Remote wired I/O over long distance.

I have an application where there is a leased phone line connecting one site with another 1 mile away and one more 5 miles away. They are wanting to issue a command from the base site and turn on equipment at the other sites. They are replacing old equipment that was simply using a switch to send 110VDC (rectified 120VAC) down the line to engage relays. According to the phone company I am now restricted to 24VDC which, as you can imagine, doesn't work due to the significant voltage drop. So now I need to find some other way to do it using the existing dry pair phone lines and keep the V on the line to 24VDC or under. Wireless I/O is not an option to due the distance and dense forest between the sites. I just don't think the signal would make it. Any ideas?

You could use a modem connection, or an sms-send and recieve if you have mobile reception.

Some googling will result in a high amount of support for the ulogix platform.

I'd use a simple, slow, tough Bell 202 type modem and some small PLC's for this application because I'm a "PLC guy".

You could probably also find some modem-to-modem I/O multiplexers.

I like the Data-Linc LLM-1100 modems for their size and simplicity and because the factory is just miles from my office. There are a handful of other makers of these old-fashioned modems, which will run a slow RS-232 signal (1200 baud is often the fastest) over nearly any sort of wire pair.

Your selection of controller depends on what you're familiar with. I would do it with a MicroLogix 1200R or 1100 at the head end and MicroLogix 1000's at the remote sites. I wouldn't use a ML1000 for the head end because it won't do DF1 Half Duplex Master, and I want a controller at the head end that I can monitor through a separate port.

Twido and Click! and DL05 could do the trick too.

This (modem comms) is new ground for me, so forgive my ignorance. I'm usually a local I/O type of guy. I already have a ML1100 at the head end. I would like to try to do this without PLC's at the remote sites. Could I use something like the Phoenix Contact Basic modems (part#2313067) at each site and use their Modbus/RTU bus coupler (phoenix part# 2878696)to provide the digital output I need?

Well, now looking at the data sheet for the bus coupler, it is RS-485 while the modem is RS-232.

Well, I hate to call myself an idiot, but sometimes it's justified. I re-read the email from the phone company and it only says "Voltage must be DC" Me being so used to using 24VDC just assumed there was a 24 in front of the DC. Duh.

Ken, I am going to recommend your solution below to one of my customers who wants to do the same thing via a phone connection.

I like the Data-Linc LLM-1100 modems for their size and simplicity and because the factory is just miles from my office. There are a handful of other makers of these old-fashioned modems, which will run a slow RS-232 signal (1200 baud is often the fastest) over nearly any sort of wire pair.

Click to expand...

Thanks,
Joe_WaZoo

I suggest eliminating the phone line completely and going to spread spectrum radios. Depending on the terrain you might need a repeater station to get out five miles, but in general these work quite well. they are available from a variety of sources. The elimination of the monthly phone line will eventually pay for the hardware. Turk and ohters have I/O repeater only models, but you can also get data units that will allow you to do all sorts of things if you put an RTU or PLC on the far end.

Just an update because I hate when I find posts where ppl solve problems that I also have and don't update their posts to tell how (though I'm guilty too). I wired (2) 48VDC power supplies in series and used timers from Sq.D that will operate anywhere from 12V-240V AC/DC. The site 1 mile away worked great, but the 5 mile site was just a bit too far to pick up the relay. I swapped the timer for a 12VDC 1P relay (one of the real tiny ones) and it picked right up. I don't doubt they will burn out a few relay coils on high voltage, but sometimes you just gotta get past startup

I would look at using Turk Banner wireless I/O to do this, I,ve used several of there units and had no problems, they have link loss which also means you can activate an alarm if you loose comms, very easy to setup. To give you some sort of idea I used the Dx80 units to control a lighthouse on the end of a pier, the port authority was 5.5 miles away as the crow flies and wanted to acheive several things like turning the lighthouse on / alarm monitoring etc, no problems have arrisen yet with the equipment and it,s been in service for the last six months...

Regards

John V

If I run into this again, I will definately budget for wireless I/O. This time, however, wireless was not in the scope/specs/budget and the owner was set on using this existing phone line WITHOUT complex (ha!) "stuff" like modems. Anyway, he's happy, so I'm happy.

Moore Induasties make a module called a Data Concentrator that works well for that. Send a bunch of different signals in one end and they come out the other faithfully reproduced. You can mix analog and discrete over 1 pair of wires.
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