Measuring Set including a Virtual Standards®Technologybased
Superimposed Ultrasonic Flow Meter

The problem of finding means of end methodes for improving measurement accurecy often arises in measurement conducted usuing superimposed ultrasonic flow meters, elaborate S.M. Yermishin and A.V. Lopatin

 

Introduction
The problem of finding means of and methods for improving measurement accuracy often arises in measurements conducted using superimposed ultrasonic flow meters. An individual adjustment of superimposed ultrasonic flow meters often provides an opportunity for solving this problem, in particular when one does not want to pay extra money for precise measuring devices. An appropriate standard and adjusting devices are required to achieve that. The Virtual Standard® technology has been developed to adjust measuring devices so that measurements could be conducted with a higher class of accuracy, but without using standards or adjusting devices. Virtual Standard® technology is a universal technology for determin- ing and introducing corrections in measuring device readings to reduce their errors. The measuring device for which reading corrections are determined is called ‘Virtual Standard® system measurement module’. The digital computing device where reading corrections are determined is called ‘Virtual Standard® system processing module’. The Virtual Standards® system is a functional implementation of the Virtual Standards® technology and some corresponding additional service functions: exchanging data between measuring module and processing module, establishing an interface between measuring module and processing module, establishing an interface between the Virtual Standards® system and users, automating measurements and the document management, and supporting accounting payment operations. Present-day flow meters consist of transducers in both hardware and software implementations. A higher measurement accuracy is achieved through increasingly correct and precise measurements. Software has traditionally been used in flow metering to improve measurement accuracy through improving precision i.e., to reduce the random error component. The most popular processing methods used for that purpose are various statistical processing and filtering algorithms. However, the question whether software can be used to increase flow meter correctness i.e., to take into account the systematic error component, and what processing methods should underlie such software, remains open. This work is designed to answer this question, in particular, to superimposed ultrasonic flow meters for liquid media.

Target setting
The measured flow of liquid medium in a pipeline and a superimposed ultrasonic flow meter interact in a field created by radiators, which is accompanied by transformation of the radiated energy on measurement object into other forms of energy in sensors. The measured liquid medium disturbs the field of the radiated energy and introduces errors in measurement results. The principal meaning of the measurement procedure is converting an interacting, and thus closed reciprocal ‘measured flow of liquid medium in the pipeline – superimposed ultrasonic flow meter’ system that is isomorphic in terms of abstract algebra, into a one-way (homomorphous) system. The true value of the measured quantity corresponds to this ideal state with oneway (homomorphous) ‘measured flow of liquid medium in the pipeline– superimposed ultrasonic flow meter’ links. The actual value of the measured quantity differs from the true value by the measurement error. Assume that, a set of states S is observed on ultrasonic flow meter radiators over measurement time ti, and a set of measurement results J is registered at sensor outputs. Assume that
where s11 and s21 are values of the measured quantity in the measurement plane (measuring beam) on the measurement object to the left of axis of symmetry .1 at moments of time t1 and t2, respectively; s12 and s22 are values of the measured quantity in the measurement plane (measuring beam) on the measurement object to the right of axis of symmetry -.1 at moments of time t1 and t2, respectively. Then

where j11 and j12 are DC values at moments of time t1 and t2. Let us use an ultrasonic flow meter described by linear operator T:

where d1, d2 is an operator describing the nature of conversion (for example, voltage growth at the input amplifier or voltage reduction at the input divider, etc.) at the moment of time t1, t2. It should be noted that in virtually all cases, measurements transform energy (poles relative to the axis of symmetry) received from the measurement object in the measuring device, therefore, the linear operator of type (1) is a general form used to present measurement information signal conversions in flow meters. At the same time, (4) is actually a form of coordinate conversion that is most frequently used in the flow measurement process. Linear operator T (3) perturbations due to external factors are present in the real technical measurement process:

cont....

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