Yokogawa EXAxt PH450 4-Wire Analyzer for pH and ORP - Manual (Page 51)

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IM 12B07C05-01E
7
MAINTENANCE
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. The
pH measurement uses high impedance sen-
sors and may otherwise be prone to problems
caused by exposure of the circuitry to conden-
sation.
Note! Never use harsh chemicals or
solvents. In the event that the window
does become heavily stained or
scratched, refer to the parts list 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.
To perform correctly, pH sensors should be
clean. This may be an obvious statement, but it
has some implications for routine maintenance.
The user should consider the reason behind a
drift seen in a pH sensor system, rather than to
blindly recalibrate frequently, and hope to thus
minimize the errors. Most drift in pH systems
can be traced to fouling or deposits of some
sort building up on the sensor. It is often the
case that a simple frequent cleaning regime
can replace a (too) frequent calibration with the
associated saving in labor and costly calibra-
tion solutions.
Neutralization processes where lime or soda is
used to raise the pH are well known for causing
coatings and blocking reference junctions with
the insoluble hydroxides that are precipitated.
In such an application, daily washing of the
sensors in a dilute acid will yield a far better
performance than a daily buffer calibration. It
will also take a fraction of the time.
Each application should be judged on it’s own
merits, some will have greasy deposits that will
need a soapy solution to clean, some may even
require organic solvents to remove resinous
deposits. In any case, avoid harsh chemicals
like concentrated acids and abrasive cleaners
as these will destroy the conditioning of the
sensors, and will require a re-hydration period
before full function is restored. After cleaning
the sensors, and prior to a calibration, always
rinse thoroughly in distilled water to ensure that
there is no residue of the cleaning medium to
contaminate your calibration solution.
Note! Some applications will poison simple
sensors with non-reversible chemical
changes. These systems do not
improve with cleaning. If you suspect
that your system is one of these,
contact your local Yokogawa sales
office or representative for advice. An
alternative sensor type will improve the
performance.
7. MAINTENANCE