YSI 556 MPS - Manual (Page 96)

YSI Incorporated YSI 556 MPS Page 90
11. Maintenance
11.1 Sensor Care and Maintenance
Once the sensors have been properly installed, remember that periodic
cleaning and DO membrane changes are required.
11.1.1 DO Sensor
For best results, we recommend that the KCl solution and the membrane cap
be changed at least once every 30 days.
1. It is important to recognize that oxygen dissolved in the
sample is consumed during sensor operation. It is therefore
essential that the sample be continuously stirred at the sensor
tip. If stagnation occurs, your readings will be artificially low.
Stirring may be accomplished by mechanically moving the
sample around the sensor tip, or by rapidly moving the sensor
through the sample. The rate of stirring should be at least 1
foot per second.
2. 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 electrolyte solution. The average replacement interval
is two to four weeks.
3. If the membrane is coated with oxygen consuming (e.g.
bacteria) or oxygen producing organisms (e.g. algae),
erroneous readings may occur.
4. Chlorine, sulfur dioxide, nitric oxide, and nitrous oxide can
affect readings by behaving like oxygen at the sensor. If you
suspect erroneous readings, it may be necessary to determine
if these gases are the cause.
5. Avoid any environment that contains substances that may
attack the probe module and sensor materials. Some of these
substances are concentrated acids, caustics, and strong
solvents. The sensor materials that come in contact