DEVELOPMENT OF AN AUTOMATIC ELECTROMECHANICAL NULL-SEEKING DEVICE FOR THE PCA ROAD METER

THE ORIGINAL PCA ROAD METER INCORPORATED A UNIQUE ROAD METER SWITCH PLATE THAT SIMPLIFIES CALCULATION OF THE SUMMATION OF SQUARED ROAD--CAR DEVIATIONS (SSD). SINCE THE NUMBER AND MAGNITUDE OF DEVIATIONS ARE DISTRIBUTED IN A PLUS--MINUS ARRAY, THE SUM OF DEVIATIONS IS PRACTICALLY ZERO. HOWEVER, THE METHOD DEPENDS ON ABILITY TO MAINTAIN INITIAL STATIC NULL REFERENCE BETWEEN THE ROLLER CONTRACTOR AND THE NULL SEGMENT OF THE SWITCH PLATE AFTER THE TEST BEGINS. DURING THE TEST THE ORIGINAL STATIC NULL CAN BE CHANGED BY (1) ERROR IN THE INITIAL ADJUSTMENT ITSELF, (2) CHANGE IN POSITION AND WEIGHT OF THE CAR LOAD, (3) EXCESSIVE BRAKING OR ACCELERATION, OR, MOST IMPORTANT, (4) LIFTING OF THE CAR BODY (DEVIATION DATUM) BY AERODYNAMIC FORCES CREATED BY CAR SPEED AND AMBIENT WIND VELOCITY AND DIRECTION RELATIVE TO CAR TRAVEL. THE COMPOSITE DATA ARE THEN A COMBINATION OF GROUPS OF HIGH-FREQUENCY ROAD ROUGHNESS RECORDINGS, EACH SEPARATED IN THE SWITCH PLATE BY EXTRANEOUS MOVEMENT OR TRANSLATION NOT ASSOCIATED WITH PAVEMENT ROUGHNESS. USE OF COMPOSITE DATA WILL RESULT IN AN SSD STATISTIC THAT IS ALWAYS GREATER THAN THE SSD ATTRIBUTABLE TO ROAD ROUGHNESS ALONE. A SOLUTION TO THE PROBLEM IS TO HAVE A MECHANISM ATTACHED TO THE ROAD METER THAT SENSES EXTRANEOUS INPUTS, CORRECTS FOR THESE IN AMOUNT AND DIRECTION, AND THUS ENSURES DIGITAL COUNTER RECORDINGS THAT ARE A RESULT OF ROAD ROUGHNESS ALONE. AN INEXPENSIVE DEVICE CAPABLE OF ACCOMPLISHING THIS SOLUTION IS DESCRIBED.

• Record URL:
  • https://onlinepubs.trb.org/Onlinepubs/sr/sr133/133-015.pdf
• Supplemental Notes:
  • Distribution, posting, or copying of this PDF is strictly prohibited without written permission of the Transportation Research Board of the National Academy of Sciences. Unless otherwise indicated, all materials in this PDF are copyrighted by the National Academy of Sciences. Copyright © National Academy of Sciences. All rights reserved.
• Corporate Authors:

  Transportation Research Board

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  Washington, DC  United States  20001
• Authors:
  • Brokaw, M P
• Conference:
  • Workshop on Pavement Evaluation Using Road Meters
  • Location: West Lafayette Indiana, United States
  • Date: 1972-4-18 to 1972-4-20
• Publication Date: 1973

Media Info

• Media Type: Digital/other
• Features: Figures; References; Tables;
• Pagination: pp 93-96
• Monograph Title: PAVEMENT EVALUATION USING ROAD METERS
• Serial:
  • Highway Research Board Special Report
  • Issue Number: 133
  • Publisher: Highway Research Board

Subject/Index Terms

• TRT Terms: Road meters
• Old TRIS Terms: Null indicators
• Subject Areas: Highways; Pavements;

Filing Info

• Accession Number: 00207539
• Record Type: Publication
• Files: TRIS, TRB, ATRI
• Created Date: May 21 1973 12:00AM