711449 (Rev.3) 02/2016
Effects of Pressure, Humidity and Temperature
To ensure accurate and reliable oxygen monitoring, it is necessary to have a thorough understand-
ing of the effects of pressure, humidity, and
temperature on the sensor.
Effects of Pressure
The sensor responds to partial pressure (not per-
centage) of oxygen. Changes in barometric pressure
change the reading, even if the percent of oxygen in
the sample remains constant.
Partial pressure of oxygen (PO
2
) equals the percent of
oxygen (%0
2
) times the pressure at which the sample
is measured (mmHg).
PO
2
= (%O
2
) (mmHg)
For example: at sea level, the pressure equals 760
mmHg and dry air contains 21% O
2
. Therefore:
PO
2
= (21%) (760 mmHg)
PO
2
= 160 mmHg
If you calibrate an instrument to read 21 % at 760
mmHg partial pressure and then take the instrument to
an area above sea level, a lower reading occurs due to
a lower partial pressure. For a pressure of 700 mmHg:
PO
2
= (21%) (700 mmHg)
PO
2
= 147 mmHg
The percent reading on the instrument is derived from
the following formula:
PO
2
Actual 147 mmHg
=
PO
2
Sea level 160 mmHg
When PO
2
sea level is 21 %
(21%) (147 mmHg)
PO
2
Actual = (160 mmHg) = 19.3%
Therefore, to eliminate error due to pressure changes,
the instrument must be calibrated at the pressure in
which it is used.
Do not expose the sensor to pressure outside
the range of 600 to 900 mmHg (23.62 to 35.43
inches Hg), as this may cause inaccuracies.
Effects of Humidity
The presence of humidity in an oxygen sample de-
creases the actual concentration of oxygen. Humidity
in a sample has the same effect as diluting the sample
with another gas. For example, if 100% oxygen is satu-
rated with 100% humidity, the actual concentration of
oxygen drops to 96% -97%.
As with all oxygen gas sensors, condensation on the
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-
ing in a lower oxygen concentration reading and an
increased response time. This is a typical problem re-
sulting from locating the sensor downstream from the
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However, to avoid this problem when using the sensor
in a breathing circuit, position the sensor upstream of
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pointing downward to prevent moisture from draining
onto the sensor membrane.
Effects of Temperature
Due to an internal thermistor (temperature variable re-
sistor), the MiniOX
®
3000 sensor is minimally affected
by temperature change. Variations in the sensor read-
ing from temperature change are less than 3% when
the instrument is calibrated and used in a monitoring
environment of 0
o
C to 40°C (32°F to 104°F).
Operating Temperature Range:
0
o
to 40
o
C (32
o
to 104
o
F)
Do not use instrument outside operating
temperature range.
Do not handle the sensor unnecessarily. Body
heat can cause the sensor’s thermistor to
change disproportional to the change in gas
sample temperature at the sensing electrode.
This may produce some error until thermal
equilibrium is restored.
MiniOX
®
3000 Oxygen Monitor
Appendix B, Effects of Pressure, Humidity and Temperature
CAUTION
CAUTION
B-1
CAUTION
CAUTION
