Technical Information
76
Safety features and fault
detection
Hardware safety features
Key hardware safety features include a watchdog timer
circuit, motor driver and motor watchdog circuits, and
a voltage detector circuit. Each safety circuit performs a
unique function to ensure the overall safety of the pump.
Watchdog timer circuit
e microprocessor must send an appropriate signal
to the watchdog circuit at least once per minute. If the
microprocessor does not send this signal, the circuit ini-
tiates a “time out” and shuts down the pump controller.
Watchdog timer circuitry is provided to monitor the sta-
tus of the microprocessor, disable the motor, and cause
the pump to beep if the microprocessor malfunctions.
e microprocessor must strobe the watchdog circuit
at least once per minute in order to prevent the watch-
dog from performing its reset function. e micropro-
cessor tests the watchdog circuit on every power up.
By setting a ag in the memory and not strobing the
watchdog, the microprocessor can force a watchdog time
out. Aer being reset, the microprocessor checks the
status ag to see if this was a time out test. If it was, the
microprocessor continues its normal power up routine.
If the reset occurred when the microprocessor was not
expecting it, the microprocessor traps the event, an
alarm is given (either beep or vibrate), and an error mes-
sage appears in the display.
Motor drive/motor watchdog circuit
Motor drive circuitry is composed of a series of FET
transistors, passive components, two voltage compara-
tors and the second microprocessor. e second mi-
croprocessor times how long the motor runs each time
it is turned on. If the motor runs for longer than the
primary microprocessor species, the circuit times out
and disables the motor. A unique feature of this circuit is
that control lines to and from the microprocessor circuit
allow the microprocessor to perform the complete func-
tional test of the motor drive circuit without running
the motor. e microprocessor performs this test every
several minutes to assure its continued functionality. An
input from the watchdog circuit prevents motor opera-
tion if the watchdog timer expires. e soware veries
this function during the watchdog test described above.
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