Easy? PLCs to RS485

mike123

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Join Date
Oct 2006
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sydney
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Hi, I would like to know how we can connect PLCs to RS485 bus.For example we have 5 PLCS, 3 in separate location, and 2 in the same room. using RS232-RS485 at one end of the PLC then the other end need to connection to RS485 bus, how can we accomplish this, what equipments we need to use?? Suppose the RS485 cable is 400m long, does it come with pre-made connector at both ends of the cable or we have to make them ourself. is RS485 bus just cable for connection PLCs together or we have to do some setup before the cable become a bus?? I don't know much about RS485, so please help me. Thank you

Mike

PS: looks like I lost the one just typed so if 2 posts of the same come up please forgive
 
Rs485 is a daisy chain connection, so there are no special connections needed. You could always use the Allen Bradley AIC m odules.
 
Thank you Mickey & UNSW1 for your information about RS485 bus. I will read more into them much later; it does not seem easy as I thought that someone could suggest a direct answer of what equipment need to connect one end of a RS485 to a RS485 bus. Hopefuly I will diggest more about these reading but for now I do not have anough time, as I am preparing for an interview for a job. And I wonder if after reading these could get out the answer that I sought. Mickey, I do not have a brand of PLC in particular, just say SquareD, they call Sy/NET network but I think RS485 is the same (just terminology for a particular brand?). Thanks

Mike
 
mike123 said:
Thank you Mickey & UNSW1 for your information about RS485 bus. I will read more into them much later; it does not seem easy as I thought that someone could suggest a direct answer of what equipment need to connect one end of a RS485 to a RS485 bus. Hopefuly I will diggest more about these reading but for now I do not have anough time, as I am preparing for an interview for a job. And I wonder if after reading these could get out the answer that I sought. Mickey, I do not have a brand of PLC in particular, just say SquareD, they call Sy/NET network but I think RS485 is the same (just terminology for a particular brand?). Thanks

Mike
Click to expand...

I don't think so. It does not look like the same thing to me.
http://www.niobrara.com/html/synet_cables.html
http://www.phoenixdigitalcorp.com/pdf_directory/SquareD.pdf
 
Mickey said:
I don't think so. It does not look like the same thing to me.
http://www.niobrara.com/html/synet_cables.html
http://www.phoenixdigitalcorp.com/pdf_directory/SquareD.pdf
Click to expand...

Hi Mickey,

Oh thank you very much for your help, these info are quite useful. Yes, the Sy/NET and RS485 is different as the setup here, but in some connection of SquareD PLCs I saw they also used RS485 bus. I named SquareD because I am more familar with it long ago (not using it). Many generic PLCs bus using RS485, and I am very curious to know HOW ONE END of RS485 cable can be connected to RS485 BUS. That's ALL my curious/ I have read quite a fews topic on RS485 but could not know how they conenct to RS485 bus, ANY SPECIAL EQUIPMENT, YOU KNOW OF???

Mike
 
No special equipment.As nswu1 said Daisy-Chain is prefered, you can have
drops but keep them short as possible. You need termination resistors
at both ends of network. You will need a RS232 to RS485 converter at each PLC ( if the PLC port does not support RS485). RS485 networks only support one Master. The slave units cannot talk to each other, only responed to the Master unit.
Brand of PLC and protocol is a factor.
 
Mickey said:
No special equipment.As nswu1 said Daisy-Chain is prefered, you can have
drops but keep them short as possible. You need termination resistors
at both ends of network. You will need a RS232 to RS485 converter at each PLC ( if the PLC port does not support RS485). RS485 networks only support one Master. The slave units cannot talk to each other, only responed to the Master unit.
Brand of PLC and protocol is a factor.
Click to expand...

I really don't understand how can we connect if no special equipment. One RS485 bus cable has only two(2) ends, and we have 5 PLCs (suppose), then we need ATLEAST 5 open ends/connectors of RS485 bus, so there must be some equipment (or we have to cut and solder 5 places(!)). NOW, about "you can have drop" that could where all the problem come from, how can we connect between drops. One PLC has one RS485 end and that's it!===>MUST HAVE AN EQUIPMENT!!!(special or not, dont' know the name, or a mean to do it).Thank you for your reply, need more input please

Mike
 
Mickey said:
Are you reading the reference material I posted?
Try this one:
http://www.rs-485.com/download/485%20network%20topology.pdf

The only special equipment is needed just RS232 to RS485 converters.( only if the PLC does not support RS485, some do). No special wiring, twisted pair phone wire will work. Better to have shielded wire.
Click to expand...

Mickey, I was busy preparing for an interview that's why could not have much time to look everything much. By examing the reference you provide I think that a repeater(s) is what required for node (PLCs) connections to the RS485 bus. How could I not discover that, always thought that a repeater just extend the lenght of the bus but actually can do the job of noding PLCs. I think that is the solution. and Thank you very very much for your patiently trying to explain to me.

kind regards!
Mike
 
No, if your network is only 400 meters you do not need a repeater. Just daisy-chain. Most RS232 to Rs485 converters have terminal strips on there
RS485 side. Make your connection for your daisy-change at these terminal strips.
 
Mickey said:
No, if your network is only 400 meters you do not need a repeater. Just daisy-chain. Most RS232 to Rs485 converters have terminal strips on there
RS485 side. Make your connection for your daisy-change at these terminal strips.
Click to expand...

I am lost, RS485 daisy-chain is a fully completly shielded by rubber all the way or not? Or it has unshielded portions or it has many connectors along the cable??? If no connectors along the cable then how can we connect it to more than 2 RS232-RS485 convertor ends. I'm lost!!!
 
Christoph said:
Go Ethernet!
Click to expand...

"Go Ethernet"???, do we have to setup a computer server for the network before we can use it as an Ethernet and have to REGISTER with some government administrator so that we can have ip address for each PLC node??? with some simple cable types with appropriate connectors. Anyone can answer this? thanks
 

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