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SIGMA Manual Number 41019
Revision AA
tured by separate, independent manufacturers. Likewise, these processors use different soft-
ware compilers and math libraries, which yields additional independence. This processor
pair uses a master/slave checked redundancy scheme where safety critical computations are
computed by the master processor and checked by the slave processor. If either processor’s
check calculation does not match its own computation or if a fault condition is detected, the
processor can independently fail the system to a safe state, which includes an audible alarm.
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The third processor is used to charge the battery (Backflex – 35149), interface to the bar-
code scanner, and pass asynchronous data through the rear case connector.
Pumping Mechanism
Physical Method
The SIGMA Spectrum uses a linear peristaltic motion to pump the fluid. That is, the tubing is repeat-
edly squeezed to create fluid pressure and thereby flow of fluid.
Operation
There are two phases of the pumping cycle:
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Fill phase
■
Pumping phase
The fill phase allows the tubing to be filled from the proximal or “upstream” end of the pump. The
second phase of the cycle is the pumping phase. The pump consists of two valves, one of which
occludes the administration set tubing at all times. The proximal valve occludes the tubing during
the pumping phase of the cycle. Similarly, the distal valve occludes the tubing during the fill phase of
the cycle. There are two “fingers” whose function is to squeeze fluid towards the distal end of the
pump, thereby creating fluid pressure and fluid flow during the pumping phase of the cycle. During
the fill phase of the cycle, the fingers are in a position that allows maximum volume of fluid to fill
the tubing proximal to the distal valve.
Pumping Mechanism Assembly
This assembly is comprised of a cast aluminum chassis and doorplate assembly. The motor, cams,
pumping fingers, upstream sensor and downstream sensor are also part of this assembly. All compo-
nents are fastened with standard, Phillips and socket head machine screws.
Motor
The motor is connected to the I/O Board (60091) through a 10-conductor, 1 mm pitch flex circuit.
Motor Drive
The motor drive circuitry will only allow the motor to run in a clockwise direction, which creates
fluid flow from the proximal end of the pump to the distal end of the pump. Both the PIC and Sharp
processors have the ability to independently remove power from the motor through independent
hardware switches, thereby halting the pump in the event that single fault condition is detected.
There are two mechanisms for detecting rotation of the motor. The first rotation sensing mechanism
is the two-channel encoder, which can sense motor angular velocity as well as rotation direction. The
second rotation sensing mechanism is the once-per-revolution hall effect sensor. These two sensing