Quality Control and Quality Assurance Maintenance Procedures Reproducibility and Calibration Strateg

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Quality Control and Quality Assurance Maintenance
Procedures Reproducibility and Calibration
Strategy of the Dynatest Falling Weight
Deflectometer
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History of Dynatest FWDs in the Texas Department
of Transportation

• TxDOT owns 15 FWDs
• 1984 - 024
• 1986 - 038, 039, 040, 041
• 1987 - 046, 047
• 1989 - 069, 070, 071, 072 1990 - 089, 090
• 1998 - 159, 160

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How the FWDs are used

• Network Level 5-10 of the state highway system
  for the Pavement Management Information System
  (PMIS).

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How the FWDs are used

• Project Level - load zoning, design, forensic
  studies, joint load transfer on Jointed Concrete
  Pavement (JCP), and many projects for determining
  structural adequacy.

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Three Objectives

• Present a maintenance assessment for quality
  control and assurance.
• Present a maintenance evaluation format.
• Present The Comprehensive Calibration Strategy
  for Texas Department of Transportation Falling
  Weight Deflectometer Fleet.

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Maintenance Assessment

• From 1996 to 1998 time spent investigating
  random/intermittent errors was about 85.
• Approximately 95 of errors were not
  reproducible/repeatable at the shop.

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Maintenance Assessment

• Apparent high rate of geophone failure (35
  sensors)?
• Unexplained decreasing Load Cell gains.
• Develop a maintenance and pre-calibration
  evaluation procedure.

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Random/intermittent Errors

• Example 1 Channel 4 reported inconsistent
  ranges from one calibration setup to the next.
• Example 2 Geophones produced non uniform
  signals.
• Example 3 Trailer error codes.

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Example 1. Channel Non-Repeatability
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Channel 4 Standard Deviations
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Example 2. Geophone signal

• Apparent geophone failure.
• System signal versus raw signal.

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Example 3 Trailer Error Codes

• Common to all FWDs except s 159 and 160.
• 507 Trailer PCB 8V Off Range
• 542 Raise Weight Timeout
• 554 PL was Activated
• 543 Drop Timeout

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Where to Begin?

• What is known?
• - Components removed from the system function
  properly.
• - FWD is a DC system.
• - SOURCES are low frequency.
• - SYSTEM is susceptible to interference.
• What is unknown?
• - Condition of the COUPLING MECHANISM.

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Why The Term Interference?

• A general definition of interference is
• ANY UNWANTED ENERGY WITH SUFFICIENT INTENSITY TO
  CAUSE A PROBLEM.

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Why The Term Interference?

• Interference requires a
• - Source alternator, battery, PCB, processor,
  inverter, relay.
• - Coupling Mechanism connector, terminal,
  cable, isolator, relay.
• - System processor, PCB, control panel, hyd
  motor, valves, relay.

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Basic Electrical Principles

• Currents RETURN to their source.
• Currents take the shortest path or largest wire.
• Use single point chassis grounding to eliminate
  ground loops.
• Continuous currents require continuous shielding.

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Van Cables Terminals

• Basic grounding coupling mechanisms.

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How to Begin?

• Power Alternator, cables and terminals.
• FL 40 Carbon Analyzer

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Engine Compartment
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Replace Damaged Cables
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Recondition Chassis Grounds
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Recondition Chassis Grounds
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Trailer Cable/Terminal Inspection
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Trailer Cable/Terminal Inspection
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Error Elimination Progress

• VAN - Recondition Chassis Ground Couplings and
  Replace Power Cables
• Eliminated the inconsistent and radical geophone
  data.
• Eliminated any erroneous errors associated with
  the processor i.e. Battery voltage(s) off range,
  5V supply off range, Offset beyond /- 2mV and
  Trailer control.
• A systematic shift in gains of all devices on FWD
  units during calibration.

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Error Elimination Progress

• FWD Trailer - Replace fuse blocks, damaged cables
  and grounding of data cable shield.
• Eliminated all erroneous error codes.
• IE Trailer PCB 8V Off Range, Raise Weight
  Timeout, PL was Activated, Drop Timeout and
  others.

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Maintenance Summary

• The following steps reduced erroneous errors by
  95.

• Reconditioning of chassis grounds.
• Ensuring power and ground cables are not damaged
  (frayed or burnt).
• Data cable is continuously shielded.

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Decreasing Load Cell Gains
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Effect of Cleaning Swivels
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Calibration Maintenance Form

• Parts Replacement
• Evaluation
• Calibration
• Post Calibration
• Repair
• Operator Forms

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Evaluation From

• Van Charging System
• Internal systems implies AC, High Beams, Strobe
  Lights and any other accessories normally used.

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Point to Point Condition Assessment Form
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Buffer Degradation

• Through observation of the non-linear forces,
  gained or lost, over a period of time, TxDOT
  standardized buffers.
• Research indicated rubber responds differently to
  chemicals.
• This was the reason why some buffers became
  harder while others softened.

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Conclusion

• The following steps reduced erroneous errors by
  95.
• Reconditioning of chassis grounds.
• Ensuring power and ground cables are not damaged
  (frayed or burnt).
• Data cable is continuously shielded.

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Conclusion

• Cleaning and repacking the swivel can effect the
  gain significantly.
• Load Cell gains returned to or close to the as
  arrived gain.
• Their was a reduction in systematic change in the
  gains on all geophones.
• Depending on the environment and conditions clean
  the swivel as required.

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Improving Repeatability Reproducibility of
TxDOT FWD Fleet (Project 0-1784)
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Impact of Components

• Studying Impact of Components on FWD Response for
  3 FWDs
• Buffers
• Geophone Holders
• Neoprene Pad
• Structural Design of FWD

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Impact of Buffer Age
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Buffers should be similar
Buffers should hit Strike Plate simultaneously
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Sensor Holder components should be replaced
frequently
Load Plate should be in good condition
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Sensor Holder Components(Springs)
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Vibration of Sensor Bar should be minimized
Vibration of Frame should be minimized
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FWD Calibration

• Maintain FWD
• Check Electrical and Electronic Parts
• Replace Mechanical Parts (i.e. springs, neoprene
  Guide etc.)
• Ensure reasonable vibration levels in system
  (replace buffers)
• Ensure smooth and centered load application
  (remove, clean reinstall load cell and load
  plate)
• Conduct Preliminary Calibration
• (Very Similar to SHRP Protocol)
• Compare deflections and load with embedded
  sensors
• Conduct Comprehensive Calibration for Diagnosis
• Identify source of problem with sensors not
  calibrating

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FWD Load Cell Calibration
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Geophone Calibration
Embedded Geophones
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Comprehensive Calibration Setup
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Conclusions

• Through observation of behavior of different
  components, replacement strategies and tune-up
  of the FWD has been carried out.
• A new protocol has been developed in a manner
  that all data collection and manipulation are
  done real-time and automatically.
• The new methods not only improves the performance
  of the FWD, it should assist in reducing the
  breakdown of the systems

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• Reports
• Reproducibility of The Texas Department of
  Transportation Falling Weight Deflectometer Fleet
• 1784-1 Evaluate Reproducibility and Recommend
  Improvements
• 1784-2 A Comprehensive Calibration Strategy
• 1784-3 Impact of Load Plate on Response