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3.0 Principles of Operation
3.1 General
The Gemini 501-B Aerosol Generator/Smoke Detector Analyzer operates on the principle of nebulization of a
liquid to produce a poly-dispersed micro-sized spray with a relatively large mass median diameter. An
impactor reduces the median diameter by selectively removing the larger diameter particles. The remaining
aerosol is diluted by a large volume of room air at a constant rate from the blower. Hose and wands carry
the aerosol up to a shroud, which covers the test detector at the ceiling.
A dual-head compressor/vacuum diaphragm pump is used in the system. The compressor line provides the
air pressure necessary for the operation of the nebulizer. Aerosol output and particle size distribution from
the nebulizer is kept constant by maintaining a constant pressure from the compressor. The vacuum line
provides suction to vary the aerosol concentration of the test stream by diverting part of the aerosol from the
generator. The amount of diversion is controlled by an adjustable valve and measured by a flow meter.
3.2 Main Elements of the Instrument
Figure 1 shows the locations of some of the elements (pages4).
3.2.1. Compressor / Vacuum Pump
The compressor line generates the air pressure necessary to operate the nebulizer.
The vacuum line removes a specified quantity of aerosol using a control valve that varies the final
concentration of the aerosol in the test stream. This flow is monitored by a flow meter.
3.2.2. Nebulizer and Nebulizer Reservoir (Figure 1 (9))
The nebulizer produces the aerosol from the Rudol liquid using the pressurized air. Calibration of
each instrument is based on the particular nebulizer supplied. Therefore, nebulizer is not
interchangeable with other testers with different serial numbers.
WARNING: Oil for the nebulizer is stored in the 30-ml transparent acrylic nebulizer reservoir.
Before storage, oil has to be emptied from the nebulizer reservoir to prevent oil
from flowing back into the system, which may damage the electronic components
of the tester.
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