Model 106-L Ozone Monitor Manual Rev. E
19
Select
ppb
, depress the select switch to obtain a blinking cursor and rotate the
select switch to choose between units of ppb, pphm, ppm, µg/m
3
and mg/m
3
.
Press the select switch again to remove the blinking cursor, and return to the
Unt
menu using the left arrow. Ozone concentrations will now be calculated
and reported in the chosen units.
Select T/P from the
Unt
submenu to change the units reported for temperature
and pressure:
T/P Units Menu
T:C P:mbar
You may now select units of
o
C or K for temperature and mbar or torr for
pressure using the same procedure used to set the units for ozone
concentration.
Lamp Test
If the instrument is excessively noisy (standard deviation greater than 2 ppb) or
always reads near zero in the presence of ozone, it is useful to perform the
lamp test to make sure that the lamp is turning on and does not fluctuate too
rapidly. Before performing the lamp test, allow the instrument to warm up for at
least twenty minutes.
Choose
Lmp
from the main
Menu
. The display will momentarily read “
Lamp
Test
”. The photodiode voltage will then be displayed, and after a few lamp
measurements have been made, the electronic offset and standard deviation
also will be displayed as, for example:
PDV= 0.89801 V
1.2+/-1.85
The photodiode voltage (PDV) is a measure of the lamp intensity and should be
in the range 0.6-2.2 volts. Since absorbance is a ratio measurement, the
absolute value of the voltage is not particularly important. However, above 2.5
volts, which could occur if the instrument is allowed to become too hot, the
photodiode is saturated and the calculated ozone concentration will be zero.
Photodiode voltage less than 0.6 volts is indicative of either a weak lamp or a
dirty detection cell and may result in a noisy measurement. The photodiode
voltage will typically increase as the instrument warms up. Lamp drift is
continuously monitored and corrected for in the firmware and thus has very little
effect on the measured ozone concentration. Once the instrument is warmed
