SECTION 10: CIRCUIT DESCRIPTION
Part No. 715-0080, Rev. B
- 84 -
MAIN INCUBATOR ALARM AND POWER INDICATORS
Of the twelve remaining alarm and indicator LEDs for the incubator, nine are driven by
U8
and
U9
,
which are open collector Darlington arrays. Two indicators (
BAT CHG
and
PWR FAIL
) are driven
directly since they must operate when the incubator power is turned off. One indicator (>37
C) is
driven by the microcontroller through open collector Darlington array
U10
. The audible alarm is turned
on as determined by logic on the control board. The audible alarm can be silenced for approximately
60 seconds by pressing the
MUTE
button. This charges
C13
raising the voltage above the reference
voltage generated by
R25
and
R27
. The comparator
U14-B
compares these voltages and turns off
Q3
, which turns off the audible alarm until the
C13
discharges through
R26
. It also turns off an input to
U10, which in turn turns on an input to U10, thus causing the alarm muted LED to come on. The
MUTE
button is overridden by a
PWR FAIL
alarm turning on
Q5
.
TEMPERATURE SETPOINT
The temperature setpoint is entered from the membrane keypad as described in the Operator’s
Manual. The microcontroller firmware then converts this setpoint to a voltage output, which is written
to the serial digital-to-analog converter
U6
. This voltage in turn controls the current across fixed
resistor
R16
(inserted between
TP1
and
TP2
) and thereby emulates the passive resistor model of an
ordinary thumbwheel switch. The equivalent resistance is input to a temperature sensor circuit on the
control board. The microcontroller
U4
also monitors the voltage out of
U6
directly to guard against any
failure in the temperature setpoint circuit.
SETPOINT ALARM
This alarm activates when the incubator temperature is more than 1
from the setpoint. The display
will flash HI or LO every 5 seconds. An audio alarm sounds every minute until the incubator
temperature is within 1
of the setpoint.
PULSE, SpO
2
, AND OXYGEN DISPLAYS (OPTIONAL FEATURES)
The seven-segment display LEDs (
DS20
-
DS28
), the pulse-oximeter / oxygen display mode LEDs
(
D38
-
D44
), and the pulse bar graph LEDs (
D45 - D49
) are updated at 120 Hz by the microprocessor
on the display daughter card. The oxygen low setpoint below 21% warning LEDs (
D35 - D36
) is also
driven by the microprocessor on the display daughter card.
Содержание AirBORNE A750i
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