Geometric part of uncertainties in the calculation constant of the primary four electrode conductivity cell

Abstract

The paper presents the construction of a primary four electrode conductivity cell with calculated constant for the Ukrainian primary standard of electrolytic conductivity (EC). The equations for calculating the cell constant and the error budget for calculating uncertainty are presented. The components of the budget are: errors due to the non-uniformity of the force lines of the electric field; errors due to the accuracy of measurement standards and measuring instruments for determining length and diameter of the tube; and errors due to manufacturing techniques of tubes and their assemblage. The article considers in detail the errors due to the non-ideal profile of the central part of the tube. Two methods to reduce the standard deviation are given: the method of linear interpolation for compensation of the concave form which occurs along the axis of the tube and the method of equivalent triangles to compensate for deviations from a circle that occur across the axis of the tube.