Thermo Scientific 42iQD, Инструкция по эксплуатации

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Introduction
Principle of Operation
Thermo Scientific 42iQD Instruction Manual 1-3
The 42iQD operates on the principle that nitric oxide (NO) and ozone
(O
3
) react to produce a characteristic luminescence with an intensity
linearly proportional to the NO concentration. Infrared light emission
results when NO
2
molecules decay to lower energy states. Specifically:
ν h +
O
+
NO
O + NO
2 2 3
→
Nitrogen dioxide (NO
2
) must first be transformed into NO before it can
be measured using the chemiluminescent reaction. NO
2
is converted to
NO by a molybdenum NO
2
-to-NO converter heated to about 325 °C.
The ambient air sample is drawn into the 42iQD through the sample
bulkhead, as shown in Figure 1–2 . The sample flows through a capillary, to
the NO
2
-to-NO converter, and then to the reaction chamber (NO
x
mode).
A flow sensor prior to the reaction chamber measures the sample flow.
Dry air enters the 42iQD 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
2
molecules. A photomultiplier tube (PMT) housed in a
thermoelectric cooler detects the luminescence generated during this
reaction. From the reaction chamber, the exhaust travels through the ozone
(O
3
) converter to the pump, and is released through the vent.
The NO
x
concentrations are stored in memory. The 42iQD outputs NO
x
concentrations to the front panel display and the analog outputs, and also
makes the data available over the serial or Ethernet connection.
Principle of
Operation