Conductivity/TDS

Electrical Conductivity sensors are used to measure the ability of water to carry an electrical current. Absolutely pure water is a poor conductor of electricity. Water shows significant conductivity when dissolved salts are present. Over most ranges, the amount of conductivity is directly proportional to the amount of salts dissolved in the water.

The amount of mineral and salt impurities in the water is called total dissolved solids (TDS). TDS is measured in parts per million. TDS tell how many units of impurities there are for one million units of water. For example, drinking water should be less than 500 ppm, water for agriculture should be less than 1200 ppm, and high tech manufactures often require impurity-free water. One way to measure impurities in water is to measure the electric conductivity of water.

A conductivity sensor measures how much electricity is being conducted through a centimeter of water. Specific conductivity is expressed as mhos per centimeter (M/cm), sometimes called siemens per centimeter (S/cm). Because a mho (or siemen) is a very large unit, the micromho (microsiemen) or millimho (millisiemen) typically is used (mS/cm).

To convert the electric conductivity of a water sample (mS/cm) into the approximate concentration of total dissolved solids (ppm), the mS/cm is multiplied by a conversion factor. The conversion factor depends on the chemical composition of the TDS and can very between 0.54 – 0.96. A value of 0.67 is commonly used as an approximation if the actual factor is not known [(TDS)ppm = Conductivity µS/cm x 0.67].

Since conductivity varies with temperature, it is necessary to correct the readings for changes in temperature. Most instruments contain circuits that automatically compensate for temperature and correct the readings to a standard 25°C.

Sensors for Water Conductivity / TDS Measurement

The following sensors are sold by Stevens for the measurement of conductivity or total dissolved solids. Click on any product to learn more.

Schlumberger CTD-Diver

Schlumberger CTD-Diver

The Schlumberger CTD-Diver is a small, self-contained water level sensor that can also monitor conductivity (10 ÁS/cm to 120 mS/cm range) and temperature. It features an internal data logger and battery that can operate for up to 10 years.

Greenspan EC 3000

Greenspan EC 3000

The Greenspan EC 3000 is a water conductivity and temperature sensor that has been designed to handle a wide measurement range of 0-1,000 ÁS/cm to 0-70,000 ÁS/cm. The sensor can be configured with an internal battery and data logger for stand-alone measurement.

Greenspan CTDP 1200

Greenspan CTDP 1200

The Greenspan CTDP 1200 is a multi-parameter sensor that can monitor conductivity, temperature, depth, and pH. The sensor features internal logging and SDI-12 output.

Hydrolab DataSonde 5 Series

Hydrolab DataSonde 5 water quality probeHydrolab MiniSonde 5 water quality probe

The Hydrolab DataSonde 5 series of water quality probes can be configured to measure any one of 15 water quality parameters, including conductivity. The Hydrolab DataSonde can be deployed to log internally or output the data to an external logger or telemetry system.

Return to the Stevens Water Quality Analyzers and Sensors Overview