Yokogawa DO30G Dissolved Oxygen Sensor - Manual (Page 20)

<4. Maintenance>
4-3
IM 12J5B3-01E
(3) Completely drain the electrolyte within the sensor unit. Tilt the sensor tip downward and then
use the syringe to force air into the inlet for refilling the electrolyte. Position the beaker so it
will catch any of the electrolyte that drains through the gaps around the silver electrode.
Sensor unit
Place a beaker
underneath to catch the
draining electrolyte.
Silver electrode
Syringe
Inlet for refilling electrolyte
Needle (syringe needle)
Insert the syringe needle into
the inlet for refilling electrolyte
and force air inside.
F09.ai
Figure 4.1 Draining the Electrolyte
(4) Hold the sensor level and polish the silver electrode.
Apply an abrasive (alumina) to wet gauze and polish the surface of the silver electrode until
it becomes glossy. After finishing polishing, completely wipe off any abrasive that remains
on the electrode.
(5) Make sure the sealed surfaces are free from dust. Install a new O-ring.
(6) Inject 8 ml of electrolyte into the sensor body with the syringe (see Figure 4.2).
Note: Always use an electrolyte prepared by Yokogawa for exclusive use with the DO30G.
First, fill the sensor with the electrolyte (approx. 9 ml) and then remove approximately 1 ml
so that a layer of air is present inside the sensor body.
(7) Install the permeable-membrane assembly.
It is strictly not possible to allow a layer of air to form between the membrane and the sil-
ver electrode. To prevent such a layer from forming, first apply a drop of electrolyte to the
surface of the silver electrode. Lightly press the permeable-membrane assembly so that the
O-ring touches the groove on the inside. Tighten the locknut fully without letting the assem-
bly turn.
Surface of the silver electrode
Apply a drop of electrolyte when
installing the permeable-membrane
assembly.
Fill with electrolyte
and then remove
approximately 1 ml.
Syringe
Inlet for injecting electrolyte
O-ring
F10.ai
Figure 4.2 Injecting the Electrolyte
All these steps complete the inspection procedure for the permeable-membrane assembly. By
way of precaution, make sure the membrane is free from wrinkling. Note that a stable detection
signal is not possible right after refilling with the electrolyte. Make a zero or span adjustment ap-
proximately a half a day or longer after refilling. It may indicate a minus value for about 10 min-
utes zero adjustment.
4th Edition : Apr 05,2011
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