Contents I. Introduction
For a solution, the level of conductivity directly reflects the ability of the solution to conduct electricity. Through the measurement of the conductivity value can be industrial water, water quality testing of domestic water, so the accurate measurement of conductivity is of great significance [1]. There are two main types of conductivity sensors: electromagnetic [2] and electrode [3]. Electromagnetic conductivity sensors have certain requirements on the conductivity of the solution, and they are usually suitable for high conductivity solutions, with lower measurement accuracy and sensitivity for low conductivity solutions (fresh and pure water), and the electromagnetic induction effect relies on the homogeneous distribution of solution conductivity, which may affect the measurement accuracy for inhomogeneous solutions or for the presence of vortexes, bubbles, and other interfering factors in the For inhomogeneous solutions or in environments with disturbing factors such as eddy currents and bubbles, the accuracy of the measurement may be affected [4]. Electrode-type conductivity sensors with a wide measuring range for a wide range of conductivities, both for freshwater with low conductivity and seawater solutions with high conductivity [5]. For rapidly changing conductivity environments, electrode-based sensors provide fast response times. Planar seven-electrode conductivity sensor is one of the electrode-type conductivity sensors with higher accuracy, which has the advantages of both threeelectrode [6] and four-electrode [7]. The conductivity cell of the planar seven-electrode conductivity sensor [8] achieves the separation of the current electrode and the voltage electrode, which can reduce the polarisation effect of the electrodes [9], and no pump is required during the measurement process, which also ensures high-precision measurement [10].
