Force measurement systems with integrated load cells and strain gauges often operate in tough environments. However, even the highest-quality load cells are delicate instruments. Since a load cell’s accuracy depends on elastic, micro deformations in its flexure, any permanent structural compromise can render the load cell’s readings unreliable. These structural integrity issues don’t just develop while the load cell is in service. They frequently result from improper storage and handling between deployments. For this reason, documented quality control (QC) procedures should cover all aspects of the load cell’s lifecycle, including handling, preservation, and storage. This guide outlines these essential QC best practices.
Key Takeaways
- Mechanical Sensitivity: Load cells convert micro-inch structural deformations into electrical signals; improper handling or minor impact drops permanently deform Wheatstone bridge elements and ruin calibration accuracy.
- Cable Integrity Rules: Never lift or support a load cell by its signal cable. Cable pulling tears internal wire bonds and breaks waterproof cable seals, introducing moisture into the gauge cavity.
- Installation Protections: Use dummy load cells during heavy frame construction and always ground welding equipment directly near the weld joint to prevent high currents from melting internal strain gauges.
- Storage Environment Control: Store load cells in temperature-controlled, low-humidity enclosures with silica desiccant, and protect wiring using rodent-proof conduit or sealed containers.
- Routine Maintenance Checks: Perform periodic visual inspections for corrosion, cable jacket cracking, and zero-balance shifts before redeploying stored sensors into service.
- Qualified Technicians: Train personnel on these best practices to maintain load cell integrity and performance.
Why Quality Control Matters for Strain Gauge Sensors
A load cell can lose accuracy for plenty of reasons, including electromagnetic interference (EMI), harsh operating environments, or sheer mechanical wear. Often, though, the real culprit is how the sensor is handled between measurements or between deployments. Rough transport, accidental drops, and improper storage ruin sensitive electronics far faster than normal operation.
Most industrial force sensors can tolerate a little real-world abuse, but establishing clear, documented handling protocols ensures the entire team knows how to protect the equipment. Training everyone on these best practices protects both your hardware investment and your project schedule from preventable downtime.
The Dos and Don’ts of a Measurement Device’s Service Life
The sections below offer the “dos” and “don’ts” when handling load cells during installation, operation, and storage. We recommend that you include these in your documented quality processes.
Installation Procedures and Mounting Safety
The following should be part of documented quality control processes for properly handling a load cell during installation.
| Installation Phase | Recommended Practice (DO) | Destructive Practice (DON’T) |
| Lifting & Moving | Support the sensor body with both hands or lifting straps. | Never lift or carry a load cell by its signal cable. Do not drop it or bump it into other objects while transporting it. |
| Structural Assembly | Insert a solid steel “dummy” cell during hopper/tank welding and frame assembly. Ensure the load path perfectly aligns with the sensor’s load axis. | Never leave live load cells in place during heavy structural construction. Avoid structural assembly that creates non-axial load paths. |
| Fastening & Bolting | Use a calibrated torque wrench and tighten bolts in a two-stage crisscross sequence. Use proper mounting hardware. | Do not over-torque mounting bolts or force/twist the load cell body into place during installation. Do not under-torque or use mounting hardware that will allow the cell to shift position while in use. |
| Welding Near Sensors | Ground the welding electrode on the same structural piece being welded. | Never allow welding current to pass across the load cell flexure or cable. |
One last thing to keep in mind when installing and handling load cells is the importance of cable integrity. Failed cables are most often the source of load cell failures. Therefore:
- Never cut a 4-wire load cell cable, since this changes the total excitation line resistance, introducing a systematic voltage drop that, in turn, alters the output signal. (See this load cell cable FAQ for a mathematical explanation of this effect.) If cable length adjustments are needed, always choose a 6-wire load cell with a sense wire.
- Never allow the load cell cable to experience any tensile force, as this can sever the seal where it connects to the spring element. This can allow moisture to intrude, permanently damaging the cell.
- Avoid designing fixtures that pinch or abrade cable insulation.
Operational Care and Overload Protection
By following these operational practices, you can ensure a load cell operates as expected during its service life.
| Operational Area | Recommended Practice (DO) | Destructive Practice (DON’T) |
| Capacity & Loading Range | Choose a load cell so that working loads fall near the middle of its rated capacity range. Account for transient forces like wind or vibration. | Never operate consistently near full capacity, as minor environmental spikes such as wind gusts or vibrations can cause unseen flexure overload. |
| Applying Loads | Place or lower loads gently and smoothly onto the weigh platform or mounting structure. | Do not drop loads or subject the sensor to sudden impact shocks; these can permanently deform the internal circuitry or overload the element. |
| Cleanliness & Maintenance | Keep the load cell body, mounting brackets, and flexure gaps completely free of dirt, oil, and debris, even if they are hermetically sealed. | Do not allow debris to build up around the load cell, as trapped material can bind the weigh platform or elastic elements, creating false weight readings. |
| Visual Inspections | Perform scheduled visual checks for surface corrosion, frame cracks, cable jacket wear, or moisture entry. Replace damaged load cells. | Never leave a visibly damaged, corroded, or moisture-compromised load cell in active service. |
| Routine Recalibration | Recalibrate the measurement system periodically against certified standards with proven traceability (e.g., NIST). | Do not skip scheduled service calibrations or assume long-term signal accuracy without regular verification. |
Removal and Fault Inspection Protocols
When a load cell experiences trouble despite following installation and operating best practices, follow these guidelines.
| Removal & Replacement Phase | Recommended Practice (DO) | Destructive Practice (DON’T) |
| Troubleshooting | Follow a formal, step-by-step procedure (such as the one in our guide, How to Test for Faults in Load Cells) when a device performs unpredictably. | Do not remove or discard a sensor without systematically isolating the fault to verify the load cell itself is at fault. |
| Defective Device Documentation | Document specifics relating to the removed device’s failure and usage information using a physical tag attached directly to the device. | Never place a removed device into storage or ship it for repair without clear failure notes and traceability information. |
| Disconnecting Wires | Leave sufficient wire length attached to the load cell body if cutting cables during removal. | Never cut connecting wires flush at the cable gland entry, which prevents the manufacturer from connecting test leads for failure analysis. |
| Replacement Calibration | Calibrate the replacement load cell or the end-to-end weighing system before resuming measurements. | Do not put a replacement load cell directly into active service without verifying system calibration. |
Environmental Storage Guidelines for Load Cells
The intent of storing a measuring device is to preserve it for future use. To ensure the measurement device is in a ready-to-go condition when needed, include these steps in quality control procedural manuals. These actions prevent environmental damage between uses.
| Storage Factor | Recommended Practice (DO) | Dangerous Practice (DON’T) |
| Device Cleaning | Thoroughly clean the sensor body and mounting surfaces, ensuring the device is free of debris, oil, and chemical deposits prior to storage. | Never place a dirty load cell into storage, as trapped contaminants cause surface corrosion and seal degradation over time. |
| Moisture Control | Store sensors in a humidity-controlled location (or inside sealed containers with desiccant). | Do not leave load cells in unconditioned storage areas where ambient condensation can collect on cable glands and electrical contacts. |
| Temperature Verification | Verify that the storage location’s ambient temperature strictly meets the storage temperature limits listed in the manufacturer’s product literature. | Never store devices in areas subject to temperature extremes, as excessive heat or freezing can cause zero-balance temperature shifts. |
| Physical & Pest Security | Enclose the wiring assembly in rodent-proof sheathing, or store the entire device inside rigid, pest-proof containers. | Never leave cable leads exposed or loosely draped on open shelving, where rodents can gnaw through the cable jacket and wire insulation. |
| Vibration Isolation | Store sensors in cushioned, shock-absorbing packaging located away from heavy plant machinery, compressors, or structural vibration sources. | Do not store load cells on unpadded metal shelves, as constant micro-vibrations weaken internal strain gauge bonds. |
| Environmental Monitoring | Monitor and record storage conditions routinely to ensure climate parameters remain within manufacturer-specified limits. | Do not assume long-term storage facilities remain within safe limits across changing seasons. |
| Visual Examinations | Perform scheduled visual inspections on stored units, and conduct immediate checks following environmental shocks, HVAC outages, or seismic events. | Never leave devices in long-term storage for extended periods without routine visual checks for corrosion, cracking, or insulation damage. |
Summary Checklist for Quality Control Compliance
Long-term sensor reliability relies on systematic quality control. Use this five-part compliance checklist as a quick reference guide for your team’s handling, storage, and maintenance procedures:
1. Documentation & Traceability
- [ ] Maintain Sensor Records: Store the original Certificate of Calibration, product datasheet, and user manual in a central, accessible database.
- [ ] Log Usage & Field History: Document installation dates, operating environments, peak loads, and any observed zero-balance shifts for every active sensor.
- [ ] Tag Disconnected Units: Attach a physical tag with failure notes, serial numbers, and usage history to any load cell removed from service before storing or returning it to the manufacturer.
2. Personnel Training
- [ ] Standardize Procedures: Ensure documented corporate protocols for load cell handling, mounting, and storage are actively maintained.
- [ ] Train Operations Teams: Educate all field technicians, installers, and project managers on strain gauge fragility, cable care, and the standardized procedures before handling hardware.
3. Environmental & Rating Verification
- [ ] Verify Application Limits: Check that the sensor’s rated capacity, operating temperature range, and IP rating match the environmental demands of each new deployment.
- [ ] Assess Enclosure Sealing: Ensure potted load cells are restricted to mild environments, reserving hermetically sealed (laser-welded stainless steel) units for washdown or submerged applications.
4. Moisture Control & Load Cell Body Integrity
- [ ] Protect Cable Entries: Keep all wiring, junction boxes, and cable gland connections clean, dry, and elevated away from standing water.
- [ ] Inspect for Corrosion & Surface Wear: Routinely check sensor bodies and cable entries for physical wear, surface degradation, or cracks in protective sealants..
5. Routine Inspection & System Maintenance
- [ ] Inspect Cable Jackets: Check wiring assemblies regularly for cuts, abrasion, rodent damage, or hardening from chemical exposure.
- [ ] Check Flexures & Mounts: Verify that load cell flexure gaps, mounting plates, and weigh assemblies remain free of dirt, ice, and industrial debris.
- [ ] Monitor Zero Balance & Recalibrate: Watch for baseline zero-point shifts during visual checks, and schedule periodic system recalibrations.
References
- TO 32-1-201, Technical Manual: Care, Use and Maintenance; Measuring Tools, Class 5200, March. 1997
- MIL-STD-1312-21, Military Standard, Fastener Test Methods, Method 21, Shear Joint Fatigue, July 31, 1985
