Document ID: chunk:federal_register_of_legislation:F2011C00805:reg:120:p17
Version: federal_register_of_legislation:F2011C00805
Segment Type: reg
Provision Reference: reg 120 (pt 17/23)
Character Range: 280283–283614

start-up and after major maintenance.

         4.3. Calibration of the critical-flow venturi (CFV)

         4.3.1. Calibration of the CFV is based upon the flow equation for a critical venturi:

where:

         Qs = flow,

         Kv = calibration coefficient,

         P = absolute pressure (kPa),

         T = absolute temperature (K).

         Gas flow is a function of inlet pressure and temperature.

         The calibration procedure described below establishes the value of the calibration coefficient at measured values of pressure, temperature and air flow.

         4.3.2. The manufacturer's recommended procedure shall be followed for calibrating electronic portions of the CFV.

         4.3.3. Measurements for flow calibration of the critical flow venturi are required and the following data shall be found within the limits of precision given:

                                          barometric pressure (corrected) (Pb)   0.03 kPa,
                                          LFE air temperature, flowmeter (ETI) 0.15 K,
                                          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,
                                          CFV inlet depression (PPI)  0.02 kPa,
                                          temperature at venturi inlet (Tv)   0.2 K.
         4.3.4. The equipment shall be set up as shown in Figure 3 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.

         4.3.5. The variable-flow restrictor shall be set to the open position, the blower shall be started and the system stabilised. Data from all instruments shall be recorded.

         4.3.6. The flow restrictor shall be varied and at least eight readings across the critical flow range of the venturi shall be made.

         4.3.7. 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 flowmeter 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.

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Annex 4 - Appendix 7

TOTAL SYSTEM VERIFICATION

         1. To comply with the requirements of paragraph 4.7. of Annex 4, 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