Remote I/O over a leased line modem

[stefanvg]

Hi

Anyone out there using remote I/O over a leased line circuit (or 2 wire circuit). Specificaly interested in Allan Bradley gear if I can be so picky!

 

[drewcrew6]

Allen Bradley rio is pretty picky when it comes to wire. The termination details must be kept or erretic operation could/will result.

Why not put in a processor and a modem? Should be much more reliable and definetly possible then trying to replace the "blue hose" with
telephone wire.

Drewcrew6

 

[akreel]

This post is kind of old, but I thought I'd share some information I learned from my new friends at Westermo in Sweden. Tuck this away in your back pocket, it may come in handy.

As I've always suspected, Profibus, DH+, RIO, and (they said) DeviceNet/CAN use the RS485 electrical standard. In the case of DeviceNet, there are extra conductors that carry power and other features of the network. But, the important thing to note is that the BITS are still being transmitted on a twisted pair, RS485 cable just like the rest of your serial protocols.

If you can find hardware that will keep up with the baud rate of the network, you can do pretty much whatever you please with the physical media. They even showed us a Profibus over radio application.

They also told me that the data compression used by modems should allow you to transmit a high speed protocol like RIO. I assume the modem needs to be able to do some buffering, though. And the network has to accept some delays between messages. They also said it was a good idea to have the same brand of modem on both ends. There seem to be a number of different chipsets available, and you really want to make sure you're copmaring apples to apples on both ends of the line.

In response to the specific question posted here: try a leased line modem with RS485 connections. But, be sure to get tech support to look at your application before you buy anything. Or, get some demo units to try out.

AK

 

[Ken Roach]

I think the guys at Westermo are simplifying a little. Profibus is essentially RS-485, and can run at data rates down to 9600 baud.

A-B DH+ and RIO networks are Manchester-encoded, transformer-coupled, differential signalling systems. I know absolutely that you cannot use a modem (as in a conventional leased-line or dialup) with DH+ or RIO protocol directly.

You can run 10,000 feet with RIO, and repeaters can extend that an awfully long way. For very-long-distance or dialup comms I always choose an asynchronous protocol like Modbus or DF1.

 

[akreel]

You can run 10,000 feet with RIO, and repeaters can extend that an awfully long way. For very-long-distance or dialup comms I always choose an asynchronous protocol like Modbus or DF1.

Thanks, Ken.

That would be my method of choice as well.

They didn't really seem too sure about cramming a higher-speed protocol over a modem, which is why I said to check with tech support.

I found this interesting, because it makes me want to try a few things. Westermo offers DH+ to fiber converters, but I want to see if I come up with other conversions. For example, I could drop the fiber to RS232 or RS485. That might be interesting to see (if it can work). Using 2-3 converters on each end, you MIGHT be able to put DH+ on ethernet (Yes, I know... RSLinx, KT card... Bingo). It would be expensive, but there could be an application. Since I have access to the hardware, I just might have to play with it a bit.

If the networks really are RS485, as they said, then you can get isolators and repeaters from whoever your preferred vendor is. BUT, you'll be taking your chances with getting tech support from Allen-Bradley.

AK