Connect to PLC via Modem

[JRoss]

Have any of you ever programmed a PLC using the modem on your laptop? I have a customer that wants to be able to dial in to a remote machine to do diagnostics and machine upgrades. Ethernet is not an option. We're using a Mitsubishi FX3U. Basically, I see this as a two part requirement. First is some kind of modem that connects serially to the PLC. Second is software that allows me to dial to that modem and establish a connection, which is then seen by my computer as a serial COM port. Then I open my programming software, set the COM, and I'm connected, just like if I had a direct serial connection. Any ideas?

[gtsuport]

I did this several years ago with a TI545 system that was in Mexico. You have the concept correct. You should have a dedicated phone line to the modem. Set up an external modem connected to the plc for Auto Answer, with proper baud rate and com settings. As long as the programming software will recognize the computer side modem com port, I would think you should be good. Hope this will help.

[DanW]

I used an A-B RADES 9300 modem that linked to ethernet on the PLC side when dialed into. I've never used a telephone modem to a serial port, but comments from that era (a decade ago) generally regarded industrial modems as having better connection ability and better support than the PC modems of that era. Those who worked with phone modems also became somewhat proficient at the AT commands that modems use. Dan

[Sleepy Wombat]

AT /E0

[Nathan]

That's probably a true statement. I dealt with remote PLC programming via industrial modems. One time it worked great and the other time it was a pain. Unfortunately, I wasn't the one who set up either case, so I can't really comment. I have set up the old NT modem based RAS before - industrial modems couldn't have been as painful as that! I know this isn't an option for you, OP, but for all other readers, VPNs! Routable communication is our friend - it makes life easy and expands your capabilities.

[PdL]

Have a look at Westermo modems. Very reliable industrial modems with very flexible configuration possibilities. For just about any thinkable configuration. Good documentation too, very important.

[beegee]

Is ethernet not an option due to the customer or due to the PLC? If it is due to a hardware limitation, another solution would be Moxxa ethernet to serial converters. They just create a virtual com-port on your PC and are transparant on PLC side...

[PdL]

Yep, also a good idea. The Moxa N-port server is a piece of cake.

[JRoss]

Ethernet is an option at some end-user locations, and we'll probably go with that as a basic solution. However, there are locations where the network either does not exist or is not available. In this case the customer wanted a possible way to connect with their machines remotely. I'll check out Westermo, thanks a lot!