Implementing Modbus using radio modems


Thread Starter

M. Cowley

I need to set up a network of radio modems, slave/masters, in order to gather industrial data from remote oil well sites. Each well site has 3 separate devices that can independently interface to a Modbus RTU master (in this case a Honeywell C200 PLC) using Modbus protocol. I intend to daisy chain the 3 devices using RS485 data transmission and then convert to RS232 for radio modem transmission. The problem I face is I don't know anything about how to map the individual device parameters and then decipher them in the Honeywell PLC for display on the control station. Where can I find this information directly (without endlessly searching Web sites)? Any help is much appreciated.
Dear Mr Cowley

Motorola make a great system called MOSCAD.

Each unit is a PLC with integrated radio modem and Motorola radio transceiver.
You would put one at each well site.
Each unit would collect data from the C200 PLCs.
In your case the MOSCAD units would not have any I/O modules, just RS485 modbus comms to talk to the C200 PLCs.

The master MOSCAD unit collects data from all the other MOSCAD units. This radio polling is handled automatically so its very easy to set up.

Programming the MOSCAD system is amazingly easy. It is all done from a PC at the master system i.e. you program over the radio links.

I first saw a MOSCAD system in 1991 running remote water pumps at a gold mine in Australia. It was interfaced to a FIX/DMACS SCADA system.

I think MOSCAD is still the best telemetry system around.

Jamie Downs
[email protected]

Issac Issachar

> I need to set up a network of radio modems, slave/masters,

You need to repost your inquiry with a header more along the lines of "mapping Modbus devices in HoneyWell C200" because that appears to be your stumbling block, not the radio modem link, if I understand your message properly.

The header of your message is likely to get more explanations of how radio modems replace copper wire, in your case the RS-485 link between the 3 remote slave devices and H-W C-200 master; and not address the mapping problem you have.

Sorry, I can't help you on the H-W problem.