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Publication Number: FHWA-HRT-07-040
Date: October 2011
The purpose of this guide is to describe the installation and proper use of the following components of the FWD calibration system (see figure 103):
The instructions provided here assume the use of the WinFWDCal software package.
Figure 103. Photo. Calibration system components.
Calibration center facilities require the following characteristics:
While a specially built test area for FWD calibration is not required by AASHTO R32-09, some agencies either need or prefer to build a concrete test pad.(1) If so, the test pad should have the following specifications:
|Reference load cell assembly||1||Drawing CLRP-LC01|
|¼ 28 x 1-inch socket head cap screw||6||McMaster-Carr® part number (p/n) 92196A325|
|¼ 28 x ¾-inch socket head cap screw||6||McMaster-Carr® p/n 92196A321|
|Vishay signal conditioner||1|
|Load cell signal cable||1||Drawing CLRP-DAQ02|
|3⁄16-inch hex wrench||1|
|Torque wrench||1||Capable of 100 inch-lbf|
1 inch = 25.4 mm
Figure 104. Photo. Reference load cell assembly.
The reference load cell requires annual calibration to ensure accuracy. To calibrate the reference load cell, a universal testing machine with a load capacity of 120,000 lbf (500 kN) or more is needed. Although the load cell is calibrated to only 24,000 lbf (107 kN), the higher capacity of the testing machine assures that the test frame will be adequately rigid.
The Vishay 2310 signal conditioner, Keithley KUSB-3108 DAQ, the reference load cell, and the load cell signal cable are considered one system and must be calibrated together. Once the calibration is complete, it only applies to the entire system that was used during the calibration. If any component of the system changes, then the load cell needs a new calibration.
The bolts that hold the cover plate and feet onto the load cell (see figure 105) should not be removed under any circumstances. If any of these bolts are removed, the load cell calibration becomes invalid and must be returned to an approved calibration center for recalibration.
Figure 105. Photo. Bottom view of the reference load cell.
Figure 106. Photo. Reference load cell positioned under the FWD load plate.
The concrete anchors suggested for use with the FWD calibration hardware are of the drop-in variety (see figure 107). These instructions are for anchors from McMaster-Carr® p/n 97082A031 only. For any other equivalent anchor, refer to the manufacturer’s installation instructions.
|Concrete anchors||2||McMaster-Carr®, p/n 97082A031|
|Anchor setting tool||1||McMaster-Carr® p/n 97077A120|
|Drill||1||Optionally a hammer drill|
|¼-inch masonry drill bit||1|
|½-inch masonry drill bit||1|
|3⁄8-inch inside diameter washers||2||McMaster-Carr® p/n 94744A273|
1 inch = 25.4 mm
Figure 107. Photo. Concrete anchor.
Figure 108. Photo. Concrete anchor installation step 3.
Figure 109. Photo. Concrete anchor installation step 6.
Figure 110. Photo. Concrete anchor installation step 7.
|B03||Clamp base||1||Drawing CLRP-BJ02|
|B04||Base bar||1||Drawing CLRP-BJ03|
|B05||Rest stop||1||Drawing CLRP-BJ04|
|B06||M6 x 16-mm socket head cap screw||4||McMaster-Carr®
|B07||M8 x 16 mm socket head cap screw||6||McMaster-Carr®
|B08||M8 x 25 mm socket head cap screw||2||McMaster-Carr®
|B09||Loctite® #242 threadlocker||1|
|B10||5-mm hex wrench||1|
|B11||6-mm hex wrench||1|
|B12||Dow Corning Molykote G-4500 alum thickened grease, 14.1-oz, Nlgi #2||McMaster-Carr®
1 inch = 25.4 mm
Figure 111. Photo. Parts and tools for ball-joint assembly
Figure 112. Photo. Proper alignment of ball-joint screws.
Figure 113. Photo. Assembly of the ball-joint anchor.
|A01a||Accelerometer||1||Silicon Designs model 2220-005|
|A01b||Amphenol PT02A-10-6P box mounting receptacle||1||Mouser p/n 654-PT02A106P|
|A01c||Accelerometer wiring||1||Drawing CLRP-AB05|
|A02||Box bottom||1||Drawing CLRP-AB02|
|A03||Box top||1||Drawing CLRP-AB03|
|A04||Calibration platter||1||Drawing CLRP-AB04|
|A05||#4-40 x 3⁄8-inch flat head Phillips machine screw||4||McMaster-Carr® p/n 96877A209|
|A06||#4-40 x ½-inch pan head Phillips machine screw||2||McMaster-Carr® p/n 91400A110|
|A07||#4 retaining washer||2||McMaster-Carr® p/n 91755A205|
|A08||#4-40 x ¼-inch fillister head Phillips machine screw||7||McMaster-Carr® p/n 91737A072|
|A09||#10-24 x ½-inch knurled head thumbscrew||2||McMaster-Carr® p/n 91746A876|
|A10||Bubble level, glass surface mount||1||McMaster-Carr® p/n 2198A85|
|A11||Leveling mount with polyethylene base, 3⁄8-inch
16 x 1-inch stud
|3||McMaster-Carr® p/n 23015T64|
|A12||3⁄8-inch 16 locking wig nut||3||McMaster-Carr® p/n 98520A145|
|A13||#1 Phillips head screwdriver||1|
|A14||Loctite® #242 threadlocker||1|
1 inch = 25.4 mm
Figure 114. Photo. Parts for accelerometer box assembly.
Figure 115. Photo. Accelerometer box assembly.
Figure 116. Photo. Accelerometer box attached to calibration platter.
|S01||Geophone calibration stand assembly||1||Drawing CLRP-GCS01|
|S02||Seismometer calibration stand
|S03||Phenolic handle, 3⁄8-inch
16 x ½-inch stud
|S04||Bubble level, glass surface mount||2||McMaster-Carr® p/n 2198A85;
Also No. A10 in this guide.
|S05||#4-40 x ¼-inch fillister head Phillips machine screw||6||McMaster-Carr® p/n
91737A072; Also No. A08 in this guide.
|S06||Carl Bro geophone adapters with
M8 1 mm threaded through hole
|10||Morton Machine Works p/n
|S07||JILS geophone adapter with 3⁄8-inch
24 threaded through hole
|0||Morton Machine Works p/n
|S08||¾-inch inside diameter washer||10||McMaster-Carr® p/n
|S09||3⁄8-inch inside diameter washer||10||McMaster-Carr® p/n
Also No. B11 in this guide.
|S10||3⁄8-inch -24 x 5⁄8-inch hex head cap
|S11||#10-24 x ½-inch knurled head thumbscrew||2||McMaster-Carr® p/n
91746A876; Also No. A09 in this manual
|S12||Two-piece clamp-on shaft collar
20-mm bore, 40-mm outside diameter
|10||McMaster-Carr® p/n 6063K19|
|S13||Magnet assembly with #10-24 button head cap screw and nut||10||McMaster-Carr® p/n 5685K26,
p/n 92949A246, and p/n
|S14||Modified knurled rim knob||10||McMaster-Carr® p/n 6121K93|
1 inch = 25.4 mm
See figure 117 for a photograph of the equipment necessary for calibration stand assembly.
Figure 117. Photo. Equipment for calibration stand assembly.
Figure 118. Photo. Calibration stand with handles, bubble level, and pushbutton.
On the geophone calibration stand, the accelerometer box is fastened to a shelf half way up the stand with two #10-24 x ½-inch (12.7-mm) knurled head thumbscrews (S11).
On the seismometer calibration stand, the accelerometer box sits in the middle of the third shelf up on the stand and is held on with two thumbscrews (S11). The accelerometer box needs to be attached before the seismometers to ensure ease of use.
For the geophone calibration stand, there are four different types of geophones that can be calibrated: Carl Bro, Dynatest®, KUAB, and JILS.
The Carl Bro and the JILS geophones are fastened to the stand in similar manners, though they each require their own adapters. The geophone and its respective adapter (S06 and S07) screw together with a ¾-inch (19.05-mm) inside diameter washer (S08) placed between the adapter and shelf of the stand and a 3⁄8-inch (9.53-mm) inside diameter washer (S09) placed between the geophone and the shelf. Figure 119 shows a JILS geophone and adapter fastened to the stand. Carl Bro geophone adapters (S06) have different size threads and are painted red.
The Dynatest® geophones use a magnet to couple to the stand (see figure 120). To accomplish this, the JILS adapter (S07) is turned upside down and fastened to the stand with a 3⁄8-inch (9.53-mm) to 24 x 5⁄8-inch (609.6 x 15.88-mm) hex head cap screw (S10) as shown in Figure 121. The Dynatest® geophone then sits on top of the adapter.
The KUAB geophones use a collar (S12), magnet (S13), and modified knob (S14) to attach to the stand, as shown in figure 122 and figure 123. The knobs are painted gold. The modifications to the knob are to drill and tap for a #10-24 machine screw thru the length of the knob, and to mill out a 1⁄8-inch (3.18 mm) deep by 1-inch (25.4-mm) diameter recess at the top of the shank to allow the magnet assembly to fit inside.
Figure 119. Photo. Attachment of a JILS or Carl Bro geophone to the stand.
Figure 120. Photo. Placement of the accelerometer box on the geophone stand.
Figure 121. Photo. Attachment of a Dynatest® geophone to the stand.
Figure 122. Photo. KUAB geophone adapter equipment.
Figure 123. Photo. Attachment of a KUAB geophone adapter.
For the KUAB seismometer calibration stand, the seismometers are aligned in a two-column configuration as shown in figure 124. Users should tighten the setscrew at the bottom of the seismometer onto the standoffs on the stand.
Figure 124. Photo. Seismometer stand with sensors attached.
During deflection sensor calibration, the calibration stand should be set up in the following order:
The following procedure is used when going from one trial to the next in relative and reference calibration:
To couple the stand to the ball-joint, use the following:
Figure 125. Photo. Coupling the calibration stand and ball-joint anchor.
|USB||Standard USB cable||1|
|D01||Vishay to KUSB DAQ cable||1||Drawing CLRP-DAQ01|
|D01A||Vishay 2310B to KUSB DAQ
|D01B||Vishay 2310B to DAQ cable
|D02||Vishay to load cell cable||1||Drawing CLRP-DAQ02|
|D03||Accelerometer signal cable||1||Drawing CLRP-DAQ03|
|D04||Pushbutton to KUSB DAQ
|D05||Keithley KUSB-3108 16-bit
|D06||Vishay 2310 signal
Note: Blank cells indicate no notes area available.
All cables should be fabricated according to their respective drawings. A full set of calibration cables includes an accelerometer signal cable (D05), a load cell signal cable (D04), a Vishay to KUSB DAQ cable (D03), and a pushbutton assembly (D06).
Figure 126 illustrates FWD data acquisition system components and connections. The following list explains the connection breakdown:
Figure 126. Illustration. FWD data acquisition system components and connections.
|Vishay 2310 Setting||Load Cell||Accelerometer|
|Excitation||10 V||10 V|
|Filter||1 kHz||1 kHz|
|Gain||Load cell dependant1||2.0 x 1|
|Auto balance||Procedure dependant2||Always off|
|AC in||Fully extended||Fully extended|
1Indicates that each calibration center is provided with the correct gain for its reference load cell from the annual calibration.
2Indicates that during the FWD load cell calibration, WinFWDCal provides instruction for when to use the auto balance switch on the Vishay signal conditioner.
Table 48 presents the minimum requirements for a calibration computer. A laptop is recommended for portability.
|Operating system||Microsoft Windows XP® SP3 or
later (not including Windows 7®)
|Physical memory (RAM)||1 GB|
|Hard disk space||At least 25 GB free space|
|Display||17-inch external color monitor
(15-inch liquid crystal display on laptop)
|Optical drive||CD-RW (DVD ±RW preferred)|
|Removable storage||3.5-inch floppy disk drive and
256 MB USB flash drive
|USB 2.0 ports||At least four|
|Printer||Inkjet or laser|
1 inch = 25.4 mm
Topics: research, infrastructure, pavements and materials
Keywords: research, infrastructure, pavements and materials, Deflection measurement, Falling weight deflectometer, FWD, Backcalculation, Calibration, PDDX
TRT Terms: research, facilities, transportation, highway facilities, roads, parts of roads, pavements