Automatizuotų skaitmerninių sistemų mažiems pokyčiams įvertinti tyrimas

Abstract

1. The method for automatic digital balancing of Wheatstone resistance bridge was developed and investigated using DAC R-2R matrix for evaluation of resistance small changes. Balancing method enables reducing of external influence impact to evaluation results and avoids most disadvantages that are common to classic systems based on unbalanced Wheatstone bridge. The parameters of connecting wires and channel switches are not impacting evaluation results in the system developed. Advantages of the system developed are proven by experiments. System developed allows low cost implementation of systems for evaluation of resistance small changes. 2. Possibilities for simplification of circuit for resistance small changes evaluation by using digital signal processing means are proven. It is established that by using known and the proposed methods for improvement of reliability of evaluation results resolution of the evaluation is 12–14 bits (0,024 % - 0,006 % accuracy). It is established that it is necessary to use digital signal processing methods for achieving such resolution. 3. New structures of resistance small change evaluation systems ensuring resolutions of 212 and 28 intended for laboratory investigations and monitoring of constructions are proposed. Experimental model of system with resolution of 28 was made and investigated. Methods of reducing noises in long cables were established during experiment. In general it was proven that the model is suitable for monitoring tasks. 4. The new structure of multichannel system for evaluation of high-speed logic elements, triggers, registers, counters, etc. was developed. It is comparatively simple and not using high-speed switches and coaxial cables. Newly created multichannel compensating sampling converter is used as the base of the system. 5. Experimental investigation of multichannel sampling converters approved that converters with multiplexer on output may be scaled up to 6-12 channels. Sampling converters with multiplexer on input may be scalt virtually to an unlimited number of channels. Multichannel converters with parameters of the elements obtained during digital modelling are maintaining the same dynamic parameters as one channel sampling converters. Observation of the models of signal delay time evaluation systems shown that the results are stable and instability does not exceed ±2 %. 6. It is established that it is necessary to use digital signal processing methods used for evaluation of resistance small changes in order to increase reliability of evaluation of voltage and time interval small changes. Usage of digital processing methods solves data storage problems. It is shown that only by using compensating peak detection sampling converters together with digital signal processing it is possible to develop automatic system for evaluation of dynamic parameters of high-speed high resolution DACs. 7. The new structure of settling time evaluation system using digital signal processing and digital evaluation of settling time is developed. For experimental investigation Virtual instrument using LabView software package and implementing digital signal processing is developed. It was achieved that accuracy of the settling time evaluation of signal influenced by various noises and instabilities is exceeding 1 % by using digital signal processing while the accuracy of the evaluation without digital signal processing is not possible.