A checkweigher is an automated inline weighing machine that checks the weight of every single pack on a production line — at full production speed — and rejects any pack that falls outside a defined weight tolerance. It is one of the most important quality control instruments in a packaging operation.
How a Checkweigher Works
Packs travel from the upstream packaging machine onto the checkweigher's conveyor system. As each pack passes over the weigh cell — a precision load cell mounted beneath a short conveyor section — the system captures a dynamic weight reading in real time.
This reading is compared against preset upper and lower limits. If the pack is within tolerance, it continues down the line. If it is underweight or overweight, an automatic rejection mechanism — typically an air blast, pusher arm, or diverter flap — removes it from the line without stopping production.
Modern checkweighers can operate at speeds of 50 to 400+ packs per minute depending on the pack size and conveyor configuration.
Why Checkweighing Matters
Legal compliance. In most markets, packaged goods are subject to weights and measures legislation. Selling underweight product is a legal violation. A checkweigher provides the automatic control and data logging needed to demonstrate compliance during audits.
Consumer protection. Underweight packs mean the customer receives less than they paid for. Consistent short-filling erodes brand trust.
Cost control. Overweight packs mean you are giving away product for free. Even a few grams of overfill per pack, multiplied across millions of units, adds up to significant material cost. A checkweigher pays for itself quickly by tightening your fill weight distribution.
Upstream process feedback. Advanced checkweighers feed weight data back to the filling machine, enabling automatic mean weight adjustment. This is called closed-loop control and it keeps your average fill weight as close to the nominal as possible without manual intervention.
When Do You Need a Checkweigher?
If you are selling packaged goods by declared weight, you need a checkweigher. Regulatory requirements aside, any line producing more than a few thousand packs per shift will find manual weight sampling statistically inadequate for real process control.
Checkweighers are standard on lines producing food, pharma, personal care, and industrial products. They are typically positioned at the end of the packaging line, after the filling and sealing station, before case packing.
Key Specifications to Evaluate
When selecting a checkweigher, evaluate:
- Weighing range — minimum and maximum pack weight the machine can handle
- Accuracy — typically expressed as ±0.1g to ±1g depending on the weight class
- Speed — packs per minute at your required throughput
- Rejection system — air blast for light packs, pusher or diverter for heavier ones
- IP rating — IP65 or IP69K for wash-down environments in food production
- Data output — SPC data, OPC-UA connectivity, audit trail logging
Vedvik Machinery supplies checkweighing solutions suited for mid to high-speed packaging lines. Contact us to discuss the right specification for your application.