22
Connect one end of the grounding cable to the instrument’s potential equalization and connect
the other end to the ground. It can enhance the reliability of ground connection .It is forbidden to
use water pipe or other pipes as grounding cable. Otherwise, the first-class safety protection will fail
and patients may get electric shock.
3.5 Principle and Schematic diagram
3.5.1 Principle
Multi-channel ECG is made up of amplifier circuit, print controller, keyboard controller, LCD
controller, CPU system and other parts. Lead signals from optical coupler are received by
CPU .After digital filter, sensitivity adjustment and print driver, then the signals are sent to print
controller for the waveform printing. When printing finished, the measurement and analysis will be
processed by the CPU system. Besides, the CPU system will receive the interrupt signal and button
codes to finish the interrupt processing. And CPU system will handle lead-off signal
，
no paper
detection
，
auto power off of batter voltage management, sampling and print of CRO simulation
output and EXT input. Keyboard controller produces scanning signals, finishes the key
anti-vibration, generate keypad number and interruption signals, which are processed by the CPU
system. LCD controller receives the data and orders from the CPU system and achieves the display
for the ECG control state.
3.5.2 Schematic diagram
ECG Patient
Cable
ARM9 Platform
Keyboard
Circuit
LCD Display system
Thermal Printing Module
Power
module
ECG
Amplifier
A/D
Conversion
Circuit
Isolation
Circuit
Cover
