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BobB

Communications Over 5 kilometers

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I have also posted this in the lounge but have posted it here as well as Omron people seem to get into some 'interesting' circumstances - hope you do not mind. I have been asked to have a look at a job where they wish to control a diesel engine powered pump on a barge. There will be monitoring and control involved. I was looking at using an Omron CJ1M PLC with a couple of comms cards, 1 input and 1 output card. Set up Modbus RTU comms to the Cummins engine, Modbus RTU comms to another barge and a small SCADA system to monitor and control. The barge will only have the engine start batteries on board and I was looking at using a 24VDC powered PLC off the start batteries with a switchmode power supply between the batteries and the PLC. Next problem - the barges could be up to 5 kilometres apart. Probably not good for line of site wireless - may have to shoot off a satellite. Anyone have any suggestions/ideas/recommendations? Any help would be much appreciated.

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... Hi Bob, We have used UHF radios with RS232 installed over much larger distances than 5km. (40km on one link). Proper selection and engineering of the radio link is important, you would need to consult an expert. Choosing the correct frequency etc for the topography(each radio path) can make quite a difference - we use licensed bands as there is much less chance of any outside interference. I note that some of our remote sites are down a gully, and are certainly not line of site, however we do acheive reliable communication. Over here we are currently using Tait radios, however, I think Trio(among others) may be worth a look in Aus. Note that I am not involved with engineering of the radio links, we use a sub-contractor for that aspect. I suspect you have already given due considration and ruled out direct point to point radio links ... Nibroc Edited by Nibroc

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Hi Bob, I've had an OMRON setup over 50km pipeline using TRIO (now Schneider) JR radios over Ethernet. You have a choice of freeband 900Mhz or licenced band of 450Mhz from Schneider. All OMRONs over the pipeline talk over FINS Ethernet given appropriate timeout allowed, it is a very straightforward setup. Radios are powered through solar power regulated 24V supply with battery bank, they take 12V too. One car battery can run it for weeks without ever need to charge up. I like these Ethernet radios as it is a transparent network for the Omrons and no mocking around with Modbus and serial comms. I had more trouble with serial comms over the UHF radio because it involves more setup in the PLC and other stuff. Hope this helps. Edited by digispark

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Assuming you're not working on a offshore platform, you may consult in getting multiple repeater links in between to solve your line of sight issue. Put a repeater on each hill with a high mast for LoS to each radio. You'll need to consult to radio surveyor for your terrain topology and antenna selection.

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