Thermo Scientific 49iQ, Instruction Manual

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Introduction
Principle of Operation
Thermo Scientific 49iQ Instruction Manual 1-3
The 49iQ operates on the principle that ozone (O
3
) molecules absorb UV
light at a wavelength of 254 nm. The degree to which the UV light is
absorbed is directly related to the ozone concentration as described by the
Beer-Lambert Law:
KLC


e
o
I
I
where:
K = molecular absorption coefficient, 308 cm -1 (at 0°C and 1
atmosphere)
L = length of cell, 38 cm
C = ozone concentration in parts per million (ppm)
I = UV light intensity of sample with ozone (sample gas)
I
o
= UV light intensity of sample without ozone (reference gas)
The sample is drawn into the 49iQ through the sample bulkhead and is
split into two gas streams, as shown in Error! Reference source not found. .
One gas stream flows through an ozone scrubber to become the reference
gas (I
o
). The reference gas then flows to the reference solenoid valve. The
sample gas (I) flows directly to the sample solenoid valve. The solenoid
valves alternate the reference and sample gas streams between cells A and B
every 10 seconds. When cell A contains reference gas, cell B contains
sample gas and vice versa.
The UV light intensities of each cell are measured by detectors A and B.
When the solenoid valves switch the reference and sample gas streams to
opposite cells, the light intensities are ignored for several seconds to allow
the cells to be flushed. The 49iQ calculates the ozone concentration for
each cell and outputs the average concentration to both the front panel
display and the analog outputs, and also makes the data available over the
serial or Ethernet connection.
Principle of
Operation