ifm O2D/O2I — No Evaluation & 'Trigger Overrun'

ifm · beginner · 20 min

When an ifm O2D/O2I vision sensor produces no evaluation or its output won't switch, the usual cause is the trigger mode or a 'Trigger overrun' from re-triggering too early. Check the trigger timing in ifm Vision Assistant.

ℹ️ The O2D/O2I captures on a trigger and can't accept a new trigger while it's still processing. Re-triggering too early is discarded as a 'Trigger overrun' — the classic 'it skipped a part' cause.

How triggering works

An ifm O2D / O2I vision sensor captures an image on a trigger signal — internal or external, depending on the selected trigger mode. Crucially, during an active trigger process no new trigger can be activated: a trigger that arrives too early is discarded and treated as a 'Trigger overrun' error. So a sensor that 'skips' parts or gives no evaluation on some triggers is often being re-triggered before it finished the previous one.

Why you get no evaluation / output won't switch

1. Trigger overrun (re-triggered too early). The PLC/sensor fired the next trigger while the sensor was still busy with the previous image. Increase the time between triggers, or gate the trigger on the sensor's ready/busy so you don't fire during processing.
2. Wrong trigger mode. If the sensor is set to external trigger but no external trigger arrives (or vice versa), it won't evaluate on the schedule you expect. Confirm the trigger mode in ifm Vision Assistant matches how the line actually fires the sensor.
3. No trigger reaching the sensor. The external trigger line isn't electrically toggling the sensor's trigger input — check the wiring and watch the input.
4. Application/threshold. If it triggers and captures but the output won't switch, the evaluation result may simply be failing the configured model/threshold — review the application (contour/model, ROI, thresholds) in Vision Assistant against the real part.

Configure and diagnose in ifm Vision Assistant

Set up and diagnose the sensor with ifm Vision Assistant (or the on-device teach app). Use it to:

• Confirm the trigger mode (internal vs external) and timing.
• Watch the live image and evaluation result to see whether the sensor is capturing and what it's deciding.
• Review the model / ROI / thresholds if it captures but the output stays off.

Step-by-step

1. Check for Trigger overrun — if parts are skipped, increase trigger spacing or gate on ready/busy so you never re-trigger during processing.
2. Confirm the trigger mode in Vision Assistant matches the line (internal vs external).
3. Verify the external trigger electrically toggles the sensor input (wiring, polarity).
4. Output won't switch on a good part? Review the application/model and thresholds in Vision Assistant against the real part and presentation.
5. Re-test and confirm each trigger yields one evaluation and the output switches as expected.

When it's really hardware

Once trigger timing, mode, wiring, and the application check out, a sensor that still won't evaluate points to the optics/lighting or the unit — view the live image in Vision Assistant before replacing anything.