PASCO CI-6729 (1X) CONDUCTIVITY SENSOR - Manual (Page 8)

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Conductivity Sensor 012–06485B
However when dealing with a chemical solution ranging from extremely
dilute to very concentrated chemical, use of conductivity units of µS/cm and
mS/cm are common. In these applications, conductivity has the advantage
of an almost direct relationship with impurities, especially at low
concentration. Hence, a rising conductivity reading shows increasing
impurities, or a generally increasing concentration in the case of a chemical
stream (with some exceptions in concentrated solutions). See Table 1 for a
comparison of resistance and conductivity.
Conductivity Electrodes (Cells)
Simple conductivity sensors are constructed of an insulating material imbedded
with platinum, graphite, stainless steel or other metallic pieces. These metal
contacts serve as sensing elements and are placed at a fixed distance apart to
make contact with a solution whose conductivity is to be determined. The length
between the sensing elements, as well as the surface area of the metallic piece
determine the electrode cell constant, defined as length/area (Figure 1). The cell
constant is a critical parameter affecting the conductance value produced by the
cell and handled by the electronic circuitry.
A cell constant of 1.0 will produce a conductance reading approximately equal
to the solution conductivity. For solutions of low conductivity, the sensing
Table 1. Conductivity Of Various Aqueous Solutions At 25 0 C
Solution Conductivity Resistivity
Pure water 0.05 µS/cm 18 M
Ω · cm
Power plant boiler water 0.05–1 µS/cm 1–18 M
Ω · cm
Distilled water 0.5 µS/cm 2 M
Ω · cm
Deionized water 0.1–10 µS/cm 0.1–10 M
Ω · cm
Demineralized water 1–80 µS/cm 0.01–1 M
Ω · cm
Mountain water 10 µS/cm 0.1 M
Ω · cm
Drinking water 0.5–1 mS/cm 1–2 k
Ω · cm
Waste water 0.9–9 mS/cm 0.1–1 k
Ω · cm
KCl solution (0.0l M) 1.4 mS/cm 0.7
Ω · cm
Potable water maximum 1.5 mS/cm 0.7
Ω · cm
Brackish water 1–80 mS/cm 0.01–1
Ω · cm
Industrial process water 7–140 mS/cm rarely stated
Ocean water 53 mS/cm rarely stated
10% NaOH 355 mS/cm rarely stated
100/0 H
2
50
4
432 mS/cm rarely stated
31% HNO
3
865 mS/cm rarely stated