INVESTIGATING THE ERRORS OF A DIGITAL METER OF RC-TWO-POLE PARAMETERS

Abstract

A device for an invariant measurement of the electrical parameters of RC-two-pole poles based on the phase method is described. The device implements a structural-algorithmic method of increasing the accuracy of measurements with time division of the measurement channel. A programmable microcontroller (MCC) is used to control the measurement process and to process the measurement results, which allows to minimize the number of parameter and signal transformations and increase the measurement accuracy. In the measuring circuit (MC), two sample resistors are connected in series with the two-pole under study: the main and additional (switchable). The reference voltage is formed in the feedback circuit of the operational amplifier. The MC is powered by a current generator of a sinusoidal signal of a programmable frequency. The MC has two output voltages, the phase shift angle between which is an informative parameter. The output voltages of the MC are supplied to the analog inputs of the MC. In the MCC, the angle is converted into a time interval, which is measured by the discrete counting method by quantizing it with pulses of the MCC clock generator. By analyzing the MC, algorithms for determining the measured parameters are obtained. The parameters of the IC elements are calculated, at which the required measurement ranges of the investigated object parameters are provided. The main content of the article is devoted to the development of the methodology of theoretical calculation of measurement errors. The errors are caused by inaccuracy and instability of the parameters of the MC and MCC elements appearing in the obtained algorithms. The calculation technique is accompanied by numerical example applied to specific measurement ranges. It is shown that in the total errors of measurement the private error caused by the inaccuracy and instability of resistances of sample resistors used in the MC, is predominant.