OPC Tag Scan Rate 800ms Causing Bad_ConfigurationError, but 1000ms Works

Ignition
1

Hi Everyone,

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I am facing an issue with OPC tag scan rates in Ignition.

Issue Description:

When I configure the scan rate as 800ms, the tag quality shows:

Bad_ConfigurationError: There is a problem with the configuration that affects the usefulness of the value.

However, when I change the scan rate slightly to 1000ms, the same tag starts working normally without any issues.

What I Have Checked:

  • PLC: Siemens S7-1500

  • Optimized Block Access: Disabled

  • Data types: Verified and correct

  • Tags accessible from HMI: Enabled

  • PUT/GET communication: Enabled

  • Tag paths: Verified

  • Issue occurs only at exact 800ms scan rate

Questions:

  1. Is this expected behavior due to scan class synchronization with PLC cycle time?

  2. Are there any recommended best practices for scan class intervals to avoid such issues?

  3. Could this be related to OPC UA subscription publishing interval alignment?

  4. What could be the root cause of this behavior, where the tag quality changes based on slight variations in the scan rate?

Any guidance or best practices would be greatly appreciated.

Thanks in advance!

2

It's more likely that by putting it into the 800ms tag group, you've joined it up with other tags already in that group, and the tag has ended up in a request for a combination of tags that is failing because it includes an invalid (non-existent) address or something.

Assuming this is the legacy Siemens driver, Bad_ConfigurationError is typically only used for address syntax errors or when the read result contains an error code.