Advertisement
Principle of
Operation
Thermo Scientific
The 42iQHL 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 NO
molecules decay to lower energy states. Specifically:
2
NO
+
O
Nitrogen dioxide (NO
be measured using the chemiluminescent reaction. NO
NO by a stainless steel NO
optional molybdenum converter is heated to 325 °C).
The ambient air sample is drawn into the 42iQHL 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
chamber pressure is measured to infer the sample flow. Pressure deviations
outside of the acceptable range are reported as a fault.
Dry air enters the 42iQHL through the permeation dryer, 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 42iQHL outputs NO, NO
2
NO
concentrations to the front panel display and the analog outputs, and
x
also makes the data available over the serial or Ethernet connection.
+
+
h
NO
O
3
2
2
) must first be transformed into NO before it can
2
-to-NO converter heated to about 625 °C (the
2
Figure
1–2. The sample flows through a capillary,
Introduction
Principle of Operation
is converted to
2
-to-
2
mode). The reaction
x
modes
x
, and
2
42iQHL Instruction Manual
1-3
Advertisement
Chapters
