Deister electronic LogIdent UDL500 Wiring & Installation Instructions
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3. RS485 interfaceMost RS485-buses require termination resistors across the conductor pair. The need fortermination has to be checked for each installation. Especially for high data rates, steepedges or long cables termination resistors are absolutely mandatory. Only both ends of themain cable, i.e. at the first and the last device, require termination resistors, additionalresistors excessively load the drivers. The resistor value matches the cable´s differentialmode characteristic impedance (in most cases 100 ... 120Ω).Attention!This termination resistor (Terminator, 120Ω) has been factory built-in intoall UDL500 and has to be removed if necessary (see chapter 2).At the RS485-bus you need a controller with fail-safe biasing meaning a pull-up and apull-down resistor on the cable. The fail-safe biasing provides a known-state, in whichthere is no active driver on the bus. Therefore this is absolutely mandatory regardless ofdata rates and length of cables.Technical data (for baud rates up to 100kBps):Max. bus length: 1200m (4000 feet)Max. stub length: because of reflections stubs should be kept asshort as possible; exceptions allow a length upto 5m (16 feet)Recommendation for the cable: twisted pair, cable-cross section at least0.22mm2 (AWG 24) differential-modecharacteristic impedance 100 ... 120ΩV17/01/08 deister electronic GmbH 30890 Barsinghausen Germany 9Wiring & Installation Instructions UDL500 |
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