Manual

44
The problem is, on the other side of the membrane is an unknown test
solution, not potassium chloride. The outside electrode, also called

plug in place of a glass barrier to


migration of liquids through the plug


occur, and this limits the lifetime of a
pH junction from depletion of solution
inside the reference junction or from
contamination. The junction may
be damaged if dried out because
insoluble crystals may form in a
layer, obstructing contact with test

4. 
The sensor in the Ultrameter II

construction in an easily
replaceable package. The sensor
body holds an oversize solution
supply for long life. The reference
junction “wick” is porous to provide
a very stable, low permeable
interface, and is located under the
glass pH sensing electrode. This
construction combines all the best
features of any pH sensor known.
 
The basics are presented in

a. 
The most common sensor problem will be a clogged junction because
a sensor was allowed to dry out. The symptom is a drift in the “zero”
II 6Psi does not allow more
than 1 pH unit of offset during calibration. At that point the junction is
unreliable.
b. Sensitivity Problems

can diminish sensitivity and cause a long response time.
Glass surface
Figure 33
KCl solution
Electrode wire
Electrode
wire
H
+
ions
Junction
Plug
KCl solution
Figure 34
Junction plug
Platinum button
H
+
ions
Electrode wires
Glass
Glass
Surface