Myron L TH1 - Manual (Page 35)

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Figure 15 shows a typical 2
component pair.
Migration does 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 solutions.
(ref. pH, pg. 20).
D. Myron L Integral pH Sensor (TPH1 & TH1)
The sensor in the TechPro II (see figure 16)
is a single 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 formed in a
ring around the pH sensing electrode.
This construction combines all the best
features of any pH sensor known.
E. Sources of Error (TPH1 & TH1)
The basics are presented in pH, pg. 20.
1. Reference Junction
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” setting
at 7 pH. This is why the TechPro II does not allow more than 1 pH unit of
offset during calibration. At that point the junction is unreliable.
2. Sensitivity Problems
Sensitivity is the receptiveness of the glass surface. A film on the surface
can diminish sensitivity and cause a long response time.
3. Temperature Compensation
pH sensor glass changes its sensitivity slightly with temperature, so the
further from pH 7 one is, the more effect will be seen. A pH of 11 at
40°C would be off by 0.2 units. The TechPro II senses the sensor well
temperature and compensates the reading.
KCl solution
Figure 16
Junction plug
Electrode wires
Glass
Sleeve
Glass Surface
Glass surface
Figure 15
KCl solution
Electrode wire
Electrode wire
H + ions
Junction Plug