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Old December 26th, 2017, 09:01 AM   #12
Aardwizz
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Join Date: Dec 2017
Location: Swindon
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Are you aware of the existence of Single Loop Controllers ("SLC" -- not to be confused with the AB PLC with the same initials) ?

These cheap gizmos (~$100) do all the PID control for you, and have a display where the setpoints can be entered and temperature monitored. They also have communication capability (typically RS485 modbus) to talk to/from PLCs.

Your PLC would thus not need ANY AI/RTD or AO cards to talk to the thermocouples and glycol control valves, just a Prosoft module to talk to these guys. I think this is the kind of solution that your customer is expecting from you -- local control at the vat's; supervisory control at the HMI.

Technically / in theory you don't even need a PLC -- an open-source HMI like the AdvanceHMI that's popular on this site could do the Modbus interfacing with the SLCs. I've seen this sort of thing done; whether it's a good idea or not depends on one's ability to service/troubleshoot it down the road.

Anyway, just throwing it out there. Generally speaking, telling a client that he shouldn't want what he wants (local control) isn't a great way to get that client to come back to you. It's easier to keep clients than find new ones.

Good luck!
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