Our plant has a Bailey Infi 90 system, and that's the only system I know well. To talk to a modbus device with an Infi 90 there are a couple things you need:
- A Processor Module, this would be a Multi-Function Processor or a Bridge Controller (15-20K CDN)
- Software. This can be done 3 ways: Write a C Program to talk to the devices, use a DOS based program that you just "fill in the blanks" and the C Program is built automatically, or use the new Windows based GPI (General Purpose Interface) software (I believe this is the only one supported currently ).
To use the Windows based GPI software it is of course licensced. It's liceneced by points/Processor Module. The smallest (1500 points) is around 7K CDN for the license. If you have a large plant like we do, and DCS nodes, as well as Modbus devices are spread throughout the plant, it makes it tough to bring everything through 1 licensed module. So it wouldn't be hard to have a few GPI modules in a plant that are not even close to being fully utilized (1500 points is a lot)
So my question is how do other DCS manufactures do it? (Bailey can only do Modbus, and DH+ as far as I know) The only thing I know is that Fisher Delta V has special modules for Modbus, ASI, DeviceNet, ... Are these modules big $, and is there licensing on them as well?
In our plant, we have a lot of devices that can communicate Modbus, but I don't see how it can be cost effective when licensing is set up the way it is.
Thanks for any insight.