Model 202 Ozone Monitor Manual Rev. J-4
18
3.20. To Test the Lamp Voltage and Precision
A diagnostic lamp test is provided in the
Lmp
submenu of the main menu. Before the lamp
test begins, “Pump On or Off?” is displayed. Turning the pump off during the lamp test is
recommended because it eliminates any noise associated with air flow in order to better
focus the test on the lamp stability. Comparing the results from testing with the pump off
and with the pump on can help determine the source of noise and whether to clean the
instrument or possibly replace the lamp. If the noise is greater with the pump on, this is a
good indication that the flow path needs to be cleaned and the ozone scrubber replaced.
During the lamp test, the instrument measures the “effective” ozone concentration in the
detection cell without switching the solenoid valve on and off. This is an electronic zero
and should after a few readings settle down to ± a few ppbv. If this value is outside the
range -9 to +9, the instrument may not be operating correctly. The display also gives a
standard deviation of the electronic zero. For best results, the standard deviation
should be not greater than ±2.5. Note that because less averaging is involved, this is
not equal to the overall precision of the instrument; it is a diagnostic test of lamp
fluctuations. The lamp test also measures and outputs the voltage level of the detector.
For best performance the voltage should be in the range 0.7-2.0 volts. For a detector
voltage less than about 0.7 volts, the data may be noisy due to insufficient light
intensity to make precise measurements. If the voltage is zero, the lamp is not ignited
and may have burned out. For voltages above 2.5 volts, the A/D converter is
saturated and the measured ozone value will always be zero. This could happen if
the instrument is very hot so that the lamp output is too bright.
To exit the
Lmp
test mode, hold in the Select switch and release to return to the
Main Menu
.
3.21. To Read the Number of Hours of Ozone Monitor Use
The instrument keeps track of the total number of hours of use. This is helpful for
determining when the instrument should be serviced, a pump replaced, etc. To read
the number of hours of operation, choose
Menu
/
Cfg
/
I
/
O
/
Hrs
.
3.22. To Turn the Optional Lamp Heater On and Off
If the Cold-Weather Option has been purchased, the lamp has a heater. This heater
can be toggled by use of the serial commands (see Section 4).
3.23. To Read Flow Rate on the Display
The flow rate may be read by rotating the Select Switch while the instrument is making
measurements. The flow rate will be momentarily displayed on the display screen. It
might read, for example
Flow = 879 cc/min
As noted in Sections 3.5 and 3.12, the flow rate is also output in the serial data line.
