wireless comm between PLCs ?

is it possible to make several PLCs to communicate between each other using radio waves or something like that , thus eliminating the needs of communication cables? is there any sample or have you got any opinons and/or suggestions about this subject?

Antenna

At our factory, we have some antenna (Symbol) plugged to a NT network.

In our laptop, we have a card (Symbol). This card transmitt and receive data from antenna.

This antenna look's like a bridge between NT network and our laptop.
You must having a link between your plc and Nt network.
Us, it's 1756-ENBT
--------------------------------------------------------------------
To talk with our plc, We have two controllogix with ethernet card 1756-ENBT that make a bridge between our two DH+ network.
Of course, each DH+ are plugged into a 1756-DHRIO

The company is SYMBOL

There are lots of vendors out there to do what you want. I haven't had an excuse to try it myself (my radio apps have been licensed frequency), but I have heard good reports from a number of guys that have done it.

The technology you want is probably "spread spectrum" radios. These are unlicensed, generally short distance (less than ten miles for many manufacturers) and line of sight transmission. Most will work inside buildings but the more structural steel and piping between the radios the less distance you will get. A number of companies make them for serial data (Gina and Locus are two) and also for ethernet.

Control Engineering Magazine recently did an article on this topic - http://www.controleng.com/ - try doing a search there for spread spectrum radios.

Expensive: Wireless LAN / ethernet. If your PLC have TCP/IP connection, you could maybe use a wireless LAN.
Check for instance: http://www.wlana.org or do a internet search (Wireless + TCP/IP)

Cheap: Radio modems with RS232/RS485 interfaces.
For example: http://www.satel.fi/bb/home.nsf/pages/Satelline or http://www.elpro.com.au/405/405_2.htm
Do a search on the web.

An example:
We have an water and wastewater application in a county. It consist of about 80 PLC's (still increasing)
Every PLC are connected to the top system. About 40 PLC's uses private line modems on leased lines and about 40 is connected in a multidrop using radio modem.
The customer wants to use radio modem on the further expansion because he saves a lot money. (The frequency is free, there is no charge is our country)
Because of geography, all stations can't use a radio modem. But with link stations, also difficult station's can be connected. Also protocols without adressing (point to point protocols) can use radio modem, because some of them can decide the link, that is, you decide wich modems that shall communicate.

You can also use GSM-modems if you don't need an online connection. For installations where there are no other solutions, it is possible to connect f.example once a day or on command read/send data and hang-up.
Has been done on application's out in the wilderness or during installation/service.

ethernet ethernet ethernet

I have to be careful to not talk above my knowledge base, but I do have a recipe for success for what you are trying to do.

I set up all of my plc's as if they were going to be communicating via a hardwired ethernet connection. I hired a company that specialized in setting up a spread spectrum wireless ethernet network to do a topography of the land.

It was so easy and flawless, that I really didn't have an opportunity to learn much.

Yes, ethernet radios are a little pricey, but I really do believe that they pay for themselves over and over and over again in the long run.

I have some customers that use serial radios and the amount of money spent on programming, wait time, hmi work arounds far surpassed the price of a wireless ethernet network.

Not to mention, that when you are doing I/O checkout or troubleshooting, it is really cool to be able to walk right up to the end devices with your laptop.

The possiblities here are endless. You could walk around the equipment with your laptop while viewing the HMI screens.

Also, a word of advice. If you go this route, set up your plcs' to send message instructions only when their data changes. You will be shocked at how fast your HMI screens will update. Now, you won't have to program two tags for every thing you do in the HMI. Nor will you have to flash "updating" text on your screens when an operator makes a change.

Anyone agree/disagree? I am interested in hearing opinions on this matter. Terry? Allen?

thank you all guys for your helps.. You're very kind.
we have a starting point at least.

Allen-Bradley wireless communications

Micro Wave;

Call an Allen-Bradley Rep., they will be happy to visit you at your facility and help you set up a communication scheme. (FREE)