Temperature compensated conductivity measurement from Foxboro

December 2018 Analytical Instrumentation & Environmental Monitoring

Measuring the conductivity of a liquid can reveal the concentration of salts dissolved in the solution. In fact, conductivity is often the method of choice for measuring the amount of salts dissolved in water – the salinity of natural water. When seawater mixes with fresh water the conductivity measurement can tell how much of each is present, referred to this as the percentage or concentration of seawater.

Thousands of process control applications involve solutions of an electrolyte in water or other solvent. From a conductivity measurement it is possible to monitor and control such solutions. It is a fairly simple, fast and accurate method. When measuring conductivity and converting this into a percentage concentration, the instrument will have programmed into it a predetermined conductivity vs concentration curve.

Temperature dependence

However, the temperature of the sample liquid also needs to be taken into account. This is essential because the conductivity reading changes with temperature, so it is important to know if it is the temperature or conductivity of the process that is varying.

To solve this problem, Foxboro has introduced its new 876EC conductivity transmitter, in which a temperature compensated conductivity measurement is performed and the concentration calculated in accordance to the chemical periodic table against a range of specific chemicals with predetermined curves.

The displayed value is referred to as the compensated percentage of the chemical concentration range. Using the Foxboro 876EC, this is determined by simply measuring the conductivity value.

For more information contact Johan van Jaarsveldt, EOH, +27 87 803 9783, [email protected], www.eoh-pas.co.za

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