horiba APOA-370, Operation Manual, Page: 101 / 111

10 APPENDIX
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10 APPENDIX
10.1 Measurement Principle
The ultraviolet absorption method is based on ozone's characteristic of absorbing ultraviolet
rays of specific wavelength. In this analysis method, the sample gas which has passed
through the filter is divided into two flow paths. The sample gas in one path is introduced to the
deozonizer, where its ozone is eliminated, and then sent to the cell as “reference gas.” The
sample gas in the other path is sent to the cell directly, as “sample gas,” by switching a
solenoid valve.
The measurement cell is exposed to direct radiation by a low-pressure mercury lamp which
generates ultraviolet rays with central wavelength of 253.7 nm, and a detector, which involving
a photodiode and electric system to obtain electric signals, measures ultraviolet absorption by
ozone.
The “sample gas” and the “reference gas” are sent to the cell alternately, switched by 1 Hz
with the solenoid valve. The deference in ozone content between the reference gas and the
sample gas can be obtained from the deference in the measured ultraviolet absorption.