Wireless RS485 communication

[Cooky]

Hi,

I am trying to communicate with a Lange SC100 controller using a Modbus protocol operating on RS485. I have established 'hard wired' communication with an OPC server running on a PC with Win XP.

Having established hard wired communication, I am now using a pair of X8200 wireless modems that support RS485 to eliminate a long cable run (several kilometers). I have spoken with the manufacturers of the equipment, but still can't get the comms to work via the radio modems.

Has anyone tried this before?, or can anyone offer any advice??

Thank you,

Cooky

 

[danw2]

I haven't worked with that particular brand radio, but I have done other 485 wireless in the ISM band @ 1 watt.

I assume your RS-485 hard wired link works OK.

Might I suggest that you break the hardwired RS-485 wired link close to the PC and connect both radios to fill in the gap in the wiring.

That will eliminate "wireless" radio problems: inadequate signal strength, attenuation, distorted fresnel zone, whatever; and allow you to confirm that the radios actually communicate properly under ideal conditions (when they are practically next to each other).

When you have radios setup and working under ideal conditions, then you move the remote radio to the far end, connect it up and see how it works.

At a several kilometers distance, I assume you've got either a high gain omni antenna or even a directional antenna (yagi)?

No trees in the way? Not transmitting over water? both of which suck up ISM frequencies.

Be aware that some serial data radios are baud rate limited internally (to rates like 9600), they buffer and forward higher baud rate inputs. Don't know if your model is one or not.

Dan

 

[Cooky]

Thanks your your advice Dan. We dropped the OPC server and wrote a Visual Basic program to poll the serial card directly. This works great and we have good reliable communication via the radio modems.

The tech support from the modem suppliers is very good.

http://www.radiomodem.org.uk/#Radiomodems

Cheers,

Cooky