Load Cell Hazards & Failure Prevention
Understanding Risks and Implementing Protective Measures
As a load cell manufacturer, we see daily the results of improper load cell use. Even though load cells are designed to withstand specific environmental and use conditions, there are a number of common mistakes made that result in failed load cells or inability to meet performance expectations.
Fundamental Understanding
A load cell is a passive device that reacts to forces around it. It doesn’t get better or worse with age, but it has specific limitations. The strain gage can only accommodate small changes, and the cell must meet specific design criteria to function properly within its original specifications.
Common Failure Causes
1) Overload Conditions
Most Frequent Cause – Despite 150% overload design capability
- Static Overload: Gradual force exceeding rated capacity
- Shock Overload: Sudden impact forces
- Effects: Permanent deformation, broken strain gage bonds
- Detection: Physical bending, altered zero balance
2) Electrical Damage
Lightning, Grounding, Voltage Spikes
- Lightning Strikes: High voltage surge damage
- Improper Grounding: Welding machines, spray systems
- Power Surges: Electrical system problems
- Effects: Burns strain gages, destroys electronics
3) Environmental Factors
Moisture, Chemicals, Temperature
- Moisture Penetration: Cable damage, seal failure
- Corrosive Environments: Chemical attack on materials
- Temperature Extremes: Thermal cycling stress
- Effects: Insulation breakdown, corrosion, drift
4) Installation Issues
Side Loading, Binding, Foundation Problems
- Side Loading: Forces perpendicular to load axis
- Binding: Thermal expansion restrictions
- Foundation Problems: Uneven settlement, vibration
- Effects: Inaccurate readings, premature failure
Understanding Shock Loading
Critical Point: A load that suddenly impacts the cell can damage the critical bond between the strain gage and sensing element. Even minute damage registers as resistance changes, causing the load cell to no longer perform to original specifications.
Failure Prevention Strategies
1) Proper Selection
- Capacity Selection: 2-3 times maximum expected load
- Dynamic Loading: Account for impact and shock factors
- Environmental Matching: Material selection for conditions
- Future Planning: Consider potential system modifications
2) Installation Best Practices
- Foundation: Level, stable mounting surface
- Alignment: Proper load cell orientation
- Clearances: Space for thermal expansion
- Protection: Guards against accidental damage
3) Electrical Protection
- Surge Suppressors: Voltage spike protection
- Proper Grounding: Lightning and fault protection
- Cable Protection: Routing and strain relief
- EMI Shielding: Electrical noise protection
4) Maintenance Programs
- Regular Inspection: Visual checks for damage
- Calibration: Periodic accuracy verification
- Environmental Monitoring: Condition changes
- Documentation: Service and calibration records
Warning Signs of Impending Failure
Performance Indicators
- Drift: Gradual changes in zero balance or span
- Instability: Fluctuating or noisy readings
- Non-linearity: Calibration errors at different load levels
- Temperature Sensitivity: Excessive temperature-related changes
Physical Indicators
- Visible Damage: Cracks, deformation, corrosion
- Cable Problems: Damaged jacketing, loose connections
- Environmental: Water intrusion, chemical attack signs
- Mounting Issues: Loose hardware, misalignment
Electrical Indicators
- Resistance Changes: Bridge resistance outside specifications
- Insulation Problems: Low resistance to ground
- Signal Issues: Weak or erratic output signals
- Zero Balance: Significant zero shift
Specific Hazard Mitigation
Lightning Protection
Proper electrical grounding systems
Installation of surge suppression devices
Avoid overhead power lines and exposed routes
Increased vigilance during storm seasons
Overload Prevention
Electronic overload detection systems
Clear procedures for maximum loads
Operator education on load limits
Mechanical overload prevention where possible
Environmental Control
Appropriate weather protection enclosures
Drainage systems to prevent water accumulation
Temperature and humidity management
Material selection for process environments
Emergency Procedures
Immediate Actions
- Safety First: Ensure personnel safety and process shutdown if needed
- Documentation: Record all symptoms and conditions
- Isolation: Disconnect power and signal connections if safe
- Inspection: Perform visual examination for obvious damage
Temporary Measures
- Bypass: Temporary instrumentation if available
- Load Redistribution: Shift loads to undamaged cells if possible
- Process Modification: Reduce loads or operating rates
- Monitoring: Increased surveillance of remaining equipment
Professional Assistance
- Factory Support: Contact manufacturer technical support
- Field Service: Request on-site technical assistance
- Emergency Repair: Expedited factory repair services
- System Integration: Consult with weighing system specialists
Cost Analysis of Failures
Direct Costs
- Replacement load cells and hardware
- Installation and calibration labor
- Emergency freight charges
- Field service and technical support
Indirect Costs
- Lost production time (downtime)
- Product quality problems during failure
- Customer delivery delays
- Regulatory compliance issues
Prevention Economics
- Regular inspection and calibration programs
- Operator and technician education investment
- Overload and surge protection systems
- Reduced failure rates and downtime costs
Economic Reality: The cost of prevention is always less than the cost of failure. A comprehensive approach to load cell protection results in improved reliability and reduced maintenance costs.
Training and Education
Operator Training
- Proper Procedures: Correct loading and unloading techniques
- Warning Signs: Recognition of potential problems
- Emergency Response: Actions to take when problems occur
- Documentation: Proper record keeping for maintenance
Maintenance Personnel
- Inspection Techniques: Proper visual and electrical testing
- Calibration Procedures: Routine accuracy verification
- Installation Standards: Correct mounting and wiring practices
- Safety Procedures: Electrical and mechanical safety protocols
Management Awareness
- Cost of Failure: Understanding downtime and replacement costs
- Preventive Maintenance: Value of proactive programs
- Quality Systems: Integration with overall quality management
- Performance Monitoring: Key performance indicators
Key Success Factors
Load cell failures are often preventable through:
Proper Selection: Choosing the right load cell for the application
Correct Installation: Following manufacturer guidelines and best practices
Appropriate Protection: Implementing safeguards against common hazards
Regular Maintenance: Proactive inspection and calibration programs
Operator Training: Education on proper use and warning signs
Environmental Control: Managing the operating environment
Quality Documentation: Maintaining records for analysis
Remember: The key to successful load cell operation is understanding that these precision instruments require proper care, installation, and operation to deliver reliable, long-term performance.