Common Checkweigher Errors and How to Fix Them

Checkweighers play an important role in manufacturing, food processing, packaging, and quality control by verifying product weights during production. These systems help businesses identify underweight and overweight products, maintain consistent packaging standards, and reduce product giveaway. However, like any weighing equipment, checkweighers can develop errors that affect measurement accuracy, production efficiency and quality control.

Understanding common checkweigher errors and how to fix them can help Australian manufacturers minimise downtime, reduce waste and maintain reliable weighing performance. From incorrect calibration to product handling issues, identifying the underlying cause is the first step towards an effective solution.

What Is a Checkweigher?

A checkweigher is an automated weighing system that measures the weight of products as they move along a production or packaging line. It compares each measurement against predefined minimum and maximum weight limits and identifies products that fall outside the acceptable range.

Depending on the system, rejected products may be diverted automatically using a reject mechanism, such as an air blast, pusher or drop gate.

Checkweighers are commonly used in food manufacturing, pharmaceuticals, beverage production, logistics and consumer goods packaging. Regular maintenance and correct setup help ensure consistent performance.

1. Inaccurate Weight Readings

One of the most common checkweigher problems is inconsistent or inaccurate weight measurement. Products may appear heavier or lighter than expected, even when their actual weights have not changed.

Possible causes:

• Incorrect calibration or zero settings.
• Damaged or worn load cells.
• Product vibration affecting the weighing platform.
• Unstable equipment installation.
• Dirt or product residue accumulating around the weighing mechanism.

How to fix it:

Start by checking that the checkweigher is installed on a stable surface and that the weighing section is free from obstructions. Clean the equipment according to the manufacturer's instructions and inspect the conveyor and weighing platform for vibration.

Verify the zero reading and perform the recommended calibration or performance checks using suitable test weights. If readings remain inconsistent, arrange an inspection by a qualified technician to assess the load cells, electronics and mechanical components.

2. Frequent False Rejects

False rejects occur when a checkweigher rejects products that should fall within the acceptable weight range. This can increase product waste, slow production and create unnecessary rework.

Possible causes:

• Incorrect upper or lower weight limits.
• Excessive vibration.
• Incorrect product settings.
• Poorly stabilised products moving through the weighing section.
• Incorrect filtering or weighing parameters.

How to fix it:

First, confirm that the correct product recipe and target weight are selected. Check the configured weight limits against the approved production specifications.

Next, inspect conveyor alignment, product spacing and equipment stability. If the machine uses filtering or averaging settings, review them according to the manufacturer's guidance rather than changing parameters randomly.

Test the system with representative products to determine whether false rejects occur consistently or only under particular operating conditions.

3. Underweight Products Passing Inspection

A checkweigher that allows underweight products to pass can create quality problems and potentially expose a business to compliance risks.

Possible causes:

• Incorrect minimum weight settings.
• Measurement drift.
• Poor calibration or verification procedures.
• Product-to-product contact on the conveyor.
• Faulty reject mechanisms.

How to fix it:

Verify that the minimum acceptable weight is configured correctly and matches the relevant product specification. Check the weighing system using appropriate test weights and representative products.

Inspect product spacing to ensure each item is weighed individually. Then test the reject mechanism to confirm that products identified as underweight are removed reliably.

For packaged goods sold by weight, confirm that the weighing and control process meets applicable Australian trade measurement requirements. Do not rely solely on the checkweigher's displayed reading without appropriate verification procedures.

4. Checkweigher Calibration Problems

Calibration problems can cause systematic measurement errors and reduce confidence in product weight records. Calibration may be affected by equipment movement, component wear, environmental conditions or incorrect setup.

Possible causes:

• Calibration not performed according to the manufacturer's procedure.
• Incorrect test weights or testing technique.
• Changes to the installation or weighing environment.
• Load cell damage.
• Missed maintenance or verification checks.

How to fix it:

Follow the manufacturer's calibration procedure and use suitable, traceable reference weights where required. Ensure the weighing section is clean, level where specified and free from interference.

Distinguish between calibration and routine performance verification. Calibration establishes the relationship between an instrument's indication and reference values, while verification checks whether its performance remains acceptable for the intended application.

If the equipment cannot meet its required performance criteria, stop relying on it for critical weight decisions until the issue has been investigated and corrected.

5. Conveyor Speed and Product Handling Issues

Checkweighers measure products while they move through a weighing section. Incorrect conveyor speed, poor product spacing or unstable movement can affect measurement repeatability.

Possible causes:

• Conveyor speed exceeding the configured operating range.
• Products touching or overlapping.
• Irregular product shapes.
• Slipping belts or inconsistent movement.
• Incorrect transfer between conveyors.

How to fix it:

Check the conveyor speed against the checkweigher's rated operating specifications. Ensure products enter and leave the weighing section smoothly, with sufficient spacing for individual measurements.

Inspect belts, rollers and transfer points for wear or misalignment. Where necessary, adjust the product handling process or conveyor configuration in accordance with the equipment manufacturer's instructions.

6. Reject Mechanism Failures

Even when a checkweigher measures product weight correctly, a malfunctioning reject system can allow non-conforming products to continue down the production line.

Possible causes:

• Worn pneumatic components.
• Blocked or damaged reject gates.
• Incorrect timing settings.
• Sensor faults.
• Insufficient air pressure where pneumatic rejection is used.

How to fix it:

Inspect the reject mechanism for visible damage, obstruction and wear. Check the relevant sensors and confirm that the reject timing matches the product's position on the conveyor.

For pneumatic systems, check the manufacturer's specified air pressure and inspect for leaks. Test rejection using controlled procedures to confirm that the correct products are diverted.

Follow lockout and isolation procedures before inspecting moving machinery. Repairs involving electrical systems or pressurised equipment should be performed by appropriately qualified personnel.

7. Unstable Readings Caused by Environmental Factors

Environmental conditions can influence checkweigher performance, particularly in demanding production environments.

Possible causes:

• Floor or machine vibration.
• Air currents affecting sensitive weighing systems.
• Temperature fluctuations.
• Moisture or washdown exposure.
• Electromagnetic interference from nearby equipment.

How to fix it:

Identify whether measurement errors occur at particular times, during nearby machine operation or after cleaning. Check the installation against the manufacturer's environmental requirements.

Improve equipment isolation where appropriate, maintain suitable temperature conditions and ensure the system has the required protection against moisture and dust.

For washdown environments, verify that the checkweigher is designed for the cleaning methods used in the facility.

8. Incorrect Product Settings and Recipe Selection

Modern checkweighers may store separate recipes for different products, package sizes and production runs. Selecting the wrong recipe can result in incorrect weight limits, unsuitable operating parameters and unnecessary rejects.

How to fix it:

Confirm that operators select the correct product recipe before starting production. Establish a documented changeover procedure covering target weights, acceptable limits, conveyor settings and reject configuration.

Where the system supports user permissions, restrict unauthorised changes to critical settings. Maintain clear records of recipe updates and verify the setup before restarting production.

Preventive Maintenance Tips for Checkweighers

Preventive maintenance helps reduce unexpected failures and maintain consistent weighing performance.

• Clean regularly: Remove product residue and debris using approved cleaning procedures.
• Inspect load cells: Check for signs of damage, corrosion or mechanical interference.
• Verify performance: Conduct routine checks at intervals appropriate to the application and manufacturer's recommendations.
• Monitor reject performance: Confirm that non-conforming products are consistently removed.
• Review production data: Track false rejects, weight variation and recurring alarms.
• Train operators: Ensure staff understand correct setup, product selection and escalation procedures.
• Schedule servicing: Arrange professional inspections when performance deteriorates or maintenance is due.

Maintaining a record of faults, repairs and verification results can help identify recurring issues before they cause significant production disruption.

When Should You Call a Checkweigher Technician?

Basic checks, such as confirming product settings and removing accessible debris, may resolve some issues. However, recurring measurement errors, failed calibration checks, damaged load cells, electrical faults and unreliable reject mechanisms require further investigation.

Contact a qualified weighing equipment technician if the problem persists after following approved troubleshooting procedures. Professional servicing can help identify mechanical, electrical or software-related faults and restore the equipment to suitable operating condition.

Frequently Asked Questions

Why does my checkweigher keep rejecting products?

Frequent rejection may result from incorrect weight limits, unstable product movement, vibration, incorrect recipes or measurement drift. Check the product settings and conveyor conditions before arranging a technical inspection.

How often should a checkweigher be calibrated?

The appropriate interval depends on the equipment, operating environment, usage and required measurement performance. Follow the manufacturer's recommendations and establish a documented calibration and verification schedule based on operational risk.

Can conveyor speed affect checkweigher accuracy?

Yes. Operating outside the recommended speed range or allowing products to overlap can affect measurement performance. Check the equipment specifications and ensure products move smoothly through the weighing section.

What is the difference between a checkweigher fault and a calibration issue?

A checkweigher fault may involve mechanical, electrical, sensor or software problems. A calibration issue specifically concerns the relationship between the instrument's readings and reference values. Both can lead to unreliable results and may require professional assessment.

Conclusion

Common checkweigher errors, including inaccurate readings, false rejects, calibration problems and reject mechanism failures, can affect production efficiency and product quality. By checking product settings, maintaining stable conveyor operation, verifying weighing performance and following a preventive maintenance schedule, businesses can reduce avoidable downtime and improve reliability.

For Australian manufacturers, choosing suitable checkweighing equipment and maintaining it correctly supports consistent product weights, effective quality control and compliance with applicable requirements. When errors persist, professional inspection and servicing can help restore dependable weighing performance.

I am a senior weighing solutions Specialist at Able Scale, Australia’s trusted provider of industrial and commercial scale systems. With over 15 years of expertise in material handling, manufacturing and warehouse logistics, and many more.