Abacus
4
Service Manual
54
6.6.3. External electrical noise
If another instrument is near the analyzer can radiate electromagnetic signals in the 1 kHz - 100
kHz frequency region it can be picked up by the system (especially if they are very close to each
other, or the grounding is not quite perfect).
You can easily identify this noise source: by relocating the instrument noise (high PLT blank)
disappears. In this case you have to identify the possible noise source (switch mode power
supplies, computer monitors, since they are not shielded, centrifuges due to high switching
noise of rotor contacts, etc.), the power of the electromagnetic source, because if high power is
present, maybe relocation does not solve your problems, sometimes the electric power supply
makes the coupling, so UPS solves the problem.
Another source of coupling in external noise can be the reagent tanks and tubes. Especially
radio transmitters can cause problems of radiating so that even the reagents (diluent) guides in
the noise. A metal pack for the diluent tank, then a good earth grounding of this metal box
allows this coupling to disappear forever.
6.6.4.
Internal noise sources
The most annoying but real cause is some sort of internal noise. The reason for this
phenomenon is that inside electrode - hot point - of the measuring circuit must be well insulated
from surrounding electronics, otherwise inside noise sources can take their effect.
A. Bad chamber insulation:
bad shielding of the chamber
(floating shield couples signals to the chamber, and does
not prevent against them). Check grounding of shield, remove it and clean the surface
between the shield and the metal base.
bad reference electrode connection
(floating ground reference). Repair is required.
bad sealing of aperture
. Replacement of measuring tube is required.
broken measuring chamber
starts to conduct through the gaps (ground path).
Replacement of chamber is required.
contaminated draining tube
starts to conduct due to protein or lipid build-up. It is very easy
to identify this case. After replacing the drain tube of the measuring chamber (mainly WBC),
WBC histogram peak, or PLT becomes low soon. Normally a good cleaner is required to
dissolve lipid or protein build-up. Sometimes the cleaner is not strong enough to keep this
tube clean enough. Periodic washing using 1% hand warm bleach solution helps.
