INCREASING OF LINEARITY OF THE HIGHLY SENSITIVE IMPEDANCE-MEASURING SYSTEMS WITH SENSORS
В. Г. Мельник, О. В. Сліцький · Sensor Electronics and Microsystem Technologies · 2016
The article is devoted to development the principles of construction of the measurement channels of the systems with impedance sensors that combine high sensitivity, wide measuring range, accuracy and high speed. To do this, used the combination of the methods of measurement with rapid, low-discrete, and with slow, high-discrete, converting by comparing of measured and standard signals, which are implemented using the AC bridges and integrating ADC with variable discharge rate. In such devices, on certain levels of signals, some instability of readings may occur due to exposure to noise at the low-discrete comparison. This leads to the presence on the conversion characteristic of the channel of evenly spaced narrow zones with abnormally elevated dispersion of results. Such dispersion is the cause of emergence in these areas of the peculiar differential nonlinearity under averaging the data obtained. The possibilities of eliminating the impact of such circumstances on the accuracy of the measuring channel are discussed in the article. The proposed methods of detection of instability zones are based on the analysis of the form of responses on the stepped form modulation of the measurement signals in the bridge circuit, and the probability distribution of the obtained data values.Criteria for such analysis, articulated in the article, allow doing it in real time, simultaneously with averaging of the results of measurement and with another data processing. The principles of construction of the measurement channel described in this work allow realize the intelligent measurement algorithms, significantly improve resolution and reduce the error of the instrument without noticeable loss of performance. The article presents experimental data, confirming the possibility reducing of the non-linearity of the sensor signal conversion to the level of 0.001% and the relative error of measurement in the ten-fold range of the results change to 0.01%.