IO-Link Device Is Online—But Is Its Measurement Valid?
An online IO-Link port does not guarantee that every process value is currently usable. Preserve the device and process-data validity information alongside the number.
Original validity example; status mapping depends on the master and device.
What is happening?
Communication state describes the link, while data validity and device diagnostics describe the measurement context. Startup, internal faults, and application-specific conditions can leave a plausible value present while its quality is unsuitable for control.
Check these five things
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Identify the master process-data validity indication.
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Read the device status and diagnostic events.
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Check how the PLC maps quality alongside the value.
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Review startup and replacement behavior.
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Define the approved response to invalid measurement data.
Worked example
A teaching sensor remains communicative while its simulated measurement is invalid during initialization. The numeric field retains its last value. Using only the online bit would make the application treat that stale number as a fresh valid measurement.
Quick diagnostic reference
| Signal | Meaning |
|---|---|
| Port online | Communication established |
| Data valid | Measurement usability indication |
| Device event | Diagnostic context |
The mistake to avoid
Do not replace invalid data with a plausible constant without making the condition visible and following the application design. That can conceal the fault.
How to verify the fix
Test startup, device fault, and recovery in a controlled environment. Confirm invalid values cannot silently enter normal calculations.
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
IO-Link Community: System description. The examples and diagnostic tables above are original teaching material; they do not replace the product manual.