Gravity-Assisted, Passive Cancellation of Disturbances for Inertial Sensors

2013 ◽  
Author(s):  
Taras Karpachevskyy ◽  
Swavik Spiewak
Keyword(s):  
High Speed ◽  
Vibration Isolation ◽  
Inertial Sensors ◽  
Inertial Sensor ◽  
Broad Class ◽  
Signal Transmission ◽  
Low Frequency ◽  
Cost Ratio ◽  
Low Frequencies ◽  
Digital Circuitry

Continuing enhancements in Microsystem Technologies facilitate the development of inertial sensors — accelerometers and gyroscopes — of unprecedented performance to cost ratio and broaden the frontiers of their application. Of particular interest, because of their immunity to ambient disturbances, are sensors equipped with high resolution Electro-Mechanical ΣΔ converters and with a high speed, digital serial signal transmission. The digital circuitry of these sensors reaches the accuracy of 0.02 parts-per-million (ppm). However, the analogue transducers of measured physical quantities into electrical signals inside of the even best inertial sensors are prone to inherent imperfections of analog systems such as nonlinearity, cross-sensitivity, or noise. The best accuracy of these transducers is about two orders of magnitude worse than that of the electrical circuitry. The overall accuracy can be greatly improved by using corrective filters that cancel the effects of imperfections in the analogue transducers. The effectiveness of these filters hinges upon the accuracy of identifying comprehensive models of the analogue transducers. Ambient disturbances, in particular mechanical vibrations, greatly deteriorate the accuracy of identification. Their impact can be attenuated to some extent by using vibration isolation platforms. The effectiveness of attenuation is usually good at the frequencies above 5–10 Hz, however it is poor at low frequencies. This poor attenuation is a significant disadvantage since the low frequency phenomena in inertial sensors have pronounced impact on their suitability for a broad class of applications (e.g., navigation). The presented research focuses on the design of a passive vibration isolation device in which horizontal movement is coupled to tilt in a way that a component of the gravity perceived by the tested inertial sensor effectively cancels out the horizontal acceleration coming from the ambient vibrations.

Measurement of Dynamic Strain

1943 ◽  
Vol 10 (2) ◽  
pp. A85-A92
Author(s):  
C. O. Dohrenwend ◽  
W. R. Mehaffey
Keyword(s):  
High Speed ◽  
Shock Loading ◽  
Low Frequency ◽  
Dynamic Strain ◽  
Time Axis ◽  
Low Frequencies ◽  
Strain Measurements ◽  
Moving Vehicles ◽  
Machine Parts ◽  
Dynamic Strains

Abstract The measurement of dynamic strains of both high and low frequency give rise to a variety of problems in instrumentation. Two types of equipment and circuits designed and used by the authors are discussed in detail. The first type based on the amplitude-modulated method is for low frequencies from zero to about 15 per cent of the carrier frequency of 1025 cycles per sec. The equipment has application to strain measurements varying from static values to those produced in moving vehicles, various machine parts, structures such as crane bridges, in fact all strain measurements where the frequency is 150 cycles per sec or less. The second type of equipment discussed is a potentiometer type and is for high-frequency strain measurements from 100 cycles per sec to 8000 cycles per sec. This high-speed equipment is conveniently used for impact strain, such as produced in hammer blows, shock loading, forging equipment, and impact-factor determination. Both units are designed to be used with a cathode-ray oscillograph which lends itself to a variety of recording methods. The methods discussed include both the type where the time axis is obtained by sweeping the oscilloscope beam on a stationary film and where the time axis is obtained mechanically.

A new method to reduce the noise of the miniaturised inertial sensors disposed in redundant linear configurations

2013 ◽  
Vol 117 (1188) ◽  
pp. 111-132 ◽  
Author(s):  
T. L. Grigorie ◽  
R. M. Botez
Keyword(s):  
Inertial Sensors ◽  
Inertial Sensor ◽  
Low Frequency ◽  
Minimum Variance ◽  
Measurement Unit ◽  
Time Step ◽  
Accelerometer Sensor ◽  
Sensor Model ◽  
Input Acceleration

Abstract This paper presents a new adaptive algorithm for the statistical filtering of miniaturised inertial sensor noise. The algorithm uses the minimum variance method to perform a best estimate calculation of the accelerations or angular speeds on each of the three axes of an Inertial Measurement Unit (IMU) by using the information from some accelerometers and gyros arrays placed along the IMU axes. Also, the proposed algorithm allows the reduction of both components of the sensors’ noise (long term and short term) by using redundant linear configurations for the sensors dispositions. A numerical simulation is performed to illustrate how the algorithm works, using an accelerometer sensor model and a four-sensor array (unbiased and with different noise densities). Three cases of ideal input acceleration are considered: 1) a null signal; 2) a step signal with a no-null time step; and 3) a low frequency sinusoidal signal. To experimentally validate the proposed algorithm, some bench tests are performed. In this way, two sensors configurations are used: 1) one accelerometers array with four miniaturised sensors (n = 4); and 2) one accelerometers array with nine miniaturised sensors (n = 9). Each of the two configurations are tested for three cases of input accelerations: 0ms−1, 9·80655m/s2 and 9·80655m/s2.

scholarly journals Superluminal Motion in CTA 102

1989 ◽  
Vol 134 ◽  
pp. 529-530
Author(s):  
Ann E. Wehrle
Keyword(s):  
Flux Density ◽  
High Speed ◽  
Low Frequency ◽  
Precise Determination ◽  
Flux Variation ◽  
Low Frequencies ◽  
Superluminal Motion ◽  
Low Frequency Variability ◽  
Expansion Speed

Sholomitskii (1965) discovered that the flux density of the quasar CTA 102 varies at low frequencies on a timescale of a few months. Low-frequency variability can be explained by “superluminal flux variation” (Romney et al. 1984): If the intrinsic brightness of a component moving in a relativistically beamed source varies by only a few percent, the observer sees its flux density change by a much larger factor δ3-α when the optically thin blob moves almost directly toward the observer. Such a relativistically beamed source is likely to exhibit superluminal motion if studied with sufficient resolution and sensitivity. Superluminal motion in CTA 102 was discovered by Bååth (1987) who concluded on the basis of maps made at three epochs at a frequency of 932 MHz that two components were separating at a rate of 0.65 milliarcseconds (mas) per year. Using a redshift z = 1.037 and H0 = 100 km s−1 Mpc−1, q0 = 0.5, this expansion speed corresponds to (18 ± 4)h−1c. The extraordinarily high speed led us to make VLBI images of the source at a higher frequency in order to increase the resolution and make a more precise determination of the speed.

Simultaneous TR-PIV and CH* Chemiluminescence During Combustion-Instability Triggered Flame-Flashback in a Backward Facing Step Combustor

2019 ◽  
Author(s):  
Pankaj Pancharia ◽  
Vikram Ramanan ◽  
Baladandayuthapani Nagarajan ◽  
S. R. Chakravarthy
Keyword(s):  
Turbulence Intensity ◽  
High Speed ◽  
Combustion Instability ◽  
Low Frequency ◽  
High Amplitude ◽  
Static Stability ◽  
Low Frequencies ◽  
High Speed Data Acquisition ◽  
Flame Imaging ◽  
Flame Flashback

Abstract The present study is an experimental investigation of the nature of acoustically induced flashback in a lab-scale dump combustor. The control parameters varied include the inlet Reynolds number (Re) and the inlet turbulence intensity. The primary bifurcation plots of the combustor from stable to the unstable condition are seen to be significantly altered by the inlet turbulence intensity, with the latter delaying the onset of combustion instability to higher Re. The analysis of multivariate high-speed data acquisition and processing (viz. unsteady pressure, flame imaging and velocity field by means of PIV) reveals the role of low-frequency high amplitude acoustics in modulating the flame. It is seen that high amplitude oscillations are sustained by two mechanisms 1. Modulation of the flame by coherent structures shedding at the step and 2. The bulk flame motion in-and-out at the edge of the step. It is seen that flow reversal at sufficiently low frequencies provide enough duration for the hot products to ignite fresh reactants upstream of the duct, which in-turn reinforces the coherent unsteadiness in the system, thereby increasing the propensity of the mixture to be ignited more upstream with every cycle. This ultimately leads to the flame flashing back till the point of premixing. This work thus addresses and reforms the occurrence of flashback being an example of loss of static stability, whereby the overriding presence of dynamic combustion instability results in a flashback to behave in a dynamic manner.

Vibration Control of a Rigid and Flexible High-Speed Railway Vehicle

2020 ◽  
Author(s):  
Semiha Türkay ◽  
Aslı S. Leblebici
Keyword(s):  
High Speed ◽  
Low Frequency ◽  
Railway Vehicle ◽  
Allowable Limit ◽  
Low Frequencies ◽  
Railway Line ◽  
Power Spectral ◽  
Spectral Density Functions ◽  
The Right ◽  
Euler Bernoulli Beam

Abstract In this paper, the vertical carbody dynamics of the railway vehicle excited by random track inputs are investigated. The multi-objective ℋ∞ controllers for carbody weight of the actual, heavy and a mass confined in a polytopic range have been designed with the aim of reducing the wheel forces, heave, pitch and roll body accelerations of the vehicle. Later, the carbody mass is modelled as a free-free Euler Bernoulli beam and the low frequency flexural vibrations of the train body are examined. An omnibus ℋ∞ controller is synthesized to suppress both the rigid and low frequencies flexible modes of the railway vehicle. The performances of the ℋ∞ controllers are verified by using the passive and active suspension responses on the right and left rail track disturbances that are represented by the power spectral density functions authenticated for the stochastic real track data collected from the Qinhuangdao-Shenyang passenger railway line in China. Simulation results showed that all controllers exhibit a very good performance by effectively reducing the car-body accelerations in vicinity of the resonanat frequencies while keeping the wheel-rail forces in the allowable limit.

Cold Atom Interferometer activities for measuring the Earth’s gravity field

2020 ◽  
Author(s):  
Luca Massotti ◽  
Olivier Carraz ◽  
Paolo Bensi ◽  
Roger Haagmans ◽  
Philippe Martimort ◽  
...  
Keyword(s):  
Gravity Field ◽  
Attitude Control ◽  
Inertial Sensor ◽  
Low Frequency ◽  
Cold Atom ◽  
Expected Improvement ◽  
Airborne Gravity ◽  
Integration Time ◽  
Low Frequencies ◽  
The Earth

<p>In the past decade, it has been shown that atomic quantum sensors are a newly emerging technology that can be used for measuring the Earth’s gravity field. Whereas classical accelerometers, based e.g. on capacitive sensing and electrostatic actuation, are limited by relatively high noise at low frequencies, Cold Atom Interferometers (CAI) can be highly accurate over the entire frequency range, which also has the benefit that they do not need any calibration phase. Several studies related to these new sensor concepts were initiated at ESA, mainly focusing on technology development for different instrument configurations (gravity gradiometers and  satellite-to-satellite ranging systems) and including validation activities, e.g. two successful airborne surveys with a CAI gravimeter. We will present the first conclusions of these different mission and instrument studies:</p><ul><li>The first airborne gravity survey during the ESA Cryovex/KAREN 2017 campaign using this technology was conducted by DTU and ONERA. The measurements did not show any drift and the accuracy was found to be less than 4 mGal at 11 km resolution. A second campaign has been conducted by ONERA and CNES in 2019 in the South of France and improved the accuracy by a factor 4, reaching classical airborne survey state-of the art performance.</li> <li>A first space quantum gravity mission concept is based on a gravity gradiometer that delivers a very high common mode rejection, greatly relaxing the drag-compensation requirements.</li> <li>The second concept is based on quantum accelerometers for correcting low frequency errors of electrostatic accelerometers that are used in a low-low satellite-to-satellite ranging concept in order to measure non-gravitational accelerations.</li> </ul><p>For both concepts we will present the expected improvement in measurement accuracy and in the derived Earth gravity field models, taking into account the different types of measurement (e.g. single axis vs. three axis, integration time, etc.) and different mission parameters (e.g. attitude control, altitude of the satellite, lifetime of the mission, etc.). A technology roadmap will be outlined for potential implementation of a quantum inertial sensor geodesy mission within 10-15 years.</p>

scholarly journals Spectra of Low-Frequency Ground Vibrations Generated by High-Speed Trains on Layered Ground

1997 ◽  
Vol 16 (4) ◽  
pp. 257-270 ◽  
Author(s):  
V.V. Krylov
Keyword(s):  
High Speed ◽  
Low Frequency ◽  
Ground Vibration ◽  
Ground Vibrations ◽  
Frequency Spectra ◽  
Low Frequencies ◽  
High Speed Trains ◽  
Frequency Components ◽  
Noticeable Reduction ◽  
Layered Ground

Increase in speeds of modern railway trains is usually accompanied by higher levels of generated ground vibrations. In the author's earlier paper [V.V. Krylov, Applied Acoustics, 44, 149–164 (1995)], it has been shown that especially large increase in vibration level may occur if train speeds v exceed the velocity of Rayleigh surface waves in the ground cR., i.e., v > cR. Such a situation might arise, for example, with French TGV trains for which speeds over 515 km/h have been achieved. The present paper investigates the effect of geological layered structure of the ground on ground vibrations generated by high-speed trains. It is shown that, since Rayleigh wave velocities in layered ground are dispersive and normally increase at lower frequencies associated with deeper penetration of surface wave energy into the ground, the trans-Rayleigh condition v > cR may not hold at very low frequencies. This will cause a noticeable reduction in low-frequency components of generated ground vibration spectra. Theoretical results are illustrated by numerically calculated frequency spectra of ground vibrations generated by single axle loads travelling at different speeds and by TGV or Eurostar high-speed trains.

scholarly journals Characterisation of Signal Amplitude-Frequency for Indoor Power Line Communication Channel in the 1 — 30 MHz Broadband Frequencies

2021 ◽  
Vol 12 (1) ◽  
pp. 33-41
Author(s):  
Adedayo Oluyomi Ajibade ◽  
llesanmi Banjo Oluwafemi ◽  
Israel Esan Owolabi
Keyword(s):  
High Speed ◽  
Communication Channel ◽  
Power Grid ◽  
Signal Transmission ◽  
Low Frequency ◽  
Signal Amplitude ◽  
Power Line ◽  
Power Grids ◽  
Power Lines ◽  
Power Line Communication

The transmission of data signals over power lines is a very promising technique for delivering indoor broadband communication services. However, since power grids were originally designed for high-voltage low-frequency signal transmission, there is a frequency mismatch between the power grid and high-frequency data signals. This mismatch poses a challenge to deploying power lines as a communication channel. Although, studies and researches conducted in several countries have made transmission of data over power lines possible, the behaviour and properties of the power grid cannot be generalised. Hence, the need for in-depth experiment and measurement on the suitability and capability of the Nigerian power grid for data transmission is crucial for proper characterising and modelling of the power line communication (PLC) channel. In this paper, we present experimental measurements and results of the effects of frequency variations on the attenuation experienced by broadband high-speed data signals transmitted over the Nigerian indoor power line network.

Harnessing the Quasi-Zero Stiffness From Fluidic Origami for Low Frequency Vibration Isolation

2017 ◽  
Author(s):  
Sahand Sadeghi ◽  
Suyi Li
Keyword(s):  
Vibration Isolation ◽  
Low Frequency ◽  
Harmonic Balance Method ◽  
Design Parameters ◽  
Base Excitation ◽  
Design Guideline ◽  
Low Frequencies ◽  
Cellular Solid ◽  
Low Frequency Vibration ◽  
Internal Volume

This research investigates a quasi-zero stiffness (QZS) property from the pressurized fluidic origami cellular solid, and examines how this QZS property can be harnessed for low-frequency base excitation isolation. The QZS property originates from the nonlinear geometric relations between folding and internal volume change, and it is directly correlated to the design parameters of the constituent Miura-Ori sheets. Two different structures are studied to obtain a design guideline for achieving QZS: one is identical stacked Miura-Ori sheets (ismo) and the other is non-identical stacked Miura-Ori sheets (nismo). Further dynamic analyses based on numerical simulation and harmonic balance method, indicate that the QZS from pressurized fluidic origami can achieve effective base excitation isolation at low frequencies. Results of this study can become the foundation of origami-inspired metamaterials and metastructures with embedded dynamic functionalities.

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