Leased Tags not working as expected

Ignition
1

I have a popup with a lamp test one-shot button button on it:

image
image497×599 6.38 KB

When I press it, it changes state to writing... and just stays there. Here's a screenshot of the tag:
image
image1209×492 37.1 KB

Here it is in the PLC program:

image
image546×175 3.07 KB

I have confirmed the bit does turn on in the PLC briefly before our Ignition PB AOI turns it off, and we have an output bit that triggers in the program, that is also working. The timestamp on the tag in Ignition was over 2 minutes old when I took the screenshot.

Here is how the tag group is set up:

image
image744×532 38.6 KB

I'm at a loss. I thought the popup would lease the tag because it is displayed. It should be updated every 1,000ms. I know that it can take up to 8 seconds for Ignition's driver to switch polling times on leased tags, but we're sitting at over 6 minutes right now as I type this, and even the slow polling rate of the leased group didn't update it.

I thought this was the whole point of a leased tag. Does it not work on popups?

2

I'm working around it by making a new "LeasedPolled" tag group for each section of my project and setting my push button bits to that group instead. The only difference is I made that group polled instead of subscribed. I suspect that somehow the tag changes aren't being "noticed" so the subscribe mode is making it not pick up. Doesn't seem to have hurt my comms load on my PLC at all.

3

Using "Read After Write" with a Subscribed mode Tag Group is unsafe with OPC tags and leads to race conditions exactly like you just experienced. It's called out in the user manual but still trips people up from time to time.

1 Like