remote monitor and control services

[mikey431 3]

We are looking for some remote monitoring and control of our equipment.We prefer something over wireless or maybe sateliite since our systems can be a very remote location. Is there anybody here has any solutions and pro/cons of each ? Thank you.

[Stupidav 1]

It depends on how critical your equipment is. I have seen Wifi being "licence free" shot upwards of ten miles, with minimal disturbance issues. That means it was reported to have a 91% of scheduled up time. Wirelss is fine but anything from weather to someone playing with some microwave communication devices could cause a disturbance. If the "Control" is minimal / nondeadly, it is easy and relativly cheap. Monitoring, by price comparison, I think it is the way to go, if you can

[paulengr 44]

Assuming you are doing just monitoring, it's really no big deal. You can easily get radio modems that can go for tens of miles. If you can get tall enough towers and mountain tops in your favor, you can go for hundreds of miles. These are almost always never 802.11 because except for very tight antennas, 802.11 standards never intended for more than hundreds of feet. If you are pushing for locations where you don't have line of sight, then forget about this option for the most part. Some commercial band radio modems and/or utilizing towers and "tight" antennas can help but eventually this option reaches its limits. Beyond that, there are a few choices. If there is ANY nearby communication utility such as telephone service or cellular phone service, these work very well. In fact, the public utility at the plant I work at now reads the meter once or twice a day via a cellular data phone so that they don't have to actually go into the plant (substation is located roughly in the center of the plant). I believe they even control their own remote switch yards pretty much the same way. There's obviously some "delay" involved (no instant response) but it's not too bad. Outside of that, there are basically only two choices. You can go meteor scatter, or you can go satellite. Meteor scatter communication allows you to squirt through about 10K bits per hour to virtually any point within about an 800-1000 mile radius. There are not very many companies using this. What it does is that it continuously broadcasts the packets over and over again for close to an hour. The Earth is constantly being bombarded by micrometeors. If one hits that weighs about a kilogram, it will leave an ionization trail in the atmosphere big enough to act like a radiowave mirror in the 40-80 MHz range big enough to bounce a signal off it. The trail lasts for just a few seconds and you need one to come through in the right spot which works out to just about once per hour. One of the companies that was using it at one time was Schneider trucking. They used it to send/receive E-mail and GPS location updates with their drivers. The advantage is that you buy and maintain the equipment for meteor scatter. The disadvantage is that the communication rate is very low and the latency is very long and statistically random. With satellite, the key word to look for in google is "VSAT". This will get you what you want and avoid all the consumer grade satellite TV stuff. Satellite is the most expensive option both in terms of hardware and monthly fees. However, you can pretty much order as little or as much bandwidth as you want. The other problem with satellite is that twice a day for about 10-15 minutes once per day, you will lose communication because the sun will be directly behind the satellite and blind's the receiver. The time of day is very predictable, but it is something you just have to live with. Outside of monitoring, if you are doing control, this is a classic "RTU" configuration. First, you've got to write your code to be "fail safe". As in for any particular scenario, the PLC (and even just the hardware independently) has a definite defined reaction to any particular failure which leads to a safe state. In other words, the PLC might be receiving remote "commands" but that's about it. It should be acting somewhat autonomously to any particular alarm, and if the PLC and/or IO itself fails, it should have a defined failure mode. I'm normally 100% against using redundant PLC's and redundant I/O simply because the extra expense and having more parts frequently increases the rate of failures and the cost to repair but doesn't significantly help out MTBF. However in the case of very remote locations such as remote pumping stations where it can take hours to reach them for repairs, this is a situation where redundancy is frequently cost effective. Latency is another issue to deal with. If it's a short wireless hop, you can probably effectively ignore this because the communication delay will be a small fraction of a second. But, almost everything else I mentioned (the worst being meteor scatter) has much longer delays. This is another reason for the "semi-autonomous" way that you want to set things up. Also when it comes to errors and data logging, you will probably want to configure everything in such a way that it can do "bursts"...whenever the communication link is working, send a batch of data through that contains everything from the last time that communication was working to the current time. Just doing the traditional "set a bit/clear a bit" whenever an alarm should be turned on/off may not be effective if you have long communication latencies.

[mikey431 3]

i came across a company named " M2Mdata corp" and they offer remote monitor and control services through sattelite on monthly or per subcription basis. I wonder is there other companies and how reliable these kind of service. ... Edited 9 Mar 2008 by mikey431

[paulengr 44]

Do a google search for "VSAT". There are lots of them.

[Camel 1]

You could check out the 802.1 equiptment. This is where I shop alot. http://www.meshoutlet.com