1.
Load Cell 101
lnterface Webinar Wed nesd any
with Albert & jack
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2.
Agenda
« Definitions
- Load Cell Basics
~ Strain Gages
« Moment Compensation
- Temperature Compensation
« Calibration
- Performance
~ Applications
- Q&A
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3.
Definitions
« Axial Load
- Calibration Additional definitions and
- Capacity more are available in our
~ Deflection website library under:
- Eccentric Load Load Cells / Load Cell
« Hysteresis Terminology
- Nonlinearity
—- Output
~ Rated Output (RO)
~ Static Error Band (SEB)
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4.
What is a Load Cell?
- Device that converts a force into an electrical
signal
~ Designed to measure loads:
~ Tension
~ Compression
- Both
~ No moving parts
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- No wear and tear " ~Q“r--7’57- ,
between main
components /
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5.
Types of Load Cells
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Dual Bending Beam
Column Style
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6.
Types of Load Cells
Load Button
S-Beam
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7.
Anatomy of a LowProfileTM Load Cell
Hub
Strain Gage
lnterconnectingwires
Base
Diaphragm
Connector
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8.
Main Components
- Flexure
- Load bearing component
- Deflects under load
- Strain Gages
- Measure strain of flexure '-°WP"°fi'e"“ Flexure
- Form load cell's electrical circuit
using aWheatstone bridge
Flexure deformation
changes gage resistance strain Gage
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9.
Flexure Design
- Construction materials:
0
6
~ 2024 aluminum
« E4340 steel
« I7-4 PH SS
Design considerations:
« Beam Thickness
- Beam Height
Beam functions:
- Stress Concentration
~ Gage bonding location
Beam Thickness
Beam Height
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10.
Strain Gages
I. Grid Lines 4:
- Strain sensitive pattern 3
2. End Loops
4 >
- Provide creep compensation
3. Solder Pads
- Solder wires to gage
4. Fiducials 2
- Assist w/ gage alignment
5. Backing
J
- lnsulates and support foil
P f '
- Bonded to flexure art“ “tram gage
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11.
Gage Configurations
« Linear E‘: i
~ Measure strain under bending l l _
~ Mini Beam (MB Cells)
« Shear
~ Measure strain under shear
- LowProfi| eT"" cells
- Poisson
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- Measure strain under normal stress l* I if if
- 2| 00 Series Column cells
- Chevron
~ Measure strain under torsion
i 5400 Series flange cells
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12.
Wheatstone ridge
- Identical gages RED
~ Half in tension <’' E“)
« Half in compression
GREEN
. ‘ ’ - WHITE
Gage resistance varies. (+ SIG)
(- SIG)
- Increases under tension
- Decreases under compression
BLACK
(- EXC)
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13.
Resistance Changes
- Wire under tension strains: T j
_s’_
- Cross section decreases I L I
- Decreased current flow
- Increased electrical resistance
- Wire under compression strains: j—
DI
- Cross section increases I
~ Increased current flow l——-— L. ———-l
- Decreased electrical resistance
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14.
Gage Area {no load condition)
- No deflection in gage area
- Designed to be weakest section
G age
Areas
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15.
Gage Area (axial load applied)
- Deforms under load
- Shear stress concentration g
Strain lines in gage area
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16.
How does deformation change gage
resistance?
- Grid lines parallel to strain lines
- Gage is under tension
‘ Resistance increases —
Shear gage under tension
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17.
How does deformation change gage
resistance?
- Grid lines perpendicular to strain lines
~ Gage is under compression
- Resistance decreases
Gage under compression
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18.
Bending Application
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19.
Bending Beam — Tension 8:.
Compression
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20.
Why do we make our own Strain Gages?
« Proprietary Interface foil strain gages are thermally
matched to the load cell material.
~ As a result our load cells do not require modulus
compensation resistors.
- This allows for far superior temperature
performance along with higher output (typically
4mVN) at lower mechanical strain levels.
~ Higher output means higher resolution and better
signal-to-noise ratio.
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21.
Moment Compensation
- Reduces force measurement
errors due to eccentric loads
~ Performed by
- Loading cell eccentrically
- Rotatingload
- Recording output signal
~ Compensating to
minimize errors
Moment Setup
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22.
Moment Compensation
Output Signal (Uncompensated)
280.0 ‘
A2780 V
2276.0 l
3274.0
3272.0 '
3270.0 '
268.0
266.0
0 135 180 225 270 315 360
Rotation (Degrees)
45 90
Output Signal (Compensated)
222.5
222.0 »
52215 a
$2210 a
5 220.5 ~
3 220.0 ~
° 219.5 A
219.0
135 180 225 270 315 360
Rotation (Degrees)
0 45 90
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23.
eratnre Compensation
* Reduces force measurement
errors due to ambient
temperature changes
+ Performed by
* Recording output signal
- Cold — Hot (I5 — I |5F)
«v Undera No-Load condition
+ Adding compensating wire to
minimize temperature induced errors
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24.
Temperature Compensation
12
1 1 UNCOMPENSATED
_L
9
Zero Balance (lb; equivalent)
c-h COMPENSATED
NQIJBUIOINGID
0 20 40 60 80 100 120 140
Temperature (°F)
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25.
Calibration
- Performed to verify
load cell meets
performance parameters _ g
- Hysteresis
- Non—| inearity
- Static Error Band
Calibration Setup
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26.
Non-Linearity and ysteresis
ado Pom BEST Fll’ snwsur une
---ZERO Bl! .ANCE-——
40 6
0 20 0
FORCE, °/ o RATED LOAD
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27.
Static Error Band (SEB)
0 20 40 60 80 1 00
FORCE, % RATED LOAD
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28.
Performance Specifications
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PAflAMETERS 1110 1210 1220
CAPACITY
U. S. Models lb 300 $00.1K. 1K 10K 25K. 50K
1.5 2.5 5.10 100.250
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VDC MAX
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ACCURACY - (MAX ERROR)
813 : Error BTH'O-'5 F5
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29.
Applications — Iilaterials Testing
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30.
Applications — Aerospace
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31.
Applications — RFC Mirror Lab
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32.
Applications
« Automotive
+ Oil & Gas
* Medical
~+ | ndustria| Weighing &Automation
~ Robotics
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33.
Thank You!
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