Document ID: chunk:federal_register_of_legislation:F2024L00446:reg:16:p44
Version: federal_register_of_legislation:F2024L00446
Segment Type: reg
Provision Reference: reg 16 (pt 44/108)
Character Range: 1007844–1010918

pressure at venturi inlet, kPa.
              To determine the range of subsonic flow, Cd shall be plotted as a function of Reynolds number Re at the SSV throat. The Reynolds number at the SSV throat shall be calculated using the following equation:
              where:
           A1 is 25.55152 in SI, ;
                  QSSV is the airflow rate at standard conditions (101.325 kPa, 273.15 K (0 °C)), m3/s;
           dv is the diameter of the SSV throat, m;
           µ is the absolute or dynamic viscosity of the gas, kg/ms;
           b is 1.458 x 106 (empirical constant), kg/ms K0.5;
           S is 110.4 (empirical constant), Kelvin (K).
              3.4.4.2.2. Because QSSV is an input to the Re equation, the calculations shall be started with an initial estimate for QSSV or Cd of the calibration venturi, and repeated until QSSV converges. The convergence method shall be accurate to at least 0.1 per cent.
              3.4.4.2.3. For a minimum of sixteen points in the region of subsonic flow, the calculated values of Cd from the resulting calibration curve fit equation shall be within ±0.5 per cent of the measured Cd for each calibration point.
              3.4.5. Calibration of an ultrasonic flow meter (UFM)
              3.4.5.1. The UFM shall be calibrated against a suitable reference flow meter.
              3.4.5.2. The UFM shall be calibrated in the CVS configuration that will be used in the test cell (diluted exhaust piping, suction device) and checked for leaks. See Figure A5/8.
              3.4.5.3. A heater shall be installed to condition the calibration flow in the event that the UFM system does not include a heat exchanger.
              3.4.5.4. For each CVS flow setting that will be used, the calibration shall be performed at temperatures from room temperature to the maximum that will be experienced during vehicle testing.
              3.4.5.5. The manufacturer's recommended procedure shall be followed for calibrating the electronic portions (temperature (T) and pressure (P) sensors) of the UFM.
              3.4.5.6. Measurements for flow calibration of the ultrasonic flow meter are required and the following data (in the case that a laminar flow element is used) shall be found within the limits of accuracy given:
              Barometric pressure (corrected), Pb ±0.03 kPa,
              LFE air temperature, flow meter, ETI ±0.15 °C,
              Pressure depression upstream of LFE, EPI ±0.01 kPa,
              Pressure drop across (EDP) LFE matrix  ±0.0015 kPa,
              Air flow, Qs  ±0.5 per cent,
              UFM inlet depression, Pact ±0.02 kPa,
              Temperature at UFM inlet, Tact ±0.2 °C.
3.4.5.7. Procedure
              3.4.5.7.1. The equipment shall be set up as shown in Figure A5/8 and checked for leaks. Any leaks between the flow-measuring device and the UFM will seriously affect the accuracy of the calibration.
Figure A5/8
UFM calibration configuration

              3.4.5.7.2. The suction device shall be started. Its speed and/or the position of the flow valve shall be