37
3.2
Dissolved Oxygen Sensor Maintenance
Membrane Cap Installation
The DO sensor (Polarographic and Galvanic) is shipped with a dry, protective red cap that will need to be removed before using.
Remove the protective cap or used membrane cap and replace it with a new membrane cap following these instructions:
Polarographic Sensors
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 to resurface the electrodes if the sensor has difficulty
stabilizing or calibrating after a membrane change.
To resurface the sensor using the fine sanding disk, 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 not recommended or supplied by YSI.
First dry the sensor tip completely with lens cleaning tissue. Wet a sanding disk
with a small amount of clean water and place it face up in the palm of your hand.
Sensor Maintenance
1.
Remove the sensor guard to access the sensor tip.
2.
Unscrew and remove any old membrane cap by holding the sensor when
unscrewing the membrane cap and discard.
3.
Thoroughly rinse the sensor tip with distilled or DI water.
4.
Fill a new membrane cap with O2 sensor 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 membrane cap to
release bubbles that may be trapped.
5.
Thread the membrane cap onto the sensor. It is normal for a small amount
of electrolyte to overflow.
Figure 56
Installing the
membrane cap
