ACOEM Met One Instruments GAS-1060, Руководство пользователя

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Introduction Page 25
1.5.4 Sample DFU
The sample disposable filter unit (DFU) is a very fine filter used to remove particulates down to 0.01
micron from the sample as absorption from particulars is the main interferent to this measurement
method.
1.5.5 Dryer
The dryer is constructed of Nafion tubing and is designed to remove water vapour from the sample
drawn in to the measurement cell. The water is absorbed and moves through the walls of the tubing,
evaporating into the surrounding air. The remaining gas is unaffected. The flow control is performed
by utilising a critical orifice between the measurement cell outlet and the gas dryer’s dry purge gas
inlet. This creates a pressure differential between the dryer’s polymer tube increasing efficiency.
1.5.6 Pressure Sensor PCA
An absolute-pressure transducer is mounted on the measurement cell and used to measure the
sample pressure in the cell. This pressure is used to check for flow and correct readings for pressure
variations.
1.5.7 Interface PCA
Provides complex timing signals to the LED light source, and splits the frequency signal from the
Mixer Preamp PCA into the 4 separate phases for the Main Controller PCA.
Various power supplies and LED light source adjustments are also controlled on this PCA.
1.5.8 Measurement Cell Assembly
Measurement Cell
The measurement cell consists of an optical source, two focusing lenses, mirrors, optical 450nm
bandpass filter in a stainless steel cell 30cm long. Internally two very highly reflective mirrors create a
very long optical path length. The cell is temperature controlled to improve its stability. The optical
source utilizes a blue light emitting diode (LED) to provide a direct absorption measurement of
nitrogen dioxide at 450 nm using phase shift measurement technique.
Measurement Cell Inlet DFU
This is a disposable filter unit (DFU), it is a very fine filter used to protect the measurement cell from
particulates down to 0.01 micron. Located on the inlet of the measurement cell.
Measurement Cell Exhaust DFU
This is a disposable filter unit (DFU), it is a very fine filter used to protect the measurement cell from
particulates down to 0.01 micron. Located on the exhaust of the measurement cell.
LED Light Source
Consists of a single surface mount blue LED mounted on a heat sink to dissipate the heat.