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Old August 7th, 2007, 12:21 PM   #1
M. HASSAN
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How to establish communication between SLc 5/03 and multiple Modbus devices

If any body have the solution of the following problem, please help me out.

The problem is that I have an SLC 5/03 PLC in the control room and four microcontroller based compressors situated in class I, Division 2. All of these microcontrollers have RS232 port with Modbus PTU protocol. (Two compressors are 'AMOT' make and other two are 'Selectronics' make). The distance of each compressors from control room are 160m, 140m, 180m and 80m. Please suggest;

1. which type of protection do I use on the signals going to the hazardous area i.e. isolators or safety barriers or some thing else and do I have to place it on both sides?

2. Do I have to put a DH485 to RS232 converter at each end of the microcontrollers and put them in daisy chain and connect it to the SLC 5/03.
Does it will work or do I have to adopt some other scheme?

3. Please, suggest that how can I connect two personnel computers (both are running Rsview 32) and two printers, to the above network.

Please guide me I any one had such experience and thanks in advance.

Hassan.
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Old August 7th, 2007, 02:03 PM   #2
Joe_WaZoo
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Hassan,

The DataStation Plus from Red Lion could allow you to talk to 3 of the Modbus RTU devices and also to the AB 5/03 via DH485 with the use of the expansion card. Or you could use the RS-485 port from the Red Lion unit to talk Modbus485 and then have a 485 to 232 converter at each microcontroller. And then use the Red Lion RS-232 port to talk DF1 to your SLC. The Red Lion DataStation Plus also has Ethernet port on it to talk Native Tags to RS_View 32. Here is a link to that on the web.

DataStation Plus

This product will allow you to get the Modbus info into the AB PLC world very easily.

I would reccomend the DSPLE model at the least.

Joe_WaZoo
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Old August 7th, 2007, 09:07 PM   #3
Kim Gold
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Another product you might want to look into is a ProSoft 3150-MCM module. It will fit into the SLC 5/03 rack and will allow you to talk to Modbus devices.

http://prosoft-technology.com/content/view/full/5757

Kim
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Old August 18th, 2007, 12:08 PM   #4
M. HASSAN
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As I have mentioned that the distance between the SLC and the micro_controllers is around 600m. Please tell me, if I connect a cable from the Prosoft card to the micro_controllers and put them in daisy chain than does it will work or not. Secondly, should I use a 02 wire Cable based on Rs-485. Please, reply.

Last edited by M. HASSAN; August 18th, 2007 at 12:16 PM.
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Old August 18th, 2007, 01:05 PM   #5
Kim Gold
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The longest installation we have using a Prosoft card is approx. 300'. We are connecting to 3 Multilin 469's in series. We are using RS485 at 9600 baud.
We are using the recommended cable which is Beldon #9841.

The maximum length of RS485 is listed as 4000 ft or 1200 meters.
I believe the max. length of RS232 is listed as 50 feet although we have found it will generally works even at longer lengths.

I would not think RS232 will work at a distance of 600 metres. I would think you may need a convertor.

Kim

Last edited by Kim Gold; August 18th, 2007 at 01:08 PM.
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Old August 25th, 2007, 12:40 AM   #6
M. HASSAN
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Thanks a lot for your replies. Mr. KIM you are right, we have to place a repeater for long distance communication (600m in our case)via prosoft card. Can you please tell me, if I have to place a safety barrier or Isolator at both ends, because I have to establish a communication link from control room to compressor's (04 in nos.) located in a hazardous area, class I, division 2.
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Old August 25th, 2007, 04:14 PM   #7
danw
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1) EIA spec for RS-232 is short distance, somewhere on the order of 15 or 20 meters. The distances in this application definitely require RS-485. RS-485 can go to 1,000m distances. Use shielded comm cable that includes a wire for a ground.

RS-485 should not need a repeater, but if you need use an RS-232 port on something like a Prosoft card, then you need an RS-232-RS485 converter.

2) An RS-232-485 converters can be rated for Class 1, Div 2 hazardous areas.

For example:
http://www.bb-elec.com/product_multi...ltiFamilyId=59

Models like these also provide isolation, which is very important for protecting the relatively expensive RS-232 ports on the drives and whatever Modbus module you use on the SLC.

I always recommend isolators even when hazardous areas aren't an issue to protect the hardware ports.

3) Mr. Yazoo's comments on the RedLion DS+ as a converter between Modbus RTU and DH+ seems to work for others.
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