JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD B.Tech IV ANALYTICAL INSTRUMENTATION Previous Question Paper (July/August - 2022 - R18)

Conductivity measurement is a critical parameter in industrial process control for assessing the ionic concentration of aqueous solutions. Its primary importance lies in monitoring water purity, such as in boiler feed water, where high conductivity indicates the presence of dissolved solids that can cause scaling and corrosion. In chemical manufacturing, it is used to monitor the concentration of reagents or the efficiency of ion-exchange resins. Furthermore, it serves as an effective tool for detecting process leaks, managing cooling water systems, and ensuring environmental compliance by monitoring wastewater quality for pollutant discharge.

A high-frequency conductivity meter, often referred to as an electrodeless or inductive conductivity meter, is designed to overcome the limitations of traditional contact-type sensors, such as electrode polarization and fouling. The operation relies on the principle of electromagnetic induction.

The sensor consists of two toroidal coils encapsulated in a chemically resistant material. The first coil, known as the drive coil, is energized by a high-frequency alternating current (typically in the kHz range). This creates an alternating magnetic field that induces an electric current in the process liquid passing through the center of the toroid.

The induced current in the liquid is directly proportional to the conductivity of the solution. This current, in turn, creates a secondary magnetic field that induces a voltage in the second coil, known as the pickup coil. The magnitude of the voltage induced in the pickup coil is proportional to the current flowing in the liquid, and consequently, proportional to the conductivity of the medium.

The electronic circuitry processes this signal by comparing the induced voltage against a reference signal. Because the electrodes are not in direct contact with the process fluid, the system is immune to electrode coating and polarization effects, making it highly suitable for measuring high-conductivity solutions, corrosive chemicals, or fluids containing suspended solids.