ZOLL PD 2000 - Pacer

SERVICE MANUAL
Discharging the high voltage capacitor
Discharge of the patient relay is a two step process. The power provided
‘to the patient relay is routed through the discharge switches on either the
defibrillator paddles or on the Multi-Function Cable. The CPU then
senses when the DISCHARGE buttons are pressed with a signal called
PADMON. When the CPU has decided that all other conditions have
been met, such as in the SYNC mode, it activates the signal XPATREL.
This signal drives Q12 which activates the patient relay.
When the patient relay activation is complete, the CPU releases the
XPATREL signal and allows the patient relay to return the capacitor
terminals to the PD™ 1400-series system side. Several hundred
milliseconds later, the safety relay is closed to ensure the high voltage
capacitor energy is completely dissipated.
4B. PACER
The Pacer circuit produces and delivers user-controllable pace pulses to
the pacing electrodes. Pacing is initiated when the front panel switch is
turned to PACE and the OUTPUT and RATE controls are set. Pacing
current amplitude is constant during the pulse and is determined by the
position of the front panel PACER OUTPUT dial. Pacing pulse rate is
determined by the position of the front panel PACER RATE dial. The
pacing pulse duration is fixed at 40 msec.
The CPU provides five signals used by the Pacer circuit. They must be as
indicated for pace pulses to be generated:
1. XSAFE hi No safety hazard detected (EPU)
2. XPWR RESET hi Power on
3. P/XD hi Pace mode
4. XLORATE low Pace charging rate
5. XPWRENB low PWM enabled during pulse
6. VCTL Sets current amplitude
The CPU provides two signals to control the pacing pulse:
VCTL sets the pacing current amplitude. It is an analog signal derived
from the position of the front panel pace pot PACER OUTPUT. Current
sense transformer T1 and operational amplifier U3 measure actual pacing
current (VPACE) and compare it to VCTL to provide loop control.
XPWRENB is a digital signal turned on and off by the CPU to start and
stop the pacing pulse. The CPU sets the pace pulse duration by the
XPWRENB on time and the pace pulse rate by the XPWRENB on-to-on
interval.
IV-16