1

Mechanical System VerificationLVDT Calibration

• Use NIST traceable micrometer

• Eight point calibration

• Acceptance Criteria

– Near zero intercept– R-squared > 0.99

2

Mechanical System VerificationLoad Cell Zero

• Use strain indicator• Measure load cell zero

reading• Used to determine if load

cell has been fatigued or overstrained

• Acceptance Criteria– Zero reading < 1.5 % of full-scale sensitivity

3

Mechanical System VerificationLoad Cell Calibration Certificates

• Check laboratory documentation to determine last NIST traceable calibration

• Acceptance Criteria– NIST traceable calibration within one year

4

Mechanical System VerificationLoad Cell Calibration Verification

• Requires NIST traceable proving rings

• Utilizes static loading• Verifies load cell calibration• Measures unwanted friction• Measures unwanted

bending and deflections

5

Mechanical System Verification Load Cell Calibration Verification

• Procedure– Apply static (ramp) load from

10 - 90% of proving ring capacity @ 10% intervals

– Register load cell/LVDT readings with data acquisition system

– Read dial gauge on proving ring

Figure A.1. 500 lb Static (Ramp) Testing, Load versus Time

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0 50 100 150 200 250 300 350 400

Time, sec

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6

Mechanical System Verification Load Cell Calibration Verification

• Acceptance Criteria– Proving ring versus load cell

value within ± 5% of each other

– Proving ring dial gauge versus LVDT reading within ± 5% of each other

Load cell reading versus proving ring load values, run #1

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0 100 200 300 400 500Proving Ring Load, lb

Lo

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Upper Load Limit

Lower Load Limit

7

Mechanical System VerificationDynamic Response

• Verify overall equipment ability to conduct Resilient Modulus testing– Verify data acquisition

process– Verify data format

8

Mechanical System Verification Dynamic Response

• Procedure– Remove dial gauge from proving

ring

– Use external LVDTs or internally mounted LVDT for displacement measurements

– Apply haversine shaped load pulse (.1 seconds on, .9 seconds off)

9

• Procedure (continued)– Apply dynamic load from 10 -

90% of proving ring capacity @ 10% intervals

– Read deformation using data acquisition system

Mechanical System Verification Dynamic Response

10

Acceptance Criteria Generated haversine close to

ideal Deformation response close to

haversine Deformation within 5% of

standard R-square > 0.99 .002 second or less phase shift

between load and deformation Ymax/Ymin < 1.10 (10%)

Load-deformation characteristics, run #1 - 500 lb dynamic (haversine) test.

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500.00

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Deformation, in

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Upper Limit

Low er Limit

Mechanical System Verification Dynamic Response

11

• Dynamic sinusoidal tests– Verify overall system

electronics (phase angle measurements)

– Detect misalignment problems through the use of phase angle measurements

Mechanical System VerificationPhase Angles

Figure A.4. Dynamic Response Check of 500 lb Proving Ring, 1 Hz

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Time, sec

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• Acceptance Criteria– Phase angle < 2.8 degrees

12

• Procedure– Use autonomous pressure

reading device to verify pressure

Mechanical System VerificationTriaxial Pressure Chamber

• Acceptance Criteria– Gauge readings ± 2.5 % of target values– Hold for 10 minutes

13

The 3-Phase Startup Process

• Verification of Electronic System

• Verification of Mechanical System

Verification of Laboratory Ability to Conduct P46 Resilient Modulus Test

14

Laboratory Proficiency Testing

• Focuses on laboratory ability (personnel/equipment)• Sample preparation• Operator’s ability to conduct a

test• Proper sequence and magnitude

of loading• Proper data format• Analysis of raw data to detect

any discrepancies• Investigation of within and

between laboratory variability

15

Laboratory Proficiency Testing

• Acceptance Criteria– Vertical deformations within 30%

– Approval by Representative based on visual observations

– Conformance to all aspects of the protocol

– Haversine wave form close to ideal

– Deformation response reasonable

– Resilient Modulus relationship reasonable

16

PRESENTATION OBJECTIVES

• What is the Resilient Modulus (Mr) Startup Procedure Product Line

• Why Mr Testing and the Startup Procedure is Important

• Development of the Mr Startup Procedure

• How to Conduct the Mr Startup Procedure

• How to Get Information on the Mr Testing and Startup Product Line

Who Should Use the Mr Testing and Startup Product Line and Why

17

Who Should Use the Product?

• Any organization performing resilient modulus testing– State DOT’s– Universities– Consultant laboratories

• Can be used for other tests as well– Complex modulus– Creep compliance– Indirect tensile testing, etc.

18

When Should Product Be Used?

• General– Prior to starting a testing program– Every year during production testing– After a period of system inactivity

• Other recommendations– Verify the operation of older machines

for new applications– When equipment is replaced– When equipment is moved– Whenever a suspected overload or

malfunction occurs

19

Uncover and Avoid Problems Electronics

• Over-ranged load cell• Inadequate filters

– Amplitude roll off: 2 Hz - 50 Hz

• Unmatched filters– Excessive time delay (phase

angle) between channels– Filters on and off

20

Uncover And Avoid Problems Software

• Software not controlling the load adequately

• Inadequate sampling rate• Raw data with no units• Automatic gain control, error range

too big• Lack of gain control adjustment

during testing• Improper raw data format -

command values were saved rather than the feedback values

21

Uncover And Avoid Problems Mechanical

• System not fast enough to apply proper haversine loads - complete upgrade of signal conditioning and control

• Oversize servo-value• Friction in servo-value piston• Friction in triaxial cell seals• Misalignment caused by improperly

designed triaxial cell fixture• Excessive deformation, up to 76% of

total deformation due to bending of triaxial cell base plate

22

Uncover And Avoid Problems Mechanical (continued)

• Excessive deformation due to unrestrained triaxial cell

• Slippage of LVDT holders• Lack of control of pressure

transducer• Malfunction of air pressure

regulator

23

Benefits of Use

• Provides guidelines for standardization of test process

• Provides a benchmark performance standard for equipment

• Minimizes equipment and operator variability

• Promotes greater confidence in resilient modulus testing and resulting pavement design

24

Current Status of Product

• P46 test procedure established• Videos produced and

distributed• Startup procedure published• Startup procedures completed

– FHWA– Kansas– North Carolina– Minnesota– University of Rhode Island– Consultant laboratories

25

PRESENTATION OBJECTIVES

• What is the Resilient Modulus (Mr) Startup Procedure Product Line

• Why Mr Testing and the Startup Procedure is Important

• Development of the Mr Startup Procedure

• How to Conduct the Mr Startup Procedure

• Who Should Use the Mr Startup Procedure and Why

How to Get Information on the Mr Startup Procedure?

26

Get and Use Mr Testing and Startup Procedure Product

Line• Download procedure manuals

from– LTPP homepage at

www.tfhrc.gov• Order procedure

manuals/videos:– Through LTPP homepage– Through LTPP customer service

• (Tel Number: 865-481-2967)