What is Conductivity?

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Electric Conductivity is a quite a comprehensive and difficult subject and there are many publications that cover the topic in depth. For the purpose of this article, we will discuss the fundamentals of conductivity to give you a basic understanding of conductivity and conductivity meters. With the introduction of the SI (International Systems of Units), “Electric Conductivity” has been adopted as the standard formal term, but in practice, the word “Conductivity” on its own is commonly used. We will refer to Electric Conductivity as EC throughout this article which is a common abbreviation.

What is Conductivity?

EC measures the ability for a material to conduct electricity meaning how well can the liquid carry an electric current through it. When looking at EC in water or liquid, we will generally find water in it’s natural state such as rain, lake water, rivers etc. will have a low level of EC (pure water has no EC). When water is subject to pollution, contamination, or impurities, we will see a change in the EC of that water as the dissolved substances increase the level of EC. As such, EC can be a good indicator of pollution in water. It is worth noting, however, that impurities such as salt in seawater for example, cause very high EC readings as the water contains a large amount of dissolved salt. This is because when salt is dissolved, it separates into ions (electrically charged atoms).

Conductivity is usually measured in microSiemens (µS/cm) and readings generally fall between 30 µS/cm to 2000 µS/cm. Seawater, for example, will have a reading of approximately 50,000 µS/cm. An interesting fact worth mentioning is that conductivity will actually increase when the temperature of the water increases, hence EC is commonly recorded at a 25°C with temperature and EC being recorded simultaneously. Another unit of measurement for EC is mS/cm or milliSiemens per centimetre. 1 mS/cm = 1000 µS/cm and you will often find measurements displayed as mS/cm for higher levels of EC (i.e. 2000 µS/cm or more).

How to Measure EC?

In general, the conductivity of a solution varies significantly depending on the temperature of the liquid. When carrying out conductivity measurements, liquid temperature should be controlled as accurately as possible.

  • Measurement using a constant temperature bath: Carry out measurements whilst maintaining the sample liquid temperature at 25°C using a constant temperature bath. To ensure that the cell temperature is equal to the sample liquid temperature, immerse the cell in the sample for an appropriate period prior to performing measurements.
  • Measurement at room temperature: When carrying out measurement at room temperature, avoid locations where the temperature may change. To ensure that the cell temperature is equal to the sample liquid temperature, immerse the cell in the sample for an appropriate period prior to performing measurements.

When measuring EC, please ensure that you:

  • Use a thoroughly cleaned conductivity cell.
  • Immerse the cell in the sample such that the electrode plates are completely submerged in the liquid.
  • If air bubbles remain between the outer cylinder and supporting tube, remove them by shaking the cell.

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