Yokogawa SC72 Personal Handheld Conductivity Meter - Manual (Page 57)

IM 12D03D02-01E 7-2
7. Measuring Principles of this Instrument
7.2 Principles of Operation
F0702.EPS
AC power supply Ammeter
Figure 7.2 Operational Schematic
Dip two metallic plates (used as sensor electrodes) in a solution and apply a certain
voltage to flow current (I):
I = (1)
E
Rc
where Rc = solution resistance between two sensors
The relationship between Rc and conductivity K is expressed by:
Rc = J • (2)
1
K
where J = constant (also called cell constant) — determined by
sensor and distance between two sensors
From equations (1) and (2) above, we obtain:
K = • I (3)
J
E
E and J are constant, so the conductivity (K) can be obtained by
measuring the current (I).