Load Cells

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
Classification and Application

• Single point

Bending beam
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
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
• DONT 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
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Manufacturers

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