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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