Issue link: https://www.e-digitaleditions.com/i/1518209
Inhalation April 2024 21 Pa (each were Model 432, Furness Controls, Indian Trail, NC, US; precision of 0.25% of reading). In every test of a filter disc, it was important to measure the absolute pressure and temperature just upstream of the filter disc so that the gas density, and therefore the approach velocity of the air, could be known (vol- umetric flow rate at the filter face divided by the area of the filter face). Whether testing the protective inlet filter or a fil- ter disc, we measured the ambient and system tem- perature with a platinum 3-wire transducer (Model number P3A-NPT4-125-PX-0.5-PFSB-72-STWL, Evolution Sensors and Controls, Mullica Hill, NJ, US; precision of 0.1 K). e system operated at the laboratory ambient temperature throughout (approximately 295 K). e filter disc holder of choice for these tests was a dose uniformity sampling apparatus (DUSA) suitable holder, a control valve and a vacuum pump (Figure 1). e apparatus had several ports where absolute pres- sure or pressure drop could be measured. We found that it was sufficient to measure the ambient pressure and the pressure just downstream of the protective fil- ter when a protective inlet filter was tested (namely, the filters in Table 1). We made these measurements with a Model CPT 6020 pressure transducer (Mensor LP, San Marcos, TX, US; measurement range 55,200 to 117,200 Pa; precision 0.02% of reading). We measured the pressure just upstream and down- stream of the filter disc holder whenever we evaluated a filter disc (Table 2). We used the Model CPT 6020 transducer and two differential pressure transducers for this purpose, depending on the magnitude of the pressure drop across the filter disc. One of the differ- ential pressure transducers had a full-scale range of 750 Pa, and the other had a full-scale range of 8,000 Figure 1 Equipment for withdrawing air through an inlet filter and a filter disc held inside of a dose uniformity sampling apparatus (DUSA) Inlet Filter Flow Meter Total Dose Tube Metering Valve Vacuum Pump Figure 2 Dry powder inhaler (DPI) dose uniformity sampling apparatus (DUSA) chosen as filter holder for testing filter discs Pressure tap Total dose tube with silicone rubber inlet cap Exit cap removed Filter location