Lunch & Learn
Interface: Brian Peters, Ken Vining
T&M Instruments: Jace Curtis
Lunch & Learn Topics
• Interface History
• Load Cell Design & Theory
• Application Considerations
• Factors of Performance...
Our Heritage
• Family owned in Scottsdale, AZ since 1968
• World’s largest manufacturer of low profile load
cells
• Guaran...
Trust our Experience
• We’ve been in the business of manufacturing
load cells for 45 years
• Building our 1 millionth load...
Performance Second to None
• Metrology grade load cells with performance as
high as 0.02% F.S.
• Lower load limit of 4% on...
Vast Capabilities
• Performance: as high as 0.02% F.S.
• Capacity: 50 grams to 2.25 Million lbf
• Millivolt, Voltage or Cu...
We Sell Solutions
• Application engineers will discuss your
application to understand your priorities in your
force or tor...
Over 100,000 configurations of
load & torque cells
Over 10,000 instruments and
signal conditioners sold in last
10 years alone
What is a Load Cell?
How a load cell works
• Wheatstone bridge
• 2 voltage dividers fed
by the same input
creating a balanced
bridge.
How a load cell works
• Deflection causes an
offset or unbalanced state
which creates a change
in resistance.
• The result...
Choosing the Right Load Cell
• Application considerations – what is
important?
• Mechanical (dimensions & mounting)
• Elec...
Choosing the Right Load Cell
• Mechanical - Mounting
• One of the most critical aspects
that can determine the success
of ...
Low Profile mating surface
• Surface must be clean and flat
• Mounting surface must be flat to 0.0002 Total Indicator
Read...
Design Alternatives
• Many choices to choose from
Choosing the Right Load Cell
• Electrical
• Excitation voltage available
• Millivolt, voltage or current output
• Acceptab...
Choosing the Right Load Cell
• Environmental – Thermals
Choosing the Right Load Cell
• Environmental – moisture or humidity?
• Dual diaphragm, or welded, sealed units available
•...
Choosing the Right Load Cell
• Environmental - submersible
• Underwater applications are a possibility
• Media density and...
What Major Factors
Impact Sensor
Accuracy in Testing
Applications?
Factors
• Specifications
• Mounting
• Calibration
• Instrumentation
• Cables
• Uncertainty of calibration
Specifications
• No “Accuracy” term on
data sheets
• Apply specifications
according to application
• %FS, %RO, %, %/°F,
ti...
Nonlinearity
The algebraic difference
between OUTPUT at a
specific load and the
corresponding point on the
straight line d...
Hysteresis
The algebraic difference
between output at a given
load descending from
maximum load and output
at the same loa...
Static Error Band
The band of maximum
deviations of the ascending
and descending calibration
points from a best fit line
t...
SEB Output
A computed value for Output at capacity
derived from a line best fit to the actual
ascending and descending cal...
Interface compensates every low profile load cell
Each load cell is tested, adjusted, and retested until it is within
requ...
Maximum allowable off-axis loads
vary by model as shown
Moment and Side Load Error Limit
Example
Assume Model 1220ACK-
50K-B Spec
Limit
Load
Cell
Capacity
Allowable
Extraneous
Lo...
Creep
• The change in load cell signal occurring with
time while under load and with all
environmental conditions and othe...
Temperature Compensation
Temperature effects both zero balance
and output signal
Errors can either be positive or negative...
Temperature effect on output
Expressed as a
% of Reading / °F
Effects the slope of the
output curve
Temperature effect on zero
Expressed as
%Rated Output / °F
Shifts entire curve
parallel to itself
Relatively larger effect...
Typical Interface Specs for
Temp Effect on Zero Balance
1100 Spec
– High Accuracy
– ± .0004%RO / °F
1200 Spec
– Medium Acc...
Temperature Compensation of ZB
Every load cell is temperature
compensated for zero balance
Compensation flattens the curve...
Symmetry Error
The algebraic difference between the
Rated Output in tension and the average
of the absolute values of Rate...
Mounting Considerations
Extraneous loads
Parasitic load paths
Mating surface and adapters
Live end vs. Dead end
Live End vs. Dead End
Calibration
Characterization
Calibrate as used in application
Additional points
Ascending and descending points
Multiple r...
3-Run calibration
Nonrepeatability
The maximum difference between output
readings for repeated loadings under
identical loading and environm...
Cable Length
Lowered sensitivity
Increased temperature
error
6-wire vs. 4-wire
Instrumentation
Zero adjustment
Span adjustment
– Applied load
– mV/V input
– Simulator
– Shunt calibration
Simulator
Connects in place of load
cell
Ratiometric mV/V output
Can be used to calibrate
instrument in mV/V
Shunt Calibration
Shunt calibration uses a resistor to
stimulate one leg of the wheatstone bridge
The resulting output sig...
Shunt Calibration
Internal shunt cal can also be used to
determine to which bridge a remote
connection has been made, assu...
We provide solutions
Vast Range of Load and Torque
Sensing Solutions
• Clevis pin
• Miniature
• Sub-miniature
• Load buttons
• Load washers
• A...
Why Should you Choose Interface?
Capabilities
• Capacities from 10 grams to 2,250,000 lbf
• Accuracy as high as 0.02% FS
•...
Why Should you Choose Interface?
Capabilities
• Fatigue rated
• ATEX, FM, CE, RoHs ratings available
• Submersible – IP68
...
40% of our business
is custom or special
Why Should you Choose Interface?
Performance second to NONE
• Guarantee: Our load cells will outperform our
competitor’s –...
Vertically Integrated Manufacturing
• All machining, gaging and fabrication controlled in house
Why Should you Choose Inte...
Stocking program
• Interface will maintain stock of the finished goods for same day
shipment if orders are received by noo...
What’s behind our performance
guarantee?
What makes Interface Better?
Proprietary Interface Strain Gages
• Made in house at our facility in Scottsdale, AZ
• Featur...
What makes Interface Better?
Feature: Proprietary Interface Strain Gages
• Benefit: Compensation resistors cannot be therm...
What makes Interface Better?
Feature: Proprietary Interface Strain Gages
• Benefit: Our strain gages allow us to provide a...
What makes Interface Better?
Feature: Rigorous Temperature Testing
• Interface performs both hot and cold thermal compensa...
Feature: Moment compensation
• Interface compensates every low profile load cell
• Competitors do not know their performan...
Eccentric & Side Load Specifications
What makes Interface Better?
What makes Interface Better?
Feature: Moment Compensation
Benefit: Known maximum error
New Product Releases
New Product Releases
 New and Improved Low Profile
 Better overall static error specifications
 Enhanced off axis perfo...
New Product Releases
 Flange load cell
 Extremely popular in Europe
 Ease of installation due to elimination of thread ...
New Product Releases
Model 2300 flange load cell
 0.05% F.S. static error band
 High capacity: 1M lbf
 Eccentric load ...
New Product Releases
 Load Pins
• Capacities from 100 lbs to 300,000 lbs
• Various sizes and shapes, lengths and diameter...
Load Pin Configurator
 Lots of choices
Diameter
Sensing section length
Anti-rotation techniques
Cable exit
Amplified...
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Load Cell Lunch and Learn Presented by Interface

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This in-depth presentation is a detailed crash course on load cells and force measurement for a wide variety of applications. Learn more about our history, unparalleled track record and our products.

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Load Cell Lunch and Learn Presented by Interface

  1. 1. Lunch & Learn Interface: Brian Peters, Ken Vining T&M Instruments: Jace Curtis
  2. 2. Lunch & Learn Topics • Interface History • Load Cell Design & Theory • Application Considerations • Factors of Performance • What Makes Interface Better • Questions?
  3. 3. Our Heritage • Family owned in Scottsdale, AZ since 1968 • World’s largest manufacturer of low profile load cells • Guarantee: Our load cells will outperform our competitor’s – PERIOD • Made in the USA
  4. 4. Trust our Experience • We’ve been in the business of manufacturing load cells for 45 years • Building our 1 millionth load cell in 2013! • Both PTB & NIST are Government standards for measurement traceabilty: They use INTERFACE
  5. 5. Performance Second to None • Metrology grade load cells with performance as high as 0.02% F.S. • Lower load limit of 4% on Gold Standard series cells and 2% on Platinum Series • Provide additional specifications not standard in the industry • A2LA Accredited calibration
  6. 6. Vast Capabilities • Performance: as high as 0.02% F.S. • Capacity: 50 grams to 2.25 Million lbf • Millivolt, Voltage or Current output available • Hermetically sealed, submersible, vibration rated, dual bridge, overload protected • ATEX approved for hazardous environments • 200 page catalog represents 60 – 70% of our business. The rest is modified standard or custom
  7. 7. We Sell Solutions • Application engineers will discuss your application to understand your priorities in your force or torque measurement • We will propose a solution specific to your application be it a standard, modified or custom design • This has been our approach for 45 years…there’s a good chance we already have a solution to meet your needs
  8. 8. Over 100,000 configurations of load & torque cells
  9. 9. Over 10,000 instruments and signal conditioners sold in last 10 years alone
  10. 10. What is a Load Cell?
  11. 11. How a load cell works • Wheatstone bridge • 2 voltage dividers fed by the same input creating a balanced bridge.
  12. 12. How a load cell works • Deflection causes an offset or unbalanced state which creates a change in resistance. • The result is a ratiometric output directly proportional to the force applied. • Specified as mV/V output
  13. 13. Choosing the Right Load Cell • Application considerations – what is important? • Mechanical (dimensions & mounting) • Electrical (output & excitation) • Environmental (temperature, moisture, etc) • Performance (accuracy, thermals)
  14. 14. Choosing the Right Load Cell • Mechanical - Mounting • One of the most critical aspects that can determine the success of your application • Various possibilities: Threaded connections, adhesive, inline, through hole, • Direction of load will impact your decision of the best approach
  15. 15. Low Profile mating surface • Surface must be clean and flat • Mounting surface must be flat to 0.0002 Total Indicator Reading • Suitable thickness and material • Recommended hardness of Rc 30 or higher • Mounting bolt torque according to specifications
  16. 16. Design Alternatives • Many choices to choose from
  17. 17. Choosing the Right Load Cell • Electrical • Excitation voltage available • Millivolt, voltage or current output • Acceptable input to data acquisition • Noise immunity • Cable length • Proper grounding
  18. 18. Choosing the Right Load Cell • Environmental – Thermals
  19. 19. Choosing the Right Load Cell • Environmental – moisture or humidity? • Dual diaphragm, or welded, sealed units available • High humidity, splash down or oil bath applications can be addressed • Nema or IP ratings as industry standards • Some designs cannot be sealed at all • Take caution selecting cable • Environmental connectors available
  20. 20. Choosing the Right Load Cell • Environmental - submersible • Underwater applications are a possibility • Media density and depth need to be understood • Barometric pressure compensation • Susceptibility to media/corrosion • Vented cable?
  21. 21. What Major Factors Impact Sensor Accuracy in Testing Applications?
  22. 22. Factors • Specifications • Mounting • Calibration • Instrumentation • Cables • Uncertainty of calibration
  23. 23. Specifications • No “Accuracy” term on data sheets • Apply specifications according to application • %FS, %RO, %, %/°F, time related
  24. 24. Nonlinearity The algebraic difference between OUTPUT at a specific load and the corresponding point on the straight line drawn between minimum load and maximum load. Normally expressed in units of %FS.
  25. 25. Hysteresis The algebraic difference between output at a given load descending from maximum load and output at the same load ascending from minimum load. Normally expressed in units of %FS.
  26. 26. Static Error Band The band of maximum deviations of the ascending and descending calibration points from a best fit line through zero output. It includes the effects of nonlinearity, hysteresis, and non-return to minimum load. Expressed in units of %FS
  27. 27. SEB Output A computed value for Output at capacity derived from a line best fit to the actual ascending and descending calibration points and through zero Output.
  28. 28. Interface compensates every low profile load cell Each load cell is tested, adjusted, and retested until it is within required performance tolerance A history of every load cells moment compensation data is retained Graphs of moment load test results can be provided Eccentric Load Sensitivity • ECCENTRIC LOAD - Any load applied parallel to but not concentric with the Primary Axis. Results in Moment load. • SIDE LOAD – Any load at the point of Axial Load application at 90° to the primary axis.
  29. 29. Maximum allowable off-axis loads vary by model as shown
  30. 30. Moment and Side Load Error Limit Example Assume Model 1220ACK- 50K-B Spec Limit Load Cell Capacity Allowable Extraneous Load Maximum Error Due to Allowable Extraneous Loads Eccentric Load Sensitivity (% per inch) ±0.25 50K lbf (40% capacity) x (1 inch) 20K in-lb (20K in-lb) x (0.25%/in) / 50K lbf 0.10% Side Load Sensitivity (%) ±0.25 50K lbf 40% capacity 20K lbf (20K lbf) x (0.25%) / 50K lbf 0.10% Assume Model 1110ACK- 10K-B Spec Limit Load Cell Capacity Allowable Extraneous Load Maximum Error Due to Allowable Extraneous Loads Eccentric Load Sensitivity (% per inch) ±0.10 10K lbf (40% capacity) x (1 inch) 4K in-lb (4K in-lb) x (0.10%/in) / 10K lbf 0.04% Side Load Sensitivity (%) ±0.10 10K lbf 40% capacity 4K lbf (4K lbf) x (0.10%) / 10K lbf 0.04%
  31. 31. Creep • The change in load cell signal occurring with time while under load and with all environmental conditions and other variables remaining constant. Expressed as % applied load over specific time interval.
  32. 32. Temperature Compensation Temperature effects both zero balance and output signal Errors can either be positive or negative Effects are repeatable from test to test
  33. 33. Temperature effect on output Expressed as a % of Reading / °F Effects the slope of the output curve
  34. 34. Temperature effect on zero Expressed as %Rated Output / °F Shifts entire curve parallel to itself Relatively larger effect at lower signals
  35. 35. Typical Interface Specs for Temp Effect on Zero Balance 1100 Spec – High Accuracy – ± .0004%RO / °F 1200 Spec – Medium Accuracy – ± .0008%RO / °F As specified by customer
  36. 36. Temperature Compensation of ZB Every load cell is temperature compensated for zero balance Compensation flattens the curve about room temperature A history of temp comp data for every load cell is retained Shape of curve isn’t changed by compensation Standard compensated temperature range is 15ºF to 115ºF Interface will perform temp compensation at your requested temperatures
  37. 37. Symmetry Error The algebraic difference between the Rated Output in tension and the average of the absolute values of Rated Output in tension and compression. %RO
  38. 38. Mounting Considerations Extraneous loads Parasitic load paths Mating surface and adapters Live end vs. Dead end
  39. 39. Live End vs. Dead End
  40. 40. Calibration Characterization Calibrate as used in application Additional points Ascending and descending points Multiple runs ASTM E74
  41. 41. 3-Run calibration
  42. 42. Nonrepeatability The maximum difference between output readings for repeated loadings under identical loading and environmental conditions. Expressed in units of %RO
  43. 43. Cable Length Lowered sensitivity Increased temperature error 6-wire vs. 4-wire
  44. 44. Instrumentation Zero adjustment Span adjustment – Applied load – mV/V input – Simulator – Shunt calibration
  45. 45. Simulator Connects in place of load cell Ratiometric mV/V output Can be used to calibrate instrument in mV/V
  46. 46. Shunt Calibration Shunt calibration uses a resistor to stimulate one leg of the wheatstone bridge The resulting output signal can be useful for calibrating or scaling instrumentation Resistor tolerance is generally unimportant but TCR should be carefully considered Resistors may be internal or external to the load cell Internal resistors don’t get lost
  47. 47. Shunt Calibration Internal shunt cal can also be used to determine to which bridge a remote connection has been made, assuming each bridge has a different resistor value When using external shunt cal, remember long cable lengths affect shunt cal values
  48. 48. We provide solutions
  49. 49. Vast Range of Load and Torque Sensing Solutions • Clevis pin • Miniature • Sub-miniature • Load buttons • Load washers • Axial torsion • Multi-axis • Low Profile (pancake) • Column design • S Beam • Single point • Diaphragm design • Through Hole • Rotating torque • Reaction torque
  50. 50. Why Should you Choose Interface? Capabilities • Capacities from 10 grams to 2,250,000 lbf • Accuracy as high as 0.02% FS • Internally amplified (4-20mA, 0-5V, 0-10V) • Hermetically Sealed • -65˚ - 400˚F thermal compensation • Multiple bridge configuration
  51. 51. Why Should you Choose Interface? Capabilities • Fatigue rated • ATEX, FM, CE, RoHs ratings available • Submersible – IP68 • Dual diaphragm • Overload protection • TEDS IEEE 1451.4 • Customer specified electrical & mechanical connection
  52. 52. 40% of our business is custom or special
  53. 53. Why Should you Choose Interface? Performance second to NONE • Guarantee: Our load cells will outperform our competitor’s – PERIOD • There are fundamental reasons why we can make that claim
  54. 54. Vertically Integrated Manufacturing • All machining, gaging and fabrication controlled in house Why Should you Choose Interface?
  55. 55. Stocking program • Interface will maintain stock of the finished goods for same day shipment if orders are received by noon MST. • Interface maintains a perpetual inventory subassemblies of standard products. This practice minimizes availability to 10 days or less. No other competitor can match this capability. • When availability is a concern, please contact the factory to discuss your needs Why Should you Choose Interface?
  56. 56. What’s behind our performance guarantee?
  57. 57. What makes Interface Better? Proprietary Interface Strain Gages • Made in house at our facility in Scottsdale, AZ • Feature: Interface strain gages precision matched to counteract the temperature characteristics of the modulus of the load cell structural material • Benefit: The output is temperature insensitive and does not require compensation resistors which produces simpler and more reliable circuit.
  58. 58. What makes Interface Better? Feature: Proprietary Interface Strain Gages • Benefit: Compensation resistors cannot be thermally connected with the cell’s flexure which results in dynamic thermal performance, resistance to thermal gradients, and delayed thermal response • Benefit: Elimination of modulus comp resistors allow for higher output
  59. 59. What makes Interface Better? Feature: Proprietary Interface Strain Gages • Benefit: Our strain gages allow us to provide a higher output - 4mV/V • Competitors provide 3mV/V or less • Benefit: Higher signal-to-noise ratio • Benefit: Higher resolution in precision measurement applications • Benefit: Superior fatigue life compared to Constantan
  60. 60. What makes Interface Better? Feature: Rigorous Temperature Testing • Interface performs both hot and cold thermal compensation from 15˚ - 115˚F • Most competitors provide only the hot side (60˚ - 160˚F) • Benefit: The slope of the curve is much flatter near room temperature and identical at both ends of the slope. The result is minimal variation across the entire thermal range. • Custom calibrated ranges available
  61. 61. Feature: Moment compensation • Interface compensates every low profile load cell • Competitors do not know their performance in this regard What makes Interface Better?
  62. 62. Eccentric & Side Load Specifications What makes Interface Better?
  63. 63. What makes Interface Better? Feature: Moment Compensation Benefit: Known maximum error
  64. 64. New Product Releases
  65. 65. New Product Releases  New and Improved Low Profile  Better overall static error specifications  Enhanced off axis performance  Improvements will be implemented at no additional cost to customer  STEP files are available for download via website
  66. 66. New Product Releases  Flange load cell  Extremely popular in Europe  Ease of installation due to elimination of thread alignment issues  Good alternative especially with large thread diameter
  67. 67. New Product Releases Model 2300 flange load cell  0.05% F.S. static error band  High capacity: 1M lbf  Eccentric load compensation  Ease of installation  Gaining popularity in Europe
  68. 68. New Product Releases  Load Pins • Capacities from 100 lbs to 300,000 lbs • Various sizes and shapes, lengths and diameters • Small quantity orders are acceptable • ATEX rating for hazardous environment
  69. 69. Load Pin Configurator  Lots of choices Diameter Sensing section length Anti-rotation techniques Cable exit Amplified output?

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