Conductivity reveals a lot about the degree of purity of a body of water - provided that temperature and substance are correctly taken into account. We show how conductivity can be reliably measured and evaluated - including temperature compensation.
Conductivity is a key measured value in the analysis of water and other liquids. However, depending on the substance and area of application, different aspects need to be taken into account - above all temperature as the biggest influencing factor.
What does conductivity mean?
Conductivity is expressed in microsiemens per centimeter(µS/cm) and describes the ability of a liquid to conduct electricity. The conductance is the reciprocal of the electrical resistance. This means that the higher the conductivity, the lower the resistance - and the more dissolved ions there are in the liquid.
Conductivity measurement in natural waters
Pure water has a very low conductivity of only around 0.055 µS/cm. Water only becomes conductive through dissolved substances such as chlorides, sulphates or mineral salts - to around 500 µS/cm for drinking water. Increased conductivity can indicate contamination and is therefore an important environmental indicator.
Typical areas of application:
- Monitoring of landfills to control groundwater
- Early detection of saltwater intrusion into wells
- Monitoring surface waters for pollution
Please note: Conductivity only provides an initial indication. For a precise analysis, additional chemical tests are necessary - for example for hormones or pesticides, which do not form ions and are therefore not conductive.
Determining flow direction and speed
Another area of application is hydraulic analysis: the conductivity can be artificially increased by adding salt at a specific point. Point measurements along the river or canal then allow conclusions to be drawn about the direction and speed of flow.
Influence of temperature - and why it must be compensated for
Conductivity is strongly dependent on temperature. Two samples of the same liquid can show different conductivity values at different temperatures - without their chemical composition having changed. Temperature compensation is therefore essential for comparable results.
The solution: Modern sensors measure conductivity and temperature simultaneously. Temperature compensation converts the measured conductivity value to a uniform reference temperature - usually 25 °C.
Which compensation function is the right one?
That depends on the substance being analyzed:
- Natural waters: Non-linear compensation according to DIN EN 27888 ("Water quality")
- Salt solutions, acids, alkalis: Linear compensation
The formula for calculating the percentage temperature dependence is
α = (ΔK(T)/ΔT) / K(25°C) * 100Example calculation: Determination of the temperature dependency for a rapid descaler:
- Measurement 1: 122.37 mS/cm at 20 °C
- Measurement 2: 133.10 mS/cm at 25 °C
- Measurement 3: 135.20 mS/cm at 26 °C
Calculation:
ΔK = 135.20 - 122.37 = 12.83 mS/cm ΔT = 26 - 20 = 6 °C K(25 °C) = 133.10 mS/cm α = (12.83 / 6) / 133.10 * 100 ≈ 1.60 %/°CConclusion
Conductivity measurement is a simple and effective method for analyzing liquids - provided that the temperature and medium are taken into account correctly. Whether in environmental technology, water analysis or industry: modern sensor solutions with integrated temperature compensation provide reliable values and therefore enable safe decisions to be made.
