GE b30, Technical Reference Manual

Page: 49 / 252

E-PSM(P)W module introduction
1-35
Document no. 2044677-001
ECG amplifiers and baseline restoration
The function of the ECG amplifiers and baseline restoration is to amplify the signal and to
restore the baseline of the signal in the middle of the display after the change of the signal
level, e.g. after the change of the DC offset voltage.
Pacer detection
Pacer detection has been made by using four slew rate detector circuits. The pacer detection
amplifiers have been realized at the front of the slew rate detectors independently of the ECG
measuring channels.
Respiration impedance supply
The 31.25 kHz sine wave generator is used as the respiration measurement signal supply.
Analog switches are used for connecting the sine wave to the ECG leads to be measured.
Respiration impedance amplifiers
Buffer amplifiers are used in respiration measurement. Analog switches are used for selecting
the measurement leads. There are also additional amplifiers for increasing the respiration
signal gain. When ECG measurement is 5-lead, the respiration measurement is always done
between R and F, independently on the ECG lead selection. When ECG measurement is 3-lead,
then the respiration measurement is happened at the same lead as the ECG measurement (I, II
or III).
ECG CPU
The CPU is a 16 bit H8/3052 single-chip microcomputer. It contains 128 kbytes of flash
memory and 4 kbytes of RAM. The clock frequency is 16 MHz.
RS485 communication
The communication to the CPU board of the monitor uses RS485 protocol. The RS485 driver
circuits are optically isolated from the processor of the module.
Power supply
The ECG board has a driver-controlled half-bridge switching power supply with 5 kV isolation.
The supply voltages have been regulated with linear regulators.
4.4.4 ECG filtering
B30 monitors have three ECG filtering modes:
MONITORING 0.5 to 30 Hz (with 50 Hz reject filter)
0.5 to 40 Hz (with 60 Hz reject filter)
DIAGNOSTIC 5-lead ECG 0.05 to 150 Hz
ST FILTER 0.05 to 30 Hz (with 50 Hz reject filter)
0.05 to 40 Hz (with 60 Hz reject filter)
The purpose of filtering is to reduce high frequency noise and low frequency (e.g. respiratory)
movement artifacts.
The monitor filter is used in normal monitoring. The diagnostic filter is used if more accurate
diagnostic information is needed. The ST filter gives more accurate information of ST segment,
but reduces high frequency noise.
The high-pass filters 0.5 Hz and 0.05 Hz are done with software. The monitor sends a command
to the hemodynamic module determining which of the corner frequencies 0.5 Hz or 0.05 Hz is
to be used.
The 50 Hz and 60 Hz reject filters are both low-pass filters with zero at 50 Hz or 60 Hz
correspondingly. They are software based filters used for the mains supply filtering. With these
filters the 3 dB value for low-pass filter is 30 Hz or 40 Hz.