Re: Communication between EPICS and PLCs at your facility?

["Kasemir, Kay via Tech-talk" <tech-talk at aps.anl.gov>]

Hi Ayaz,

I'd say there are at least two aspects to EPICS PLC integration.

First is of course the basic protocol, which depends on the PLC that you're using.

In the US, Allen Bradley is quite common, and there's an EPICS device driver for that.

In Europe, Siemens is prevalent, and there's an EPICS device driver for that.

There are many more, just look for "PLC" on https://epics.anl.gov/modules/manufacturer.php

Those device drivers allow you to read some number from a PLC into an EPICS analog input record, or a bit from the PLC into a binary input record, or to write a number from an EPICS analog output record to the PLC and so on. Each PLC model and the corresponding EPICS support have some details of how you may have to place the data on the PLC for efficient communication.

The second aspect of PLC integration is deciding who's in charge. Do you want to read a number from the PLC into an analog input record, and then add alarms to that record, with interlock logic on the IOC, so the PLC is just I/O and all the rest is handled in EPICS? Or do you handle the I/O, the alarming, the interlocks all on the PLC, so the IOC reads the current value into an analog input, the OK/trouble indication into a binary input, the alarm threshold into another analog input? Do you allow changing the alarm threshold on the PLC via an analog output record on the IOC? Can both the EPICS IOC and some PLC touch screen write the alarm threshold?

Putting logic into the IOC means it's more accessible. At least people who know EPICS can inspect the alarm thresholds of an analog input record at runtime. If you move them into the PLC, you can't see any of it unless you have the source code for the PLC, and/or make each piece of information available via additional records.

One approach is to place interlock logic onto the PLC, where you might argue that it's more 'secure'. Alarm logic on the other hand is meant to help operators do their job, but alarms don't perform any safety critical function, so they're better handled on the IOC where they are more accessible and easier to implement/modify.

Cheers,

Kay

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From: Tech-talk <tech-talk-bounces at aps.anl.gov> on behalf of Samadli, Ayaz via Tech-talk <tech-talk at aps.anl.gov>
Sent: Wednesday, July 6, 2022 5:46 AM
To: tech-talk at aps.anl.gov <tech-talk at aps.anl.gov>
Subject: [EXTERNAL] Communication between EPICS and PLCs at your facility?

 

Dear All,

At the European XFEL, we have an R&D project to replace the current custom communication protocol between our in-house SCADA system, Karabo, and PLCs (Beckhoff). I would be interested in your recommendations and current implementations for communications between EPICS (or other SCADA systems) and PLCs at your facility. Can you please share your experiences and suggestions with us?

If you want to get more details, please feel free to reach out to me.

Best Regards,
Ayaz


Ayaz Samadli

Controls - Control Software Engineer


European XFEL GmbH

ayaz.samadli at xfel.eu

www.xfel.eu


Headquarters: Holzkoppel 4, 22869 Schenefeld, Germany


Managing Directors: Prof. Dr. Robert Feidenhans’l, Dr. Nicole Elleuche

Registered as European X-Ray Free-Electron Laser Facility GmbH at

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