Temperature; Pressure; Discrepancy In Readings - Teledyne AX300-I Operating/Service Instructions Manual

Portable Oxygen Analyzer

2.3.2 Temperature

The R17MED oxygen sensor compensates for ambient temperature changes
in the range of 0–40°C (32–104°F). Since the thermistor that compensates for
these changes is located in the rear of the sensor assembly, it is important that
gas mixtures, flowing over the front of the sensor, be at room temperature, which
is assumed to the temperature around the rear of the sensor. Reading errors may
occur if gases at higher temperature from devices such as heated humidifier are
used to measure oxygen with R17MED oxygen sensor.
A small thermal tracking error may be encountered in applications where
the entire sensor assembly is placed in the gas mixture to be analyzed (such as in
the incubators). Holding the sensor in your hand for more than a few minutes can
also affect the temperature tracking which appears as a slow drift on the LCD.
No adjustments should be made during this period since this error will be elimi-
nated when both the thermistor and sensing electrode have had sufficient time to
come to thermal equilibrium. This can take up to 2 hours.

2.3.3 Pressure

Virtually all gas sensors and analyzers measure the partial pressure of the
gas that they sample. The only time that these analyzers can accurately read per-
centages is when the total pressure does not vary over time between calibrations
and use. For this reason it is important to calibrate the AX300-I oxygen analyzer
(with R17MED oxygen sensor) at regular intervals. It is recommended that the
unit be calibrated prior to each use or every 8 hours. It is recommended that the
analyzer be calibrated at the same pressure as the gas it will be used to analyze.
If the gas being analyzed flows through some length of tubing, use similar tub-
ing/apparatus and same pressure/flow rates when calibrating the analyzer.
When a ventilator is a part of the breathing system, the alternating "breath-
ing" pressure cycles generated by the ventilator will be sensed as pressure pulses
by the sensor, and over time, such pulses manifest as pressure increases in the
fast-reacting sensors such as R17MED. This perceived pressure increase results
in correspondingly higher oxygen reading. While the concentration of oxygen is
not changing, it is the total pressure that is increasing producing a corresponding
increase in the partial pressure of oxygen.

2.3.4 Discrepancy in Readings

When a discrepancy in oxygen readings is detected, the oxygen analyzer's
readings should be verified by checking the AX300-I battery condition and cali-
bration using 100% oxygen. If the analyzer can be calibrated, the unit can be as-
sumed to be in good working order. If, after reinstalling the unit, the discrepancy
in oxygen readings persists, the problem is most likely elsewhere in the breathing
system. Resolve the cause(s) for the discrepancy before using the analyzer. The
Teledyne Analytical Instruments
Operating Instructions
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