Teledyne MX300 - Manual (Page 26)

Operating Instructions MX300
Teledyne Analytical Instruments 18
2.3 Factors Affecting Sampling Accuracy
2.3.1 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 de-
creases the oxygen concentration. Your portable oxygen Monitor accurately
measures the decreased oxygen concentration.
As with all diffusion based 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 system at all times.
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 monitors measure the partial pressure of the
gas that they sample. The only time that these monitors 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 MX300 Oxygen Monitor
(with R17MED oxygen sensor) at regular intervals. It is recommended that the
Monitor be calibrated prior to each use or every 8 hours, and at the same pressure
the monitor normally operates after calibration. If the gas being monitored flows
through some length of tubing, use similar tubing/apparatus and same pres-
sure/flow rates when calibrating the Monitor.