YSI PRO20 Mode D'emploi page 34

First dry the sensor tip completely with lens cleaning tissue. Wet a sanding disc
and place it face up in the palm of you hand. Next, with your free hand, hold the
sensor in a vertical position, tip down. Place the sensor tip directly down on the
sanding disc and twist it in a circular motion to sand the gold cathode. The goal is
to sand off any build-up and to lightly scratch the cathode to provide a larger
surface area for the O solution under the membrane. Usually, 3 to 4 twists of the
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sanding disc are sufficient to remove deposits and for the gold to appear to have a
matte finish. Rinse thoroughly and wipe the gold cathode with a wet paper towel
before putting on a new membrane cap. If the cathode remains tarnished, contact
YSI Technical Support or the Authorized dealer where you purchased the
instrument.
Silver Anode
After extended use, a thick layer of Silver Chloride (AgCl) builds up on the silver
anode reducing the sensitivity of the sensor. The anode must be cleaned to remove
this layer and restore proper performance. The cleaning can be chemical and/or
mechanical:
Chemical cleaning: Remove the membrane cap and rinse the sensor with
deionized or distilled water. Soak the sensing section of the sensor in a 14%
ammonium hydroxide solution for 2 to 3 minutes or in a 3% ammonia solution
overnight for 8-12 hours (most household ammonia cleaners are typically around
3%). Rinse heavily in cool tap water followed by a thorough rinsing with distilled
or deionized water. The anode should then be thoroughly wiped with a wet paper
towel to remove the residual layer from the anode. You can smell the tip of the
sensor to help ensure all the ammonia has been rinsed off. Trapping residual
ammonia under the new membrane cap can quickly tarnish the electrode and/or
give false readings.
Chemical cleaning should be performed as infrequently as possible.
First attempt a membrane change and recalibrate. If a new
membrane does not resolve the problem, then proceed with
cleaning.
Mechanical cleaning: In order to sand the silver anode along the shaft of the
sensor, simply hold the sensor in a vertical position. Wet the sanding disc and
gently wrap it around the sensor and twist it a few times to lightly sand the anode
(the goal is to simply sand off any build-up without scratching or removing layers
of the anode itself). Usually, 3 to 4 twists of the sanding disc are sufficient to
remove deposits. However, in extreme cases, more sanding may be required to
regenerate the original silver surface.
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