Chapter 2 THEORY OF OPERATION
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mechanism that lifts the wiper on the plunger drive potentiometer if the plunger is not
properly captured, this open circuits the potentiometer.
The syringe size is determined by a linkage between the barrel clamp and a potentiometer
that enables the pump to determine the size of the syringe installed.
The progress of the infusion is monitored by a number of sensors. There are three
separate sensors to monitor the advancement of the plunger. The primary encoder
measures the movement of the rotor of the DC motor that drives the lead screw. The
secondary encoder monitors the rotation of the lead screw. The tertiary encoder is
accomplished by monitoring the plunger drive potentiometer, it determines if the plunger
drive mechanism is advancing properly.
Motor control is monitored and controlled by a careful interaction between the master and
slave CPU’s and associated fail-safe logic circuitry.
The occlusion pressure is determined indirectly by measuring the pressure applied to the
plunger of the syringe by measuring the reaction force on the lead screw via a strain gauge
force measuring system. A tilt switch is used to detect and compensate for the vertical
attitude of the pump for small diameter syringes.
Power is provided by a 5 cell battery pack. The pack is charging when the AC Charger is
present. The battery pack must be present as the device is not intended to be operated on
AC power alone.
2.2.3 Syringe Barrel Clamp
2.2.3.1 Syringe Barrel Diameter
Syringe barrel diameter is sensed by a mechanical linkage of the barrel clamp to a soft pot
on the syringe holder mechanism. This signal passes through the zebra strip connector to
the I/O board to the digital board as “SYR_SIZE” at P2A-3. This signal is filtered by R40
and C27 to a frequency of 125 KHz.
2.2.3.2 Flange Detector
Syringe flange detection is provided by a membrane switch in the barrel clamp assembly.
The signal comes through the zebra strip connector to the I/O board to the digital board on
P2A-1 as “FLANGE*” and is pulled up to +5V by R50.
NOTE
Signal lines followed by an asterisk indicate a logical NOT of the signal, or the
signal becomes true when logically low and false when logically high.
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