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The intensity of light is converted into a voltage by the detector/preamp module. The
voltage is converted into a number by a voltage-to-frequency (V/F) converter capable of
80,000 count resolution. The digitized signal, along with the other variables, are used by
the CPU to compute the concentration using the above formula.
Every 6 seconds the M450 completes a measurement cycle consisting of a 2 second wait
period for the sample tube to flush, followed by a 1 second measurement of the UV light
intensity to obtain I. The sample valve is switched to admit scrubbed sample gas for 2
seconds, followed by a 1 second measurement of the UV light intensity to obtain I
o
.
Measurement of the I
o
every 6 seconds minimizes instrument drift due to changing
intensity of the lamp due to aging and dirt.
P/N 02395D1 Teledyne API Model 450 O
3
Monitor Instruction Manual - Page 10