GE Corometrics 126, Руководство по обслуживанию

Страница: 95 / 440

Revision B 120 Series Maternal/Fetal Monitor 4-37
2015590-001
Theory of Operation: NBP Board
NBP Board Manufactured by CAS Medical Systems, Inc.
This blood pressure module is manufactured by CAS Medical Systems, Inc. The
following technical information is a summary of the module circuitry. This
information is provided to give the hospital biomedical engineer an overall summary
of the module’s functions in relation to the 120 Series Monitor—to assist in isolating
troubleshooting problems to the board level. This information is not intended to
provide a complete circuit theory and should not be used to repair any problems on
the board itself. When a problem does exist with the CAS Blood Pressure Board,
contact your GE Service Representative for information about repair/exchange of
the board.
Processor Circuitry
Eight-bit processor U1 controls all communication with the 120 Series Monitor
through its integral serial port; it also controls the pump and valves, calculates the
measurement results, and performs the board’s self-test. The microprocessor has an
internal clock divider that divides down the 9.216 MHz crystal-controlled clock to
4.608 MHz. One section of U6 also divides down the clock to provide 2.304 MHz
to analog-to-digital (A/D) converter U4. Memory consists of 64k x 8 EPROM U2
and 8k x 8 bit RAM U3. Decoding of the processor’s address lines is performed by
U8, U9, U10, and U11 which select the EPROM, RAM, A/D, pump and valve
drivers, and provide amplification control.
A/D Conversion
A/D converter U4 performs a 10-bit conversion that digitizes the signals
representing static pressure in the cuff and cuff pressure caused by arterial volume
changes. A 2.5 V reference is supplied by U5; a 5 V supply is provided by linear
regulator U13 which converts the module’s 12 V input to 5 V. The output of U4 is
sent to the microprocessor for calculations.
Watchdog Circuitry
Watchdog functions are provided by U7 which performs three functions: if the
software fails to execute properly, the watchdog resets the processor, disables the
pump, and opens the valves; or if the module’s 5 V power supply falls below 4.5 V,
the watchdog will also reset the module; or if overpressure switch S1 detects a cuff
pressure above 300 mmHg (40 kPa), it works in conjunction with U7 to reset the
module.