Teledyne 4250, Installation And Operation Manual, Page: 133 / 204

4250 Flow Meter
Section 4 Options and Accessories
4-23
4.11.2 Probe Preparation The following describes how to prepare a new probe for use, or
how to change membranes on an existing probe. First, unscrew
the sensor guard; remove the O-ring and membrane, then thor-
oughly rinse the sensor with distilled water. Prepare the KCl
electrolyte according to the directions on the bottle. Use distilled
water only. You install the membranes by hand. The probe is
shipped with a small folder containing several replacement mem-
branes.
Steps for installing a new membrane:
1. Secure the probe body so it is in an upright position. You
can use a vise, adjustable wrench, or locking pliers, etc.,
whatever is satisfactory. Do not apply too much force to the
probe body, or you will crack it.
2. Fill the cavity around the silver anode with electrolyte to
the point where any more electrolyte would spill over. The
liquid should be free of bubbles and should completely
cover the tip of the sensor.
3. Lightly lay the membrane across the top of the probe. If
you do this carefully, there will be no bubbles under the
membrane.
Note
Handle the membrane material with care, touching it at the
ends only.
4. Place the O-ring on top of the membrane, generally con-
forming to the circumference edge of the probe.
5. Place the thumb and index finger from both hands opposite
each other on the O-ring at equal distances.
6. Roll the O-ring down over the end of the probe, being care-
ful not to touch the membrane where it covers the probe.
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
Teledyne Isco supplies a 2 mil (.002") thick membrane for use
with the D.O. probe. This membrane is recommended for
long-term monitoring situations only, typical of our users’ appli-