Conductivity Measurement Basics For The Process Industry
The ability of a substance (or solution) to convey an electrical current is determined by its electrical conductivity. Since many years ago, conductivity has been one of the process industry’s most widely used analytical metrics.
Measurements of conductivity represent the total amount of dissolved ionic activity present in a sample solution. This is significant since the measurement method cannot distinguish between particular ions. Conductivity measurements are used in every sector to keep track of water quality, process concentrations, solution cooling breakthroughs, and even wastewater discharge into local streams and rivers. The measurement procedure is accurate, repeatable, and affordable to produce. Conductivity is also affected by process temperature. Integral temperature detectors are a feature of electrodes that allow for continuous measurement and adjustment of the measured value.
The three most popular ways to measure conductivity are examined in the following bullet points, along with the advantages of each measurement methodology.
Two-Electrode Conductivity Measurement Principle
The most popular sensors on the market are two-electrode conductivity sensors, sometimes known as “contacting conductivity” sensors. They are made up of two electrodes spaced at a specific distance from one another. Current between the electrodes is induced when they are submerged in a sample solution. The current increases with the amount of ions in the sample solution, which raises the conductivity value of the solution.
However, the geometry of the two electrodes plays a crucial role in determining the conductivity. The cell constant is the geometric composition. It is both the separation between the two electrodes and the surface area of each electrode. The most crucial element in determining your sensor’s measurement range is the cell constant. The measurement range is tighter the lower the cell factor is (for example, 0.03/cm for high purity applications 0-1,000 S/cm), while the measurement range is wider the higher the cell constant is (for instance, 1.0/cm for typical applications 10 S/cm – 20 mS/cm).
Four-Electrode Conductivity Measurement Principle
Two additional electrodes are added to the sensor by a four-electrode conductivity cell. A current flows through the sample media when an AC voltage is applied to the outermost pair of electrodes. The conductivity of the sample determines how much potential difference is measured by the two innermost electrodes, which are “current-less” electrodes. Afterward, the transmitter takes into account the recorded potential difference and the supplied current. Next, a conductivity measurement that is unaffected by “polarisation” is provided. For applications requiring a wide measurement range, four-electrode conductivity sensors are excellent.
Inductive/Toroidal Conductivity Measurement Principle
“Non-contacting” is a term that is sometimes used to describe an inductive or toroidal conductivity sensor. This is due to the technology’s lack of electrodes that come into contact with the process directly. Two tightly wrapped metal toroids are used in toroidal sensors. These toroids were enclosed in a plastic body that was corrosion resistant. The sensor adjusts measured values using an integrated temperature detector located inside the plastic body.
As the “drive” coil, the first toroid receives an alternating voltage. This produces a voltage that causes an ionic current to flow proportionate to the liquid’s conductance in the liquid around the coil. The “receive” coil is the second coil. Your transmitter measures the electric current that is created when the ionic current is converted to electricity. Due to their resistance to accumulation, toroidal conductivity sensors have a wide measuring range and are excellent for use in filthy settings. We frequently utilise these types of sensors in concentration applications due to their large measuring range.
Summary
Conductivity sensors are crucial in process applications across a wide range of sectors, whether it’s preventing corrosion and scaling in your process or keeping track of the water’s cleanliness. Simply put, choosing the right sensor for your application will depend on your awareness of the key distinctions between the three conductivity measurement technologies.
