YSI 55 - Manual (Page 11)

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4.5. Probe Operation and Precautions
1. Membrane life depends on usage. Membranes will last a long time if installed properly and
treated with care. Erratic readings are a result of loose, wrinkled, damaged, or fouled
membranes, or from large (more than 1/8" diameter) bubbles in the electrolyte reservoir. If
erratic readings or evidence of membrane damage occurs, you should replace the membrane
and the KCl solution. The average replacement interval is two to four weeks.
2. If the membrane is coated with oxygen consuming (e.g. bacteria) or oxygen evolving organisms
(e.g. algae), erroneous readings may occur.
3. Chlorine, sulfur dioxide, nitric oxide, and nitrous oxide can affect readings by behaving like
oxygen at the probe. If you suspect erroneous readings, it may be necessary to determine if
these gases are the cause.
4. Avoid any environment which contains substances that may attack the probe materials. Some of
these substances are concentrated acids, caustics, and strong solvents. The probe materials that
come in contact with the sample include FEP Teflon, acrylic plastic, EPR rubber, stainless steel,
epoxy, polyetherimide and the polyurethane cable covering.
5. For correct probe operation, the gold cathode must always be bright. If it is tarnished (which
can result from contact with certain gases), or plated with silver (which can result from
extended use with a loose or wrinkled membrane), the gold surface must be restored. To restore
the cathode, you may either return the instrument to the factory or clean it using the YSI Model
5680 Probe Reconditioning Kit. Never use chemicals or abrasives not supplied with this kit.
6. It is also possible for the silver anode to become contaminated, which will prevent successful
calibration. To clean the anode, remove the O-ring and membrane and soak the probe overnight
in 3% ammonium hydroxide. Next, rinse the sensor tip and KCl reservoir with deionized water,
add new KCl solution, and install a new membrane and O-ring. Turn the instrument on and
allow the system to stabilize for at least 30 minutes. If, after several hours, you are still unable
to calibrate, return the YSI Model 55 system to an authorized service center for service.
7. If the sensor O-ring is worn or loose, replace it with the appropriate O-ring provided in the YSI
Model 5945 O-ring Pack.
8. To keep the electrolyte from drying out, store the probe in the calibration/storage chamber with
the wet sponge.