Mindray Passport 5-Lead, Service Manual

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Passport 5-Lead, 5L, LT, XG Service Manual 0070-00-0420 2 - 27
Theory of Operation Block Diagrams
The device measures the relative attenuation of two specific wavelengths of light (red and
infrared) by the arterial blood. A sensor from the instrument contains two sets of LED’s to
illuminate a portion of the body (e.g., a fingertip), and a single photo-detector to sense the
amount of light which exits. The two sets of LED’s are alternately pulsed so that the circuitry
can discriminate the infrared light. Each time the heart pulses arterial blood into the finger,
the photo-detector’s signals return to their original level. The electronic instrumentation
processes only this changing portion of the photo-detector’s outputs.
The determination is based upon the assumption that hemoglobin and oxyhemoglobin are
the only two significant attenuators of light in the arterial blood. The device exploits the
difference in their optical attenuation characteristics. But since the detector’s signal is
sensitive to the combined attenuation of both molecules, the device must use two different
wavelengths to discriminate their individual contributions, and thus their relative
concentration.
FIGURE 2-13
SpO
2
Block Diagram
DIGITAL SECTION
MA0..19
DA15..19
RSTDEV
MEMW
MEMR
SYSCLK*
SYSCLK
IOCHRDY
SROE*
ISA-WR-OF *
ISA-RD-OF*
ISA-RD-CK*
E
Q
TSC
ED
E
Q
TSC
ED
SYSCLK*
SYSCLK
A
D
D
R
ESS
DA
T
A
C
O
NT
RO
L
ISA BUS
J21
PARALLEL
I/F
U31
ISA
BUS
I/F
U37
CLR*
HALT*
FIRQ*
SR
SRCE*
SRWR*
63
C
09
SR
A
M
SW R*
MA
1
5
CLOCK
GEN
Y1
63C09 TO
ANALOG
I/F
U41
MA0..16
RD0..7
MA
0.
.2, 15
..
1
6
RD
0
SROE*
TSC
CLR*
HALT*
FI RQ*
E
Q
SR
SWR*
SRCE*
SRWR*
SROE*
SRWR*
OE*
DIR
SRAM
U44
63C09
CPU
U40
MD
0
..7
U46 U45
ANALOG SECTION
D
0
..7
AP
O
U
T
2
*
AP
O
U
T
1
*
AP
O
U
T
0
*
S/
H
G
A
IN
II
C
O
N
T
R
O
L
G
A
IN I
C
O
NT
RO
L
CH
N
L
M
U
X
D
A
C D0
..
1
1
DAC
U20
CONTROL
REGISTER
U17
IN
T
E
R
F
*
CO
M
P
*
COMP*
COMPARATOR
U14
U11A U11B U11B U13
PROGRAMABLE
GAIN I SUBTRACTION PRO GRAMABLE
G AIN II SAMPLE
AND
HO LD
PROBE
FRON
T
P
A
NEL
4
2
1
6
8
3
7
3
5
7
13
14
J23
CURRENT
TO
VOLTAGE
PREAMP
U1A
DEMULTIPLEXER
U4
18 HZ
FILTER U8A
18 HZ
FILTER U8B
REMULTIPLEXER
U10A
DIAG RUN/CAL*
IR DRIVE
RED DRIVE
SEQUENCER
U24
LED
DRIVE
Q1, Q2
INTERF.
DETECTOR
U2A
IR0, IR1, RED0, RED1
RUN*/CAL
RUN/CAL*
DIAG
INTERF*
S1
..
6
CL
K
S
E
Q