Washington Administrative Code
Title 173 - Ecology, Department of (See also Titles 197, 317, 372, and 508)
Chapter 173-58 - Sound level measurement procedures
Section 173-58-030 - Instrumentation

(1) Sound level meter. The sound level meter shall meet the Type 1, Type 2, or Type 3 requirements of ANSI S1.4-1971. The meter weighting and response mode will be set as required in the specific procedure used. The sound level meter shall be returned to the manufacturer or a qualified laboratory at least once a year, to be calibrated to standards traceable to the National Bureau of Standards.

Type 1, Type 2, or Type 3 sound level meters shall be used for any initial inspection procedures, but only Type 1 or Type 2 sound level meters shall be used for the measurement of sound levels for enforcement purposes.

(2) Sound level calibrator. An acoustically coupled calibrator shall be used periodically to assure the accuracy of the sound level meter and microphone. The calibrator shall be returned to the manufacturer or a qualified laboratory at least once a year to be calibrated to standards traceable to the National Bureau of Standards.

(3) Tachometer. The tachometer shall be either one of two types: Electric or vibrating reed. The electric tachometer shall be an inductive pickup type for easy attachment to any spark plug cable, contain its own internal power supply, and shall meet SAE J197 specifications for off road electric tachometers. The vibrating reed tachometer shall be designed for use on any internal combustion engine. Calibration accuracy for both types of tachometers shall be at least +-3 percent of full scale reading. All tachometers shall be calibrated at least once a year in accordance with the manufacturer's calibration procedures.

(4) Windscreen. A windscreen of open cell foam, cloth, or other acoustically invisible material as shall be provided by the manufacturer, shall be placed over the microphone to protect it from moisture, exhaust gases and wind effects.

(5) Anemometer. An anemometer shall be used periodically during measurements to test the wind speed.