ZOLL PD 2000 - Analog Board

SERVICE MANUAL
5A. ECG
5. ANALOG BOARD
The Analog Board consists of two sections, ECG, and CRT deflection.
The ECG has a system circuit side and a patient isolated side. On the
patient isolated side there are two inputs for ECG signals. Paddle input
protection is offered by series resistors and voltage limiting components.
The three lead ECG input is protected with voltage transient suppressers,
the lead select relays, series resistors, and diode clamps. The three lead
input is sensed for a leads off condition. Both ECG inputs (leads and
paddles) follow the same signal conditioning path after the lead select
relays. The signal path consists of RF input filtering, an instrumentation
amplifier, a slew limiting stage, a gain and 100 Hz low pass stage, and
then an analog to digital serial data conversion for transmission over the
patient isolation barrier to the system side. Other circuits on the isolated
side include leads off, hi slew detection, gain and bandwidth selection,
and drive circuits for the lead select relays.
The system side circuits consist of minimal signal conditioning and the
power supply drive. The isolated power supply runs at 50 kHz from the
+11.6 V regulated supply.
Input Protection
The ECG patient connections are protected with voltage transient
suppressers at each of the three input leads and at the paddles input. A
second level of protection for the op amp inputs is accomplished with
series input resistors and diode clamps to the power supply rails. Current.
source resistors (R7, R8).are used for ECG leads off detection. Protection
between the paddles inputs and the three lead inputs is achieved by the
series resistors, Zener diodes (D21, D22), MOVS (M1, M2, M3), and the
lead select relay (K1). The MOVs limit the voltage if an external
defibrillation voltage is applied from the paddle to any of the three ECG
leads.
Lead Selection
Inputs from the ECG amplifiers may come from the three standard ECG
leads or from the defibrillation paddles. These inputs go to the lead
select relay (K1,) and selection multiplexers (U6, U7) to provide the
standard lead configurations of lead 1, П, ог Ш and to select the paddles
input. The relay also provides isolation of the paddles inputs and the
three ECG leads.
IV-18