Abbott aim Technical & Service Manual page 22

Section 4, Theory of Operation
When no occlusion condition is present, light is returned to the occlusion phototransistor and the
phototransistor is driven further into conduction. When a distal occlusion condition is present, the
cartridge when turning causes a pressure buildup of the fluid inside the cartridge. This pressure
buildup causes a small balloon segment within the cartridge sensing chamber to expand. When the
balloon expands sufficiently such that a significant amount of the balloon surface touches the plastic
on the inside of the sensing chamber, the balloon filled with fluid causes the mirror surface to become
less reflective. An occlusion condition therefore results in a decrease in occlusion phototransistor
drive and causes the transistor to go further out of conduction (towards the off state). When no
cartridge is installed in the pump, or the cartridge is incorrectly installed no light will be reflected to
the phototransistor and an occlusion alarm or check cartridge alarm will occur. In summary, an
occlusion alarm means that the occlusion phototransistor is off.
The check cartridge alarm utilizes the same phototransistor sensor as the occlusion alarm. A check
cartridge alarm is displayed whenever the lightpath is interrupted and the pump is not in the run state.
Once the pump is running, the occlusion alarm will be displayed for any interruption of the light
beam.
The latch holds the cartridge in the motor frame with tabs at two points to keep it properly aligned to
the motor and the optics assembly (refer to Figure 4-5. Latch Assembly). One capture point on the
cartridge is the indentation on the side of the cartridge near the rotor; the second point is a protruding
tab on the cartridge next to the blue foil.
Ejection
Cartridge
holding
tabs
Sa 5D-2c_25
Figure 4-5. Latch Assembiy
Two pivot pins hold the latch assembly onto the motor frame. Once the pump is assembled, tabs on
the case hold the pivot pins in place.
The latch is opened by moving the thumb tab down and then rotating it back. This action rotates the
lever arms outward from the motor frame and ejects a cartridge if one is installed. The latch is closed
and the cartridge locked into place by moving the thumb tab down, inward and then upward.
430-600035-002 (Rev. 11/99) 4-4 AIM/AIM Plus Technical Service Manual