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Thus in the past, megohm-cm was used, sometimes abbreviated to "megohm". Sometimes, conductivity is given in "microsiemens" (omitting the distance term in the unit). While this is an error, it can often be assumed to be equal to the traditional μS/cm. Often, by typographic limitations μS/cm is expressed as uS/cm.
The siemens (symbol: S) is the unit of electric conductance, electric susceptance, and electric admittance in the International System of Units (SI). Conductance, susceptance, and admittance are the reciprocals of resistance, reactance, and impedance respectively; hence one siemens is equal to the reciprocal of one ohm (Ω −1) and is also referred to as the mho.
Transresistance (for transfer resistance), also infrequently referred to as mutual resistance, is the dual of transconductance. It refers to the ratio between a change of the voltage at two output points and a related change of current through two input points, and is denotated as r m:
Conductivity μS/cm Conductivity mS/m As chloride μg/cm2 As chloride mg/m2 As sodium chloride μg/cm2 As sodium chloride mg/m2 As mixed salts μg/cm2 As mixed salts mg/m2 1 0.1 0.36 3.6 0.6 6 0.5 5 5 0.5 1.8 18 3 30 2.5 25 10 1 3.6 36 6 60 5 50 20 2 7.2 72 12 120 10 100
where TDS is expressed in mg/L and EC is the electrical conductivity in microsiemens per centimeter at 25 °C. The conversion factor k e varies between 0.55 and 0.8. [5] Some TDS meters use an electrical conductivity measurement to the ppm using the above formula. Regarding units, 1 ppm indicates 1 mg of dissolved solids per 1,000 g of water. [6]
For example, since electric field strength is voltage per unit length, its unit is the volt per centimetre, which is one hundred times the SI unit. The system is electrically rationalized and magnetically unrationalized; i.e., 𝜆 = 1 and 𝜆′ = 4 π, but the above formula for 𝜆 is invalid.
The amount of sweat glands varies across the human body, being highest in hand and foot regions (200–600 sweat glands per cm 2). [19] The response of the skin and muscle tissue to external and internal stimuli can cause the conductance to vary by several microsiemens. A correctly calibrated device can record and display the subtle changes. [21]
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