Smiths Medical Medfusion 3000 Series, Техническое и сервисное руководство

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Theory of Operation
47 40-5648-51B
Speaker test
The return signal from the speaker detects whether
current is flowing in the Speaker from analog condi -
tioning circuitry. The half-wave rectifier circuit uses
the
negative half-cycle
of the sense signal to invert and
amplify it.
•
The amplified output is demodulated by the analog
switch which creates a peak and hold circuit.
• The speaker_detect output signal from the
conditioning circuitry goes to the microprocessor’s
analog input.
Plunger board – schematic level
The plunger PCB provides pre-amplification of the
force sensor output to the Main system PCB, and
contains two photo-interrupters with supporting cir-
cuitry, one for each plunger flipper.
The referenced schematic signals of the main board
electronics are identified using names in Smallcaps .
Force preamplifier function
The force sensing system provides a measurement of
the force required in moving the syringe plunger. The
interface to the force sensor has an excitation source,
test signal, and pre-amplification.
• The Main printed circuit board provides a fixed
4.096-volt excitation to the force sensor.
• The Main printed circuit board trims this offset
range using the signal force_preamp_osadj .
• The Main PCB provides additional gain to maxi -
mize measurement resolution.
Force sensing interface description
The force sensing element is a full bridge strain gage,
and the plunger PCB pre-amplifies and filters the out-
put of this bridge. The interface has: sensor excitation,
electronic zero-offset adjustment, amplification and
filtering, and a sensor test control signal
• force_snsr_exh provides a constant voltage
excitation of 4.096 volts DC to the sensor.
• Auto-Zero Adjustment Circuit provides a voltage
to zero the pre-amplifier, force_osv_adj, from
the 8 bit system D/A converter.
• Sensor Post Filter Amplifier is a second order low-
pass filter with a 3.68x gain.
• The signal force_snsr_test* when set active low
causes Q2 to apply a resistance parallel to the force
sensor’s bridge resulting in a positive shift of the
sensor output.
• The sensing system requires calibration to de-
termine zero adjustment, offset, and gain. Cali-
bration values are stored in non-volatile (serial
EEPROM) memory.