Thermo 42i, Instruction Manual

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System Description
Ozonator
Thermo Electron Corporation Model 42
i
Low Source Instruction Manual 8-3
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.
Optical Filter
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.
Pressure Transducer
The pressure transducer measures the reaction chamber pressure.
Ozonator
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.
Ozonator Flow Switch
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.
Photomultiplier Tube
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.
Photomultiplier Tube
Cooler
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.
Pump
The vacuum pump draws the reacted gasses out of the reaction chamber.
Sample Capillary
The sample capillary along with the pump is used to control flow in the
sample line.