Model 202 Ozone Monitor Manual Rev. J-4
7
Inlet tubing may be attached to the ¼ inch nylon Swagelok fitting on the back of the
instrument. The inlet tubing should be made of PTFE (Teflon
)
, PFA, or some other
inert material that does not destroy ozone and that does not desorb plasticizers and
other organics that can contaminate the flow path. The length of tubing should be
kept as short as possible (not more than a few feet) to minimize ozone destruction.
Tygon
, polypropylene (which may look like Teflon
), and metal tubing should not be
used. Teflon-lined Tygon
tubing, which is used inside the 2B Technologies
instrument, provides the flexibility of Tygon
with the inertness of Teflon
. A Teflon
inlet filter is highly recommended to prevent internal contamination of the tubing and
absorption cell by particulate matter. The filter should be tested for ozone loss by
measuring ambient ozone with and without the filter attached. Tubing, filters, and filter
holders are available through 2B Technologies. See our website:
www.twobtech.com
.
If the instrument is being flown, the inlet should not point into the wind, because the
resulting pressure fluctuations will result in a noisy signal. Although the instrument
compensates for temperature drift, if strong temperature fluctuations are expected, as
in vertical profiling applications using balloons, the instrument should be placed in a
thermally insulated box
3.3.
Measurement of the Zero Offset
The electronic zero of the instrument may be measured by attaching an ozone
destruction cartridge to the air inlet for a period of 5-10 minutes (see Section 7 of this
manual). For an accurate measurement, the instrument must have been turned on
long enough for the internal temperature to stabilize. The observed offset, which can
amount to a few ppbv, can be corrected by changing this calibration parameter from
the front panel, as described below, or by correcting the data at a later time.
3.4.
Collecting Data from the Analog Output
The data may be logged in real time using a data logger attached to the BNC analog
output. The range of the analog output is 0-2.5 V. The output is scaled according to a
sensitivity you define in the menu. For example, you may define 1V = 100 ppbv. In
that case, the maximum output is 250 ppbv. There is a small positive offset, typically
2 mV in the analog output, but this offset varies from instrument to instrument. The
offset can be measured by simultaneously observing the panel display and measuring
the analog output with a voltmeter.
3.5.
Collecting Data over the Serial Port in Real Time
To transmit data to a computer over the serial port in real time, connect the Ozone
Monitor to the serial port of the computer using the 9-pin cable provided. Note that
this is a “straight-through” female-female serial cable. A “cross-over” cable will not
work. Start your data acquisition software, preferably using the 2B Technologies
Display and Graphing Software (available as a free download from the 2B Tech
website,
https://www.twobtech.com/downloads.html
). See Appendix A of this manual
for information about working with this software. Other terminal emulation software
