SECTION 10: CIRCUIT DESCRIPTION
Part No. 715-0080, Rev. B
- 83 -
POWER SOURCE SELECTION
Relays
K1
and
K2
are arranged by means of their contact and drive coil connections to select the
proper power source. AC power is the preferred source and is selected when the only external power
applied is AC. It is also selected when both external DC and AC are applied. External DC is selected
only when it is applied exclusively. When no external source of power is applied, the relays select the
internal battery.
DISPLAY BOARD
This section details the functions provided by the circuitry on the display board. Microcontroller
U4
is
the chief component of the incubator display portion of the board. When powered on, dedicated
firmware processes key inputs received from the membrane switch panel; continuously monitors the
incubator air temperature, skin temperature, and battery voltage inputs; selects and updates the
seven-segment digits, display mode LEDs, and temperature setpoint; and provides nonvolatile
memory to restore system settings when power is cycled.
Meanwhile, microcontroller
U19
is the chief component of the pulse oximeter and oxygen monitor.
When powered on, dedicated firmware processes key inputs received from the membrane switch
panel and continuously monitors the oxygen content and serial communications from the pulse
oximetry board. It continuously selects and updates the seven-segment digits for %SpO
2
, Pulse, and
Oxygen concentration, as well as the pulse bar graph and the pulse-oximeter / oxygen display mode
LEDs. It provides early warning for too low of a low oxygen alarm setpoint and drives the alarm
output. It also provides nonvolatile memory to restore system settings when power is cycled.
MEASURED TEMPERATURE DISPLAY
The seven-segment display LEDs (
DS1
,
DS2
, and
DS3
) and the display mode LEDs (
D53
,
D54
,
D55
,
and
D56
) are updated at 200 Hz and are driven by current source array
U11
. This refresh rate is
established by the microcontroller, which activates the common cathodes for each display component
using open collector Darlington array
U10
.
Содержание AirBORNE A750i
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