14
Air Detector
The air detector is designed to detect air in
the outlet tubing fluid path. The air detector is
detachable if not needed. The CADD‑Prizm
®
PCS II pump automatically detects the presence
of the air detector and will automatically turn
the sensor on when powered up in LL0.
When the optional air detector is installed, the
Biomed Toolbox feature allows the air detector
to be “required” or “not required.” When the air
detector is not required, it can be “turned on” or
“turned off” using the Options menu. When the
air detector is required, the option for turning
the air detector on or off will not be available.
When the air detector is turned on, the pump
will detect the presence of air in the outlet
tubing fluid path. If the air detector settings are
“not required” and “turned off,” it will Default:
to “turned on” each time the pump powers up in
Lock Level 0.
The air detector is compatible with all of the
reservoirs and sets indicated for use with
the CADD‑Prizm
®
PCS II pump, and all pump
accessories. It is powered directly from the
CADD‑Prizm
®
PCS II pump and no additional
power is required.
Specifications
The air detector will alarm when it senses a
single air bubble greater than 100 microliters
(0.1 milliliters.)
Construction
The air detector housing is made of a special
high impact plastic and has a metalized
film coating on the inside surface to reduce
interference from electromagnetic fields.
The air detector is composed of a single base
compartment with a detachable door. It is
sealed against the pump housing to ensure
the overall assembly is water resistant. The air
detector is mounted to the pump housing with
two screws, and electrically connected with a
ten pin connector.
Theory of Operation
The air detector consists of sensor electronics
and two ultrasonic transducers positioned on
opposite sides of the tubing. One transducer
acts as an acoustic transmitter and the other
as an acoustic receiver. Air detection occurs
when air in the fluid path causes a reduction
in the signal level to the receiver. When the
signal is interrupted for a preset length of
time, the sensing circuitry sends a signal to
the microprocessor indicating air in the fluid
path. To maximize the reliability of the system
and to reduce false alarms, the transmitted
signal is swept over a frequency range. This
accommodates varying resonance frequencies
of the transducer and reduces sensitivity
to tubing tolerances and other mechanical
variations.
Upstream Occlusion Sensor
Theory of Operation
The upstream occlusion sensor is a strain
gauge device capable of detecting pressure
changes in the disposable tubing set. This
is accomplished by using a loading ball or
sphere located on the bottom of the pump.
This loading ball contacts the pump tubing
when a tubing set is attached to the pump.
Under normal operation, the pump tube
pushes outward and applies a specified force
on the sensor. When an upstream occlusion
is present, the upstream tubing collapses
pulling away from the sensor reducing the
force on the sensor. It is this change of the
force that indicates an upstream occlusion.
