Probe Into Key Technique Of Steel Cable Tension In Situ Monitoring Based On Magneto-elastic Effect

Steel cable has been widely applied to some realms such as bridges with large span, huge building structures and pulling mechanism etc. because of its strong points such as fine flexibility, high intensity, low frequency and so on. To monitor the stress of steel cable simultaneously and take the reins of its change regularity dynamically are vital means to guarantee its secure function. As an important index to evaluate the health status of steel cable framework, cable stress online monitoring is an accepted world-class issue. Both traditional pressure sensors and vibration means have their own shortcomings, which are hard to meet the demand of cable stress online monitoring. The new cable stress test technique based on magneto-elastic effect has been an overseas study focus because of its outstanding advantages, e.g. high measure precision, fine dynamic response, long life-span, being ready to be inspected at any time etc. At present, there are examples in some fields. Yet, such not-finely -solved puzzles as the installation on the spot and temperature compensation, and limited by the intelligent property right and technique secrecy. But, the theoretics system of this method is not maturity, lots of key techniques is not been solved. Not anly technique information is opened, Therefore, based on magneto-elastic effect, to probe into key techniques of theoretics model, the structures of magnetic loop , selection of magnetic intension and temperature compenation etc., has its important scientific significance and enormous practical value.This dissertation firstly summarizes the methods of cable tension test at home and abroad. The difference magnetic loop structure of single bypass excitation is put forward bsaed on magneto-elastic effect, the excitation circuit and excitation magnetic loop are designed, the trial platform is set up to carry out temperature experiment and pull experiment. Specific research is as follows:i) To reveal existing problems by analyzing current researches on steel cable stress test methods and put forward key points in this dissertation.ii) To do researches on elements of cable stress test based on magneto-elastic effect. To start with the energy of magnetism domain structure, with the law of conversation of energy and thermodynamics equilibrium term in mind, model on magneto-elastic effect has been analyzed, together with numerical value.iii) To design two kinds of excitation circuits and four kinds of excitation magnetic loop with different structures. To make up for the weaknesses lying in magnetic loop structure in practical usage such as inconvenience in installation and maintenance, this dissertation puts forward magnetic loop structure of bypass excitation. Under the circumstance that steel cable magnetization curve is unknown, this dissertation puts forth a principle how to select superior magnetic field intensity in excitation magnetic loop and a method how to design magnetic loop.iv) To explore temperature's impact on magnetic-elastic effect wholly and systematically. With temperature compensation curve method failing to meet the demand of online test, the theory of difference automatic temperature compensation is put forth; automatic equalizing structure is brought forward and devised. The temperature experiments are processed in condition of zero load at the temperature ranging from -30℃to +80℃and invariable load at temperature ranging from 14.5℃to +80℃. The results shows that temperature error can be compensated automatically, after which the impact of temperature fluctuates less than 2.5%.v) To design and produce sensors of sleeve-style, bypass excitation structure and differential magnetic loop structure. In addition, to set up a trial platform and contrive two experimental schemes, one is sine AC excitation and the other is pulse constant current excitation. We have had an experiment on a pull trial mechanism, which can pull something ranging from 0kN to 20kN. With four different kinds of cable tension sensors on it, this mechanism pulls steel cable with diameter of 12mm. The experiment results contrast shows, the integration characteristic of difference structure cable tension sensor is most fine, the key problems of temperature comperence and fixing at post is settled and its repeated error is less than 1.5%.At last, this dissertation reviews the whole research work, summing up innovations as well as shortcomings in it, some important issues are expected to be perfected and lucubrated in the near future.