Nellcor OxiMax N-550 Service Manual page 118

Technical Discussion
Charging Circuits
Real-Time Clock (RTC)
Storage of Patient Data
108
Patient Data is stored by the N-550 and can be downloaded to a printer
through the data port provided on the back of the N-550. An in-depth
discussion of the data port is covered in the Data Port Interface Protocol on
page 89.
The power supply will charge the battery any time the N-550 is connected to
AC power. The voltage applied to the battery is 20 ±0.15 volts DC.
Real time is counted by the DS1307 Real-Time Clock. As long as lithium
battery power or AC power is available, the N-550 will keep time. If the
lithium battery is removed, the time clock must be reset.
Whenever the N-550 is turned on, it stores a "data point" in memory every
four seconds (regardless of whether the N-550 is monitoring a patient or not).
Alarm limit changes will also be stored in trend data. The N-550 can store up
to 24 hours of trend data. There are no limitations on displaying or printing
data.
The N-550 trend data will be lost if the battery fails or is removed.
CAUTION : Changing alarm limit settings uses up trend memory space.
Change alarm limits only as needed.
Note : Trend memory always contains the MOST RECENT 24 hours of
data, with newly collected data over-writing the oldest data on a
rolling basis. The N-550 continues to record data points as long as the
N-550 is powered on, with "blank" data points collected if no sensor
is connected to the N-550 or patient. "Blank" data will over-write
older patient data if the memory becomes full. Therefore, if you want
to save old patient data, it is important that you turn your N-550 off
when you are not monitoring a patient before it fills up and
over-writes the old data with new data (or "blank" data).