Dissolved Oxygen (D.o.) Probe - Teledyne 4250 Installation And Operation Manual

4.11 Dissolved Oxygen
(D.O.) Probe
The pH sensitive glass can also become "conditioned" to its envi-
ronment, especially when it is continuously exposed to high pH
(10 and above) solutions. The glass does have a memory and will
respond slowly when exposed to a lower pH solution after having
been in a high pH solution for any significant period of time.
Storage of a pH probe in a 4.0 buffer solution is recommended as
this has a regenerative effect on the glass and does not put a
memory on it. Tap water will work if 4.0 buffer solution is not
available. Deionized water is good for quick rinses to clean the
element, but not for prolonged storage of an electrode. Con-
tinuous exposure of the ion-sensitive membrane to a wetted, but
non-ionic solution will improperly condition the membrane.
The reference electrode is also adversely affected when allowed
to dry out. Salt crystals from the electrolyte or precipitates of the
solution measured will form salt bridges, either within or on the
surfaces of the liquid junction, causing the reference to be less
conductive and resulting in a higher reference impedance.
This condition will typically worsen until the unit no longer func-
tions. Soaking the reference electrode in a 4.0 pH solution, or tap
water if the buffer is not readily available, may bring the ref-
erence back to life. Boiling the electrode in 4.0 buffer solution or
tap water could revive the electrode in more severe situations. If
none of these solutions work, it may be necessary to replace the
probe.
This probe measures the amount of oxygen dissolved in a stream
or waterway. Oxygen dissolved in water is necessary for many
forms of life that dwell in lakes and streams. Inadequate supplies
of dissolved oxygen will cause fish and other aquatic life that
depend on them as a food source to die off or be sharply dimin-
ished in numbers. The measurement of dissolved oxygen content
is of interest to those monitoring the condition of lakes and
streams. Fish must have a certain minimum concentration of dis-
solved oxygen to thrive, typically 4 to 6 mg/l.
Various types of pollution can cause the amount of oxygen dis-
solved in water to drop sharply, placing the aquatic life forms at
serious risk. The D.O. probe measures the amount of oxygen dis-
solved in water in a range from 0 to 20 mg/l. Note that the flow
meter can display D.O. in either mg/l (milligrams per liter) or
ppm (parts per million) depending on your choice in pro-
gramming.
Note
The D.O. module has been discontinued. Probes, service kits,
and accessories are still available to maintain existing field
units.
4250 Flow Meter
Section 4 Options and Accessories
4-21