marquette hellige MicroSmart, Инструкции по обслуживанию

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Marquette Hellige GmbH MicroSmart V 2.xx Page 20
Servicing Instructions 227 470 35 B - 97.12
The ASIC chipset HECTOR, consisting of 3 Ics, is used for ECG editing on the floating side. The
MicroSmart uses 2 ICs type SDM_HEC2 as AD converters and one IC type DIGI_HEC2 as filter
and interface module. Together with the protective input circuit, a floating power supply and an
interface insulated via optical coupler, the ECG editing is the floating section of MicroSmart and
is part of the PCB MicroSmart. Discrete analog components and a PIC processor are used for PACE
detection.
ECG pre-processing comprises the following functional groups:
- Protective input circuit
- Pre-amplifier
- AD-converter
- PACE detection
- Electrode label
- Lead label
- Filter and interface module
- Power supply
- Reference editing
Protective input circuit
The protective input circuit is designed for the connection of 9 input electrodes and a push-pull
modulation, and includes 2 surge diverters and 18 high voltage diodes attached directly behind each
patient lead, as well as a hybrid (ECG input) which ensures the safety of the patient and of the
electronic components. Protection is only assured if a patient lead with series resistors of 8 k is
used.
Overvoltages reaching the input are limited in the first stage to 90 V through surge diverters and
high voltage diodes. The voltage then passes via a 47 K resistor from each input electrode on the
hybrid to 2 silicon diodes which limit the voltage to 1.2 V before it reaches the downstream
operations amplifier via 100 . The overvoltages reaching the push-pull modulation output are also
limited to 1.2 V by two high voltage diodes over 3.3 K and by two more diode line sections, while
the downstream operations amplifier is protected by 6.8 K .
Patient safety is assured by the above two diodes on the hybrid ’ECG Input’ and by the serial
resistance of 47 K . In case of a defective input amplifier, the supply voltage of ± 5 V can reach
the input. The 100 resistor on the hybrid limits the current flow to the diode, preventing damage
to the diode and limiting the supply voltage to 1.2 V. These 1.2 V are transmitted to the patient over
47 K . The current flowing through it is limited to < 50 µA by the 47 K .