USING OF ELECTRICAL METHODS OF MEASURMENTS FOR TESTING OF BRIDGES AND OTHER STRUCTURES

Abstract

Purpose. With the introduction of new designs of bridges and other structures the using of electrical measurement techniques in which the measured deflections, stresses and vibrations, using transmitters, are converted into electrical signals in their testing is of current interest. It is very important to ensure a phase-sensitivity and proportionality between the measured values of mechanical and electrical signals. Methods. For electrical measurements transducers are connected to electrical bridge-type circuits. Calculations of the Wheatstone’s bridge connections forvarious transducers were made on the basis of Kirchhoff's laws for branched electrical networks and using circuitry transformation for which in the original scheme of the Wheatstone’s bridge the group of resistances is replaced by another, equivalent resistances group. Calculations were performed for the cases of presence and absence of internal resistance of the bridge’s power supply with connecting of transducers into one, two and four arms of a Wheatstone’s bridge. Findings. From the calculations the tables and graphs of the functions fi () and f0i () , that determine the change of current in the measuring diagonal of a Wheatstone’s bridge are derived, where  is relativechange in resistance of transducers. For one active sensor functions f1() and f01() are characterized by a high non-linearity, but for strain gages at   0,01...0,02 , acceptable linearity and accuracy of the measurements are provided. Originality. Based on the result analyses for calculations conducted, relations of the current in the measuring diagonal of the Wheatstone’s bridge are determined for various connecting circuits of transducers for measurement of the stress-strain state in structural elements during tests. Also the value of the internal resistance of the bridge’s power supply is taken into account. Calculations were performed using Kirchhoff's laws and by equivalenttransformation of branched circuit. Practical value. Obtained plots for functions fi () and f0i () and the above table allow to estimate the conditions for ensuring the linearity of derived dependencies for different transducers’ connections. Bridge-type circuits for insertion of strain gages allow to distinguish stresses in structural elements from the action of normal forces as well as vertical and horizontal bending moments.