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Summary of Contents for Honeywell RS-485
- Page 1 Honeywell Process Solutions RS-485 Adapter Board Installation Guide November 2010 Revision B Honeywell...
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Page 2: Installation Guide
Installation Guide Metretek RS-485 Adaptor Board Document: 900365 Date: February 09, 2006 Revision: A www.honeywell.com... - Page 3 (approx. 4000 ft) cable length, although it is often necessary to scale back the speed at such extreme lengths. In the case of the RS-485 adaptor board coupled with the CNI, the limiting factor is the CNI board itself, which only supports data transfers up to 38,400 bps. Taking into consideration the intended applications for the CNI product, higher data transfer rates are not relevant, and it is the potential long cable runs that are beneficial.
- Page 4 RS-485 Board Installation: If the RS-485 adaptor board is not already installed into the enclosure, then Figures 1 & 2 should be referenced for assembly. Two small #4 size self-threading type screws and a cable assembly will have been included with each kit.
- Page 5 Figure-1 RS-485 Board Mounting Position Figure-2 Securing the RS-485 Board...
- Page 6 Figure-4. The six position connector shown at the left of Figure-4 attaches to J1 of the RS-485 board. The rectangular power connector (R.H. side of drawing) connects to J3 on the CNI board. Remaining are the four individual wires that must be attached to the CNI terminal block.
- Page 7 RS-485 Board Jumper Settings: Metretek RS-485 Board Jumper Settings: A number of jumpers are accessible on the RS-485 board to permit flexibility when A number of jumpers are accessible on the RS-485 board to permit flexibility when attaching to varied product types in the field. The table below lists the default jumper attaching to varied product types in the field.
- Page 8 Figure-5 RS-485 Board Connectors & Jumpers Full Duplex Wiring Configuration: A full-duplex system, as illustrated in Figure-6, is the most straightforward configuration, and offers the highest potential for data transfers as there is no latency in enabling and disabling of transmitters. The downside here is the extra cost and larger cable size associated with full-duplex wiring.
- Page 9 Metretek RS-485 end. Note that the cable has three twisted pairs, and a shield connection. The drain wire from the shield connection must only be attached to earth ground at a single point to avoid potential ground loops.
- Page 10 Another possibility is to have an arrangement where one end only has a transmitter attached, and the opposite end only has a receiver attached (not shown). Implementation and utility of this type of unidirectional system will depend on the user application. Figure-9 Point-to-Point Half Duplex Wiring www.honeywell.com...
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Page 11: Multi-Drop Configuration
When setting-up a system for half-duplex operation, it is necessary to add two jumper wires as shown in Figure-10. As previously mentioned, maintaining the correct wire polarity is required for proper operation. Figure-10 Half Duplex Configuration Multi-Drop Configuration: A hypothetical multi-drop system is illustrated in Figure-11, consisting of three transceivers and a single receiver node. - Page 12 Ground currents can be minimized however by use of a simple resistor in the circuit path. Resistor R3 on the RS-485 adaptor board provides this current limit function. Additionally, the resistor is mounted in miniature sockets so that the value can be easily changed if necessary.
- Page 13 Summary When examining the RS-485 standard, it becomes quite apparent this approach offers the potential for high performance over long distances. With this comes a price, and the price here is increased complexity in system setup. Many variables exist that must be properly selected by the user when customizing the system to his/her requirements.
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Page 14: Differential Signaling
A communications method where a pair of wires are used to transfer information without reference to a signal common. In the case of RS-485, if a person was to place an oscilloscope across the two wires of the transmitter output while a 120 ohm load was being driven, it would be found that the signal toggles between +4 volts polarity and -4 volts polarity. - Page 15 Multi-Drop: The most basic RS-485 configuration will typically have two transceivers separated by a length of cable. When additional receivers, transmitters, (or both) are added at intermediate points along the main cable run, then the system is known as ‘multi-drop’.
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Page 16: Receiver Sensitivity
T1 that is hipot rated at 1250 volts. Maximum Data Transfer Rate: Limited to 400k bps due to the isolation barrier architecture within the RS-485 conversion IC. The CNI board design further limits the serial data exchange rate at 38.4k bps maximum. - Page 18 Find Out More: To learn more about Mercury Instruments products, contact your Honeywell Process Solutions representative, visit www.mercuryinstruments.com or call 513-272-1111. Automation and Control Solutions Honeywell Process Solutions 3940 Virginia Ave. Cincinnati, OH 45227 MNL-RS485-900365-1 513-272-1111 November 2010 www.honeywell.com © 2010 Honeywell...