Document ID: chunk:federal_register_of_legislation:F2024L00446:reg:16:p39
Version: federal_register_of_legislation:F2024L00446
Segment Type: reg
Provision Reference: reg 16 (pt 39/108)
Character Range: 993876–996885

maintained at a subsonic velocity that is calculated from the physical dimensions of the subsonic venturi and measurement of the absolute temperature (T) and pressure (P) at the venturi inlet and the pressure in the throat of the venturi. Flow is continually monitored, computed and integrated throughout the test.
              3.3.6.3.2. An SSV shall measure the flow volume of the diluted exhaust gas.
Figure A5/4
Schematic of a subsonic venturi tube (SSV)

              3.3.6.4. Ultrasonic flow meter (UFM)
              3.3.6.4.1. A UFM measures the velocity of the diluted exhaust gas in the CVS piping using the principle of ultrasonic flow detection by means of a pair, or multiple pairs, of ultrasonic transmitters/receivers mounted within the pipe as in Figure A5/5. The velocity of the flowing gas is determined by the difference in the time required for the ultrasonic signal to travel from transmitter to receiver in the upstream direction and the downstream direction. The gas velocity is converted to standard volumetric flow using a calibration factor for the tube diameter with real time corrections for the diluted exhaust temperature and absolute pressure.
              3.3.6.4.2. Components of the system include:
                  (a) A suction device fitted with speed control, flow valve or other method for setting the CVS flow rate and also for maintaining constant volumetric flow at standard conditions;
                  (b) A UFM;
                  (c) Temperature and pressure measurement devices, T and P, required for flow correction;
                  (d) An optional heat exchanger for controlling the temperature of the diluted exhaust to the UFM. If installed, the heat exchanger shall be capable of controlling the temperature of the diluted exhaust to that specified in paragraph 3.3.5.1. of this annex. Throughout the test, the temperature of the air/exhaust gas mixture measured at a point immediately upstream of the suction device shall be within ±6 °C of the arithmetic average operating temperature during the test.
Figure A5/5
Schematic of an ultrasonic flow meter (UFM)

              3.3.6.4.3. The following conditions shall apply to the design and use of the UFM type CVS:
                  (a) The velocity of the diluted exhaust gas shall provide a Reynolds number higher than 4,000 in order to maintain a consistent turbulent flow before the ultrasonic flow meter;
                  (b) An ultrasonic flow meter shall be installed in a pipe of constant diameter with a length of 10 times the internal diameter upstream and 5 times the diameter downstream;
                  (c) A temperature sensor (T) for the diluted exhaust shall be installed immediately before the ultrasonic flow meter. This sensor shall have an accuracy of ±1 °C and a response time of 0.1 seconds at 62 per cent of a given temperature variation (value measured in silicone oil);
                  (d) The absolute pressure (P) of the diluted exhaust shall be measured immediately