Document ID: chunk:federal_register_of_legislation:F2012C00283:reg:21:p12
Version: federal_register_of_legislation:F2012C00283
Segment Type: reg
Provision Reference: reg 21 (pt 12/39)
Character Range: 289555–292594

(EPI) 0.01 kPa,

                Pressure drop across (EDP) LFE matrix  0.0015 kPa,

                Air flow (Qs) 0.5 per cent,

                CFV inlet depression (PPI) 0.02 kPa,

                Temperature at venturi inlet (Tv) 0.2 K.

              2.3.4. The equipment shall be set up as shown in Figure 9 of this appendix and checked for leaks. Any leaks between the flow-measuring device and the critical-flow venturi will seriously affect the accuracy of the calibration.

Figure 9
CFV Calibration Configuration

              2.3.5.  The variable-flow restrictor shall be set to the open position, the blower shall be started and the system stabilized. Data from all instruments shall be recorded.
              2.3.6.  The flow restrictor shall be varied and at least eight readings across the critical flow range of the venturi shall be made.
              2.3.7.  The data recorded during the calibration shall be used in the following calculations. The air flow-rate (Qs) at each test point is calculated from the flow-meter data using the manufacturer's prescribed method.
                Calculate values of the calibration coefficient for each test point:

Where:
 Qs     =  flow-rate in m3/min at 273.2 K and 101.33 kPa,
 Tv     =  temperature at the venturi inlet (K),
 Pv     =  absolute pressure at the venturi inlet (kPa).

          Plot Kv as a function of venturi inlet pressure. For sonic flow, Kv will have a relatively constant value. As pressure decreases (vacuum increases) the venturi becomes unchoked and Kv decreases. The resultant Kv changes are not permissible.
          For a minimum of eight points in the critical region, calculate an average Kv and the standard deviation.
          If the standard deviation exceeds 0.3 per cent of the average Kv, take corrective action.
              3.  System verification procedure
              3.1.  General Requirements
                The total accuracy of the CVS sampling system and analytical system shall be determined by introducing a known mass of a pollutant gas into the system whilst it is being operated as if during a normal test and then analysing and calculating the pollutant mass according to the formula in paragraph 6.6. of Annex 4a except that the density of propane shall be taken as 1.967 grams per litre at standard conditions. The following two techniques are known to give sufficient accuracy.
                The maximum permissible deviation between the quantity of gas introduced and the quantity of gas measured is 5 per cent.
              3.2.  CFO Method
              3.2.1.  Metering a constant flow of pure gas (CO or C3H8) using a critical flow orifice device.
              3.2.2.  A known quantity of pure gas (CO or C3H8) is fed into the CVS system through the calibrated critical orifice. If the inlet pressure is high enough, the flow-rate (q), which is adjusted by means of the critical flow orifice, is independent of orifice outlet pressure (critical flow). If deviations exceeding 5 per cent occur,