For contamination-detection equipment, "troubleshooting" covers two different problems: missed contamination (a genuine detection failure) and false rejects (good product being rejected unnecessarily). Both cost you — one is a compliance risk, the other is wasted product and line efficiency. Here are the six most common causes of each, and what a QA technician can check before escalating.
1. Rising False Reject Rate
An increase in false rejects without a product or packaging change usually points to sensitivity drift or electrical interference, not a genuine increase in contamination. Check for new equipment recently installed nearby (VFDs, motors) that could be introducing electrical noise, and confirm nothing has changed in product positioning or orientation through the aperture.
2. Product Effect Triggering Rejects
Certain products — particularly those with high moisture, salt content, or metallic packaging elements — naturally interfere with detection and can trigger false rejects if sensitivity isn't compensated correctly for that specific product. If false rejects are consistently tied to one SKU rather than random, this is likely a product-effect calibration issue for that product's settings specifically, not a general equipment fault.
3. Sensitivity Drift Over Time
Detection sensitivity drifts with vibration, electrical interference, and component aging — this is expected and why periodic calibration verification matters more for contamination-detection equipment than most other equipment types. If test-piece checks show sensitivity has drifted from its documented baseline, this is a calibration-due situation, not a fault to troubleshoot mechanically.
4. Reject Mechanism Not Actuating
Check pneumatic supply pressure to the reject mechanism first (pneumatic pusher, air-blast, or divert conveyor) — a slow leak reduces actuation force before it fails completely. If air supply is confirmed adequate, check the reject sensor or timing relative to product speed on the line, since mistimed rejection looks like a failure to actuate even when the mechanism itself works.
5. Product Memory Settings Not Loading Correctly for Mixed SKU Lines
If sensitivity performance is inconsistent across different products on the same line, verify product memory settings are correctly stored and are actually loading per SKU rather than defaulting to a generic setting. This is a common and easily missed cause of intermittent sensitivity issues on mixed-SKU production.
6. Aperture or Belt Alignment Issues (Inline Conveyor Detectors)
Product passing off-center through the detection aperture reduces effective sensitivity for that pass. Check belt tracking and product guide alignment if false negatives or inconsistent sensitivity correlate with product position on the belt.
When Sensitivity Drift Means It's Time for Calibration, Not Troubleshooting
If test-piece checks confirm sensitivity has moved from its documented baseline, stop troubleshooting individual faults and get the unit recalibrated. Calibration frequency should match your application's risk — annual is a minimum for most food and industrial applications, with quarterly or monthly appropriate for regulatory-critical or export-facing lines.
Spare Parts and Ongoing Support
Sensor coils, reject mechanism components, and control electronics are the parts most likely to need eventual replacement. ENZAC provides spare parts supply and scheduled service and maintenance for the metal detectors it supplies, and separately for third-party detectors of the same type. Calibration is available as an ongoing service — including for third-party equipment — producing a written certificate with equipment identification, reference test pieces used, before/after readings, pass/fail determination, and next due date, with ENZAC working toward SIRIM accreditation and procedures aligned to ISO 17025 principles.
Review the full Metal Detector equipment page for configuration and sensitivity specification detail.
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If false rejects or a suspected sensitivity issue aren't resolving with these checks, or your calibration is due, contact ENZAC with your equipment details and we'll schedule the right service.