YSI PRO20 User Manual page 33

Polarographic Sensors – Model # 605203
The KCl (potassium chloride) solution and the membrane cap should be changed
at least once every 30 days during regular use. In addition, the KCl solution and
membrane should be changed if (a) bubbles are visible under the membrane; (b)
significant deposits of dried electrolyte are visible on the membrane; and (c) if the
sensor shows unstable readings or other sensor-related symptoms.
During membrane changes, examine the gold cathode at the tip of the sensor and
the silver anode along the shaft of the sensor. If either the silver anode is black in
color or the gold cathode is dull, the sensor may need resurfaced using the fine
sanding disks included in the membrane kit. Do not sand the electrode every
membrane change as this is not routine maintenance. In fact, visually, the anode
may appear tarnished and operate just fine. YSI recommends using the 400 grit
wet/dry sanding disks after a membrane change if the sensor has difficulty
stabilizing or calibrating.
To clean and resurface the sensor, follow the instructions below.
Gold Cathode
For correct sensor operation, the gold cathode must be textured properly. It can
become tarnished or plated with silver after extended use. Never use chemicals or
abrasives that have not been recommended or supplied by YSI.
Fill a new membrane cap with O
solution that has been prepared according to
the directions on the bottle. Be very careful
not to touch the membrane surface.
Lightly tap the side of the membrane cap to
release bubbles that may be trapped.
Thread the membrane cap onto the sensor. It
is normal for a small amount of electrolyte to
overflow.
Replace the sensor guard.
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