Yokogawa EXAxt SC450 4-Wire Analyzer for Conductivity/Resistivity - Manual (Page 46)

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IM 12D08N05-01E
7-1. Periodic maintenance
The converter requires very little periodic main-
tenance, except to make sure the front window
is kept clean in order to permit a clear view of
the display and allow proper operation of the
touchscreen. If the window becomes soiled,
clean it using a soft damp cloth or soft tissue.
To deal with more stubborn stains, a neutral
detergent may be used.
When you must open the front cover and/or
glands, make sure that the seals are clean and
correctly fitted when the unit is re-assembled
in order to maintain the housing’s weatherproof
integrity against water and water vapor.
Note! Never use harsh chemicals or solvents.
In the event that the window does
become heavily stained or scratched,
refer to the parts list (Chapter 10) for
replacement part numbers.
Battery
The EXAxt converter contains a logbook
feature that uses a clock to provide the timings.
The instrument contains a lithium cell (battery)
to support the clock function when the power
is switched off. The cell has an expected work-
ing life of 10 years. Should this cell need to
be replaced, contact your nearest Yokogawa
service center.
Fuse
There is a circuit board mounted fuse protect-
ing the instrument. If you suspect that this
needs to be replaced, contact your nearest
Yokogawa service center.
7-2. Periodic maintenance of the sensor
Note! Maintenance advice listed here is
intentionally general in nature. Sensor
maintenance is highly application
specific.
In general conductivity/resistivity measure-
ments do not need much periodic maintenance.
If the EXAxt indicates an error in the measure-
ment or in the calibration, some action may be
needed (ref. chapter 8 troubleshooting).
When a 2-electrode sensor has become fouled
an insulating layer may be formed on the
surface of the electrodes and consequently, an
apparent increase in cell constant may occur,
giving a measuring error.
This error is:
2 x Rv/Rcel x 100 %
where:
Rv = the resistance of the fouling layer
Rcel = the cell resistance
Note! Resistance due to fouling or to
polarization does not effect the
accuracy and operation of a 4-
electrode conductivity measuring
system. If an apparent increase in cell
constant occurs cleaning the cell will
restore accurate measurement.
7-3. Cleaning methods
1. For normal applications hot water with
domestic washing-up liquid added will be
effective.
2. For lime, hydroxides, etc., a 5 ...10%
solution of hydrochloric acid is
recommended.
3. Organic contaminants (oils, fats, etc.) can be
easily removed with acetone.
4. For algae, bacteria or moulds, use a solution
of domestic bleach (hypochlorite).
* Never use hydrochloric acid and bleaching
liquid simultaneously. The release of the very
poisonous chlorine gas will result.
7-4. LCD adjustment
Contrast adjustment
During the life of the analyzer the contrast of
the display may fade. The contrast can be ad-
justed using the potentiometer on the backside
of the LCD board. This adjustment must be
done only by Yokogawa’s service personnel.
The position is shown on this picture. For units
manufactured after July 2007, the potentiom-
eter is placed behind the little hole in the LCD
bracket as shown in Figure 3-4 on page 7.
For units manufactured between April 2006
and April 2007, the potentiometer is located as
shown right.
7. MAINTENANCE