Teledyne MX300 manual Pressure

Service Manual MX300

3.7.3 Pressure

Virtually all gas sensors and monitors 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 MX300 oxygen sensor at regular intervals. It is recommended that the unit be calibrated prior to each use or every 8 hours.

When the sensor is connected to a ventilator circuit, the alternating “breathing” pressure cycles generated by the ventilator will be sensed as an increase in the oxygen percentage (especially if the sensor is fast enough to sense the changes, as is the R17MED). In reality, the percentage of oxygen is not changing; it is the total pressure that is increasing. Producing a corresponding increase in the partial pressure of oxygen. A hundred centimeter of water pressure pulse will produce a

0.11atmosphere, or an 11% increase in the total and therefore partial pressure of oxygen. Assuming that the sensor is fast enough to track this pressure pulse, an un-pressurized reading of 50% oxygen will increase to 55.3% if the sensor is subjected to a pressure cycle of 100cm H2O. The reading will rise proportionally less for smaller pressures.

3.7.4 Discrepancy in Readings

The MX300 instrument should be used to measure the oxygen concentration exiting another oxygen mixing device or life support system (i.e., a blender, incubator or anesthesia machine). The information obtained from the MX300 should never be used to adjust a life-support system, but should only be used as an indication that the life support system or device may require service and/or calibration.

When a discrepancy in oxygen readings is detected, the oxygen analyzers readings should be verified by checking the MX300 battery condition and calibration using 100% Oxygen. If the monitor can be calibrated, the unit can be assumed to be in good working order and capable of providing readings to specification. If, after reinstalling the unit, the discrepancy in oxygen readings persists, the problem is most likely elsewhere (i.e., flow blockage, primary device error, etc.). Further investigation should be made until the discrepancy in readings is resolved. The troubleshooting section of this manual may provide additional assistance in locating the problem.

Teledyne Analytical Instruments 38