Welch Allyn Atlas Service Manual page 87

15
Resp-Off
1
SpO2-Reset
2
Sw-RespReset
3
Sw-RL-V
4
MuxB
5
MonBW
6
SW-RLD-RL
7
SW-RLD-LL
9
U605-out
15
SW-RLD-LA
1
SW-RLD-RA
2
Mux-Lds-C
3
Mux-Lds-B
4
Mux-Lds-A
5
Mux-A/D-C
6
Mux-A/D-B
7
Mux-A/D-A
9
2.4 Signal Isolation
Optocouplers are used to electrically isolate signals. The following signals are transmitted across the
isolation barrier through the optocouplers:
1. SpO2 out:
Opto U411
2. Serial Data:
Opto U613
3. Serial Data Clock:
Opto U612
4. ADC Clock
Opto U611
5. PWM A/D data
Opto U610
6. Respiration Clock
U710
2.5 ECG Circuits
2.5.1 Overview
The front end will meet all applicable AAMI standards. Atlas provides a 5-wire front end, and will be
compatible with both a 3-wire and 5-wire cable. Monitor (0.5Hz to 40Hz) Extended (0.05Hz to 100Hz)
bandwidth will be provided. The ECG amplifier always transmits 0.05Hz to 100Hz data to the CPU board
(unless in baseline restore mode), additional filtering for Monitor Bandwidth is implemented in software
2.5.2 Defib Protect, RFI Filtering
The ECG lead set includes a 1K resistor for current limiting. The neon bulbs act as a voltage clamp,
limiting voltage to about 100V. Neons are chosen for their low capacitance and high DC isolation. Series
resistors and diode clamps are used as a second set of protection for the front-end amplifiers. Resistors
R506, R507 and Diodes D506, D507, are used to reverse bias the lead clamp diodes (D501 to D505). Two
passive RC filters are used to reduce susceptibility to RFI and ESU.
Appendix A
iso+5Vdig
U605
16
VCC
14
QA SER
QB
11
QC SRCLK
10
QD SRCLR
QE
12
QF RCLK
13
QG G
QH
QH
8
GND
74HCT595
D E
U606
16
VCC
14
QA SER
QB
11
QC SRCLK
10
QD SRCLR
QE
12
QF RCLK
13
QG G
QH
QH
8
GND
74HCT595
D E
SpO2 serial data, waveform and status information.
Data from the SpO2 board to the CPU board.
Serial Control data for isolated circuits.
Data from the CPU board to isolated circuits.
Data clock for serial control data.
Clock from the CPU board to isolated circuits.
Clock for PWM A/D converter, also used to latch control shift registers.
Clock from the CPU board to isolated circuits.
A/D Pulse width data.
Pulse width data from isolated circuits to CPU board.
Clock for Respiration drive circuit (same signal as power supply sync)
Clock from the CPU board to isolated circuits.
FE-Serial-Data
FE-Data-Clk
A/D-Clk
10/14/99