MAE 3272 - Lecture 5 Notes - Load Cell Desgin, Calibration, And Applications

M&AE 3272 - Lecture #5 Load Cell Background and Design

3 March 2014

1

WSachse; 3/2014;

Weeks 4-8:Module 2:• Apply mechanics and strength of materials concepts to design a

force-measuring transducer

• Learn how to mount and use strain gages and strain gage instrumentation to produce a force-measuring system

• Learn how to write and use data acquisition software (i.e. LabVIEW)

• Test, Verify and Calibrate your force sensor (Load cell)

M&AE 3272 - Lecture 5 1

M&AE 3272: Mechanical Propertyand Performance Laboratory

WSachse; 3/2014;

Weeks 4-8Module 2:

• Apply mechanics and strength of materials concepts to design a force-measuring transducer

• Learn how to mount and use strain gages and strain gage instrumentation to produce a force-measuring system

• Learn how to write and use data acquisition software (i.e. LabVIEW)

• Test, Verify and Calibrate your force sensor (Load cell)


M&AE 3272: Mechanical Propertyand Performance Laboratory


3 March 2014

2

WSachse; 3/2014;

Load Cell Design:


Materials set 2:

Materials set 3:

Materials set 4:

WSachse; 3/2014;

Load Cell Design:

Load Cell Design – Bending Beam Configuration

S-Beam Load CellsS-Beam load cells get their name from their S shape. S-Beam load cells can provide an output if under tension or compression. Applications include tank level, hoppers and truck scales. They provide superior side load rejection. Cost: $250-$400



3 March 2014

3

WSachse; 3/2014;

Commercial S-Beam Load Cells:


WSachse; 3/2014;M&AE 3272 - Lecture 5 9

Measurement of Loads/Forces,Static and Dynamic:

Omega: $ 420.00 DLC101-10• For High Frequency

Tension/Compression Force Measurements

• Ideal for Measuring Impact or Pulsating Forces

• Frequency Range up to 25 kHz• Force Ranges up to 5000 lb• Calibration Certificate Supplied• Stainless Steel Impact Cap and

Mounting Stud Provided

OMEGA's DLC101 dynamic load cell is ideal for measuring force transients or dynamic force pulsations in impact or vibration applications. This load cell contains a thin piezoelectric crystal that generates an analog voltage signal in response to an applied dynamic force. The DLC101 has 2 threaded ends, enabling installation of threaded members such as mounting studs, impact caps, and machine elements. Its welded construction encloses and protects the crystals from the environment.

SPECIFICATIONSExcitation: 2 mA nominal @ 18 to 30 Vdc, constant currentRated Output: 5V nominal FSAmplitude Linearity: ±1% FS (BSFL/0)Resonant Frequency (@ No Load): 75 kHzHigh Frequency Range: 25 kHz (approx. 1/3 of resonant

frequency, no load)

Low Frequency Range (-3 dB): 0.08 Hz

Stiffness: 11.4 lb/minOverload Recovery: 10 ms for 2x range

Maximum Shock/Vibration: 10,000/±5000 g (no load)Temperature Range: -75 to 120°C (-100 to 250°F)Temperature Sensitivity Effect: 0.03% FSPFOutput Impedance: 100 ΩBias Voltage: 10V nominalWeight: 43 g (1.5 oz) nominal


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Dynamic Force Sensor - Modeling:

Second-order Mechanical System:

( ) ( ) ( ) ( )tFtsdt

tds

dt

tsdnn =++ 2

2

2

2 ωξω

km

c

c

c

c 2==ξ

Natural frequency:

m

kfn

π2

1= [Hz]

m

kn =ω [rad/s] ;

Damping ratio:


Dynamic Force Sensor – Modeling Results:

Time response to step loading:

Magnitude

Phase


3 March 2014

5

WSachse; 3/2014;

W

FB+T


Measurement of Dynamic Forces:

How can you verify that it works?

T-Scan® System: Permits time-dependent forces as a function of position over a piezo-resistive sensor array


Measurement of Occlusal Forces in Teeth:

Sensor Array(2K Sensor elements)

T-Scan III OcclusalAnalysis System


3 March 2014

6

WSachse; 3/2014;

Load Cell Design (Week of Feb 25th – Mar 1st):


Gage Dimensions

Lpad 7/16”

Wpad 5/16”

Lgage ¼”

Dedge 1/16”

Lpadd

Wpad

Lgage Dedge

2.5 Volts DC

WSachse; 3/2014;

S-Beam Load Cell Mechanics Analysis:


Load Cell Diagram

Free Body Diagram

Where are you going to glue your four (4) gages?


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Shear/Moment Diagrams; Max Stresses/Strains

Beams

Load, P

Load, P

#1

#2

#3

C(−)

T(+)T(+) C(−)

C(−) T(+)T(+)

C(−)


Load Cell Hook-up and Output:

Beams

Load, P

Load, P

#1

#2

#3

C(−)

T(+)T(+) C(−)

C(−) T(+)T(+)

C(−)


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Calculation of Bridge

Output Voltages:

Matt Ulinski Notes (2008)

++ --


Calculation of Load Cell Sensitivity:

7.20


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Wheatstone Bridge Output per Load:

7.20

7.20


Expected Calibration Measurement Result:

Applied Load [lbs]

= Sensitivity [V/lb]

= Zero

Measured Output

Voltage [V]

Non-linear regime


3 March 2014

10

WSachse; 3/2014;

Load Cell Parts Set #3: 4x1/2x1/4 in

Predicted Sensitivity: 19078 [P/(V/V)]


Actual Calibration Measurement Result:

Predicted Sensitivity: 19078 [P/(V/V)]

WSachse; 3/2014;

Load Cell: Testing Schedule

(March 17th – 21st)



3 March 2014

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WSachse; 3/2014;

Module 2 Deliverable:

Load Cell Calibration

Data and Curve:


0 20 40 60 80

Applied Load [lbs]

0

5

10

15

20

Bri

dg

eO

utp

ut

Vo

ltag

e[m

V]

Measured Calibration DataLinear Fit: 0.215 [mV/lb]

Load Cell Calibration

4 Calibration Data Points

2 Linear Fit Line

3a Slope:Calibration Constantor 1/Sensitivity

3b Zero

6

WSachse; 3/2014;

Load Cell: Calibration

Sheet


3.

1.

4.

5.

2.

Due:Week of April 7th

to 11th

Two weeksafter you did

the Calibration


3 March 2014

12

WSachse; 3/2014;

Tasks to do during the next three Weeks, March 3rd – March 21st :


Sections: 401-404; 409; and 413

Sections 405-408; 410; 412 and 414

Mar 3rd – Mar 7th Build Load Cellin Upson B-30

Construct LabVIEW vi

in 163 Rhodes

Mar 10th - Mar 14th ConstructLabVIEW vi

in 163 Rhodes

Build Load Cellin Upson B-30

Mar 17th – Mar 21st Test and Calibratein Upson B-30

your Load Cell(see Schedule)

Done

Done

WSachse; 3/2014;

• Everyone should now have familiarity with LabVIEW.

• Sections #401, #402, #403, #404, #409, and #413 meet in B30 Upson to fabricate your Load Cell. Come prepared to show your design to your TA so that you can receive parts. Then: Prep. Glue. Wire.

• Sections #405, #406, #407, #408, #410 , #412 and #414 can go to the Lab to check out their LabVIEW vi. (Go at times when the Sections above are not session.) Thanks. Enjoy the week!

Tasks to do THIS Week, March 3rd - 7th:


• Everyone should now have familiarity with LabVIEW.

• Sections #401, #402, #403, #404, #409, and #413 meet in B30 Upson to fabricate your Load Cell. Come prepared to show your design to your TA so that you can receive parts. Then: Prep. Glue. Wire.

• Sections #405, #406, #407, #408, #410 , #412 and #414 can go to the Lab to check out their LabVIEW vi. (Go at times when the Sections above are not session.) Thanks. Enjoy the week!

• P.S.: Liquid Mountaineering is a fraud.

Documents

MAE 3272 - Lecture 5 Notes - Load Cell Desgin, Calibration, And Applications