ABSTRACT

The most essential elements of vibrating-wire transducers are: a measuring wire and an electromagnet collaborating with it. The periodically excited wire generates exponentially decaying sinusoidal vibrations Converted by the electromagnet into electric vibrations. Changes of the measured physical quantity bring about changes of the wire tension and consequently, changes of its free vibrations frequency. This frequency is then measured by means of an external meter. Nowadays vibrating-wire transducers are used only for long-term static or slow-changing measurements. A new measuring method described in this paper makes it possible, in certain conditions, to measure quick-changing quantities by means of the same transducers.

MEASURING STATIC AND SLOW-CHANGING PHYSICAL QUANTITIES BY MEANS OF VIBRATING-WIRE APPARATUS

For measuring non-electric physical quantities with electric and electronic methods it is necessary to apply measuring transducers. The task of a measuring transducer is to convert the measured quantity the value of which is expressed in units appropriate for the adopted system of measures, into an analog electric signal. One of its parameters, for instance voltage, univocally reflects the measured quantity. In this way, by taking the measurement of an electric quantity value, a non-electric quantity value is measured as well. The kind and type of both the measuring transducer and the collaborating apparatus that have been applied determine the parameters of the measurement that is, the range, sensitivity, errors, etc. In science and technology a great many types of transducers are employed, Which make use of various phenomena. For long-term (lasting tens of years) measurements vibrating-wire transducers are frequently applied.

The application of a vibrating wire for constructing transducers is not a modern solution. The dam on the Dunajec in Roznow, built between the two World Wars, Was equipped with vibrating-wire transducers, which made it possible to observe the state of the construction and possibly, to counteract in the case of any irregularities. In the Institute of Strata Mechanics Research of the Polish Academy of Sciences, in the Laboratory of Rock Deformations, for the past 30 years observations have been conducted of soil displacements in the areas affected by the underground mining exploitation (Gustkiewicz 1995a and Gustkiewicz 1995b).

(Figure in full paper)

Like every measuring transducer, the vibrating-wire transducer is not an independent functioning device. Taking measurements requires connecting its terminals with the input of the measuring device that performs the whole measuring cycle from the application of an exciting pulse to measuring the output signal frequency. In the Laboratory of Rock Deformations a few types of devices have been designed and constructed that collaborate with vibrating-wire transducers called vibrating-wire meters (Kanciruk 1994). It has been taken into account that they should be designed in such a way as to make possible their collaboration not only with transducers constructed in the Laboratory but also with other transducers produced either in the country or by firms operating on an international scale.

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