# Presentation: 265839

## Falling Weight Deflectometer (FWD) Calibration Procedures

- A            Product Line

- Penn DOT Mr Workshop

## PRESENTATION OBJECTIVES

- Why FWD Calibration is Important
- Development of the FWD Calibration Products
- Get to Know the FWD Calibration Centers
- Understanding FWD Calibration: The FWD Video
- Who Should Use the LTPP FWD Calibration Products
- How to Get More Information on the FWD Calibration Products

***What is the FWD Product Line?***

## FWD Calibration Product Line

- THE CENTERS
- LTPP FWD Calibration Centers
- Calibration Center Certification Program
- THE CALIBRATION PROCEDURES
- Reference Calibration Procedure
- FWDREFCL Software
- Relative Calibration Procedure
- FWDCAL Software
- THE VIDEOTAPE
- Videotape – Working with your FWD Calibration Center to Produce Quality Deflection Data

**Notes:**
The LTPP FWD product line is made up of:
(1)  the centers where calibration is done (including their certification), 
(2) the calibration procedures themselves (plus associated software), and
(3)  a videotape.

## FWD Calibration Videotape

- 15 minute videotape titled
- “Working With Your FWD Calibration Center”
- Addresses key questions about FWD calibration
- Provides step by step guide
- FWD operators

*What:*

*Capabilities:*

*Who Should Use:*

**Notes:**
The 15 minute video is a useful tool that addresses key questions about FWD calibration.

## FWD Calibration Videotape:  Features

- Step by step guide on
- Reference Calibration
- Procedure to check an FWD against an independent reference traceable to NIST benchmarks.  This procedure can only be done at properly equipped calibration centers.
- Relative Calibration
- Analyzes if FWD’s sensors are providing consistent data.
- Verifies the integrity of the sensors.

**Notes:**
It provides a step-by-step guide on reference and relative calibration.

## PRESENTATION OBJECTIVES

- What is the FWD Product Line
- Development of the FWD Calibration Products
- Get to Know the FWD Calibration Centers
- Understand FWD Calibration: The FWD Video
- Who Should Use the LTPP FWD Calibration Products
- How to Get More Information on the FWD Calibration Products

***Why FWD Calibration is Important?***

## What is a FWD?

- Comprised of a tow vehicle and trailer or self-contained in one vehicle
- Designed to impart a dynamic load to a pavement structure
- Measures deflection of the pavement surface
- Simulates a moving wheel load

## What is a FWD Used For?

- Structural capacity/remaining life estimates
- Load transfer efficiency between PCC pavement joints
- Void detection in PCC pavements
- Network level pavement management
- Project level pavement investigations
- Many research applications

**Notes:**
This slide elaborates on what FWDs are used for.  It should be noted that FWDs are not only used for highway pavements but are used extensively for airport runways, aprons and taxiways as well as port loading, stacking and transport pavements.  The FWD is a very versatile device with many applications.  In this presentation, however, we are mainly focused on highway applications.

## Why Calibrate a FWD?

- FWD is a complex system that contains _electrical_, _hydraulic_ and _mechanica_l systems to operate machine and collect data
- Standards needed to ensure consistency between FWD units
- Bad data = High cost (economic and political)

**Notes:**
There are several reasons to calibrate a FWD. 
The first is the reliance LTPP places on getting good data.  Being a research effort LTPP’s success depends on the quality of its data. LTPP currently utilizes eight FWDs.  The calibration procedure was developed to ensure that all of the LTPP FWDs produced comparable and accurate data.

Second, the FWD is a complex system composed of many moving and electrical parts.  It is very difficult to be sure if the data you are obtaining is good or bad without performing the reference and relative calibration procedures. Standards are needed (and have been set) to ensure comparability and accuracy among all FWDs.  

Finally, because calibration ensures good data the potential high economic and political costs of obtaining bad data can be avoided. 

## FWD Deflection Measurements

- Think of FWD deflections as shots at a target

_*Uncalibrated Sensors*_
- May or may not fall
- within 2%
- May or may not be biased

**Notes:**
Think of deflection measurements as shots at a target, with each arrow representing a deflection sensor.  We will use seven for a seven sensor rig.
The data from uncalibrated sensors of an FWD may or may not fall within the specified accuracy of 2 percent, represented by the outermost ring on the target.  They also may or may not be systematically biased (all to one side of the bull’s eye).

## FWD Deflection Measurements

- Think of FWD deflections as shots at a target

_*After Reference Calibration*_
- Randomly scattered closer to target

## FWD Deflection Measurements

- Think of FWD deflections as shots at a target

_*After Relative Calibration*_
- Very close to
- intended target

## Purpose of FWD Calibration

- Purpose - benchmark of FWD unit to known, or _*reference*_, standards
- Reference standards are NIST traceable where applicable
- Procedure completed in one day (assuming no problems)
- Reference calibration must be performed at certified FWD calibration center

**Notes:**
The main purpose of FWD calibration is to benchmark the performance of the FWD unit to known standards. In this case, where applicable, the standards can be traced to the National Institute of Technology (NIST – formerly known as the National Bureau of Standards).  

The procedure can be completed in one day if no problems arise and the FWD operator is prepared (i.e. spare parts and the like are brought with the FWD).  

The reference calibration procedure can only be performed at a certified calibration center.  The relative calibration is performed immediately after the reference calibration at the center, but it can also be performed independently on a monthly basis on any pavement that produces the desired response.

## Benefits of FWD Calibration

- Procedure necessary for all FWD users
- Organizations performing FWD  testing
- State DOT’s
- Other Government entities
- Consultants
- Academia
- Organizations contracting for FWD services
- Organizations using FWD data

**Notes:**
The calibration procedure will ensure good data is obtained for all users of the FWD and those performing FWD testing.

## PRESENTATION OBJECTIVES

- What is the FWD Product Line
- Why FWD Calibration is Important
- Get to Know the FWD Calibration Centers
- Understand FWD Calibration: The FWD Video
- Who Should Use the LTPP FWD Calibration Products
- How to Get More Information on the FWD Calibration Products

***Development of the FWD Calibration ***
***Products***

## Product Development Background

- 1987 - Strategic Highway Research Program (SHRP) selects FWDs
- 1988 – Original FWDs procured and “thump-off” conducted, need for calibration centers established
- 1989 – Calibration procedures developed
- 1989 – Host agencies for calibration centers solicited

**Notes:**
In 1987, SHRP conducted a competitive procurement for four FWDs. Selection of the units was made in late 1987.

After delivery of the units from Dynatest, a “thump-off” was conducted as part of equipment acceptance.  During the “thump-off,” it was clear that one of the units was not performing like the other three units.  After much debate and careful analysis of the data, it was deemed that the FWD’s load cell was not calibrated correctly.  Thus, this discovery prompted the decision to develop calibration procedures to ensure that all FWDs collected consistent and accurate data for the LTPP program.

During 1989 the calibration procedures were developed by the LTPP team with the assistance of Cornell University and the Indiana Department of Transportation.  At the same time host agencies were solicited.  These agencies were asked to furnish a building and part-time personnel to perform the calibrations.  Minnesota, Nevada, Texas, and Pennsylvania were selected as host agencies.

## Product Development Background

- 1989 – FWD testing begins
- 1991 – LTPP Calibration Centers established
- 1992 - FHWA assumes leadership of LTPP
- 1998 – FWD Calibration Video developed
- To date – many, many reference/relative calibrations performed at LTPP Calibration Centers

**Notes:**
LTPP FWD testing began in 1989 and the four existing calibration centers opened in 1991.

In 1998, the calibration videos were developed.  At the time of the development of this presentation, the total number of calibrations performed by the centers is not known.  Suffice it to say, that they have performed many, many calibrations over the past few years.

## PRESENTATION OBJECTIVES

- What is the FWD Product Line
- Why FWD Calibration is Important
- Development of the FWD Calibration Products
- Understand FWD Calibration: The FWD Video
- Who Should Use the LTPP FWD Calibration Products
- How to Get More Information on the FWD Calibration Products

***Get to Know the FWD Calibration ***
***Centers***

## Calibration Center Locations

- Four LTPP sponsored – State owned and 1999 LTPP certified
*Minneapolis, MN - North Central Region*
*Reno, NV - Western Region*
*Harrisburg, PA - North Atlantic Region*
*College Station, TX - Southern Region*
- Non-LTPP
- Kansas State University (Kansas DOT)
- Purdue University (Indiana DOT)
- Dynatest (manufacturer)

**Notes:**
There are four regional LTPP sponsored centers. Replacement equipment and maintenance is currently funded by LTPP. But the centers are owned by the State DOTs in which they are located. These four centers go through the certification process every year and were LTPP certified in 1999. These are the only centers in which LTPP FWDs can be calibrated. 

Calibration centers have also been established at Kansas State University, Purdue University and at one manufacturer — Dynatest. 
The Kansas and Purdue facilities were not LTPP certified in 1999 although the Kansas facility was certified in 1998.  The Dynatest facility was LTPP certified in 1999 and they generally go through certification every year.  

## Calibration Center Locations

- Other
- Australia (ARRB)
- South Africa
- Shown Some Interest
- South America
- Middle East

**Notes:**
Other established calibration centers are located in Australia at the Australian Road Research Board facilities and in South Africa.  These centers have not been LTPP certified to date.

Other facilities which are under development, are located in South Africa and at Cornell University.  The status of these facilities is currently unknown.

Countries in South America and in the Middle East have shown some interest in building a calibration center.

## Calibration Center Certification

- Independent auditors inspect facilities and personnel
- LTPP centers are required to be certified once per year
- Other centers - recommended certification once per year

**Notes:**
The LTPP calibration centers are audited every year by an external auditor (currently the LTPP Technical Services Support Contractor).  Non-LTPP centers should be certified every year but that is at the discretion of the center.

## Calibration Center Purpose

- Primarily designed to calibrate _LTPP_ FWD equipment (dynamic impulse devices)
- Have successfully calibrated Dynatest, JILS, and KUAB equipment

**Notes:**
The LTPP calibration centers were originally designed for Dynatest FWDs, the FWDs procured for the LTPP program.  Other types of dynamic equipment can be calibrated at the centers with slight modifications to the equipment.  Jils and Kuab equipment have also been successfully calibrated at the LTPP centers.  The calibration centers, however, are not suitable for use with cyclic loading or vibrating equipment.

## Certification of Calibration Centers

- Review facility
- Review reference load cell calibration procedures
- Review reference geophone calibration procedures
- Review relative geophone calibration procedures
- Review of documentation and protocols in place
- Load cell, load cell cable and vishay meter calibrated within one year

**Notes:**
The calibration center certification process involves observing all of the calibration procedures and noting any deficiencies.  

## Calibration Centers:Certification Ratings

- Fully Compliant: complete compliance with FHWA LTPP procedures/directives
- Compliant - minor changes required: substantial compliance, a few non-critical items not performed or not performed properly
- Non Compliant – major changes required: one or more critical items not performed or not performed properly

**Notes:**
The calibration center is rated on how standardized LTPP FWD associated guidelines and directives are followed. The rating is determined by the external team of reviewers based on their observations during the field and office reviews.
A "Fully Compliant" rating means that the center personnel were in complete compliance with all FHWA-LTPP directives and procedures.  
A "Compliant - Minor Changes Required" rating means that the center personnel were in substantial compliance with LTPP guidelines,  but a few non-critical items  were either not performed or not performed properly.
A "Non Compliant - Major Changes Required" rating means that one or more critical items in the procedures were not performed or the procedures were largely ignored, and some of the items in the review list were not done or were done haphazardly.

## Calibration Center Contacts

## PRESENTATION OBJECTIVES

- What is the FWD Product Line
- Why FWD Calibration is Important
- Development of the FWD Calibration Products
- Get to Know the Calibration Centers
- Who Should Use the LTPP FWD Calibration Products
- How to Get More Information on the FWD Calibration Products

***Understand FWD Calibration: ***
***The FWD Video***

## PRESENTATION OBJECTIVES

- What is the FWD Product Line
- Why FWD Calibration is Important
- Development of the FWD Calibration Products
- Get to Know the Calibration Centers
- Understand FWD Calibration: The FWD Video
- How to Get More Information on the FWD Calibration Products

***Who Should Use the LTPP FWD ***
***Calibration Products***

## Who Should Use the FWD Product Line

- Organizations performing FWD  testing
- State and Provincial DOT’s
- Other Government entities
- Consultants
- Academia
- Organizations contracting for FWD services
- Should be a part of contract to have FWD reference calibrated within 1 year, relative calibrated prior to job

**Notes:**
The FWD suite of products would be useful to a range of individuals in several organizations as shown on this slide.

## When To Use the FWD Product Line

- General
- Reference – Once per year
- Relative – After reference and once per month thereafter
- After a period of inactivity
- Other recommendations
- When taking delivery of a new FWD unit
- When equipment is replaced
- When equipment is suspect
- Whenever a major malfunction occurs

**Notes:**
In review, it is worth noting when the calibrations should be done.  This is outlined in this slide.

## Uncover and Avoid Problems

- Lack of Operator Training
- Showed up without software
- No spare parts
- Could not operate FWD
- Mechanical
- FWD not operable
- Load cell badly damaged
- Deflection sensors missing or damaged

**Notes:**
There are many reasons why the FWD Calibration procedures  should be used.  This is a partial list of the problems that have been found (and therefore avoided) by using the procedure.  This is no joke !   By being familiar with the calibration procedures and what FWD calibration entails, these problems can be avoided. 

I’m sure the calibration centers have a long list of problems encountered that would add to this list.

## Benefits of Use

- Provides guidelines for calibration of testing equipment
- Provides a benchmark performance standard for equipment
- Minimizes equipment variability
- Promotes greater confidence in FWD testing and resulting pavement design
- Minimizes risk of errant pavement rehabilitation designs

**Notes:**
The benefits of FWD calibration are many as shown here. This procedure is worthwhile insurance against errors in test results.

## Current Status of Product

- Calibration procedures established
- Calibration software developed
- Calibration centers established
- Many FWDs calibrated using procedure
- Video produced
- Cooperation of MNDOT, NVDOT, FWD manufacturers

**Notes:**
As you can see the latest development in terms of the FWD product line has been the video.  It was produced in cooperation with the Minnesota Department of Transportation, Nevada Department of Transportation and FWD manufacturers by the FHWA LTPP Implementation team, affectionately known as the “Dirt Squad” – Max Grogg, Keith Herbold and Don Petersen.  

## PRESENTATION OBJECTIVES

- What is the FWD Product Line
- Why FWD Calibration is Important
- Development of the FWD Calibration Products
- Get to Know the Calibration Centers
- Understand FWD Calibration: The FWD Video
- Who Should Use the LTPP FWD Calibration Product Line

***How to Get More Information on the ***
***FWD Calibration Products***

## Get and Use the FWD Product Line

- Download procedure manuals from
-    LTPP homepage at **www.tfhrc.gov**
- Order procedure manuals/video:
- Through LTPP homepage
- Through LTPP customer service
- (Tel Number: 865-481-2967 )
- Contacts
- Kathy Petros or Keith Herbold

**Notes:**
As you can see there are a range of sources for getting both the products and more information on them.
This ends the presentation.  Questions?