Honeywell RS-485 User Manual Download

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Honeywell Process Solutions

RS-485 Adapter Board

Installation Guide

November 2010

Revision B

Honeywell

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Summary of Contents for RS-485

Page 1: ...Honeywell Process Solutions RS 485 Adapter Board Installation Guide November 2010 Revision B Honeywell ...

Page 2: ...2 www honeywell com Installation Guide Metretek RS 485 Adaptor Board Document 900365 Date February 09 2006 Revision A ...

Page 3: ...it and no parity to transfer a single byte 8 bits of useful information Maximum practical data transfer rate is 19 2k bits per second bps with cable lengths at 50 feet and several times faster with shorter cable runs It is only possible to have a single pair of devices connected multi drop capability does not exist Immunity to electrical noise is rather poor when operating in harsh environments su...

Page 4: ...ood idea however and the RS 485 board can have the 120 ohm termination added by simply placing a jumper on JP1 RS 485 differential signaling levels are specified to not exceed a 6 volt swing for an unloaded transmitter and the receiver sensitivity must be at least 0 200 volts Since it is possible to have multiple transmitters on a bus the data transmission protocol must ensure that line contention...

Page 5: ...5 Figure 1 RS 485 Board Mounting Position Figure 2 Securing the RS 485 Board ...

Page 6: ...t would pose a mechanical assembly conflict if left intact as seen in Figure 3 Figure 3 Optional RS 232 Multiplexer Board Electrical connections to the CNI board are of course required and a cable has been provided for this purpose as illustrated in 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 drawi...

Page 7: ...red for full duplex and only the single transmitter element exists then it is possible to set the jumper for B C If the system is wired for multi drop with two transmitters on the same cable or if it has been wired for half duplex then the setting A B is mandatory to prevent line contention RS 485 Board Jumper Settings A number of jumpers are accessible on the RS 485 board to permit flexibility wh...

Page 8: ...uplex wiring Cabling is specified as two sets of twisted pair wire a common conductor and a shield In the marketplace it is easier to obtain a cable having 3 sets of twisted pairs as opposed to a more specialized cable with 2 twisted pairs and a common conductor Therefore it is more practical to simply use an entire twisted pair set to serve as the signal common Figure 6 Point to Point Full Duplex...

Page 9: ...onnections for the user end point device Naturally this connection scheme appears essentially the same as that shown in Figure 7 mandatory for proper data transfers Individual wires in a cable bundle are marked with colored stripes to make the task easier The A B Y Z notation shown here is more prevalent in the industry and the RS 485 adaptor board conforms with this practice Some manufacturers of...

Page 10: ...e controlling electronics to enable and disable the relevant transmitters at appropriate times based upon the software system protocol Otherwise there is a possibility that line contentions might occur with two or more transmitters attempting to talk at the same time Another possibility is to have an arrangement where one end only has a transmitter attached and the opposite end only has a receiver...

Page 11: ... in Figure 11 consisting of three transceivers and a single receiver node As shown two transceivers are attached at the far ends of the cable while nodes 1 2 can be attached anywhere in between Notice that the nodes do not have termination resistors attached and it is for this reason that the cable length for the stubs should be kept as short as practical to avoid signal distortion The total numbe...

Page 12: ...ies resistors The term signal common here refers to the common ground system present in the electrical device and is not to be confused with earth grounding It is desirable to maintain some equilibrium between the signal commons of all the communications devices so as to prevent them from floating away in terms of electrical potential At the same time ground loop currents could potentially develop...

Page 13: ...the system will still function just fine The following points are recommended to help speed the installation process Prepare the equipment for installation to the fullest extent possible while still at the office Attaching miniature wires and updating the CNI configuration memory can test a persons patience when the outdoor temperature is 40 degrees and blowing rain When possible short cables runs...

Page 14: ...son 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 Due to the fact that a signal common is not used as the return path any injected noise will be common to both wires and therefore tend to cancel out Isolation In this context isolation refers to...

Page 15: ...ete prefix that still finds common usage the letters stand for Radio Sector References to RS 232 and RS 485 are used throughout this text Termination Resistor A resistor placed at the far end of a far end of a transmission cable intended to absorb energy from incoming signals Due to the high impedance of the receivers used within the RS 485 system a termination resistor is often necessary to preve...

Page 16: ...e J1 connector and the TB1 connector The limiting element here is the transformer 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 Transmitter Drive Levels Typical measured values are 6 20 volts with no l...

Page 17: ...17 ...

Page 18: ...e 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 513 272 1111 www honeywell com ...

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