Checkweigher Troubleshooting: 6 Common Faults (and False Rejects) and How to Fix Them

A checkweigher's core job is producing a trustworthy reject decision on every unit — so most faults worth catching either compromise accuracy or generate false rejects that cost you good product and line speed. Here are the six most common, what to check first, and when to escalate.

1. Calibration Drift

Gradual accuracy drift is the most consequential fault because it's invisible until you compare readings against a certified reference weight. Follow your recommended calibration schedule rather than waiting for a symptom — by the time drift shows up as an obvious pattern in reject data, it's likely been affecting every unit for a while.

2. Rising False Reject Rate

An increasing false reject rate on product that should be within tolerance usually points to either calibration drift, vibration interference at the weighing platform, or product handling changes (packaging weight variation, product settling differently) upstream of the checkweigher. Isolate whether it's a checkweigher issue or an upstream product/packaging change before recalibrating.

3. Vibration or Mechanical Interference

Checkweighers are sensitive instruments, and vibration from nearby equipment, uneven conveyor alignment, or a poorly isolated weighing platform can introduce noise into every reading — showing up as inconsistent results on product that should weigh identically. Check for new equipment or layout changes near the checkweigher if this starts suddenly.

4. Load Cell Issues

A load cell reading inconsistently or drifting independent of calibration is usually a hardware fault rather than a setup issue — unusual reading patterns (not just drift, but erratic behavior) are the signal to have the load cell itself inspected rather than repeatedly recalibrating around a symptom.

5. Reject Mechanism Failing to Remove Out-of-Tolerance Product

If the checkweigher correctly identifies out-of-tolerance units but the reject mechanism (pusher arm, air-blast, or drop-gate) doesn't reliably remove them, that's a mechanical or timing fault separate from weighing accuracy. Check mechanism timing against line speed first — a reject mechanism timed for a slower line speed will miss product at higher speeds.

6. Compressed Air Supply Issues (Air-Blast Reject Systems)

For air-blast reject mechanisms, inconsistent air pressure is a common and easily overlooked cause of unreliable rejection — check supply pressure against the system's rated requirement before assuming a mechanical fault with the reject mechanism itself.

When to Call for Support vs. When to Recalibrate

Occasional drift resolved by scheduled calibration is normal operation, not a fault. If false rejects or accuracy issues are recurring despite calibration, or you're seeing erratic (not gradual) load cell behavior, that's worth escalating to a technician rather than repeatedly recalibrating around a symptom that calibration alone won't fix.

Calibration and Ongoing Support

Checkweighers need regular calibration to maintain OIML R51 accuracy and provide a defensible basis for weight compliance. ENZAC provides calibration services for weighing equipment including checkweighers — working towards SIRIM accreditation, with procedures aligned to SIRIM requirements and ISO 17025 principles, and certificates traceable to national standards. ENZAC also provides spare parts supply and scheduled service and maintenance — including annual maintenance contracts — for the checkweighers it supplies, and separately for third-party checkweighers of the same type.

Review the full Checkweigher equipment page for configuration and certification detail.