4210 Flow Meter
Section 4 Optional Equipment
4-20
7. Trim off excess membrane with scissors or a sharp knife.
Check to see that the stainless steel rod (thermistor) pro-
truding below the liquid cup is not covered by extra mem-
brane.
Note
There must be no bubbles under the membrane and no
creases in it for the probe to function correctly.
8. Shake any excess KCl solution from the probe. Reinstall
the sensor guard. Keep the sensor in a humid environment
when not in use and between measurements. The plastic
bottle that was placed over the end of the sensor when it
was shipped is ideal for this purpose. Place a piece of moist
tissue inside the bottle, and slide the bottle over the probe.
4.11.3 Membrane
Thicknesses
Isco supplies a 2 mil (.002") thick membrane for use with the
D.O. probe. This membrane is recommended for long-term moni-
toring situations only, typical of our users' applications. Use only
this thickness of membrane with D.O. probes connected to Isco
flow meters. Do not use other thicknesses of membranes, as the
Parameter Module used with the probe is calibrated only for the
2-mil membrane, and cannot be recalibrated in the field. Using
other membrane thicknesses will result in inaccuracy. Thinner
membranes are also very fragile and difficult to install.
4.11.4 D.O. Probe Installation The D.O. probe attaches to a sensor carrier bracket that snaps
into an Isco mounting ring. Use the specific size of Spring Ring
for pipes less than 15" in diameter, and the Scissors Ring for pipe
sizes greater than 15" diameter. Refer to the instruction sheet
supplied with the mounting ring.
Note
When installing the D.O. probe and its sensor carrier bracket,
make sure the mounting slots on the sensor carrier are com-
pletely pressed into the mating tabs on the ring. The probe
relies on a full engagement between tabs and slots for secure
mounting. If the slots are loose against the tabs, the probe may
be swept away by the force of the stream.
4.11.5 Probe Operation and
Precautions
The following factors determine the life of the D.O. probe and the
frequency of service.
• Membrane life depends on use. Membranes will last
longer if installed properly and treated with care during
use. Contents of the flow stream are also important, as
some substances will foul the membrane very quickly.
Erratic readings will result from loose, wrinkled or
fouled membranes, or from large bubbles in the
electrolyte reservoir. If erratic readings or evidence of
membrane damage occur, you should replace the
membrane and the KCl electrolyte.
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