Because of missing a-priori information, tolerances of the elements used in microelectronics and other circuits, nonlinearities and to check the results of models and calculations or programs especially in measurement estimation and approximation methods using the physical background are advantageous. Also in education these methods to get a first impression of the solutions of problems should be trained. In the paper a lot of typical examples will be treated as signal analysis and aliasing errors, linearisation, dynamic errors and optimal filtering including consequences for the selection of measuring systems.

Within a formal framework, where each object is characterized by a set of predicates as a binary sequence of 0 and 1, a nominal level of measurement is discussed. The nominal scale is reinterpreted as a set of predicates, and nominal measurement as an assignment of binary sequences to the objects. One remarkable character of this formalization is a reciprocal relationship between the objects and the predicates. Taking this reciprocity as a heuristic guiding principle, a new notion of generalized indiscernibility between two sets of objects is introduced, which enable us to examine various complicated relationship among subsets of objects. As an application to nominal, non-quantitative measurement, algorithm of clustering is proposed, and its merit is discussed in comparison with a method of pattern recognition based on the principle of minimum entropy. The result suggests the importance of structural inter-group relationship that cannot be reduced easily to simple numerical variables. The notion of object-predicate reciprocity will helps us to analyse complicated object-predicate relations reflected in the result of nominal measurement, and to enlarge the scope of the newly emerging measurement science.

In this paper the important problem in measuring system: ”How to eliminate the sensitivity of sensors to the influence quantity?” is replaced by the question: ”How to use this sensitivity to measure both the main and the influence quantities?” As a solution of the second problem the frequency balanced bridges as primary signal processing circuit for parametric sensors are proposed. Structure of such a two-dimensional transducer and possibilities of its realization are described. An example of transfer functions, parameters of linear model, nonlinearity errors is given when typical semiconductor pressure sensors are assumed. Some practical aspects are discussed.

The ferrous objects disturb evenly distributed Earth magnetic field. It is possible to detect the ferrous objects by measuring the magnetic field. Detection of objects under water in the Baltic Sea is difficult due to large natural magnetic anomalies. In order to eliminate the anomalies, the prediction technique in measurements was used. Before the prediction, the measured signal is filtered to remove unwanted frequencies and this way the object can be detect using a threshold peak detector. LabVIEW was used to simulate the detection of objects in the Baltic Sea.

This paper describes a single micro-optical fiber sensor capable of measuring four strains simultaneously in a composite structure. This single transducer is based on cascading four micro Fabry-Pérot cavities to measure three normal strains and one shear strain in the plane of the optical fiber cross-section. The development of the sensor fabrication and signal processing techniques are discussed. This fabrication includes designing and fabricating new optical fibers, optical fiber circuits, and an optical fiber multi-strain sensor head. This paper presents 2D and 3D finite element analysis to establish the transformation between fiber core and composite host strain states.