How to determine if PLC connection is available before attempted tag read?

[OwenDavid]

Hi all,

Before I start a tag reading thread that runs at 10hz I would like to prove the PLC connection. The thread is saving mission critical data from the PLC to a historian.

If the proof of connection fails I would like to timeout for 10 seconds before trying again.

Any thoughts on how to prove the PLC connection?

How do you guys handle this?

Thanks!

[dhunt84971]

Since pylogix will implicitly make the connection on the first attempt to read a tag value, I would just do that. If the read is successful then you could continue. If not you could initiate a timeout and then try again.

Someone else may know of a better way, but this method has worked for me.

[dmroeder]

I agree, I just read and check if .Status == "Success". If you don't like that, and there may be good reasons why you don't, then use GetPLCTime(), check that the status was Success.

[dmroeder]

If you're looking for code help, something like this should get you started:

https://pastebin.com/ySDs2qgp

Keeping in mind that this isn't solely checking for a connection, but a successful read. GetPLCTime() being successful basically means the connection is good, an unsuccessful read doesn't necessarily mean that the connection is bad. It could be a typo in the tag name, tag external access set to None, etc.