Thermo Scientific 42iQLS, Instruction Manual

Page: 270 / 318

System Description
Reaction Chamber DMC
8-2 42iQLS Instruction Manual Thermo Scientific
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Solenoid valve panel (optional)
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Flow Pressure DMC with restricting capillary
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Firmware
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Oxygen sensor (optional)
The reaction chamber is where the sample reacts with ozone and produces
excited NO
2
that gives off a photon of energy when it decays.
The reaction chamber is heated and controlled to approximately 50 °C in
order to ensure the greatest instrument stability. The sample and ozone
flow capillaries and a thermistor sensor are also housed in/on the reaction
chamber assembly.
The optical filter housed in the reaction chamber limits the spectral region
viewed by the detector and eliminates possible interferences due to other
chemiluminescent reactions.
The Photomultiplier tube (PMT) provides the infrared sensitivity required
to detect the NO
2
luminescence resulting from the reaction of the ozone
with the ambient air sample.
Optical energy from the reaction is converted to an electrical signal by the
PMT and sent to the input board that transmits it to the processor.
The thermoelectric PMT cooler reduces the PMT temperature to
approximately -3 °C to minimize dark current and increase instrument
sensitivity. The cooler helps to increase zero and span stability over a wide
ambient temperature range. The cooler housing also shields the PMT from
external electrical and optical interferences.
The Ozonator generates the necessary ozone concentration required for the
chemiluminescent reaction. The ozone reacts with the NO in the ambient
air sample to produce the electronically excited NO
2
molecules.
The ozonator flow switch located at the ozonator inlet completes an
electrical safety circuit when air flows through the sensor to the ozonator. If
airflow stops, the flow sensor breaks the electrical circuit to the ozonator
and shuts it off to prevent the ozonator from overheating.
Reaction
Chamber DMC
Optical Filter
Photomultiplier
Tube
Photomultiplier
Tube Cooler
Ozonator
Ozonator Flow
Switch