Wireless MicroPLC

[mls1]

I have a water system application in which control for several reservoirs is centralized in the master station and comms are via voice grade phone lines. I'm considering a distributed system upgrade in which a large programmable RTU or PLC will perform the control for each site (reservoir and associated wells) with spread spectrum radio modems communicating with a micro RTU or PLC at each component site. I've seen several small microPLCs with integrated radio modems but none from companies I'm familiar with. Has anyone had experience (good or bad) with such a device and what would you recommend? I'd like to stick with a common SCADA protocol (modbus, DNP, etc.).
Thanks.

 

[dgauthier]

mls1 - Sorry I can't give you the hands-on references you requested, but I considered wireless for an outdoor PLC link a while back and was sold on a company called Synetcom. Go to their website,

http://www.synetcom.com

to see if their products are what you're looking for.

Regards, and good luck.

 

[robertjo24]

mls1- If you search “Wireless RTU” on the web, you will find many companies who dabble in small wireless RTUs. Most work relatively the same, but vary in packaging and reliability. Personally, I would not use them.
Have you given consideration to separate RTUs and radios in the field? This allows for greater flexibility in planning your radio links. Many in the field seem to think you can put up antennas and the system will work. In a SCADA system where the sites are very close, this may be true. However, when some of the sites are a little further out, some of these integrated RTU/radios will have a little trouble reaching home. Typical power outputs on the integrated systems are lower than a dedicated spread spectrum radio system.
My recommendation is a small RTU set side by side with a spread spectrum radio. For radios, I like MDS, (

http://www.wicrowavedata.com).

I have used them for years and they are a solid product. There are several good manufacturers of small RTUs that are cost effective. Check out Action Instruments at

http://www.actionio.com.

They have a little of everything and are reliable and scalable. They even have a small RTU with 1AI, 1DI, & 1DO in a DIN rail mount package.

 

[Wattman]

I have done several projects of this type. In all cases the customer already had decided what PLC they wanted to use or were already using.

One project had 35 pump stations and 10 metering stations with a Main control center that gathers data and alarms and issues pages and cell messages to the to the proper Tec. This customer wanted the Koyo PLC and I was weary to start but it turned out to be the best system that I have seen. We used the Modbus RTU communication port connected to a Teledesign Modem using an unused county freq. We set the system up with 2 modes of operation , one being “Report by Request” and the other “ Report by exception”.


But I have not done a system using the spread spectrum radio freq I feel it is not adequate for this type of system

 

[robertjo24]

mls1- What Wattman says about Koyo is true, it is a very good product, and very cost effective. His comments on spread spectrum are not quite as accurate.
Spread Spectrum can and is being used in all sorts of remote telemetry applications today. For straight serial data over longer distances, the 900Mhz (902-928 ISM band)frequency hopping radios seem to be the best. For higher bandwidth applications such as wireless LAN, Modbus over ethernet, ethernet based vidio, etc, the 2.4 Ghz direct sequencing or 5.8 Ghz radios work great. By the way, many PLC makers are adding ethernet modules to their PLCs. Koyo makes a great one. This allows Modbus polling over wireless ethernet. Just a thought.
If you like, post your email and I can assemble a little more info for you.