The Design Of Strain Detection System With High Accuracy Based On Total Differential Theory

The detection of strain and stress is widely used in the field of construction, material, machinofacture and so on. In the process of measurement, sensitive components convert the measurands such as displacement, acceleration into strain or stress, the measurement of the measuring parameter is realized by using strain detection circuit of displacement and acceleration. In the actual industrial environment, most strain signal are small-single, and in the measuring process, the components are impressed by fluctuation of power-supply, the ageing of electrical components, drifting, noise jamming and so on, which make it harder to achieve the detection signal with high-accuracy.Aiming to detecting the strain with high-accuracy, the study on the basis of the differential theory, double-channel parameters measurement of the detection circuit design method is put forward, and the whole bridge type strain gauge dual channel detection circuit, the whole bridge and resistance strain gauge with dual channel detection circuit and the strain gauge half bridge type double-channel detection circuit are designed. To eliminate influences caused by the interference factors, using the total differential theory, three detection circuits are analysed, through the configuration of components in test circuit, the applicability of the detection circuit is improved, in theory, the linearization of detection circuit transfer function is realized, and the influence of the circuit components caused by outside interference factors is eliminated when the detecting circuit be at work.To eliminate the influence caused by the drifting of detecting system on the measurand, two step measurement is used in the design of the hardware circuit of this system:first step, make no input single to the system, the value named instantaneous zero drift is detected at the output; second step, measure the measuring strain signal. Dispose the two kinds of single and convert them into digital signals and let them be the input of MCU78E58, dispose the measuring single in the MCU by the converting arithmetic to eliminate the zero drift, after the calculate of the computer, the measuring strain values are received. Finally, the value of strain transfer to the PC through the interface of communication.The software corresponding the detection system is designed in the PC. Serial communi-cation is realized by MSComm. The software is compiled by C++ which is object-oriented programming language, and the data base is the SQL Server 2000 which is used for storing the values transformed by MCU, the technique named ADO is used to call the values in the data base. The software include three functions as follow:display the value instantly and dynami-cally, display the recorded data as the form of data and chart, this is convenient to analyze the strain values. This software has good portability, this make the practical applicability of the strain detection system strengthened. Meanwhile the software design process based to modul- arization, so it can increase the function of the software and upgrades according to actual application.For proving the practical applicability of system, two experiments are conducted. The one uses the standard resistances valued 120Ωand resistance box with high accuracy as the analog strain gage to detected the strain, the other one is testing the strain of the steel of NO. 235 when the steel is stretch to measuring the strain. The experiment shows that the resolution ratio of the system is 1με, the accuracy is 0.5%FS, which indicate the system has good linearity and high accuracy, and the system has excellent stability and anti-interference.