ELECTROLYTE REPLACEMENT: It is recommended that the electrolyte be replaced every 12 months. Of
course, a damaged membrane will cause replacement to be required sooner. Exhaustion of electrolyte
indicated when the instrument loses sensitivity and cannot be brought to the proper meter reading during
calibration, or by excessive drift of the calibration setting. To replace the electrolyte, remove the filling screw.
Tip the sensor so that the fill hole faces downward and shake out the electrolyte. Refill completely as described
above and tighten fill screw.
REPLACING THE MEMBRANE : The sensor has a screw-on membrane cap. It does not have to be replaced
except in the event the membrane has become torn or punctured, or is being replaced due to slow response as
described below. Use one of the replacement caps supplied in the No. 824240 Refill Membrane Kit. The kit
contains 3 membrane caps, and a 4 oz. bottle with dropper cap, of No. R-448. Unscrew the old membrane
cap. Flush the tip of the sensor with distilled water and wipe clean. Place 5 to 9 drops of R-448 Electrolyte into
a new membrane cap. Holding the sensor with the tip facing downwards, screw the membrane cap in place,
from below. Tighten the cap slowly, but thoroughly, using finger pressure only. Do not use tools. Refill the
reservoir if necessary.
When the new cap has been screwed fully into place, the membrane becomes
correctly stretched across the slightly curved cathode. Once so stretched, it would
become "too loose" if the cap were unscrewed, even partially. For this reason,
NEVER unscrew the membrane cap, even partially, unless it is being completely
replaced. It is important. to instruct all personnel NOT to tamper with the cap,
because once loosened, it must be fully removed and discarded! Loosened
membranes can cause sluggish responses, and faulty reading!
Used membrane caps can be rebuilt, consult the factory.
After replacing membrane-cap, turn the instrument on for at least 30 minutes to stabilize the sensor, and then
re-calibrate. Low sensitivity or slow response indicates an improperly installed membrane-cap. Replace with a
The membrane need be changed only when accidentally torn or punctured, no matter how long the sensor has
been in service. Occasionally the membrane may develop a tear or pin hole which cannot be seen with the
naked eye. This will result in a sudden rise in reading, even over the top of the meter. Should this occur,
replace the membrane promptly, to avoid depletion of the electrolyte. Refill the sensor with fresh electrolyte.