Model 405 nm NO
2
/NO/NO
x
Monitor Manual Rev. D
21
The status byte at the end of the serial stream tells which mode you are currently in
(see Section 5 for status codes).
4.16.1. NO
2
Mode
This measurement mode uses two 5 second cycles to measure
I
and
I
o
. After each
cycle, a new measurement of nitrogen dioxide is computed and output to the LCD and
through the serial port depending on what averaging frequency is selected (5 sec, 1
min, 5 min, or 1 hr).
4.16.2. NO
2
and NO Mode
This measurement mode uses three 5 second cycles to measure
I
for NO
2
,
I
o
for NO
2
,
which is also
I
for NO, and
I
o
for NO. After each 5 second cycle, a new measurement
of nitrogen dioxide and nitric oxide is computed and output to the LCD and through the
serial port, depending on what averaging frequency is selected (5 sec, 1 min, 5 min, or
1 hr).
4.16.3. NO Mode
This measurement mode uses two 5 second cycles to measure
I
and
I
o
. After each
cycle, a new measurement of nitric oxide is computed and output to the LCD and
through the serial port, depending on what averaging frequency is selected (5 sec, 1
min, 5 min, or 1 hr).
4.17. Auto Zeroing
The Model 405 nm is equipped with an Auto Zeroing valve to sample air drawn
through a NO
x
scrubber. The frequency and duration of the Auto Zeroing function can
be set via the display or by entering the serial menu as described in Section 5.
4.17.1. Zero Duration
The duration in minutes is set through the
Zer
menu function of the serial menu. After
each auto or forced zero is complete, the second half of all of the measurements
measured during the Auto Zero duration are averaged and used as the zero average.
This computed zero average is added to or subtracted from all future measurements.
For example, if the zero duration is set to 6 minutes, the measurements over the last 3
minutes are averaged to compute the new zero.
4.17.2. Zero Frequency
The zero will automatically occur every X minutes at the frequency set in the zero
frequency menu. For example, if the frequency is set to 60, the Auto Zero will occur
every hour. If this value is set to zero, the Auto Zero function is disabled and the
values in NO
2
zero and NO zero are cleared.
