Testing double current bridges for resistance measurements

Abstract

A new type of circuit-bridge supplied unconventionally by two current sources will be discussed. An idea of this circuit has been suggested in some publications by Zygmunt Warsza under a name: double current bridge. The bridge conditioner makes possible to operate with the resistive sensors and to measure one, two or four parameters at one time. In this paper the relations between the arm currents and voltages of DC current supply bridges will be simulated. Also a sensitivity and a nonlinearity ofthese circuits will be discussed.The bridge circuits known as balanced and unbalanced bridges supplied by a single source are applied in measuring technique for many years. Such circuits like the Wheatstone and Thomson bridges, an Anderson loop, the differential circuits powered by a current source, the active circuits with the operational amplifiers and the quotient circuits which work with the A/D converters are used to conditioning the signals from the resistive sensors.The circuits for the measurements of two or more parameters running concurrently are less developed. However, there are more and more intelligent transducers and universal programmable multiterminal conditioners on the market and the multivariable measurements are employed to evaluate some component values of one or many physical quantities in one or many places on a measured object. The aim of them is to convert the physical values which affect the sensor or the set of sensors to proper changes of values. The another aim might be to evaluate the values of internal parameters of a substitute circuit of a tested element from its external terminals (diagnostics).The selective sensors exist only for some physical quantities but often it is not possible to use them because of a lack of free place and the high cost or an interaction. Then it is necessary to use the set of sensors and their parameters depend on some values in different way at one time. Moreover, many of tested circuits and elements can not be disconnected and there is no access to their internal structure. To solve these problems Zygmunt Warsza suggested a new type of circuit-bridge, supplied unconventionally by two current sources [1]. Its characteristics will be described in this paper. DOUBLE CURRENT BRIDGES -MAIN PROPERTIESWell-known basic resistance bridges like Wheatstone bridge can work as balanced or unbalanced or with a feedback. Balanced 2J bridges should be supplied by the concurrent sources. The unbalanced bridges should have them also stabilized.2.1. Balanced bridges Two versions of four-arm bridge conditioners are shown in Fig. 1 . Basic Wheatstone bridge (Fig. la.) is powered by single source connected to one diagonal. The second diagonal gives an output voltage. 2J bridge is supplied unconventionally by two current sources connected to opposite arms. 2J bridge has two output voltages -from both diagonals (Fig. lb. and lc.).Assuming that current sources are ideal and have the same value J, the output voltages are given by equations (1) and (2). u AB R1 + + R3 + R4(1) u J.

Mažų deformacijų stebėsenos elektroninių įrenginių tyrimas

“…Yra pateikiama įvairių srove maitinamų tiltelių schemų (Idzkowski et al 2005(Idzkowski et al , 2012, kuriose nagrinėjama keturių varžų tiltelio grandinė su dviem įtampos išėjimais. Ši grandinė, pavadinta dvigubu srovės tilteliu, yra maitinama dviejų vienodų srovės šaltinių, prijungtų lygiagrečiai prie priešingų pečių arba vienas iš tokių šaltinių perjungiamas tarp šių pečių.…”