Linear Accelerometers Research Articles

Linear accelerometer with electromagnetic suspension for the sensing element

Linear accelerometer with electromagnetic suspension for the sensing element

Fiber-optic accelerometer with hydrophone applications

A fiber-optic linear accelerometer based on intensity modulation produced by lateral displacement of a cantilevered fiber has been fabricated and tested. The model reported on is constructed with multimode fiber and has a displacement sensitivity of 6.4 x 10(-13) m. The device has general application as a linear accelerometer with the inherent advantages of remote optical fiber sensing. Particular attention is given to sono-buoy hydrophone applications in which the present model has a sensitivity limit corresponding to 75 dB relative to 1 microPa at 1 kHz. Means for substantially improving the accelerometer's sensitivity as a hydrophone are discussed.

The Rotating Beam Gyroscope

This paper investigates the dynamics of a novel “multisensor” comprising a two-axis gyroscope and a single-axis linear accelerometer. The theoretical analysis indicates that the gyroscope has two modes of operation, untuned and tuned, offering, respectively, angular rate and angular displacement measurement capability, depending on the damping and mistuning present. In addition to the sensing of two-axis angular motion, the instrument is capable of measuring linear acceleration along a third axis. Experimental tests on a prototype instrument show generally good agreement with the theory giving confidence of the development potential of the instrument.

Computation of Rigid-Body Rotation in Three-Dimensional Space From Body-Fixed Linear Acceleration Measurements

The angular acceleration of a rigid body with respect to a body-fixed (moving) frame can be reliably computed from nine acceleration field measurements. Noncommutativity of finite rotations causes computational problems during numerical integration to obtain the transformation matrix, especially when the rotation is three-dimensional and there are errors in the measured linear accelerations. A method based on the orientation vector concept is formulated and tested against hypothetical data. The rigid-body rotations computed from linear accelerometer data from impact acceleration tests are compared against those obtained from three-dimensional analysis of high speed movie films.

Ship motion measurement filter design

A procedure is presented for designing Kalman filters to measure linear and angular ship motion parameters using realistic models of the ship motion dynamics. The design is based on the state space modeling of ship motion dynamics. The designed filters exhibited significant accuracy improvement (order of magnitude) over filters which do not model ship dynamics. The sensitivity of the filter mechanization to mismodeling of dynamics is investigated. Bounding filter design techniques are used to minimize the effects of mismodeling. The particular measurement system investigated consisted of linear and angular accelerometers in a strapdown mode. The design techniques are also applicable to inertial instruments in a stable inertial platform mode.

Closure to “Discussion of ‘Measurement of Angular Acceleration of a Rigid Body Using Linear Accelerometers’” (1976, ASME J. Appl. Mech., 43, pp. 377–378)

Closure to “Discussion of ‘Measurement of Angular Acceleration of a Rigid Body Using Linear Accelerometers’” (1976, ASME J. Appl. Mech., 43, pp. 377–378)

Measurement of Angular Acceleration of a Rigid Body Using Linear Accelerometers

The computation of angular acceleration of a rigid body from measured linear accelerations is a simple procedure, based on well-known kinematic principles. It can be shown that, in theory, a minimum of six linear accelerometers are required for a complete definition of the kinematics of a rigid body. However, recent attempts in impact biomechanics to determine general three-dimensional motion of body segments were unsuccessful when only six accelerometers were used. This paper demonstrates the cause for this inconsistency between theory and practice and specifies the conditions under which the method fails. In addition, an alternate method based on a special nine-accelerometer configuration is proposed. The stability and superiority of this approach are shown by the use of hypothetical as well as experimental data.

Intention tremor--a method of measurement.

A method of measuring and analysing intention tremor using a linear accelerometer is described. Reasons are given for measuring this particular parameter of the tremor, for using this specific energy conversion device, and for employing the particular form of analysis. A comparison of the numerical values obtained for the amount of tremor activity, compared with a corresponding clinical grading, is made for 30 patients with intention tremor due to a variety of pathological causes. It is shown that the method gives clear correlation with the clinical assessments, although certain discrepancies are noted, and their importance discussed.

Linear and Rotational Quartz Fiber Accelerometers for Geophysical and Inertial Use

Theme T quartz fiber accelerometers are being developed for geophysical and inertial use. Prototype models of the vertical and horizontal instruments exist and are undergoing tests. A rotation sensor capable of measuring rotational accelerations about a single axis is being designed. While most of the data gathered to date pertains to geophysical phenomena, these instruments may be used directly in any application requiring sensitive, low drift accelerometers.

Performance of LaCoste-Romberg Shipboard Gravity Meters in 1963 and 1964

Tests of LaCoste-Romberg shipboard gravity meters in a gimbaled suspension in 1963 and on a stable platform in 1964 were made on a 100-foot vessel off the coast of California. Errors during the 1963 tests ranged up to 20 mgal under conditions in which the wave accelerations did not exceed 50 gal; during the 1964 tests very large errors were observed under conditions in which the wave accelerations at times exceeded 500 gals. In both tests the errors are shown to be caused primarily by nonlinear response of the gravity meter itself. Corrections can be computed from beam position records taken during the gravity observations at sea, provided that the meter nonlinearity has been determined in the laboratory. These corrections improved the accuracy of the measurements quite considerably, and the same method can be used to reduce errors in most previously obtained results with LaCoste-Romberg gravity meters. Long-period ship motions, which had been thought to be the principal source of error at one time, are shown to be unimportant. Apparent long-period accelerations recorded on low-pass filtered accelerometer records from the gimbaled meter are accounted for in terms of nonlinearities in the inertia-bar horizontal references. These apparent motions were not present on the corresponding accelerometer records from the gyroscopically stabilized platform, which employed more linear accelerometers of the force-rebalance type.

Measuring Rotational Motion with Linear Accelerometers

Inertial navigation systems usually use gyroscopes to sense angular motion and use accelerometers to sense linear acceleration. It is feasible, however, using only linear accelerometers as sensors, to determine both the angular velocity and the linear acceleration of a vehicle. This paper presents and compares five configurations of linear accelerometers which may be used to determine both the angular motion and the linear motion of a vehicle.

The effect of acceleration on a filamentary discharge in inert gases

A horizontal filamentary discharge in inert gases, especially xenon, bows upwards owing to convection. Experiments are described on such a discharge in 90% neon-10% xenon in which an acceleration was applied to vary the lateral displacement of the discharge column. The position of the column was detected as a difference in potential between a pair of probes, which increased with increasing acceleration. The variation of this potential difference with the angle between the probes and the acceleration was examined, as was the effect of the ambient temperature. The principle described can be used in a linear accelerometer. However, individual calibration is necessary since considerable variations were observed in the behaviour of apparently identical structures, although the changes with time were small.

On the general equations of inertial navigation

Derived and investigated are the equations of ideal (unperturbed) and perturbed operation of a generalized system of inertial navigation which determines the coordinates of a moving object from the measurements of three linear accelerometers and three angular velocity meters measuring absolute angular velocity. The instruments are located along the axes of an orthogonal trihedron, the origin of which coincides with a certain point in the moving object. In contrast to [1 and 2], the orientation of the trihedron axes is arbitrary. The equations of ideal operation take into account the non-central nature of the Earth's gravitational field. The equations of perturbed operation include instrument error effects. Error equations are derived and investigated not only for small but also for the finite values of the variables of the perturbed operating conditions. The particular cases are the equations and the results of investigation of the particular control systems considered in [1 to 7].

Upper-atmosphere density obtained from measurements of drag on a falling sphere

This paper gives the density profile versus altitude from 95 to 130 km obtained from drag measurements made directly from within a falling sphere. In the test, an inflatable sphere, 2.74 meters in diameter, is ejected somewhere between 80 and 100 km during the ascent of an Aerobee 150 rocket. At the center of the sphere, supported by an inflated cylindrical strut, are the measuring instruments and the necessary electronics to telemeter the information continuously throughout the flight. The main sensors are linear accelerometers aligned to measure the X, Y and Z components of acceleration of the sphere from which total drag is obtained. From ejection altitude, the sphere continues to an altitude of approximately 250 km on what is, except for drag, a free-fall trajectory. Measurements of drag acceleration obtained by this method are supplemented by measurements of velocity and position obtained by tracking systems.

An application of strain-gage-type instruments to the analysis of the equilibrium function in human subjects and animals.

First of all introducing the principles of the strain-gage and also the characteristics of the strain-gage-type instruments hitherto described, two of the instruments specially devised by the authors for the purpose of precise recording of the body movements in human subjects or animals under various conditions, such as labyrinthine or visual stimulation, have been presented in detail. Using an unbonded strain-gage-type linear accelerometer, or the two newly devised strain-gage-type instruments, together with either electronystagmograph or electromyograph, the equilibrium function in human subjects or animals has been successfully analysed.

Acceleration ballistocardiography; design, construction, and application of a new instrument.

The construction of a linear accelerometer for use in ballistocardiography is presented including the relationship between acceleration, displacement, and velocity. The sensing element described is new in the field of ballistocardiography, being based on an electrochemical principle. A means of easily calibrating the instrument is described, thereby allowing quantitative measurements of various components of the ballistocardiogram. Tracings of one abnormal and two normal individuals are illustrated to show the relationship between displacement and acceleration.

Reduction of Flight Test Data From Linear Accelerometers

The problems discussed in this note refer to the simplest case of the use of linear accelerometers, in which the flight path is in the vertical plane of symmetry of the aeroplane, and the acceleration normal to the path is to be determined.Generally two facts are neglected:– (i)That the accelerometer senses along an arbitrary body axis ZB (Fig. 1), instead of along the wind axis Z (normal to the path).(ii)That the accelerometer is not placed exactly at the e.g. of the aeroplane but at some point A, having co-ordinates xA and zA in the body axes.