Document ID: chunk:federal_register_of_legislation:F2008C00323:reg:120:p5
Version: federal_register_of_legislation:F2008C00323
Segment Type: reg
Provision Reference: reg 120 (pt 5/23)
Character Range: 249677–252521

to the end of the pipe;

               (ii) change the nature of the exhaust gas.

         2.3.1.2. Provision shall be made for a mixing chamber in which the vehicle exhaust gases and the dilution air are mixed so as to produce a homogeneous mixture at the chamber outlet.

           The homogeneity of the mixture in any cross-paragraph at the location of the sampling probe shall not vary by more than  2 per cent from the average of the values obtained for at least five points located at equal intervals on the diameter of the gas stream. In order to minimise the effects on the conditions at the exhaust outlet and to limit the drop in pressure inside the dilution-air conditioning device, if any, the pressure inside the mixing chamber shall not differ by more than  0.25 kPa from atmospheric pressure.

         2.3.2. Suction device/volume measuring device

         This device may have a range of fixed speeds as to ensure sufficient flow to prevent any water condensation. This result is generally obtained by keeping the concentration of CO2 in the dilute exhaust gas sampling bag lower than 3 per cent by volume.

         2.3.3. Volume measurement

         2.3.3.1. The volume measuring device shall retain its calibration accuracy to within  2 per cent under all operating conditions. If the device cannot compensate for variations in the temperature of the mixture of exhaust gases and dilution air at the measuring point, a heat exchanger shall be used to maintain the temperature to within  6 K of the specified operating temperature.

         If necessary, a cyclone separator may be used to protect the volume measuring device.

         2.3.3.2. A temperature sensor shall be installed immediately before the volume measuring device. This temperature sensor shall have an accuracy and a precision of  1 K and a response time of 0.1 s at 62 per cent of a given temperature variation (value measured in silicone oil).

         2.3.3.3. The pressure measurements shall have a precision and an accuracy of  0.4 kPa during the test.

         2.3.3.4. The measurement of the pressure difference from atmospheric pressure shall be taken upstream from and, if necessary, downstream from the volume measuring device.

         2.3.4. Gas sampling

         2.3.4.1.  Dilute exhaust gases

         2.3.4.1.1. The sample of dilute exhaust gases shall be taken upstream from the suction device but downstream from the conditioning devices (if any).

         2.3.4.1.2. The flow rate shall not deviate from the average by more than  2 per cent.

         2.3.4.1.3. The sampling rate shall not fall below 5 litres per minute and shall not exceed 0.2 per cent of the flow rate of the dilute exhaust gases.

         2.3.4.2. Dilution air

         2.3.4.2.1. A sample of the dilution air shall be taken at a constant flow