Principle Of Operation - Thermo Scientific 42i Instruction Manual

Introduction

Principle of Operation

Principle of
Operation
1-2 Model 42i Instruction Manual
Thermo Fisher Scientific is pleased to supply this NO-NO
We are committed to the manufacture of instruments exhibiting high
standards of quality, performance, and workmanship. Service personnel are
available for assistance with any questions or problems that may arise in the
use of this analyzer. For more information on servicing, see Chapter 7,
"Servicing".
The Model 42i operates on the principle that nitric oxide (NO) and ozone
(O ) react to produce a characteristic luminescence with an intensity
3
linearly proportional to the NO concentration. Infrared light emission
results when electronically excited NO
states. Specifically:
NO +
Nitrogen dioxide (NO
be measured using the chemiluminescent reaction. NO
NO by a molybdenum NO
optional stainless steel converter is heated to 625 °C).
The ambient air sample is drawn into the Model 42i through the sample
bulkhead, as shown in
and then to the mode solenoid valve. The solenoid valve routes the sample
either straight to the reaction chamber (NO mode) or through the NO
NO converter and then to the reaction chamber (NO
sensor to the reaction chamber measures the sample flow.
Dry air enters the Model 42i through the dry air bulkhead, passes through
a flow switch, and then through a silent discharge ozonator. The ozonator
generates the ozone needed for the chemiluminescent reaction. At the
reaction chamber, the ozone reacts with the NO in the sample to produce
excited NO molecules. A photomultiplier tube (PMT) housed in a
2
thermoelectric cooler detects the luminescence generated during this
reaction. From the reaction chamber, the exhaust travels through the ozone
(O ) converter to the pump, and is released through the vent.
3
The NO and NO concentrations calculated in the NO and NO
x
are stored in memory. The difference between the concentrations is used to
calculate the NO concentration. The Model 42i outputs NO, NO
2
NO concentrations to the front panel display, the analog outputs, and also
x
makes the data available over the serial or Ethernet connection.
molecules decay to lower energy
2


O + + h
NO O
3 2 2
) must first be transformed into NO before it can
2
-to-NO converter heated to about 325 °C (the
2
Figure 1–1. The sample flows through a capillary,
-NO analyzer.
2 x
is converted to
2
-to-
2
mode). A flow
x
modes
x
, and
2
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