From Flow Measurement
|This property is of importance when considering magnetic flowmeters. In most|
designs, the meter is able to detect flow only if the liquid is capable of conducting
electricity to a small extent. Organic liquids such as oils and hydrocarbons are
almost perfect insulators with no significant conductivity. In most cases they cannot
be measured by magnetic meters. The minimum conductivity is always specified
by the manufacturer, and it is very important to be sure the liquid is
sufficiently conductive. A spot check for conductivity sometimes indicates that it
is high enough, but it is quite possible that, at times, the material changes and the
meter can fail to operate.
|When conductivity is borderline, be sure to make a number of tests at different times — not just once or twice.|
The dimensional units for conductivity are usually given as micromhos/cm,
micromhos/cm3, or siemens (S). Surprisingly, all these mean the same thing; they
refer to the conductance between two plates, one cm2 in area and one centimeter
apart, with the liquid in between them.
Sometimes data is presented as “resistivity” rather than “conductivity.” The two
terms are merely reciprocals of each other, and the units of resistivity are...
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