Danfoss VLT HVAC Basic Drive FC 100 Series Design Manual

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Danfoss VLT HVAC Basic Drive FC 100 Series Design Manual Manual pdf 65 page image

7 RS-485 Installation and Set-up7.1.1 OverviewRS-485 is a two-wire bus interface compatible with multi-drop network topology, i.e. nodes can be connected as abus, or via drop cables from a common trunk line. A totalof 32 nodes can be connected to one network segment.Repeaters divide network segments. Please note that eachrepeater functions as a node within the segment in whichit is installed. Each node connected within a given networkmust have a unique node address, across all segments.Terminate each segment at both ends, using either thetermination switch (S801) of the frequency converters or abiased termination resistor network. Always use screenedtwisted pair (STP) cable for bus cabling, and always followgood common installation practice.Low-impedance earth connection of the screen at everynode is important, including at high frequencies. Thus,connect a large surface of the screen to earth, for examplewith a cable clamp or a conductive cable gland. It may benecessary to apply potential-equalizing cables to maintainthe same earth potential throughout the network. Partic-ularly in installations with long cables.To prevent impedance mismatch, always use the sametype of cable throughout the entire network. Whenconnecting a motor to the frequency converter, always usescreened motor cable.Cable: Screened twisted pair (STP)Impedance: 120ΩCable length: Max. 1200m (including drop lines)Max. 500m station-to-station7.1.2 Network ConnectionConnect the frequency converter to the RS-485 networkas follows (see also diagram):1. Connect signal wires to terminal 68 (P+) andterminal 69 (N-) on the main control board of thefrequency converter.2. Connect the cable screen to the cable clamps.NOTEScreened, twisted-pair cables are recommended in order toreduce noise between conductors.61 68 69 NPCOMM. GND130BB795.107.1.3 Frequency Converter Hardware Set-upUse the terminator dip switch on the main control boardof the frequency converter to terminate the RS-485 bus.130BB966.10Illustration 7.1 Terminator Switch Factory SettingThe factory setting for the dip switch is OFF.RS-485 Installation and Set... VLT HVAC Basic Drive Design Guide64 MG.18.C2.02 - VLT® is a registered Danfoss trademark77