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i have 1 PLC and 6 devices which talks Modbus RTU via RS232 or RS485 port. The Allen Bradley PLC needs to gather the data from all 6 devices over wireless.

can someone pls advise the best and reliable way to achieve this?

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Does the PLC have an ethernet port (E/IP)? or do you need to use the serial port on the PLC?

max. distance between PLC and devices?

How many Modbus RS232 devices? Or can all do RS485?

Ok. Yes the PLC have Eth port ready. I prefer to use TCPIP. Max distance is 50 meters only. The devices can be ordered to have either RS232 or RS485. So, yes all can support RS485.

Not sure why you need to go wireless...
I assume that the devices are close to each other and thus can be connected by use of RS485.

I would set up the PLC as EtherNet/IP scanner (master) and use a wireless bridge a gateway (ethernet/ip adapter to Modbus RTU master) to read/write to the Modbus devices on RS485.

If you can skip the wireless, set up the PLC as Modbus RTU master (RS485) and run a cable to the devices..

just my 2 cents

Hi Patrick,

Normal cabling is not an option due to blockage. Can u confirm my understanding. U suggested a combination of Ethernet/IP wireless bridge AND a Ethernet/IP Modbus RTU gateway.

So for my application, i would need 6 Modbus Rtu gateway plus 6 wireless bridge for all 6 instruments. I also need 1 wireless bridge at the PLC side.

Hi Dinster,

Ok, I understand.
Now mind you that I am bias since I work for HMS, but this is how I would solve it:

6 gateways (AB7007, Ethernet/IP slave to ModbusRTU master)
http://www.anybus.com/support/support.asp?PID=110&ProductType=A nybus%20Communicator

7 Wireless bridges (021430-B,Bluetoth), where 1 is set up as master or access point.
http://www.anybus.com/support/support.asp?PID=486&ProductType=A nybus%20Wireless%20Bridge

or, If the PLC can be set up as Modbus TCP master:

6 gateways (AB7702, Modbus TCP slave to Modbus RTU master)
http://www.anybus.com/support/support.asp?PID=237&ProdType=Anyb us%20X-gateway

7 Wireless bridges (021430-B,Bluetoth), where 1 is set up as master or access point.
http://www.anybus.com/support/support.asp?PID=486&ProductType=A nybus%20Wireless%20Bridge

If you want a illustration or have any questions, you can also contact me at: pal@hms.se

//Patrick L

Another option is to utilize Ethernet Gateways. I personally use EGX100's tie them to a regular wireless router. You may have to do the same for the PLC.

I know you need wireless between the PLC and your devices but can your devices be chained via RS232/485? If so that can lower the number of gateway's you need.

http://www.powerlogic.com/product.cfm/c_id/6/sc_id/18/p_id/34

EGX100--I know it is listed as a power logic device but it works with any modbus device.

Hope this helps.

There is a ZigBee based solution, which does support Modbus RTU slaves from a Modbus TCP master. This module is the host that can connect via TCP, ZB-2570-T. The TCP master connects to it. http://www.icpdas-usa.com/products.php?PID=3700 The RTU slaves can go on the more cost effective serial only client modules, ZB-2551-T, http://www.icpdas-usa.com/products.php?PID=3928 .

Yes You can use Rs 232 Interface radios. You can visit www.prosoft-technology.com for product RLX-IFH24s which meets your requirement.