Thermo Scientific 5028i Instruction Manual page 28

Introduction
Principle of Operation
1-2 Model 5028i Instruction Manual
In the Model 5028i, a discrimination technique is applied whereby
the count rate created by the airborne natural activity is measured
and corrected for in the gross particulate count rate. This eliminates
any interference and enables the possibility to use a C-14 source with
reduced activity. The ability to count the potential interferences of
Radon gas stems from the use of a proportional detector, which enables
the Model 5028i to measure both α and β particles. The proportional
detector is filled with a rigid counting gas and has a life-time of more
than 10 years with a <100 µCi C-14 source. Any deterioration of the
detector performance will be identified before it has an effect on the
particulate measurement by the continuous plateau check procedure
performed during operation.
Another unique design of the Model 5028i is that two measurement
heads are used while Model 5014i only using one. The measurement
heads can open or close separately, and measure PM
simultaneously. In the measurement heads, beta ray is transmitted from
the bottom upwards passing through the filter tape and the accumulated
particles layer. The intensity of beta ray is attenuated by the increasing
mass load, thus reducing its intensity. The reduced beta intensity is then
measured by the proportional detector. The mass on the filter tape is
calculated from the continuous integrated count rate. The determined
count rate is continuously corrected with regard to changes in the air
density.
The sample flow rate is controlled by means of two proportional
solenoid valves. The two valves opening varies according to the flow rate
measured across a precision orifice.
A complete Dual Channel particulate measuring assembly consists of
the following main parts:
Central Monitoring Unit (5028i Continuous Particulate Monitor)
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Ambient Inlet Sampling System (TSP, PM
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particle size separator)
Dynamic Heaters
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Diaphragm Vacuum Pump
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External Ambient T/RH Sensor Assembly
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Internal Data Recording Unit and External Communication Ports
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Optional 4-Ft/6-Ft/8-Ft/10-Ft. Insulated Extension Tube(s)
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Optional Tripod Support
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The Model 5028i combines proven technology, easy to use menu-driven
firmware, and advanced diagnostics to offer unsurpassed flexibility and
reliability. The Model 5028i has the following features:
320 x 240 pixels graphics display
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& PM
2.5 10
, PM , VSCC™)
10 2.5
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