10 RS-485 Installation and Set-up10.1 OverviewRS-485 is a 2-wire bus interface compatible with multi-dropnetwork topology. Nodes can be connected as a bus, orvia drop cables from a common trunk line. A total of 32nodes can be connected to one network segment.Repeaters divide network segments. Note each repeaterfunction as a node within the segment in which it isinstalled. 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, e.g. with acable clamp or a conductive cable gland. If necessary,apply potential-equalizing cables to maintain the sameearth potential throughout the network. Particularly ininstallations 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 120 ΩCable length Max. 1,200 m (including drop lines)Max. 500 m station-to-stationTable 10.1 Motor Cable10.2 Network ConnectionOne or more frequency converters can be connected to acontrol (or master) using the RS-485 standardised interface.Terminal 68 is connected to the P signal (TX+, RX+), whileterminal 69 is connected to the N signal (TX-, RX-). Seeillustrations in 7.7.2 EarthingIf more than one frequency converter is connected to amaster, use parallel connections.130BA060.1168 69 68 69 68 69RS 485RS 232USB +-Illustration 10.1 Parallel ConnectionsTo avoid potential equalising currents in the screen, earththe cable screen via terminal 61, which is connected to theframe via an RC-link.130BB021.1012 13 18 19 27 29 32 33 20 37Remove jumper to enable Safe Stop61 68 69 39 42 50 53 54 55Illustration 10.2 Control Card Terminals10.3 Bus TerminationThe RS-485 bus must be terminated by using a resistornetwork at both ends. For this purpose, set switch S801 onthe control card to "ON".For more information, see 7.5.4 Switches S201 (A53), S202(A54), and S801.Communication protocol must be set to 8-30 Protocol.RS-485 Installation and Set... VLT® AutomationDrive FC 300 Design Guide 90-1200 kWMG34S202 - Rev. 2013-08-19 24110 10
