Document ID: chunk:federal_register_of_legislation:F2024C00356:reg:21:p9
Version: federal_register_of_legislation:F2024C00356
Segment Type: reg
Provision Reference: reg 21 (pt 9/35)
Character Range: 312006–315086

side). It is recommended that an additional coarse particle filter is situated before the HEPA filter and after the charcoal filter, if used. The purpose of the charcoal filter is to reduce and stabilize the hydrocarbon concentrations of ambient emissions in the dilution air;
              1.4.2.2. A mixing chamber (MC) in which exhaust gas and air are mixed homogeneously, and which may be located close to the vehicle so that the length of the transfer tube (TT) is minimized;
              1.4.2.3. A dilution tunnel (DT) from which particulates and particles are sampled;
              1.4.2.4. Some form of protection for the measurement system may be used e.g. a cyclone separator, bulk stream filter, etc.;
              1.4.2.5. A measuring critical-flow venturi tube (CFV), to measure the flow volume of the diluted exhaust gas;
              1.4.2.6. A blower (BL), of sufficient capacity to handle the total volume of diluted exhaust gas.

              2.   CVS Calibration procedure

              2.1. General Requirements
                The CVS system shall be calibrated by using an accurate flow-meter and a restricting device. The flow through the system shall be measured at various pressure readings and the control parameters of the system measured and related to the flows. The flow-metering device shall be dynamic and suitable for the high flow-rate encountered in constant volume sampler testing. The device shall be of certified accuracy traceable to an approved national or international standard.
              2.1.1.  Various types of flow-meter may be used, e.g. calibrated venturi, laminar flow-meter, calibrated turbine-meter, provided that they are dynamic measurement systems and can meet the requirements of paragraph 1.3.5. of this appendix.
              2.1.2.  The following paragraphs give details of methods of calibrating PDP and CFV units, using a laminar flow-meter, which gives the required accuracy, together with a statistical check on the calibration validity.
              2.2. Calibration of the positive displacement pump (PDP)
              2.2.1.  The following calibration procedure outlines the equipment, the test configuration and the various parameters that are measured to establish the flow-rate of the CVS pump. All the parameters related to the pump are simultaneously measured with the parameters related to the flow-meter which is connected in series with the pump. The calculated flow-rate (given in m3/min at pump inlet, absolute pressure and temperature) can then be plotted versus a correlation function that is the value of a specific combination of pump parameters. The linear equation that relates the pump flow and the correlation function is then determined. In the event that a CVS has a multiple speed drive, a calibration for each range used shall be performed.
              2.2.2.  This calibration procedure is based on the measurement of the absolute values of the pump and flow-meter parameters that relate the flow rate at each point. Three conditions shall be maintained to ensure the accuracy