Smiths Medical 6101, Техническое руководство

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15
6 Safety Features and Fault Detection
Figure 8. CADD‑Prizm
®
PCS II pump hardware block diagram.
Hardware Safety Features
Key hardware safety features include a
watchdog timer circuit, motor driver and
motor watchdog circuits, cassette ‘type’
sensor circuit, latch/lock sensor circuit, and
a voltage detector circuit. Each safety circuit
performs a unique function to insure the
overall safety of the device. (See Figure 8.)
Watchdog Timer Circuit
The microprocessor must send an appropriate
signal to the watchdog circuit at least once
per second. If the microprocessor does not,
the watchdog circuit will time out and shut
down the pump controller.
Watchdog timer circuitry is provided to
monitor the status of the microprocessor
and disable the motor and enable the audible
alarm if the microprocessor fails to function
properly. The microprocessor must strobe
the watchdog circuit at least once every
second in order to prevent the watchdog from
performing its reset function. The reset output
from the watchdog circuit is a pulse output.
This acts to “jump start” the microprocessor.
This unique feature allows the microprocessor
to test the watchdog circuit on every power‑
up. By setting a flag in memory and not
strobing the watchdog, the microprocessor
can force a watchdog time‑out. After being
reset, the microprocessor checks the status
flag to see if this was a time‑out test. If so,
the microprocessor continues normal power‑
up activities. If the reset occurred when the
microprocessor was not expecting it, the
microprocessor traps the event, sounds the
audible alarm and displays an error message
on the LCD.
Motor Driver/Motor Watchdog Circuit
Motor drive circuitry is composed of a
series of power FET transistors, passive
components, and two voltage comparators.
Built into the motor drive circuitry is an RC
timer which times how long the motor runs
each time it is turned on. If the motor runs
for more than an average of 4 seconds, the
circuit will time out and disable the motor. A
unique feature of this circuit is that control
lines to and from the microprocessor circuit
allow the microprocessor to perform a
complete functional test of the motor drive
circuit without running the motor. The
microprocessor performs this test function
every several minutes to assure its continued
functionality. An input from the watchdog
circuit prevents motor operation if the
watchdog timer expires.
PROGRAM
MEMORY
MB
DATA
MEMORY
MB
LCD DISPLAY
VOLTAGE
REFERENCE
MOTOR
DRIVER
WATCHDOG
REAL-TIME
CLOCK
CPU/IO/
GATE ARRAY
KEYBOARD
MOTOR
WATCHDOG
VOLTAGE
DETECTOR
SENSORS
AUDIBLE
ALARM