YSI Pro1020 - Manual (Page 20)

32 33
Remove the protective red cap by pulling it straight
off the sensor. Or, unscrew and remove the used cap
membrane by holding the sensor while unscrewing the
cap membrane. Discard the used cap membrane.
Thoroughly rinse the sensor tip with distilled or
deionized water.
Fill a new cap membrane 3/4 full with
electrolyte 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 cap membrane to
release bubbles that may be trapped.
Thread the cap membrane onto the sensor.
It is normal for a small amount of electrolyte to
overflow.
Replace the sensor guard.
Polarographic Sensors – Model # 605203
The cap membrane and KCl (potassium chloride) electrolyte solution
should be changed every 2-4 weeks during regular use. In addition, the
electrolyte solution and membrane should be changed if (a) bubbles
are visible under the membrane; (b) dried electrolyte is 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 (figure
11). If either the silver anode is black in color or the gold cathode is
dull, the sensor may need resurfaced using a 400 grit wet/dry sanding
disc included in the membrane kit. Do not sand the electrodes
every membrane change as this is not routine maintenance. In fact,
visually, the anode may appear tarnished and operate properly.
YSI recommends using the sanding disc if the sensor has difficulty
stabilizing or calibrating after a regular membrane change.
To clean and resurface the sensor, follow the instructions below.
Gold Cathode
For correct sensor operation, the gold cathode (figure 11) 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.
First dry the sensor tip completely with lens cleaning tissue. Wet a 400
grit sanding disc and place it face up in the palm of your 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 electrolyte solution under the membrane. Usually,
3 to 4 twists of the sensor are sufficient to remove deposits and for
the gold to appear to have a matte finish. Rinse the sensor thoroughly
with distilled or deionized water and wipe the gold cathode with a wet
paper towel before installing a new cap membrane. If the cathode
remains tarnished, contact YSI Technical Support or the YSI authorized
dealer where you purchased the instrument.
Figure 11, DO sensor with membrane removed.