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• Calibrate the MAXO
2
®
+
at the same pressure as the sample gas.
• If sample gases flow through tubing, use the same apparatus and flow rates
when calibrating as when measuring.
3.4 Humidity Effects
Humidity (non-condensing) has no effect on the performance of the MAXO
2
®
+
other than diluting the gas, as long as there is no condensation. Depending on
the humidity, the gas may be diluted by as much as 4%, which proportionally
reduces the oxygen concentration. The device responds to the actual oxygen
concentration rather than the dry concentration. Environments where condensa-
tion may occur are to be avoided since moisture may obstruct passage of gas to
the sensing surface, resulting in erroneous readings and slower response time.
For this reason, the following is recommended:
• Avoid usage in environments greater than 95% relative humidity.
• When used in a breathing circuit, place the sensor upstream of the humidifier.
HELPFUL HINT: Dry sensor by lightly shaking moisture out, or flow a dry gas at two liters per
minute across the sensor membrane.
4.0 CALIBRATION ERRORS AND ERROR CODES
The MAXO
2
®
+
analyzers have a self test feature built into the software to detect
faulty calibrations, oxygen sensor failures, and low operating voltage. These are
listed below, and include possible actions to take, if an error code occurs.
E02: No sensor attached
MAXO
2
®
+
A: Open unit and disconnect and reconnect sensor. Unit should perform
an auto calibration and should read 20.9%. If not, contact Customer Service for
possible sensor replacement.
MAXO
2
®
+
AE: Disconnect and reconnect external sensor. Unit should perform an
auto calibration, and should read 20.9%. If not, contact Customer Service for
possible sensor replacement or cable replacement.
E03: No valid calibration data available
Make sure unit has reached thermal equilibrium. Press and hold the Calibration
Button for three seconds to manually force a new calibration.
E04: Battery below minimum operating voltage
Replace batteries.
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4. Allow the oxygen to saturate the sensor. Although a stable value is usually
observed within 30 seconds, allow at least two minutes to ensure that the
sensor is completely saturated with the calibration gas.
5. If the MAXO
2
®
+
is not already turned on, do so now by pressing the
analyzer “ON” button.
6. Press the Cal button on the MAXO
2
®
+
until you read the word CAL on the
analyzer display. This can take approximately 3 seconds. The analyzer
will now look for a stable sensor signal and a good reading. When
obtained, the analyzer will display the calibration gas on the LCD.
3.0 FACTORS INFLUENCING ACCURATE READINGS
3.1 Elevation Changes
• Changes in elevation result in a reading error of approximately 1% of reading
per 250 feet.
• In general, calibration of the instrument should be performed when elevation at
which the product is being used changes by more than 500 feet.
3.2 Temperature Effects
The MAXO
2
®
+
will hold calibration and read correctly within ±3% when at thermal
equilibrium within the operating temperature range. The device must be thermally
stable when calibrated and allowed to thermally stabilize after experiencing tem-
perature changes before readings are accurate. For these reasons, the following
is recommended:
• For best results, perform the calibration procedure at a temperature close to
the temperature where analysis will occur.
• Allow adequate time for the sensor to equilibrate to a new ambient temperature.
CAUTION: “CAL Err St” may result from a sensor that has not reached thermal equilibrium.
• When used in a breathing circuit, place the sensor upstream of the heater.
3.3 Pressure Effects
Readings from the MAXO
2
®
+
are proportional to the partial pressure of oxygen.
The partial pressure is equal to the concentration times the absolute pressure.
Thus, the readings are proportional to the concentration if the pressure is held
constant. Therefore, the following are recommended:
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