Laser interferometry is the preferred method currently used by National Metrology Institutes for primary calibration of
accelerometers. Highly accurate calibrations require well controlled environmental conditions. Laboratories usually
focus on the control of ambient air temperature and humidity. Another important source of influence is the vibration
exciter, which besides uniaxial motion can generate undesirable secondary effects. This paper will treat the problem of
differential heating of an accelerometer under calibration, when caused by a rise in temperature of the vibrator moving
element. A simple device used to evaluate the change in the charge sensitivity of an accelerometer due to heating through
its mounting base is presented. The sensitivity to differential heating can then be determined by the use of accurate
interferometric methods. The knowledge of this sensitivity enables the calibration laboratory to correct the calibration
results obtained with vibration exciters, which exhibit significant temperature variations. For instance, some commercial
models can present variations higher than 20 °C, when the Bessel function J1 minimum-point method is applied. The
experimental setup, which has been developed at INMETRO to evaluate this characteristic is described and some
measurement results are presented.
This paper presents an automated accelerometer calibration system based on an homodyne quadrature interferometer. The vibration exciter and the interferometer are mounted on separate seismic blocks. To minimize the influence of low frequency noise due to the relative movement between the blocks, a high-pass recursive moving average filtering algorithm is implemented. The vibration and the measuring system are fully synchronized. A flexible setting of the acquisition rate is used to improve the computational efficiency and allow the calibration at any desired frequency within the frequency range from 10 Hz to 10 kHz. The theory of the method is briefly described. The experimental set-up is presented and some results are given.
This paper deals with some basic problems of interferometric length measurements. Traditionally, all the deformations of a material artifacts, associated with the wringing procedure, were included into the length of a block, as there were no reliable ways to measure these deformations and to apply the corresponding corrections. Here, we present the first measurements of the surface texture deformations, arising in the wringing contact between the two gauging surfaces of similar materials and surface finish. The deformation value is obtained as a result of the measurements of the peak-to-peak length value of a free, unperturbed block and of the mechanical length of the block, which is obtained with the reproducible wiring technique and the slave-block method. Basically new concept for the optical length metrology - the physical length of a free artifact has been introduced in to the measuring practice. The way for crucial improvement of the realization of the SI length unit in the corresponding range has been outlined.
Deceleration of an atomic beam of calcium was achieved by using the radiation of a frequency double diode laser at 845.2 nm. In order to enhance the violet beam generation the doubling crystal, KNbO3, is placed inside an external build-up cavity. The laser beam at 423 nm, counter- propagating with the atomic beam, is put into resonance with the 1S0 yields 1P1 transition of Ca. To keep the laser in resonance with the atomic transition during the cooling process, the Zeeman technique is used.