Document ID: chunk:federal_register_of_legislation:F2021C00509:front:0:p23
Version: federal_register_of_legislation:F2021C00509
Segment Type: other
Provision Reference: 
Character Range: 69344–72184

interfered with during the sound level measurements.

           3.2.5.3. Measuring of noise in proximity to the exhaust (see appendix, fig. 2)

           3.2.5.3.1. Positions of the microphone

           3.2.5.3.1.1. The height of the microphone above the ground should be equal to that of the outlet pipe

            of the exhaust gases, but in any event shall be limited to a minimum value of 0.2 m.

           3.2.5.3.1.2. The microphone must be pointed towards the orifice of the gas flow and located at a distance of 0.5 m from the latter.

           3.2.5.3.1.3. Its axis of maximum sensitivity must be parallel to the ground and must make an angle of 45 degrees +/- 10 degrees with the vertical plane containing the direction of the gas flow. The instructions of the manufacturer of the sound level meter with regard to this axis must be respected. In relation to this plane, the microphone shall be placed in such a way as to obtain the maximum distance from the longitudinal median plane of the vehicle; in case of doubt, the position which gives the maximum distance from the contour of the vehicle shall be selected.

           3.2.5.3.1.4. In the case of an exhaust provided with two or more outlets spaced less than 0.3 m apart and which are connected to the same silencer, only one measurement is made; the microphone position is related to the outlet nearest to one extreme edge of the vehicle or, when such outlet does not exist, to the outlet which is the highest above the ground.

           3.2.5.3.1.5. For vehicles with a vertical exhaust (e.g. commercial vehicles) the microphone should be placed at the height of the exhaust outlet. Its axis should be vertical and oriented upwards. It should be placed at a distance of 0.5 m from the side of the vehicle nearest to the exhaust.

           3.2.5.3.1.6. For vehicles having an exhaust provided with outlets spaced more than 0.3 m apart, one measurement is made for each outlet as if it were the only one, and the highest level is noted.

           3.2.5.3.2. Operating conditions of the engine

           3.2.5.3.2.1. The engine is operated at a constant speed having the following value: 3/4 S for both controlled ignition engines and for diesel engines.

           3.2.5.3.2.2. When constant engine speed is reached, the throttle shall be returned swiftly to the idle position. The sound level shall be measured during a period of operation consisting of a brief maintenance of constant engine speed and throughout the entire deceleration period, the maximum sound level meter reading being taken as the test value.

           3.2.6. Results

           3.2.6.1. Readings, rounded off to the nearest decibel, shall be taken from the measuring instrument.
            Only those values obtained from three consecutive measurements which do not differ by