Where is the failed product?
A product sensor and stable delay—or an encoder tied to conveyor movement—maintains identity between inspection and rejection.
Fail-safe engineering guide
Reject verification and fail-safe monitoring.
Prove the expected product left accepted production, supervise the conditions that make rejection possible and define what the line does when the sequence fails.
Track • Act • Confirm • RespondWhat is reject verification?
Direct answer
Reject verification independently confirms that the expected failed product reached the reject chute, lane or bin. If the confirmation does not arrive within the calculated window, the controls can raise a fault and stop the line.
Commanding a reject actuator is not the same as proving product removal. A cylinder-position switch may show that a pusher moved, yet it does not prove that the failed pack reached secure containment. A reject confirmation sensor closes that gap by observing the outcome after the product leaves the accepted path.
The required monitoring level should be set by the customer’s risk assessment and quality process. Higher-risk applications may combine product tracking, actuator feedback, reject confirmation, bin-full sensing, access supervision and line-stop logic.
Monitoring layers
Each sensor answers a different control question.
Clear sensor roles make fault finding and challenge testing more meaningful. One device should not be assumed to prove every part of the sequence.
Did the mechanism move?
Position feedback can confirm a pusher, flap or diverter reached and returned from its commanded position on time.
Did the product leave?
An independent sensor detects the expected item in the reject chute, lane or bin within the correct time window.
Is containment available?
A bin-full sensor warns before rejected product can build up, obstruct the chute or compromise the next reject.
Is rejected product secure?
A door or bin-present switch can supervise access and prevent normal running when the required containment is unavailable.
Can the reject still work?
Low-air-pressure monitoring can stop a pneumatic system before pressure falls below the level needed for a dependable stroke or blast.
How does reject confirmation work?
1. Register the failed product
The inspection machine provides a fail signal while a product reference—usually a photocell event or known inspection position—identifies the physical item.
2. Track it to the reject point
For stable-speed, short-distance applications, a validated time delay may be sufficient. If speed changes, an encoder can measure conveyor movement so the rejection window follows distance rather than elapsed time.
3. Define an expected confirmation window
The controls open a time or encoder window in which the separate reject sensor should see the failed item. The window needs to tolerate normal product variation without becoming so wide that the next item could be mistaken for the reject.
4. Compare expected and actual outcomes
A valid confirmation completes the event. No confirmation, an unexpected confirmation or conflicting sensor states should lead to the agreed response: warning, line stop, hold state or another controlled action.
5. Reset under a documented procedure
The system should make the fault visible and support a clear recovery process. Reset permissions, product clearance and any required inspection challenge should be agreed with production and quality teams.
Fault-response matrix
A fail-safe system needs a defined response—not just more sensors.
Stop and identify the risk window
Alarm, stop the conveyor and apply the customer’s procedure for products between the inspection point and confirmed containment.
Prevent the next unreliable reject
Stop before the system attempts another pneumatic reject or before the reject destination can no longer receive product safely.
Protect controlled containment
Prevent normal running when required reject security or containment is unavailable, subject to the agreed safety and quality architecture.
What should be included in testing?
Commissioning should test normal rejection and credible fault conditions. The exact protocol depends on the application, but a useful plan can include:
- Challenge products at minimum and maximum line speed
- Single, consecutive and closely spaced failed products
- Smallest, largest, lightest and least stable formats
- Missing reject confirmation and unexpected sensor activation
- Low-air, bin-full, access-open and bin-absent inputs where fitted
- Stop, alarm, reset and product-clearance behaviour
- Power interruption, restart and recipe change where relevant
- Recorded acceptance criteria and responsibility for approval
Testing proves the configured operating envelope; it does not remove the need for routine challenge procedures defined by the site’s quality system.
Frequently asked questions
Fail-safe reject answers.
Monitoring should be proportionate to risk and matched to a defined production response.
What is a reject confirmation sensor?+
It is an independent sensor positioned to detect the product after it leaves the accepted production path. It proves a different condition from an actuator-position switch.
What happens if a reject is not confirmed?+
The controls can alarm and stop the line, retain the fault and support the site’s product-clearance procedure. The exact response must be agreed during specification.
What does a bin-full sensor do?+
It detects when rejected product reaches a defined level so the system can warn or stop before containment becomes obstructed or another reject cannot enter reliably.
Is encoder tracking always required?+
No. Stable-speed applications may use validated timing. Encoder tracking is valuable where conveyor speed changes or physical distance must remain the tracking reference.