Service manual

PN 4237242C
2.3-2
INSTRUMENT DESCRIPTION
FLUIDICS PANEL
Diluter Panel
The Diluter Panel is located in the lower front of the instrument and is the main fluidic
module of the MD II. It holds all the fluid solenoid valves, the VIC, the sweep-flow tubing,
the aperture and bath components, and the Hgb LED and detector. See Figure 2.3-2. The
Sensor Preamp Adapter card is also attached to the back of the Diluter Panel through the
Aperture Electrode module cable shield. This shield provides grounding for the Diluter Panel
through the Sensor Preamp Adapter card. The Diluter Panel itself is isolated from the chassis.
The aperture system is made up of an open sample bath with an external ground electrode, an
Internal Electrode module and an aperture block that fits into the Internal Electrode module.
There are two aperture systems, one for the WBC dilution and one for the RBC/Plt dilution.
The WBC side has a 100-µ aperture similar to other COULTER instruments, except that the
aperture has been reversed to make a flatter external surface. This is done to minimize
carryover in the WBC bath. The RBC bath uses a 50-µ aperture. There is one difference in the
way these components are used in the MD II from other COULTER systems. The outside or
shield conductor of the external electrode coaxial cable is used for the signal return path. The
external or ground electrode from the bath is connected to this conductor and is fed to the
Sensor Preamp Adapter card inside a metal shield.
Hgb components are mounted directly to the WBC bath. There is an LED to supply light for
the colorimetric measuring system. It is supplied with a low constant current source and does
not generate very much heat. The light emitted from the LED is sent through a 525-nm filter.
A photodetector is mounted on the other side of the bath. The output from this detector is
sent to the Hgb Preamp inside the lower chassis.
A sweep-flow system is used by the RBC aperture to sweep red cells from the sensing zone
after they have passed through the aperture. The sweep-flow tubing is housed on a spool that
rests in a cavity below and between the baths. The cavity provides shielding, so no elaborate
canister or isolation grounding system is needed. Sweep flow on the MD II uses 13 ft of
tubing. This is possible because the diluent source is from a vented reservoir in the
instrument and independent of external reagent location.
As with other COULTER instrumentation, a VIC is used to provide constant vacuum to both
apertures while electrically isolating the electrolytic fluids drawn through the apertures. This
count vacuum is regulated at 6 in. Hg, and the vacuum sensor is directly connected to the
VIC, reducing the possiblility of inaccurate count vacuum.
The VIC is also used as a waste reservoir for the probe wipe. Raw pump vacuum of about
15 in. Hg is applied to the chamber for use by the probe wipe mechanism. How the VIC is
tubed is very important. The probe wipe produces a great deal of splashing which causes salt
bridges, eliminating the electrical isolation for the apertures. There are splash guards inside
the VIC to prevent splashing from the outside ports and the probe wipe waste should enter
these outside ports.