Teledyne MX300 User Manual download pdf (Page 38)

Service Manual MX300

Teledyne Analytical Instruments 38

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

0.11 atmosphere, 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 H

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.

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Teledyne MX300 User Manual Page 38