One trigger. Up to four pictures. When is the inspection actually finished?

Imagine inspecting a package with a vision camera. One light might reveal the printed label; another might help expose a reflective defect. A single photo is not always enough to evaluate everything you need.

That is where multi-step acquisition becomes useful. But it creates a common mistake: a trigger being received is not the same thing as the acquisition sequence finishing—or as a final inspection result being ready.

1. What Sequence mode does

The Cognex In-Sight Spreadsheet 26.2.1 Acquisition Panel guide describes Sequence mode as a way to configure multiple acquisition steps from one trigger. Imaging and illumination settings can be configured for each step. A single acquisition can contain up to four sequence steps.

This is scoped to supported In-Sight Spreadsheet jobs and devices. Do not assume that the same controls exist on every Cognex camera or every acquisition mode.

2. One trigger is not one image

Hypothetical flow — not actual acquisition timing

1 triggerImage 1Image 2Image 3Run job

Here is a conceptual example, not a measurement from a connected camera:

Trigger → Image 1 with light A → Image 2 with light B → Image 3 with different exposure → Sequence completes → Spreadsheet logic runs.

The manufacturer states that Spreadsheet logic executes once all sequence steps have been acquired. The A0 acquisition cell holds the frame containing the steps; GetImage can extract each step's image as needed.

So seeing an intermediate frame is not proof that the final decision is available.

3. The Job Validation limitation

The official Cognex Job Validation Panel guide explicitly says its Job Validation panel does not currently support Sequence imaging mode.

A successful Job Validation test for a different, supported configuration should not be presented as evidence that your Sequence-based workflow was validated the same way. A separate test plan should verify the real acquisition steps and output behavior of the supported equipment.

4. What to separate on the PLC side

When diagnosing an integration, keep four facts apart: 1) Evidence a trigger was sent or accepted. 2) Evidence all configured images were acquired. 3) Evidence the inspection job finished calculating its result. 4) Evidence the PLC consumed the correct, current result ID and value.

The real signal names, packet fields and interlocks are device- and protocol-specific. Verify them using the matching device documentation rather than using this article as a PLC safety design.

Related MACHCTRL article: Trigger ACK received, but did the PLC read the previous inspection? https://machctrl.com/en/learn/cognex-trigger-ack-results-handshake.html

5. Quick checklist

Does your camera and Spreadsheet job support Sequence mode?
How many steps are configured (up to four in the documentation)?
Do lighting and exposure settings differ between steps?
Is the final logic executed only after the full sequence?
Do you need to use A0 and GetImage for step-specific images?
Have you marked the Job Validation panel's Sequence limitation?
Are you separating trigger acknowledgement from a fresh completed result?

Takeaway: A command to acquire an image is not proof that the inspection decision is ready.

Sources and limits

Cognex In-Sight Spreadsheet 26.2.1 Acquisition Panel and Job Validation Panel documentation (see the manufacturer references below). The timeline and PLC example here are hypothetical, not hardware timing or factory measurements.