Changing the OPC Path of a Tag

Ignition
1

Is there any side effect or performance issue with changing the OPCItemPath property of a Tag within a gateway script?

I want to do a reduntant data source scheme, if one device stops responding then the data will come from the second device. I’ve tested this with scripts to change the OPCItemPath of the tag, but before I go any further I would like to know if this will cause any issues in the long term.

2

Technically this should be possible. However dynamically changing all your tag settings based on some condition may not actually work as smoothly as you hope. It just seems like you’re venturing down a road that could potentially have a lot of unforeseen pitfalls.

I don’t have a good solution for an individual device to device redundancy setup which is what is sounds like you’re trying to achieve. Usually redundancy is done at the server level, not at the device level.

You could always try this out on a small scale and see what sort of results you get.

3

I have tried it with one tag, changing the item path every 5 seconds (to put it under pressure), cycling through the memory of the same device, and it seems to work pretty good from a users point of view. I was just wondering if there were any logs or new tags being created in any tables that would eventually cause any problems.

I will give it a try on a slightly bigger scale with two devices.

4

If all you change is the OPCItemPath property, I don’t think you’re going to run into anything too unexpected. Editing the tag will make the quality go to Unknown for some time, so that would be logged historically if you were using tag history, and may be visible to the user. If auditing is turned on, the edit action would be logged. Besides that, you shouldn’t have a problem.

My concern is about things becoming inconsistent, and knowing which device tags are currently coming from. It seems like it would be easy to get out of sync and have tags coming from both.

Support for failover devices has been requested a number of times, though I’ll have to check as to where it stands…

Regards,

5

Colby do you know if Device Failover will be implemented any time soon?

thanks

Hazey

6

It is not among the features that are currently in the works.