Knowledge of gravitational acceleration in metrology is required for traceable force and pressure calibrations, furthermore the redefinition of the SI base unit of kilogram requires absolute accomplishment of the gravitational acceleration. A direct free-fall gravimeter is developed using pneumatic grippers for test mass handling and a semi-rotary actuator for repositioning, i.e. automated re-launching. The catch and release system is powered by compressed air. This eliminates electric interferences around the test mass. A simplified method of signal capturing and processing is used on the designed gravimeter. A digital frequency trigger is implemented in the post processing algorithms to ensure that the signals are analysed from the identical effective height. The experimental results measured the site gravitational acceleration of 9.786043 ms��2 with a statistical uncertainty of #6;29 ms��2.
The paper presents the properties of a strain sensor, which was made using the micro hole collapse method and operates in the configuration of a Mach-Zehnder modal interferometer with a PM-1550-01 polarization maintaining photonic crystal fibre. The sensor’s transfer curve was determined analytically. Its strain sensitivity, determined from measurements, decreases slightly with increasing wavelength and is in a range from 2:01 to 2:23 pm/me in the wavelength range 1520–1580 nm. Based on the Fourier analysis of the wavelength spectrum of the constructed sensor, the difference of the group refractive indices of the core and the cladding of the photonic crystal fibre was determined, which are in a range from 7:45#1;103 to 1:01#1;102. The temperature sensitivity of the sensor, determined on the basis of measurements performed in a range from 23 to 60◦C, is positive and equals 5.9 pm/K.
This paper presents two methods for evaluation of the effective wavenumber of nearly-Gaussian beams in laser interferometers that can be used for determination of a so called diffraction correction in absolute gravimeters. The first method, that can be simply used in situ, is an empirical procedure based on the evaluation of the variability of g measurements against the amount of light limited by an iris diaphragm and transmitted to a photodetector. However, precision of this method depends on the beam quality similarly as in the case of the conventional method based on measurement of a beam width. The second method, that is more complex, is based on beam profiling in various distances and on calculation of the effective wavenumber using the second spatial derivative of a non-ideal beam field envelope. The measurement results achieved by both methods are presented on an example of two absolute gravimeters and the determined diffraction corrections are compared with the results obtained by measurements of beam width. Agreement of methods within about 1 mGal have been obtained with average diffraction corrections slightly exceeding +2 mGal for three FG5(X) gravimeter configurations.
The results of surface texture measurements obtained with the stylus equipment, white light interferometer and confocal profilometer of the same samples were compared. Machined isotropic and anisotropic surfaces, of symmetric and asymmetric ordinate distribution were measured. Forms were removed using polynomials. Sampling intervals and measuring areas during computations of parameters were the same. Discrepancies between the results obtained with various methods were observed and discussed. It was found that errors of surface texture measurement with the optical methods depend on the type of surface topography.
In recent years organic semiconductors have been given attention in the field of active materials for gas sensor applications. In the paper the investigations of the optoelectronic sensor structure of ammonia were presented. The sensor head consists of polyaniline and Nafion layers deposited on the face of the telecommunication optical fiber. The elaborated sensor structure in the form of Fabry-Perot interferometer is of the extremely small dimension its thickness is of the order of 1 um. Many sensor structures of diffierent combinations of the polyaniline and Nafion layers were constructed and investigated. The optimal solution seems to be the structures with small number of polianiline layers (up to three).