allows the modbus master to controlseveral important functions of the frequency converter:• Start• Stop of the frequency converter in various ways:- Coast stop- Quick stop- DC brake stop- Normal (ramp) stop• Reset after a fault trip• Run at a variety of preset speeds• Run in reverse• Change the active set-up• Control the frequency converter’s built-in relayThe bus reference is commonly used for speed control. It isalso possible to access the parameters, read their values,and, where possible, write values to them. This permits arange of control options, including controlling the setpointof the frequency converter when its internal PI controller isused.System Integration Design GuideMG20N602 Danfoss A/S © 09/2014 All rights reserved. 833 3