Plc

[Salim]

We have ALLEN BRADLEY PLC-2/30 system with distributed I/O architecture. The system is employed for material handling application. Some of the cables to the I/Os run up to three k.m. CPU talks to the I/O through ALLEN BRADLEY's proprietary REMOTE I/O protocol. We want to upgrade the CPU and retain the I/O racks but we want to establish wireless links between CPU and some of the I/Os situated at far end. How to go about it? Is it a good idea to use wireless ethernet?

 

[tmccoin]

My experience with the wireless networks has not been good. They are slower generally then a regular Ethernet network, and they get even slower the further you get from the antenna. If your application can stand slow updates they'll probably work with it.

 

[glaverty]

The companies that make the things claim you can get 1000ft out of them. Maybe if you were outside with nothing in between you and the hub. Put it in an industrail environment and your talking 100-150 Ft at which point your signal strength is in the low teens. Get some of the fancier ones with external antennas and maybe you can go a little further.

The other concern is security which has proven to be pretty easy to crack on the current versions if people even turn it on at all.

To see what I am talking about check out these links:

http://www.80211-planet.com/columns/article/0,,1781_999181,00.html
http://www.cybergeography.org/atlas/wireless.html

or just put "maps of wireless networks" into google there are a bunch of links.

This sites got some software for sniffing out wireless networks, kinda interesting.

http://www.netstumbler.com/

If your going to do it I wouldn't recommend plugging into your corporate network just yet.

 

[Allen Nelson]

You're talking wireless Remote I/O !?!? Never heard of such a thing. Sounds dangerous. What should the remote I/O do if communicaiton is lost? You're only options are "All ouputs off" or "All outputs stay right where they are".

And I don't think that you'll be ablt to find a device that will act like an RIO device on the local end of the PLC, and rebraodcast the RIO handshaking/polling over the ether. Nor a reciver that the ASB will treat as a PLC scanner.

A better solutiion would be to put some "brains" (i.e., a processor) to drive the remote I/O directly. It can still take orders from the "master" PLC, but can take action if it loses comms.

 

[Tom Jenkins]

I agree with Allen on both wireless and hardwired systems. The cost differential between remote "dumb" I/O and networking micro-PLCs is insignificant in most cases and provides a lot more robust system.

 

[jdbrandt]

I have a friend who is in the material handling business,
and they use Data-Linc modems for their transfer vehicles
and rack vehicles, with no problems.

http://www.data-linc.com/abally.htm

 

[Wasaga Willy]

Check out the DS-900 or DX-900MA wireless I/O products at OMNEX Control Systems. http://www.omnexcontrols.com/[/URL]