Invacare 3LX, Service Manual

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12
INSTALLATION / SEQUENCE OF OPERATION, CONTINUED
If main power is lost, the Battery Free
TM
Power Loss Alarm will sound a short "beep", with a long pause,
intermittently. All units are equipped with a diagnostic alarm system that signals if the pneumatic pressure
or electrical systems malfunction. The Troubleshooting Guide explains the alarm system signals and
reasons in detail for your convenience.
SENSO2 OXGYEN SENSOR TECHNOLOGY CERAMIC ZIRCONIA SENSOR
Technical Description
The oxygen being produced by the concentrator flows out of the product tank and into the flowmeter.
In-line between these components is a tee fitting that directs a small flow of oxygen through a precision
orifice to the oxygen sensor mounted on a printed circuit board.
As the oxygen enters the sensor, it passes through a screen and contacts the sensing disk.
Electric current flowing through a metal film resistor heats the disk in excess of 300
O
C. Oxygen molecules
contact the electrode of the disk and pick-up extra electrons to become oxygen ions. These oxygen ions
are attracted to the electrode on the bottom of the zirconia disk. Because of the crystal structure of the
zirconia, only oxygen ions can pass through. When the oxygen ions reach the bottom electrode, the extra
electrons are released from the oxygen ions and oxygen molecules return to the air. The number of
electrons is directly related to the oxygen concentration. The electrons travel to the PC board where they
are "counted" and the oxygen concentration "reading" is calculated.
A microprocessor on the P.C. board contains software that interprets the signal being received from the
sensor. It compares the signal to clinically acceptable limits that have been selected with the indicator
switch mounted on the PC board. Signals outside of the clinically acceptable limits generate responses in
the form of lighted LEDs, audible indicators, and/or system shut-down.
Operating Sequence
Once the power switch has been turned ON, the SensO
2
circuit will wait 5 minutes for the concentrator to
begin producing clinically acceptable oxygen before activating. No LEDs will illuminate for at least 5
minutes.
After 5 minutes, if the oxygen purity exceeds 85% + 2% the GREEN LED will illuminate.
If the oxygen level is not above 85% + 2% after the first 5 minutes, LEDs will remain off. The system will
wait for a maximum of 30 minutes from start-up to reach 85% + 2% before activating an alarm. Environ-
mental factors such as low voltage, high altitude, or age of the machine will affect the time required to
reach 85% + 2%.
If the oxygen level is not above 85% + 2% within the first 30 minutes, the oxygen concentration alarm
sequence will activate, depending upon the position of the indicator switch. All units are preset at the
factory at 73% + 3%.
When oxygen concentration is above 85% + 2%, the sensor measures oxygen purity every 10 minutes.
If a reading falls below 85% + 2% and the alarm indicator is in the 73% mode or no switch is present, the
oxygen sensor measures purity continuously and a yellow LED will illuminate. If the oxygen purity falls
below 73% + 3% the RED LED/Alarm/Shut-Down mode will activate. If the selector switch is present
and it is set at 85%, the RED LED/Alarm/Shut-Down mode will activate if the oxygen purity falls below
85% + 2%.
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