Uncertain behavior of Siemens PLC tags in v7.9.3

I recently upgraded Ignition from v7.9.0 to v7.9.3
However, I observed that my PLC tags taken from Siemens S7-400 PLC behaved erratically since the upgrade.
Before the upgrade, my PLC tags remained live & connected but after upgrading, these tags go Uncertain for a few seconds, then come back live for next few seconds & again go Uncertain. This cyclical change is affecting my Trends & Charts & also my reporting.
What could be the reason for such behavior.
P.S. I also tried upgrading Siemens module from v4.9.3 to v4.9.4 but it didn’t help.


Typically this means you’re subscribed at a faster rate than can actually be achieved given the number of tags and the current load on the PLC.

The Siemens driver should have a diagnostics page that gives you stats and a “load factor” - what’s that page look like?

Where can I find it. I don’t see it on the gateway webpage.

Status section, Connections > Devices on the left side, click the Details button for the device.

This is one of my PLC device statistics. Kindly help decode this data. I have 4 such devices.

Given the periods, it looks like you are using a leased scan class. Make sure the stale timeout is significantly greater than the slow pace (2x should do). Make sure you have a lease (binding) on tags that your event logic depends on. For any such gateway-based logic (tag events and tag change scripts), only use non-leased tags.

I am using a Direct Scan Class, the Default Historical which was already present in Ignition. It already has Slow Rate of 10 sec & Stale Timeout of 30 sec.
This was all by default. I haven’t made any changes since the 10 sec poll-rate is sufficient for my purpose.

Your diagnostics for that device looked okay, but it would help if you made sure to look at the diagnostics for one the devices where the tags blip to bad quality and back.

The other possibility is that you’re simply getting disconnected from the device (and then reconnecting) and seeing bad quality because of that. Your gateway logs should have some more info in them.

Tags are live in the hindsight but quality shows unknown. The above scan class and statistics are same for all 4 of my PLCs. The Uncertainty occurs for every tag that I have created with Siemens driver.

I had a similar problem a while back (can’t remember when), but it had to do with unsigned and signed bytes and integers…
I think, that IA changed something with Siemens driver and I had to change my Shorts and Ints to Bytes and Words…

My RAMs are over 50 years old and it seems that they have a lot of dead cells… :slight_smile:

EDIT: I found the post with my problem a year ago… mybe it’ll be of some help:

I am using REAL, INT & BOOLEAN data formats from my PLC. I tried changing all my INT values into BYTE/WORD but the problem still persists.

The issue was with the Stale Threshold value. It was kept too low than the default value. When I changed it back to default value, all my PLC tags became live & stable. Will look for similar settings for Modus TCP driver as well. Those tags have also been troubling with Uncertainty for a while now despite stable communication.

Thanks a lot for your support, Kevin, Phil and Anton.

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