Smiths Medical Medfusion 3000 Series, Technical & Service Manual

Page: 35 / 184

Theory of Operation
29 40-5648-51B
Watchdog circuit
A watchdog circuit has a separate power supply and
separate (PIC) microcontroller/clock which monitors
the main microprocessor. The watchdog circuit detects
microprocessor timing failures and initiates a watch -
dog alarm through a dedicated “back-up” audible
alarm which is separate from the primary speaker.
If a watchdog or “System Failure
” alarm is gener-
ated, then watchdog circuit turns on the red alarm
indicator and backup audible alarm, and turns off the
motor current.
DC power converter
The
DC Power Converter
generates required system
DC voltages from the available power source coming
from the interconnect board. This power source can
be either battery power, or AC power, or external DC
power. The main microprocessor monitors these volt -
ages and will detect failures in any system voltages.
Real time clock
A separate Real Time clock source provides the micro -
processor with date and time information. The date
and time are used for time-stamping records in alarm
history and infusion history, and for determining the
next recommended Periodic Maintenance date.
Graphical display circuit board (LCD)
A 240 × 64-pixel liquid crystal display provides the pri -
mary visual interface for pump operation.
•
An always on LED driven back light in the LCD
enhances viewing in low light areas.
Keypad
The
keypad
is a multi-layer polyester laminate provid -
ing buttons for controlling the pump, and indicator
lights for identification of pump status.
Plunger (driver) travel sensor
The plunger travel sensor is a precision potentiometer
producing a change in voltage (resistance) with the
motion of the syringe plunger driver. This allows the
microprocessor to determine:
• plunger speed
• near end of plunger travel (i.e,. near empty alarm)
• end of plunger travel (i.e., empty alarm)
The microprocessor uses sensor output to verify
plunger travel against set flow delivery rate. The sensor
output is not used for rate correction.
Motor rotation sensor
The motor rotation sensor is an optical reflective sensor
which senses 4 pulses per motor rotation. The micro -
processor measures the frequency of this signal to:
•
Verify rotation speed against the set flow delivery
rate. It is not used for speed correction.
Stepper motor
The stepper motor drives the syringe plunger driver.
•
Each motor step is controlled by the microproces-
sor using an open loop control method.
Syringe flange loaded sensor
The syringe flange sensor requires the flange be in-
stalled in the flange locating device on the pump.
• Reports a logic state to the microprocessor to indi-
cate proper syringe flange loading.
• Uses self test signal to verify the sensor is not in an
electrically “stuck” state.
Syringe size sensor
The
syringe size sensor
is a precision potentiometer
which produces a voltage (resistance) proportional to
the outside barrel diameter of the syringe loaded into
the pump. This allows the microprocessor to measure:
•
Voltage proportional to syringe barrel outside
diameter to determine the syringe size (e.g. 10cc,
20cc etc.) or syringe not loaded.
Interconnect printed circuit board
Receives and directs the power source, either internal
12VDC power supply, internal battery, or external DC
power to the “Main” board.
a) Generates status signals to “Main” board indicat -
ing source of power supplied.
b) Contains battery charger for charging the battery.
c) Contains an infrared drivers for serial communi
-
cation interface with the pump.
d) Supplies the audio drive signal, originating from
the “Main” board, to power the speaker.