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automationprotocolsplc
John
John

Reputation: 762

PLC Programmable Logic Controller Protocols

I'd like to integrate a PLC with a computer. Set outputs and read inputs. I've looked at Modbus and its simple although if I want to act on the change in a input I would need to poll the input to detect the change. Are there any open and common protocols used by PLC's that would push/update on sensor/input change rather than requiring polling?

Upvotes: 1

Views: 362

Answers (3)

Mark Lazarides
Mark Lazarides

Reputation: 376

The two previous answer's are decent. As Nelson mentioned, you haven't specified which controller you are using. You also haven't mentioned what on the computer you'd like to integrate with the PLC. Beckhoff's TwinCAT PLCs can use MQTT, OPC-UA as well as a host of other protocols. They also offer libraries to use their ADS protocol.

As part of ADS, you can either set up an ADS server on your machine (it's very easy) and have your PLC's write to the server. The more typical way is to subscribe to variables/structure in the PLC using this ADS mechanism from within your program's runtime. An event will be fired when the variable struct changes (you can specify how much it should have changed by, if an analog value).

The method you pick is probably dictated by your architecture. If you have many PLCs, I would set up an ADS server in your computer, if you have a handful, subscribe from your program. Of course, you can mix and match these approaches too.

Here is a page of examples: https://infosys.beckhoff.com/english.php?content=../content/1033/tc3_adssamples_net/html/tcsample_net_intro.htm&id=8269274592628480035

Upvotes: 0

franji1
franji1

Reputation: 3156

OPC UA (Unified Architecture) is an open protocol standard implemented on many PLCs with many PC client implementations available. It supports both "subscription" and "event" mechanisms, in addition to polling and other communication services.

Upvotes: 3

Nelson
Nelson

Reputation: 91

Open and common, and also simple to implement, I don't think there are. You should look for terms like "report by exception" and "unsolicited reporting". DNP3 for example has this feature, it's widely used in electrical applications, but it is not simple to implement, nor is it open.

Depending on your controller, maybe you can look at MQQT, there is support for Arduinos and RPi's, and also industrial controllers like WISE-5231

Upvotes: 2

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