D.1.4 Sources Of Error - Hach MP-4 User Manual

Additional information on pH and ORP (MP-6 and MP-6p models)
1 Glass surface
+
2 H ions
3 Junction plug
4 Platinum button

D.1.4 Sources of error

D.1.4.1 Reference junction
The most common sensor problem is a clogged junction because a sensor is
allowed to dry out. The symptom is a drift in the zero setting at pH 7. This explains
why MP series meter does not allow more than one pH unit of offset during
calibration.
D.1.4.2 Sensitivity errors
Sensitivity is the receptiveness of the glass surface. A film on the surface can
diminish the sensitivity and cause a long response time.
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Figure 10 pH/ORP sensor construction
.
5 KCl solution
6 Glass
7 Electrode wires