Implementation of portable common building ground resistance measuring instrument

Abstract

According to the defect of the building ground resistance measuring device presently. A new system of building ground resistance detection which based on STM32 was proposed. This scheme was based on the principle of three-pole compensation method. Hardware and software of the master-slave machine which controlled by embedded system was applied to achieve accurate measurement of ground resistance. The detection system included synthesizer of alternating current, signal collecting and data processing platform. The detection system was consisted of a STM32 control which product alternating current with high precision frequency and waveform stability into the grounding grid. The signal of voltage and current in the grounding grid were translated into a precise grounding resistance value through band-pass filter, differential amplify, synchronous AD conversion, FFT processing. The detection system could improve the detection accuracy and efficiency, and realize the intelligent testing work. Instruction Building grounding device plays an important role in the whole building lightning protection and normal operation of electrical equipment. Grounding resistance is one of the main technical parameters of grounding device, and an important index to measure the quality of the lightning protection engineering. So the accurate detection of grounding resistance is important to ensure the safe operation of electrical equipment in buildings and personal safety. With the rapid development of modern cities, buildings especially high-rise buildings concentrated in cities, which puts forward a more difficult requirement for building grounding resistance test. The China meteorological administration currently uses mainly shake table style and 4105A-type ground resistance detector. Such instruments were operated more cumbersome, and the digital level is not high, the accuracy needs to be improved. This paper selects enhanced STM32 chip to build detection system, and uses 12 bit high-speed parallel AD converter chip AD7656 and highperformance signal conditioning circuit to achieve accurate detection of ground resistance. Detection Principle When current diffuses from earth electrode to surrounding land, soil will be showing resistance characteristics, which is called ground resistance. According to ohm's law in ground resistance measurement, the current and voltage that flow through ground pole should be got firstly, then the formula / R U I = will be used to get the ground resistance value. In the actual detection, in order to simplify the calculations, grounding grid was regarded as hemisphere, as shown in figure 1. When measuring, current probe should be placed at zero potential to eliminate the influence of grounding. However in actual wiring, long distance wiring is not possible. Three-pole compensation method was usually used in the grounding resistance detection, and it's principle is shown in Figure 1. Using electric field intensity formula E Jρ = and potential equation x U Edt ∞ = − ∫ get the potential which distance from center of sphere of r . International Conference on Information Sciences, Machinery, Materials and Energy (ICISMME 2015) © 2015. The authors Published by Atlantis Press 1881