OPC UA Deadband Changed After a Range Update? Percent Is Not Absolute
A percentage deadband depends on the engineering range, so changing that range changes the reporting threshold. If a subscription becomes less sensitive after a device update, inspect both settings together.
Normalized example; filter behavior and supported data types follow the specification.
What is happening?
Absolute deadband uses a numerical difference, while percent deadband relates to the configured engineering range under OPC UA rules. The client and server must support the requested filter, and revised or rejected settings need inspection.
Check these five things
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Record deadband type and value.
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Read the engineering range used by the server.
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Check filter acceptance and actual monitored-item configuration.
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Test changes just below and above the intended threshold.
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Document range and filter as one interface setting.
Worked example
In a teaching range from 0 to 100, one percent represents a difference of 1. If the range becomes 0 to 1000, the same percentage represents 10. A small process change can stop generating notifications without any network failure.
Quick diagnostic reference
| Setting | Threshold basis |
|---|---|
| Absolute 1 | One engineering unit |
| One percent of 0–100 | One unit |
| One percent of 0–1000 | Ten units |
The mistake to avoid
Do not confuse subscription deadband with alarm hysteresis. They act at different stages and can independently affect what operators see.
How to verify the fix
Verify accepted filter settings and reported changes using known values. Confirm alarm and history consumers still receive the information required after a range change.
Field-work boundary: These are educational diagnostic guides. Use the exact equipment manuals and approved site procedures. Electrical testing and machinery changes belong to qualified, authorized personnel; control hazardous energy and validate affected functions before release.
Technical reference
OPC Foundation: PercentDeadband. The examples and diagnostic tables above are original teaching material; they do not replace the product manual.