NON-CONTACT MEASUREMENT OF SMALL DIRECT CURRENTS

Abstract In this article, we have considered the questions of measuring small DC currents without breaking the circuit with use of magnetic-modulation converter (MMC). The aim of this study is to create a technological design of integrating circuit. The circuit should have non-branched magnetic conductor and single coil circuit. This will let us create a compact and precise lectric-pliers for small DC currents measurement. A new way of MMC implementation is proposed, for the analysis of which the basic magnetization curve of the magnetic conductor is used. As a material of magnetic conductor, electro-magnetic steel of series 1511, 0,35 mm thick, and series 3414, 0,5 mm thick are considered. The frequency of the modulating current is selected to be 50 Hz. MMC working model is created in Mathcad environment. As an informative parameter of MMC, inequality of time intervals between the extremes of the coils voltage is used. Under the influence of the measured DC current, in sections where coil voltage is growing the range between its extremes is reducing, and in voltage descending sections ? increasing. The difference between these intervals is a measure for the measured current. The graphs of MMC conversion functions for two values of the modulating current are created and found that it is almost linear. The higher is sensitivity of MMC, the greater is the degree of non-linearity of the magnetization curve of the magnetic conductor material. Scheme for Contactless measuring the DC circuit, which uses the described method implementation of MMC is presented. Also the possibility of implementing a negative feedback by applying together DC output current of device and modulating current to the coil of MMC. In this case, the coil of MMP also functions as the compensation coil, the DC component of which compensates the influance of measured DC current on magnetic conductor and the measurement is carried out by zero method.