Why is conductivity measurement important in water treatment?
The conductivity of water is extremely important when treating drinking water or industrial water because it gives an indication of the amount of dissolved material within that water.
Process Instruments supplies a range of high-quality low-cost conductivity sensors to cover the full range from deionized water all the way up to highly saturated brines.
Coupled with Pi’s controllers these sensors provide excellent and cost-effective process control in all industries and applications.
Conductivity sensors measure the ability of solutions to conduct electrical current. This is related to the ionic species that are present in that solution and can be defined as ‘the conductance in a given volume’.
Although they are similar terms which are related, conductance is more general in that it refers to a solutions ability to conduct electric current, whereas conductivity refers to conductance in a given volume. This is evidenced in the units of conductivity, which is usually measured in μS/cm or μΩ/cm.
All three models of ConductiSense have integrated temperature compensation as standard, so although changes in temperature do affect conductivity readings this is accounted for in your Pi hardware and firmware. ConductiSense will remain accurate despite temperature changes.
Conductivity measurement is not restricted to aqueous solutions. The solution being measured may affect the choice of sensor (organic compounds such as petroleum products have very low conductivities, for example), and safety can also be a concern, such as when measuring flammable liquids.
In practical terms, the cell constant (K value) refers to the distance between the electrodes within the sensor, with a lower number meaning a smaller distance. It is calculated by dividing the area (a) normal to the current flow squared by the distance (d) between the electrodes. Low K value sensors are used in lower conductivity solutions, where the smaller distance raises the conductance allowing for easier measurement. The opposite is true in high conductivity solutions, where a larger K value may be more suitable. Pi sensors are available in K values of 0.1, 1 and 10.
Creating a standard solution yourself, which matches your sample stream more accurately, is a way to get a more accurate calibration. A proportional mixture of salts based on your sample stream can be added to distilled water, where 1mg of your salt mixture 1l of distilled water will yield a 1ppm TDS solution. Try to produce a standard that is close to your expected sample in concentration, or If you expect a great deal of variation make a solution that is in the upper third of the sensor range.
Micromhos (µ℧/cm) and microsiemens (μS/cm) are the same. The former is more common in the U.S. and the latter is more common in Europe, but the two terms can be used interchangeably.
Agitate your sensor in a mild detergent or dilute nitric acid (0.1M) solution for a few minutes and then rinse with clean water. This should be sufficient, but dilute solutions of sulfuric or hydrochloric acid can also be used to remove any fouling if required.
The sensor can be stored wet or dry, but rinse with clean tap water when removing the sensor from the sample stream. Please note that if storing the sensor dry, the electrodes will need to be reconditioned before being used again.
Ensure that power is running to the sensor, and give it a short (30-60 mins) soak in a standard solution (tap water will also suffice) before use.
Salinity is a measure of the amount of salts in water, and so it is related to conductivity. A correction factor can be used to convert between these units, from microsiemens to the ppm of a specific salt.
It is often possible to integrate other sensors into Pi hardware. Please contact a member of our team, and we will be happy to discuss this with you.
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