Legacy® PLUS - Smiths Medical

Section 5: Reference
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. The software verifies this function
during the watchdog test described above.
Voltage Detector Circuit
Low voltage detection is performed by part of the Watchdog Circuit and
by the microprocessor via software. Three low voltage levels are detected.
The first 2 levels are detected by software and the third by hardware.
The first level to be reached is the Low Battery Warning threshold which
occurs when the battery voltage decays to a nominal value of 2.4 volts
when the motor is off or 1.8 volts when the motor is active. An Analog
to Digital Converter (ADC) built into the microprocessor allows the
microprocessor, via software, to monitor the battery voltage. At the Low
Battery Warning threshold, the microprocessor enables a periodic series
of beeps and displays a low battery warning message on the LCD. As the
voltage operating the motor reaches a nominal value of 4.75 volts, the
software disables delivery, places a battery depleted message on the LCD,
and enables a constant two tone audible alarm. When the battery voltage
decays to a nominal value of 1.0 volts, a hardware reset circuit is triggered
which places the microprocessor in reset. This prevents ambiguous
microprocessor operation when the battery voltage continues to decay.
The hardware reset continues until the battery is completely discharged
or until it is removed. Once the pump controller goes into low battery
shutdown, only replacing the depleted batteries with new ones will clear
the condition.
Reference