27
26
•
Make sure that the rubber O-ring sits
properly inside the membrane cap.
•
With the sensor facing down, slowly
screw the membrane cap clockwise.
Some electrolyte will overflow.
The platinum cathode should always be
bright and untarnished.
If it is tarnished or stained, which could be
due to contact with certain gases or ex-
tended use with a loose or damaged mem-
brane, the cathode should be cleaned. Use
a clean lint-free cardboard or cloth. Rub
the cathode very gently side to side 4-5
times. This will be enough to polish and
remove any stains without damaging the
platinum tip.
Afterwards, rinse the probe with deionized
or distilled water, and install a new mem-
brane cap using fresh electrolyte and fol-
low the above procedure.
Re-calibrate the instrument.
Important: For accurate and stable mea-
surements, it is important that the surface
of the membrane is in perfect condition.
This semipermeable membrane isolates the
sensor elements from the environment but
allows oxygen to enter. If any dirt is ob-
served on the membrane, rinse carefully
with distilled or deionized water. If any
imperfection still exists, or any damage is
evident (such as wrinkles or tears-holes),
the membrane should be replaced.
Make sure that the O-Ring sits properly in
the membrane cap.
PROBE & MEMBRANE MAINTENANCE
The DO probe body is made of reinforced
plastic for maximum durability.
A built-in thermistor temperature sensor pro-
vides temperature measurements. It is al-
ways recommended to keep the protective
cap on the probe when it is not used, to
provide protection against damage and dirt.
To replace the membrane or refill with
electrolyte, proceed as follows:
•
Remove the protective
cap by gently twisting
and pulling it off the
probe body (fig.1).
•
Unscrew the membrane
cap by turning it coun-
terclockwise (fig.2).
•
Wet the sensor by
soaking the bottom (2.5
cm / 1") of the probe
in HI 7041S electrolyte
for 5 minutes.
•
Rinse the new mem-
brane (HI 76407A, sup-
plied with the meter)
with electrolyte solution
while shaking it gen-
tly. Refill with fresh
electrolyte solution.
•
Gently tap the sides of
the membrane cap with
your finger to ensure
that no air bubbles re-
main trapped. Do no di-
rectly tap the bottom
with your finger as this
will damage the mem-
brane.
TWIST
AND
PULL
fig. 1
UNSCREW
fig. 2
