Mechanical System Verification LVDT Calibration

1
Mechanical System VerificationLVDT Calibration

• Use NIST traceable micrometer
• Eight point calibration

• Acceptance Criteria
• Near zero intercept
• R-squared gt 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 lt 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 _at_ 10 intervals
• Register load cell/LVDT readings with data
  acquisition system
• Read dial gauge on proving ring

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

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
Mechanical System Verification Dynamic Response

• Procedure (continued)
• Apply dynamic load from 10 - 90 of proving ring
  capacity _at_ 10 intervals
• Read deformation using data acquisition system

10
Mechanical System Verification Dynamic Response

• Acceptance Criteria
• Generated haversine close to ideal
• Deformation response close to haversine
• Deformation within 5 of standard
• R-square gt 0.99
• .002 second or less phase shift between load and
  deformation
• Ymax/Ymin lt 1.10 (10)

11
Mechanical System VerificationPhase Angles

• Dynamic sinusoidal tests
• Verify overall system electronics (phase angle
  measurements)
• Detect misalignment problems through the use of
  phase angle measurements

• Acceptance Criteria
• Phase angle lt 2.8 degrees

12
Mechanical System VerificationTriaxial Pressure
Chamber

• Procedure
• Use autonomous pressure reading device to verify
  pressure

• 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
• Operators 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 DOTs
• 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)