Portable Oxygen Analyzer Service Manual
Teledyne Analytical Instruments 33
3.6 Gas Sampling 3.6.1 Humidity Humidity does not directly affect the accuracy of the sensor's measurement.
However, when a nebulizer or other device is used to increase moisture levels in
gas mixtures, the moisture actually dilutes the mixture. This dilution effect
decreases the oxygen concentration.
For example, if an 80% oxygen gas mixture is humidified to saturation at
room temperature, the resulting gas mixture will contain only 77.5% oxygen.
Your portable oxygen analyzer accurately measures decreases in the oxygen
concentration due to the dilution effects of moisture added to gas mixtures.
As with all oxygen sensors, excessive condensation on the sensing surface
of the R17MED will block the diffusion of oxygen to the sensor, rendering it
inoperative. We recommend installing the sensor on the dry side of the breathing
circuit at all times.
3.6.2 Temperature The R17MED oxygen sensor adjusts for ambient temperature changes in the
range of 0–40°C (32–106°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. Reading
errors may occur if hot gases from a heated humidifier are directed past a sensor
teed into a breathing circuit.
A small thermal tracking error may be encountered in application areas
where the entire sensor assembly is placed in the gas mixture to be analyzed
(e.g., 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
eliminated when both the thermistor and sensing electrode have had sufficient
time to come to thermal equilibrium. This can take up to 2 hours.
3.6.3 Pressure Virtually all gas sensors and analyzers measure the partial pressure, not the
percentage, of the gas that they sense. The only time that these instruments can
accurately read percentages 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 sensor at regular intervals. It is recommended that the unit be
calibrated prior to each use or every 8 hours.