[Code of Federal Regulations]

[Title 49, Volume 5]

[Revised as of October 1, 2005]

From the U.S. Government Printing Office via GPO Access

[CITE: 49CFR325.25]



[Page 10-11]

 

                        TITLE 49--TRANSPORTATION

 

                      DEPARTMENT OF TRANSPORTATION

 

PART 325_COMPLIANCE WITH INTERSTATE MOTOR CARRIER NOISE EMISSION STANDARDS

--Table of Contents

 

                        Subpart C_Instrumentation

 

Sec. 325.25  Calibration of measurement systems.



    (a)(1) The sound level measurement system must be calibrated and 

appropriately adjusted at one or more frequencies in the range from 250 

to 1,000 Hz at the beginning of each series of measurements and at 

intervals of 5-15 minutes thereafter, until it has been determined that 

the sound level measurement system has not significantly drifted from 

its calibrated level. Once



[[Page 11]]



this fact has been established, calibrations may be made at intervals 

once every hour. A significant drift shall be considered to have 

occurred if a 0.3 dB or more excursion is noted from the system's 

predetermined reference calibration level. In the case of systems using 

displays with whole decibel increments, the operator may visually judge 

when the 0.3 dB drift has been met or exceeded.

    (2) The sound level measurement system must be checked periodically 

by its manufacturer, a representative of its manufacturer, or a person 

of equivalent special competence to verify that its accuracy meets the 

manufacturer's design criteria.

    (b) An acoustical calibrator of the microphone coupler type designed 

for the sound level measurement system in use shall be used to calibrate 

the sound level measurement system in accordance with paragraph (a) of 

this section. The calibration must meet or exceed the accuracy 

requirements specified in section 5.4.1 of the American National 

Standard Institute Standard Methods for Measurements of Sound Pressure 

Levels (ANSI S1.13-1971) for field method measurements.



[40 FR 42437, Sept. 12, 1975, as amended at 41 FR 10227, Mar. 10, 1976]