Networking 90-30 over SNP and Modem

[Mo_AB_4EVER]

Hello everybody I need set-up a SNP network over modem communications. Let me show you the setup: Two computers running Wonderware Intouch using GESNP DDE driver and two 90-30 plcs. Acutally each PLC is communicating to it's own computer directly. Each PLC is in a different building, about 5Km apart, and I have a direct wire with 3-4 free pairs. What I want to do is to setup a network where both computers can talk to both PLC, and where the PLC could use COMMREQ's to send some data to each other. Ideally, If I could manage to have an extra db-9 at each end for laptop programming, that would be great. I have already seen in manual GFK-0262G on page C-12, that SNP can be multi-dropped. So adding a 422-232 converter, a pair of modems and another 422-232 converter between two drops should do the trick. Has anyone of you already done this and can confirm that the setup works? And, if possible, what brand of modem you used, and so on... Thanks again in advance your good advice. Mo

[RussB]

The GE Fanuc SNP protocol can be 'Multi-dropped' giving each 'Slave Device' a unique SNP-ID the limitation that you will run into is that the SNP protocol allows only one 'Master' per network. Your programming software is a 'Master', WanderWere is a 'Master' and one of the PLC's will need to be a 'Master'. So if you need to communicate with all of your networks at the same time you will need 3 separate networks. You can avoid this by using ethernet.

[Mo_AB_4EVER]

Hugh. Now I'm in trouble. Ethernet is out of the question, they don't want to upgrade their PLC. The problem is that they are relying on a carlo gavazzi dupline module to exchange 4-20 mA signal from one PLC to another. That system broke down recently and they want to install something else. By the way, they are going to upgrade the plant in a drastic way in a year or two. Then they will put in Ethernet comm. They just want a cheap solution in the meanwhile. The cheapest solution is, obviously, "wait for the upgrade"... Any suggestions?

[RussB]

How many 4-20 mA signals were there? Would an Analog Output module and an Analog input module work? Or: A 16pt Output module in one PLC to a 16pt input module in the others. We used to do things like that.

[Mo_AB_4EVER]

Well, this actually is a good idea, but now I think I'm going to install standard modems on each end, hook em together with a little power supply to simulate a phone line, then have a NetDDE connection between the two wonderware stations. In this way, I can exchange a lot more data, and since it's a temporary solution, I don't have to worry about supporting this setup for too long.