Yokogawa EXAxt PH450 4-Wire Analyzer for pH and ORP - Manual (Page 52)

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IM 12B07C05-01E
Where a refillable (flowing electrolyte) refer-
ence system is employed, make sure that
the reservoir is kept topped up. The rate of
electrolyte consumption will again be process
dependent, so experience will show how often
you must refill. Pressurized systems need to
be regularly checked to ensure that the pres-
sure is adequate.
Periodic re-calibration of the sensor system
is necessary to ensure best accuracy. This
takes into account the aging of the sensors,
and the non-recoverable changes that take
place. These processes are slow, however. If
frequent re-calibration is needed, it is usually
because the cleaning technique is not effec-
tive, the calibration is not well executed or
the pH readings are temperature dependent.
Monthly calibrations should be sufficient for
most applications.
If a film remains on the pH sensor after
cleaning, or if the reference junction is partly
plugged, measuring errors can be interpreted
as a need for re-calibration. Because these
changes are reversible with correct cleaning,
or adjustment of the electrolyte flow through
the junction, make sure that these items are
correct before re-calibrating the system.
7-3. 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 the picture below.
For units manufactured after July 2007, the
potentiometer 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 below.
Touchscreen adjustment
A few years after using, the touchscreen
may deviate from the correct position due
to aging deterioration of the touchscreen.
When that happens, turn off power then on
again. The touchscreen will be calibrated
automatically to the correct touch position
at power on. It is recommended to turn
off power then on again when periodic
maintenance.
Do not turn on power with the touchscreen
pressed, otherwise inaccurate touch position
will occur. If it occurs, leave the touchscreen
unpressed, turn off power then on again.
The touch position will be accurate.
CAUTION
CAUTION