Apogee Instruments MO-200 Посібник користувача - Сторінка 9
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overwrite the oldest measurement once there are 99 measurements. Every 48 averaged measurements (making a 24 hour
period), the meter will record an average daily value.
Reset: To reset the meter, in either SMPL or LOG mode, push the mode button twice (RUN should be blinking), then while
pressing the down button, press the mode button once. This will erase all of the saved measurements in memory, but only
for the selected mode. That is, performing a reset when in SMPL mode will only erase the manual measurements and
performing a reset when in LOG mode will only erase the automatic measurements.
Review/Download Data: Each of the logged measurements in either SMPL or LOG mode can be reviewed on the LCD
display by pressing the up/down buttons. To exit and return to the real-time readings, press the sample button. Note that the
integrated daily total values are not accessible through the LCD and can only be viewed by downloading to a computer.
Downloading the stored measurements will require the AC-100 communication cable and software (sold separately). The
meter outputs data using the UART protocol and requires the AC-100 to convert from UART to USB, so standard USB cables
will not work. Set up instructions and software can be downloaded from the Apogee website
(http://www.apogeeinstruments.com/ac-100-communcation-cable/).
Absolute and Relative Gas Concentration
Gas concentration is described in two ways, absolute and relative concentration. The ideal gas law yields absolute gas
concentration often expressed in quantity per volume [mol m
where P is pressure [Pa], V is volume [m
K
-1
), and rearrangement of equation (1) to solve for n / V or P yields absolute gas concentration (in mol m
However, a simple and common way to report concentration of a specific gas in a mixture is by expressing it relative to other
gases in the mixture, as a fraction or percentage. For example, the amount of oxygen in the atmosphere, assuming a dry (no
water vapor) atmosphere, is 0.2095 kPa O
for several hundred years at 20.95 %, and this percentage is the same at all elevations. However, absolute oxygen concentration
does not remain constant, as pressure decreases with elevation. Absolute oxygen concentration determines the rate of most
biological and chemical processes, but relative oxygen concentration is often reported. This is analogous to measuring and
reporting relative humidity when absolute humidity is what determines evaporation rates. Absolute and relative gas
concentration measurements can be expressed using several different units.
Units Used to Describe Absolute and Relative Gas Concentration Measurements
Absolute Amount of Gas
moles of O
(e.g., moles per m
mass of O
(e.g., grams per liter;
O
has a mass of 32 g per mole)
2
partial pressure
(e.g., kilopascals [kPa])
], n is gas quantity [mol], T is temperature [K], R is the ideal gas constant (8.314 J mol
3
per kPa air, or 20.95 %. Atmospheric concentration of oxygen has remained constant
2
per unit volume
2
or moles per liter)
3
per unit volume
2
] or partial pressure [kPa]:
-3
PV =
nRT
Relative Amount of Gas
(e.g., 20.95 % in ambient air)
(e.g., moles of O
mole of ambient air; this can also be expressed as
0.2095 kPa O
-3
or kPa, respectively).
% O
in air
2
mole fraction
per mole of air; 0.2095 mol O
2
per kPa air)
2
9
(1)
-1
per
2