Gemini 501-B User Manual
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Contents
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18APPENDIX A: Calibration of the Gemini 501-BThe mass median diameter of the aerosol from the Model 501 Aerosol Generator was determined by usingthe Anderson Cascade Impactor*. Based on 4 replicate runs from 3 generators at a concentration of about20 mg/m3, the mean mass median diameter was found to be 0.44 um with a calculated standard deviation of±0.02 um. The estimated number median diameter is less than 0.2 um. The Model 501-B is based on anduses the same smoke generation apparatus as the original unit.The mass concentration of the aerosol was determined by a mass monitor**, which electro-statically deposits theaerosol onto a piezoelectric quartz crystal. The frequency shift of the crystal is a function of its weight gain fromthe depositing aerosol. Thus the monitor measures aerosol mass concentration in terms of frequency change ofthe crystal. Sensitivity of the monitor is in the order of 0.01 mg/m3.The UL Smoke Box and the Gemini 501-B use different methods to measure smoke. The light obscurationproperty of the smoke is used to quantify the smoke in the UL Box, whereas the mass (weight) concentrationis used for the Gemini instrument.Since the minimum amount of smoke needed to trigger the alarm of the detector, defined as its sensitivity, isequivalent for both the UL smoke box as well as for the Gemini 501-B, the alarm points of detectors are used tobridge the two systems by making equivalent scales.The alarm points in terms of light obscuration for the 6 standard reference detectors were previouslydetermined in the UL Smoke Box. The detectors cover the necessary sensitivity range and consist of bothtype detectors. There are valid physical reasons for the difference in the scales for the two types ofdetectors. |
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