GE Medical Systems marquette Dash 2000, Руководство по обслуживанию, Страница: 40 / 202

EQUIPMENT OVERVIEW: Theory of Operation
2-18 DASH 2000 Patient Monitor Revision A
2000 412-001
PCB Functions The acquisition PCB is a microprocessor based data acquisition system
with patient isolated power supply included. The DAS can be divided
into four main sections:
1. Input sensor/electrode signal conditioning,
2. Analog to digital conversion,
3. Microprocessor/digital interface, and
4. Isolated power supply.
The input sensor/electrode conditioning for NBP, SPO2, TEMP and IBP
is accomplished by the Analog input hybrids and the ECG/RESP section
is accomplished by the HECTOR chip set with its own SPI interface to
the main processor board. Input signals are received from the DAS input
connector board. The NBP pressure hose is connected to a pressure
transducer which develops the pressure equivalent electrical signal. The
signals are then routed to the appropriate hybrid for amplification and
filtering. All input signals are clamped for static protection either on the
hybrids or on the circuit board.
Analog to Digital
Conversion
(NBP, SPO2, TEMP, IBP)
Output signals from the hybrids are coupled to a series of analog multi-
plexers. Outputs from the multiplexers are then applied via a summing
multiplexer to an analog to digital (A/D) buffer. The high slew rate A/D
buffer drives the 20-volt input of the analog to digital converter (ADC).
Under microprocessor control, the channels are individually selected and
sampled at a rate determined by the frequency content of the signal.
The ADC is a complete 12-bit successive-approximation device with
tri-state output buffers for direct interface to the microprocessor bus. The
data is read in two steps, first the 8 most significant bits then the 4 least
significant bits.
Microprocessor/Digital
Interface The MC68332 is a 32-bit microcontroller which is upward compatible
with the M68000 family. It provides 24 address lines and has a 16-bit
data bus. It controls data acquisition, digital control and serial
communication across the isolation barrier.
The system clock is generated by an on-chip PLL circuit and voltage
controlled oscillator (VCO) which uses a low frequency external crystal
(31.2 kHz) and an internal frequency synthesizer to step up the frequency
to 15.7248 MHz (504
x 31.2 kHz). The frequency was selected for timing
synchronization, to be an exact multiple of 60 Hz (60 Hz x 266,240).
The MC 68332 contains intelligent peripheral modules such as the TPU,
the Queued Serial Module (QSM), the Test Submodule, the System
Protection as well as 2 kilobytes of fast static RAM and twelve
independent programmable chip selects.
The TPU provides 16 microcoded channels for performing time related
activities. It is used to control the timing critical portion of the Pulse
Oximetry function. The rest of the TPU is used for input/output (I/O)
control signals.
The Queued Serial Peripheral Interface (QSPI) synchronous serial link is
used to communicate with the MC68332 on the processor PCB via