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Load Cells PowerPoint Presentation

Load Cells

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Load Cells

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  1. Load Cells Erwin Kohler

  2. Definition • A load cell is a force transducer that converts force or weight into an electrical signal • The strain gage is the heart of a load cell

  3. Factors Affecting Load Cells • Manufacturer: • The precise positioning of the gage • Mounting procedure • Materials used • User: • Impact and hysteresis • Test modes: tension/compression • Off-axis loads

  4. S-type (tension-compression) • Compression Hanging scales 50 – 5000 Kg Silos, tanks and weighbridges5,000-60,000 Kg Classification and Application Bending beam Single point Platform scales1-1000 Kg Low profile: load and pallet scales5-500 Kg Shear beam Low profile: load and pallet scales500-5000 Kg

  5. Compression Load Cells Preferred by testing engineers • Higher output • Better fatigue life • Better resistance to extraneous loads • Greater stiffness • Overload protection

  6. Falling Weight Deflectometer (pavement testing) Load Cells in Engineering Testing Force versus deflection. Fatigue tests Adhesive and paints peel force

  7. Load Cells Errors • Impacts and hysteresis • Metal retains a history of its previous loadings • When the loading is properly done, then the curve will return to zero • If, by mistake, 80% of load is applied by impact and then returned to 60%, then the load cell would be operating on a minor hysteresis loop • DON’T IMPACT LOAD CELLS

  8. Load Cells Errors • Test modes and calibration • Load cells are routinely conditioned in one mode (either tension or compression) and then calibrated • Determine test mode needed • Some cells can be operated in both modes without reconditioning, but result in non-return to zero after looping through both modes • Special fatigue load cells: • Sharp corners and edges are polished to avoid crack propagation • Longer service life including fully reversed, full capacity loading cycles

  9. Load Cells Errors • On-axis loading • All on-axis loading generate some level of off-axis extraneous components because of load carrying members causes friction that transmits side load • Avoid flat-to-flat load, because it is impossible to maintain two surfaces parallel enough to guarantee that the force will end up being centered • Compression cells have load buttons Load button: - 4” for 10,000 lbf - 6” for 50,000 lbf -12” for 200,000 lbf 3/8” off center with 5 degrees misalignment causes large moment

  10. Load Cells Errors • Nonrepeatibility • Function of the resolution and stability of the signal conditioning electronics • Load cells typically have nonrepeatibility which is better than the load frames, fixtures and electronics used to measure it.

  11. Reference Prices LOAD SENSORS . Low Cost Compact Compression Load Cells $399 . Subminiature Compression Load Cells - High Stability $395 . Miniature Load Beams $599 . Miniature & Compact Tension/Compression Load Cells - High Output $565 . Industrial Flat Disc Tension/Compression Load Cells - Stiff Shear Design $899 ACCESSORIES . Compression Load Button Adapters for Load Cells $60 . Tension Pull Plates for Load Cells $150

  12. Manufacturers • Measurement specialists www.measurespec.com • Entran sensors and electronics www.entran.com • Tedea Huntleighwww.aboutloadcells.com • Interface www.interfaceforce.com