EUTECH INSTRUMENTS CYBERCOMM 5000 FOR CYBERSCAN 5000 Manual de instrucciones descargar pdf (Pagina 170)

Instruction Manual CyberScan PC5500/ 5000

165

Thus comes the term specific conductance or conductivity.

The relationship between conductance and specific conductivity is:

Specific Conductivity, S.C.= (Conductance) ( cell constant, k) =

siemens * cm/ cm2 = siemens/ cm

C is the Conductance (siemens)

K is the cell constant, length/ area or cm/ cm2

Since the basic unit of electrical resistance is the ohm, and

conductance is the reciprocal of resistance, the basic unit of

conductance was originally designated a “mho:- ohm spelled

backwards- however, this term has been replaced by the term

“siemen”. Conductivity measurements are reported as Siemens/ cm,

since the value is measured between opposite faces of a cell of a

known cubic configuration. With most aqueous solutions, conductivity

quantities are most frequently measured in microSiemens per cm

(uS/ cm) or milli-Siemens per cm (mS/ cm).

This meter automatically converts conductivity readings from micro or

milli Siemens to other derived units that are widely used. These are

ppt salinity, ppm TDS (total dissolved solids), and Resistivity.

The salinity scale which ranges from 2 to 42 is a measure of all salts,

not just sodium chloride. This scale was originally devised for

seawater, and is based on seawater at 15 °C having a conductivity

equivalent to that of a potassium chloride solution of a known

concentration. This solution (0.44 molal) is defined as having a

salinity of 35 ppt.

The total dissolved solids scale approximates the ppm TDS in surface

waters by multiplying the conductivity of a sample by a factor, 0.66.

Some users prefer the use of Resistivity units to describe their water,

particularly where high purity water is involved. The unit most often

used to describe Resistivity is megohm.cm, which is simply the

reciprocal of conductivity (uS/ cm). The chart below shows the

relationship between these units.

Conductivity, µS/cm Resistivity, megohmcm

0.056

0.1

1.0

2.5

10.0

1.0

0.4

0.1

1 2 ... 165 166 167 168 169 170 171 172 173 174 175 ... 181 182

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EUTECH INSTRUMENTS CYBERCOMM 5000 FOR CYBERSCAN 5000 Manual de instrucciones Pagina 170