What is the Working Principle of Checkweighers? Complete Guide

What Is a Checkweigher?

Core Working Principle of Checkweighers

1. Product conveying and spacing to ensure single-file weighing
2. Force-to-electrical signal conversion via high-precision load cells
3. Digital signal processing and weight calculation with dynamic filtering
4. Comparison with preset tolerance → pass/reject judgment

Main Components & Their Roles

1. Infeed Conveyor
   • Receives products from the upstream line
   • Adjusts speed to create proper product spacing
   • Prevents overlapping or contact that causes weighing errors
2. Weighing Conveyor (Weigh Bed)
   • The core weighing area mounted on load cells
   • Stable, low-vibration design for accurate sampling
   • Only one product stays on it at a time
3. Load Cell (Weighing Sensor)
   • Converts mechanical force into electrical signals
   • The “heart” of weighing accuracy
   • Common types: strain gauge load cells, EMFC (electromagnetic force compensation)
4. Controller & HMI
   • Processes signals, calculates real weight
   • Stores target weight and tolerance limits
   • Displays data, alarms, and production statistics
5. Reject System & Outfeed Conveyor
   • Removes underweight/overweight products
   • Common reject types: pusher, air jet, drop conveyor, flap diverter
   • Passed products continue to downstream packaging

Full Step-by-Step Working Process

1. Product Entry

   Products enter the infeed conveyor from fillers, sealers, or upstream lines.

2. Spacing & Separation

   Infeed speed increases slightly to separate products and avoid interference.

3. Position Triggering

   Photoelectric sensor detects when a product enters the weighing zone.

4. Dynamic Weighing

   Product rests on the weigh belt; load cells capture weight signals multiple times per second.

5. Signal Filtering & Calculation

   The controller filters vibration noise, stabilizes readings, and computes true weight.

6. Weight Judgment

   System compares measured weight with preset upper/lower limits:

   • Within tolerance → pass
   • Underweight → reject
   • Overweight → reject

7. Automatic Rejection

   Non-conforming products are removed immediately; qualified products proceed.

8. Data Logging & Output

   Weight data is saved for reports, CPK analysis, and MES/ERP integration.

Key Weighing Technologies (Load Cells & Signal Processing)

Load Cell Types

• Strain Gauge Load Cell

  Most widely used; cost-effective, stable, suitable for general food, beverage, and industrial products.

• EMFC (Electromagnetic Force Compensation)

  Ultra-high precision, used in pharmaceuticals, small parts, and high-accuracy applications.

Signal Processing Workflow

1. Weak analog signal output from load cell
2. Signal amplification
3. A/D conversion (analog to digital)
4. Dynamic filtering and vibration compensation
5. Weight calculation and judgment

Types of Checkweighers & Suitable Scenarios

1. In-Motion (Dynamic) CheckweigherFor automated lines; high speed, full inspection; most common in factories.

2. Static Checkweigher

   Manual sampling; low speed; for small-batch or spot checks.

3. High-Speed Checkweigher

   For cans, bottles, snacks; up to 600 pieces per minute.

4. Heavy-Duty Checkweigher

   For boxes, cases, cartons; large weight range.

5. Checkweigher with Metal Detector Combo

   Integrated weight and metal detection; common in food and pharma.

Typical Applications & Industries

• Food & beverage (snacks, beverages, frozen food, meat, bakery)
• Pharmaceutical (tablets, capsules, creams, syringes)
• Cosmetics & daily chemicals
• Small hardware & electronics
• Logistics & packaging (carton weight checking)
• Agricultural products & fresh produce

Benefits of Using a Checkweigher

• Ensure regulatory compliance (label weight laws)
• Reduce product giveaway (overfilling loss)
• Eliminate underweight complaints and recalls
• 100% inspection instead of manual sampling
• Improve production efficiency and reduce labor
• Collect data for process optimization
• Stable quality and brand protection

Factors Affecting Checkweigher Accuracy

• Product shape and stability
• Line speed and conveyor vibration
• Airflow and wind interference
• Load cell quality and calibration
• Product spacing and positioning
• Temperature and environment
• Proper maintenance and cleaning

Conclusion