CONTENTS
Martin Kollar  Sigma delta modulator for force measurement based on the use of a flipflop circuit and presentation of simulated results  3 
Marian Kampik, Łukasz Jedliński  Influence of the switching circuit on the properties of the pulsewidthmodulated DAC  21 
Leszek Radziszewski  Intrusive effect of a contact transducer on testing results  31 
Bolesław Dobrowolski, Mirosław Kabaciński, Janusz Pospolita  Numerical analysis of the flow around the averaging impact sensor  45 
Tomasz P. Zieliński  Wavelet transform applications in instrumentation and measurement: Tutorial & Literature Survey  61 
ABSTRACTS
MARTIN KOLLÁR
Department of Theoretical Electrotechnics and Electrical Measurement,
Technical University of Košice, Slovak Republic.
email: Martin.Kollar@tuke.sk
SIGMADELTA MODULATOR FOR FORCE MEASUREMENT BASED ON THE USE OF A FLIPFLOP CIRCUIT AND PRESENTATION OF SIMULATED RESULTS
This paper describes a flipflop circuitbased sigmadelta modulator for force measurement. The main part of the proposed system is a modified flipflop circuit used as a comparator, inside of which switched capacitors replace the classical load resistors. The functional principle lies in the fact that if capacitive asymmetry caused by the force to be measured, is such that the flipflop holds a stable state where, for example, a higher voltage is on a second transistor, then it produces a higher force between the parallel plates connected to the same transistor to decrease the resulting capacitive asymmetry. The main advantage of the flipflop, besides its simplicity, is the compensation of the influence of flicker noise which is mathematically described in this paper. The theoretical conclusions are compared with the results of simulations with TSPICE and MatlabSimulink, with respect to the measurement system realized in 0.8 μm CMOS technology. The results of simulations were in agreement with theoretical results.
Keywords: flipflop circuit, flicker noise, capacitive sensor, sigmadelta modulator, measurement

MARIAN KAMPIK, ŁUKASZ JEDLIŃSKI
Silesian University of Technology, Gliwice, Poland
email: mkampik@zeus.polsl.gliwice.pl
INFLUENCE OF THE SWITCHING CIRCUIT ON THE PROPERTIES OF THE PULSEWIDTHMODULATED DAC
The effect of the resistances and switching times of transistors used in the switching circuit of a pulsewidthmodulated digitaltoanalog converter on its gain and offset is analyzed in the paper. The analysis shows that the influence of the finite switching times on the relative error of the output voltage is one order higher than the influence of the finite on/off resistances of the switching transistors. A method of compensation of the offset is proposed.
Keywords: digital to analog converter, pulse width modulation, calibrator

LESZEK RADZISZEWSKI
Kielce University of Technology, Poland
INTRUSIVE EFFECT OF A CONTACT TRANSDUCER ON TESTING RESULTS
The author was inspired to study the problem by previous observations of the experiments with a pulse laser as the source of ultrasound waves. The waves, reaching the opposite free surface of investigated solid, caused its deformation. The presence of a transducer on this surface caused a change in the existing state of stresses as well as in the deformation's value. The influence of transducer's materials, the seismic mass and the ratio of the sensor and sample's surfaces on displacement and electrical output signal generated by the piezoelement are given in this paper. The evaluation was made at the front of the distortion. The case of measurements with point receiver was analyzed, as well. It was concluded that point piezoelectric transducer as receiver behaved as displacement sensor.

BOLESŁAW DOBROWOLSKI, MIROSŁAW KABACIŃSKI, JANUSZ POSPOLITA
Technical University of Opole
Chair of Thermal Engineering and Automatic Control
NUMERICAL ANALYSIS OF THE FLOW AROUND THE AVERAGING IMPACT SENSOR
The development of numerical methods and computer engineering enables a theoretical analysis of the fluid flow in the surroundings of impact flowmeters using numerical solutions of the basic equations of fluid mechanics. The paper presents a mathematical model of the fluid flow around the impact sensor based on equations of motion of a viscous fluid and equations kε RNG for a turbulence model. The equations of the mathematical model were solved with the finite volume method and the software FLUENT. The obtained results were used for the analysis of velocity and pressure fields around the sensor and inside its averaging chambers. The characteristics of impact flow sensors with different shapes were numerically determined. Numerical calculation results were completed with the data of experiments realized in an aerodynamic tunnel.
Keywords: Flow measurements; Mathematical modelling; Numerical methods

TOMASZ P. ZIELIŃSKI
AGH University of Science and Technology
Measurement Department, Kraków, Poland
WAVELET TRANSFORM APPLICATIONS IN INSTRUMENTATION AND MEASUREMENT:
TUTORIAL & LITERATURE SURVEY
Due to its many advantages the wavelet transform has become in the last decade a very popular numerical tool for general purpose signal analysis and processing. It belongs to the socalled timefrequency signal representations that are dedicated for tracking of the timevarying spectral content of a signal. The field of its potential applications is very wide since it can replace with success the discrete Fourier transform in many practical methods of signal interpretation (approximation) and filtering (different components' separation and denoising). Since many mathematically comprehensive and simple userfriendly tutorials of the wavelet transform foundations as well as computer programs for its calculation are available, the present paper will address only a very simple presentation of the wavelet transform principles mainly concentrating on the description of its contemporary state of theart instrumentation and measurement applications.
Keywords: wavelet transform, applications, instrumentation, measurement

