4220 Flow Meter
Section 5 Options and Accessories
5-18
tap water could revive the electrode in more severe situations. If
none of these solutions work, it may be necessary to replace the
probe.
5.10 The Dissolved Oxygen (D.O.) Probe Note
The 270 D.O. module has been discontinued. Probes, service
kits, and accessories are still available to maintain existing field
units.
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.
Figure 5-5 The D.O. Probe
For effective use of the D.O. Probe, please read and con-
sider the following before making the installation:
• The D.O. Probe requires constantly moving water.
The probe consumes oxygen during operation; this will
deplete the oxygen available from stagnant or stratified
waters, resulting in an inaccurate reading. Do not
install it in a stilling well or in any location where water
movement is intermittent or very low. As a guideline, a
minimum velocity of one foot per second is suggested.
• Frequent maintenance is necessary when the probe is
installed in flows with grease or solids content.