The authors paid particular attention to the problem of antenna impedance measurements in the RFID technique. These measurements have to be realized by using two ports of a vector network analyzer and dedicated passive differential probes. Since the measurement process and estimated parameters depend on the frequency band, operating conditions, type of the system component and antenna designs used, appropriate verification of the impedance parameters on the basis of properly conducted experiments is a crucial stage in the antenna synthesis of transponders and read/write devices. Accordingly, a systematized procedure of impedance measurements is proposed. It can be easily implemented by designers preparing antennas for different kinds of RFID applications. The essence of indirect measurements of the differential impedance parameters is discussed in details. The experimental verification has been made on the basis of a few representative examples.
Manual measurements of distribution of gas velocity in conduits of flue gas installations using systems with differential pressure sensors of velocity are often performed for the requirements of determining emissions of dust pollutants from industrial process plants to the atmosphere. The aim is to determine an axial velocity profile. Flows in measuring sections are not always coaxial along the run of the duct; they are characterized by different directions of the velocity vector at various measuring points. The determination of actual directions of vectors of local velocities giving a guarantee of an accurate calculation of the axial velocity is often not possible from the technical point of view and the measurement of the velocity is carried out with the parallel setting of the sensor head in relation to the axis and the walls of the conduit. Then the knowledge of the directional sensitivity of the applied velocity sensor allows either to eliminate the axial velocity measurement error or to take it into account by the uncertainty of this measurement. For specific situations of two-dimensional variation of direction of the velocity vector, the directional sensitivity characteristics and in consequence the characteristics of error have been determined for three sensors adopted to tests: a zero pressure dust sampling probe with the anemometric function as an element of the gravimetric dust sampler and comparatively - two commonly used Pitot tubes: types S and L.