System Description
Ozonator
Thermo Fisher Scientific
Model 42
i
Trace Level Instruction Manual
8-3
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 pressure transducer measures the reaction chamber pressure.
The sample flow sensor located at the reaction chamber inlet measures the
sample flow into the reaction chamber.
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.
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 external vacuum pump draws the reacted gasses out of the reaction
chamber.
The sample capillary along with the pump is used to control flow in the
sample line.
Optical Filter
Pressure Transducer
Sample Flow Sensor
Ozonator
Ozonator Flow
Switch
Photomultiplier Tube
Photomultiplier Tube
Cooler
External Pump
Sample Capillary
