High-precision accelerometers-gravimeters based on fiber-optic systems

Abstract

A significant advantage of fiber-optic sensors (FOS) over electrical sensors is their absolute indifference to the effects of electromagnetic interference. However, the high noise level of the low-intensity flux of high-energy photons in the measuring paths of analog FOS limits the accuracy of measuring devices based on them. The fact is that the analog modulation of any parameter in a FOS ultimately leads to fundamentally low-precision measurements of the degree of modulation of the intensity of the optical flux. The way out of this situation is the rejection of the analog and the transition to discrete modulation principles in the FOS of the optical flow parameters. To this end, in the modulation process, new parameters, additional to optical but not optical, are introduced into the optical flow, which will play the role of information carriers. This approach retains all the advantages of fiber optics (the optical stream remains the carrier of information), and transfers the problem of measurement accuracy to other, non-optical areas where it is properly solved. The possibility of constructing precision accelerometers (gravimeters) with measuring transducers based on new-class FOS with pulse modulation of the optical flux intensity (IFOS) is considered. The sensitive element of such an IFOS is a conical pendulum, on the basis of a cantilever mounted piece of quartz optical fiber, on the free end of which there is an inertial mass. High values of the metrological parameters of the accelerometer based on the IFOS are ensured by the possibility of precise measurements of the temporal parameters of the sequence of optical pulses generated by it. The processing of signals from the IFOS is carried out by methods and means of digital technics, which eliminates the possibility of introducing a signal processing error and allows purposefully correct the measurement results. Thanks to this, it is possible to neutralize the influence on the measurement results of both the natural flaws and imperfections of the IVOD, as well as the errors of their manufacture and adjustment. The study of the mathematical model of IFOS with real values of its design parameters and the frequency of the generator of counting pulses confirmed the possibility of obtaining high values of its metrological characteristics: the threshold sensitivity is up to 10-13 g, and the dynamic range of the measured accelerations is up to 109. These figures should be considered as illustrative. The principle of construction of the IFOS design makes it possible to easily change its metrological parameters over a wide range by a corresponding change in both the parameters of the elements of its construction and the frequency of the counting pulse generator.