How Do Conductivity Meters Work?

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A conductivity meter is an essential measuring tool for a range of applications and industries. When the probe (attached to the conductivity meter) is inserted into the solution, an electrical current flows between the electrons inside the probe which reads the electrical current, providing a conductance value. 

Electrical Conductivity or (EC) measures the ability of a material to transmit an electrical current over a certain distance, usually measured in Siemens (S) per distance. When the number of dissolved ions (charged particles) in a solution increases, so does the solution’s ability to carry an electrical charge. A conductivity meter reads the electrical charge and measures the conductance. 

How Does A Conductivity Meter Work?

Conductivity is the measurement of the electrical current of a solution, most commonly measured in microSiemens per centimeter (µS/cm). 

Conductivity values depend on the ionic strength of the solution, the ions present, and the ion concentration. As the temperature can affect a solution’s conductivity, calibration is required before use. 

A conductivity meter emits an electrical charge via a conductivity probe, which is dipped into the solution being tested. If there is an increase or decrease in the number of dissolved ions, it will result in an increase or decrease in the electrical charge. A conductivity meter can measure this charge, and provide you with the solution’s conductance. 

When the probe is inserted into the solution, an electrical current flows between the two electrons inside the probe, set apart at a specific distance. The ion concentration in the solution is what determines if the conductance is high or low. If the ion concentration is high, the higher the conductance will be, which results in a faster current. If the electrical current is slow, the conductance value will be lower because the concentration of ions in the solution is less. 

How Do Amperometric & Potentiometric Conductivity Meters Work?

Many manufacturers have produced different probes over the years to cover a wide range of applications and industries. 

Conductivity probes and circuits measure conductivity by applying a voltage between electrodes within a probe. The probes not only measure conductivity, but they are also able to report a temperature-compensated conductivity value.

All conductivity meters measure the conductance between electrodes using either the potentiometric or amperometric method. It is also important to note that conductivity meters do not provide you with the direct measurement of the number of ions in the sample, it only infers the ion number by measuring the electrical charge within the solution. 

Potentiometric: Four-electrode Probes

Potentiometric conductivity meters contain four platinum rings on the probe’s electrode body. The outside rings apply an alternating voltage to the sample you are testing, which produces a current. The rings in the center of the probe measure the current’s potential drop which is generated by the outside rings, producing an EC reading on the conductivity meter. The EC is directly related to the solution’s ion concentration, therefore, the voltage is dependent on dissolved ion concentrations within the solution. 

So, when you place the four-electrode probe into the solution, the current flows from ring 1 to ring 4, which passes the voltage across to rings 2 and 3. 

Conductivity meters also can measure the amount of total dissolved solids (TDS) in a solution, measured in milligrams per liter (mg/L) or parts per million (ppm). So, by measuring conductivity we are able to determine the overall health of water bodies. 

Potentiometric Conductivity Probe

Amperometric: Two-electrode Probes

Amperometric conductivity meters contain a probe made from a non-reactive material, and built, so the two electrodes can be in contact with the solution being tested, at the same time. 

Amperometric meters contain two electrodes with a fixed surface area, at a fixed distance from each other. The distance and surface area are known as the conductivity cell. The cell distance and surface area are known as the “conductivity cells K-constant”. 

Inside the conductivity probe, the two electrodes are positioned opposite to each other. An alternating current (AC) voltage is applied to the electrodes, which causes the cations to move to the negatively charged electrode, while the anions move to the positively charged electrode within the probe. The more ions present in the solution, the higher the EC will be.

When measuring conductivity, the entire conducting area in the probe must be submerged to get accurate readings. It is also best to have a temperature probe during calibration to ensure the solution is as close to 25 °C, because of the dependence conductivity has on temperature. This once again raises the importance of always calibrating the conductivity probe before use.

Amperometric Conductivity Probe

What Applications & Industries Use Conductivity Meters? 

Measuring conductivity is important for a wide range of applications, such as:

  • Standard lab use
  • Field use 
  • Aquariums & Aquaculture
  • Hydroponics
  • Mixed aqueous/organic
  • Samples containing heavy metals
  • Soil samples
  • Strong reducing agents

When measuring conductivity, the use of temperature sensors, pH probes, and dissolved oxygen (DO) sensors to analyze water quality is also required. 

Agriculture & Hydroponics

In the agricultural industry, conductivity meters are heavily used to measure salinity levels, dissolved nutrients, and dissolved solids in soil samples and surface water. The agriculture industry can then use this to work out if more fertilizer or water needs to be added to soils. 

Aquariums & Aquaculture

Salinity is a vital parameter to test in aquatic systems as it can affect osmoregulation in fish. Salinity can be tested with a conductivity and pH meter. If you are using a conductivity meter with a conversion feature built-in, you can convert TDS or salinity very easily.

Industrial Applications & Water Treatments

Water must be tested to ensure it is safe for drinking, or it is suitable for industrial applications. As conductivity can estimate dissolved metals in water, a conductivity meter can be used to prevent corrosion of equipment, such as water pipes. 

Conductivity meters can also be used to measure desalinization to ensure water is safe to drink, and detect leaks in heat exchangers and boilers.

Summing Up

When the probe attached to the conductivity meter is inserted into the solution, an electrical current flows between the electrons inside the probe. If the ion concentration of the solution being tested is high, the higher the conductance will read, which results in a faster current, and vice versa.
If you would like to learn more about conductivity, or what conductivity probe best suits your needs, do not hesitate to contact our world-class team at Atlas Scientific.

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