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Teledyne API Model 465L O
3
Monitor Operation Manual
20 05509F DCN6409
The intensity of light is converted into a voltage by a high resolution A/D (analog-to-digital)
converter. The digitized signal and other variables are used by the CPU to compute the
concentration using the above formula.
About every 2.5 seconds the M465 completes a measurement cycle consisting of a 1 second wait
period for the sample tube to flush, followed by a 150 ms measurement of the UV light intensity
to obtain I. The sample valve is switched to admit scrubbed sample gas for 1 second, followed by
a 150 ms measurement of the UV light intensity to obtain I
o
. Measurement of the I
o
every 2.5
seconds eliminates instrument drift due to changing intensity of the lamp caused by aging and
dirt.