LaMotte TDS 5 Meter - Manual (Page 4)

4 TDS 5 METER TDS 5 METER 21
What is Conductivity?
Conductivity is defined as the ability of a solution to conduct an electrical
current, or the reciprocal of the solution’s ability to resist the current. This
current is conducted by electrically charged particles called ions, which are
present in almost all solutions. Different solutions have different kinds and
amounts of ions. Distilled water has very few ions, and therefore a low
conductivity, while sea water has a large number of ions, and a high
conductivity.
Although a conductivity reading provides an overall measurement of the
ionic content of a solution, it is not possible to distinguish the specific
amounts of individual ions. For this reason, conductivity is often used to
measure the total dissolved solids (TDS) of a solution. TDS is defined as
the amount of solids which will pass through a 45 micron filter. Rather
than filtering a solution, the TDS can be estimated by multiplying the
conductivity measurement by a predetermined factor. This factor,
which is determined gravimetrically, will fall between 0.55 and 0.9.
A commonly used factor is 0.7.
Conductivity is measured in microsiemens per centimeter (µsiemens/cm).
Siemens are also called mhos. In waters of higher conductivity,
µ
siemens/cm may be multiplied by 1000, giving results as millisiemens per
centimeter (msiemens/cm). Total dissolved solids are measured in parts per
million. Therefore, using the information discussed above:
µ siemens/cm x 0.7 = ppm TDS
Because it is a quick, reliable, and inexpensive way of monitoring the ionic
content of a solution, conductivity measurements are widely used in many
areas of water testing, from environmental monitoring to municipal water
supplies to many industrial applications.