Oxygen Equipment User Manual

8.3 Calibration Errors

The MAXO2 Monitors have a self test feature built into the software to

detect faulty calibrations. During calibration, if the signal from the oxygen

sensor is outside the limits stored within the instrument’s memory, a

flashing “CAL Er” is displayed. The error code is displayed to indicate that

either the sensor should be replaced or that there is a fault in the

calibration process. A few simple hints can prevent calibration errors.

If you try to adjust the monitor display before the reading has stabilized,

the “CAL Er” may appear. For example, if the monitor had just been

calibrated on a known high concentration of oxygen source gas and then

exposed to ambient air, you should wait until the reading has stabilized. If

you try to adjust the display to read 20.9% before the sample line has

cleared of high concentration O

2, the sensor may actually be exposed to

residual high % oxygen. The signal from the sensor would still be high

and considered “out of spec” for air, thus resulting in a “CAL Er”. The

proper procedure is to wait for the reading to stabilize before adjusting the

display. This may take 30 seconds or more.

Externally mounted sensors, as found on the OM-25ME or OM-25ME-L

come equipped with diverter tips. The tips help direct the gas in a “T”

fitting up to the sensor for analysis. The diverter tips should be only used

with a flowing gas. When calibrating in a non-flowing environment,

remove the diverter tip.

8.4 Atmospheres of High Humidity

The MAXO

 Monitor can be used in applications where the relative

humidity of the sample gas ranges from 0 to 95%, non-condensing.

However, it should be noted that water vapor exerts its own pressure in

the same manner as oxygen does in a sample gas stream.

For example, if the monitor is calibrated in dry gas and then the gas is

humidified, the monitor will correctly display a reading which is slightly

lower than previously displayed. This is due to the dilution of oxygen in

the sample gas by water vapor.

This fact is important to note in systems where there exist both “wet” and

“dry” gas streams such as in a ventilator circuit. If the monitor is

measuring oxygen on the “dry side” of the ventilator, it will correctly

indicate an oxygen concentration slightly greater than actually found in the

“wet side” (delivered to the patient). The water vapor has diluted the gas

stream.

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