Dräger Medical AG & Co. KGaA 6173.3
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19
Function description Babylog 8000
4 Monitoring Functions
The system checks whether limit values are kept and all functions are ok. If a function fails or if the limit
values are not met, Babylog will generate an alarm.
4.1 Fraction of inspired O
2
(FiO
2
)
4.1.1 O
2
Measurement
The measured O
2
value is checked against upper and lower limit values. The alarm limits are
automatically set at ±4 vol.% below the set FiO
2
value. A time delay makes sure no alarm is activated
when the set value (O
2
) is changed or when the O
2
sensor is calibrated.
The absolute sensor voltages are checked. The differential voltage between the two sensor cells must be
lower than (U1 + U2)/8 +1 mV. The output voltage of each individual cell must be between 9.5 mV and
123.6 mV.
4.1.2 O
2
Calibration
The O
2
sensor is either automatically calibrated 24 hours after the last calibration or manually after
selection from the mode menu.
If the O
2
sensor is replaced during operation the new O
2
sensor will be calibrated automatically. However,
Babylog cannot detect a sensor replacement if the unit is switched off. In this particular case, the operator
has to calibrate the new O
2
sensor manually.
By switching over a valve the sensor is separated from the respiratory gas flow and purged with the
calibration gas (O
2
). This leads to a change in concentration at the O
2
sensor. This change in
concentration allows the Babylog to recognize the activation of the calibration valve.
The calibration valve is deactivated as soon as the calibration is completed.
A two-step calibration with 21% O
2
and 100% O
2
is carried out in order to achieve a higher measurement
accuracy over the whole concentration range and to be able to recognize a spent sensor cell.
During the calibration procedure the microprocessor system processes (synchronizes) one of the two O
2
sensor channels. The O
2
channels are then submitted to a specific sequence of states controlled by one
of the microprocessor systems and monitored for correct sequence and maximum period by the other. For
instance, searching of the calibration values for 21% or 100% must not last longer than 3.5 minutes each.
The calibration value for 21% must be between 9.2 mV and 26 mV, and for 100% between 43.6 mV and
123.6 mV; this applies to both channels. The zero voltage resulting from both values must be between
–6 mV and +6 mV.
After calibration is completed, the software checks whether the limit values respond correctly.
Calibration stops if a control gas fails.
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