What is TDS / Conductivity?

Conductivity is an expression of the ability of a solution to conduct electric current. It is expressed as a microsiemen (micro-Siemens per centimeter or µS/cm) or in higher conductivity levels as a millsiemen . 1000 µS/cm are equal to 1 mS/cm. Some industries such as water treatment have adopted a measurement expressed as TDS (Total Dissolved Solids). TDS is approximated with conductivity using a multiple factor and is expressed in parts per million (ppm).

How is TDS / Conductivity Measured?

Conductivity is measured with two surfaces in contact with the sample. These surfaces can be constructed of graphite, stainless steel, platinum and other similar materials. An AC voltage waveform is sent through one contact of the sensor (Sending) and passes through the liquid being measured. The second contact surface (Reciever) receives the signal. The resulting measurement determines the conductivity of the water and is displayed on a conductivity instrument which expresses the measurement as microsiemens, millisiems or total dissolved solids (ppm).

Another sensing method uses an inductive 2-coil system encapsulated in a plastic case to send and receive the signal from the instrument. This inductive system, known as a toroidal conductivity sensor, can eliminate polarizing effects that may affect the measurements of a contacting conductivity probe.

How is TDS Conductivity EC measured

Why is TDS / Conductivity Measurement Necessary?

From controlling biocide and scaling in cooling towers and boilers to the water you drink, conductivity plays a part in a multitude of applications across many industries.

Common Applications:

  • Monitoring reverse osmosis (RO)
  • Chemical concentration monitoring
  • Cooling tower & boiler protection
  • Environmental monitoring
  • Industrial effluent monitoring
  • Control of activated sludge process
  • Profiling conductive dissolved solids content in water


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