Publication Number: N/A
Date: February 2009

Calibrating the Falling Weight Deflectometer Video

This video addresses the question "Why should you calibrate your FWD?" It is intended to educate FWD managers, engineers and operators on the need for calibrating FWD equipment in order to collect high quality data for durable pavement designs. The following topics are covered in the video:

• Illustration of the new calibration procedure
• Explanation of the preparation that is needed to get a successful calibration
• Description of how calibration improves the quality of backcalculated data and its impact on overlay design

The new calibration procedure is performed in accordance with AASHTO Designation: R 32-09, Standard Recommended Practice for Calibrating the Load Cell and Deflection Sensors for a Falling Weight Deflectometer.  It includes 3 steps:

• Geophone Reference Calibration - in a rigid stand, against an accelerometer.
• Geophone Relative Calibration - each geophone against one another
• Load Cell Reference Calibration - against the reference load cell

The resulting adjusted gain factors are entered into the FWD data collection software. The process takes 2-3 hours, providing that the FWD is in good operating condition.