Hello all,
I am looking for a way to evaluate relay logic using Ignition on machines without PLCs. I was hoping you all have had some experience doing this for smaller systems. I would like a simple ethernet solution to read and write relay states and I have 24vdc and 120vac signals to deal with.
Thanks for your insights!
The key to this problem is ensuring outputs turn off or otherwise go to some predictable and relatively safe state when communications are broken or delayed. I/O modules generally have some form of timeout, either explicit or part of their comm protocol, that does this. However, typical polling drivers (query - response) won’t write to a device without an explicit new value. So your ladder logic replacement code will have to use system.opc.write* calls on a repeating schedule to make sure writes are sent within the timeouts for the device you choose.
FWIW, I’m working on a new driver module that implements a variety of Ethernet/IP features, including I/O scanning. This will make it possible to operate Allen-Bradley ethernet FlexIO, PointIO, and even 1756 chassis I/O from Ignition without a PLC. Send your contact info in a private message if you’d like previews as I prepare to roll it out. (Actually, anyone reading who’s interested can do so.)