Vibration Pickup Research Articles

Automation of the fringe‐disappearance method for calibrating vibration pickups

The classical fringe‐disappearance method of optical interferometry was incorporated into an automated system for calibrating vibration pickups. The new feature of the technique is the ability to set the vibration level corresponding to a fringe‐disappearance condition by an algorithm. For this purpose only the dc component of the photodetector output needs to be monitored. The complete system includes a Michelson interferometer, a minicomputer, and a digital voltmeter. Measurements of acceleration sensitivity performed by this method are compared with the results obtained by other techniques. Factors affecting the accuracy and precision of the new method have been investigated, and are discussed in considerable detail.

Horizontal contact resonances of vibration pickup with rectangular bases on soil surfaces

The horizontal contact resonance, which is formed by the resonant system due to the mass of a vibration pickup and the contact compliance of a setting point, causes errors in measurement and places restrictions on the measurement frequency range. The characteristics of the horizontal resonance depend on the type and condition of the ground surface and the method of planting the vibration pickup. This paper indicates the characteristics of the horizontal contact resonances of the rectangular vibration pickup with various base shapes, and derives expressions for a coupled motion of the pickup. It is suggested that the horizontal resonance and the response of the coupling system of the rectangular vibration pickup are significantly affected by the height of the center of gravity, the base area, and the base shape. The relationships are represented by a simple curve for the horizontal resonance. The agreements between the analog equations derived here and the values of the measurement on actual fields are well within the accuracy required for engineering analysis. The derived solutions provide adequate accuracy for practical applications to machine foundations with various rectangular bases.

Method of vibration measurement of tall structures

The method of measurement is based on the use of specially developed absolute vibration pick-ups. The frequency range of these pick-ups is 0.2–50 Hz, and the amplitude range is ±50 mm. The construction of the pick-ups gives a sensitivity to 0.001 mm. One of the most important characteristics of the apparatus is that the pick-ups have very similar amplitude-frequency responses and that they behave as linear vibration systems. The results of measurements on a tall building erected in the FEAL system are described. Measurements of the motion of the building caused by wind made it possible to distinguish bending and torsional vibrations.

Measurement of complex sound speed in sonar transducer materials using impact testing techniques

A mathematical model has been developed for evaluating the complex‐valued sound speed in transducer materials. The associated measurement scheme employs a symmetrical longitudinal vibrator, wherein the preloaded test specimen constitutes the central piece of the test resonator. By impacting the test resonator, its resonance frequency and mechanical Q can be determined using a spectrum analyzer and vibration pickup. The mathematical model of the composite longitudinal vibrator‐type test resonator facilitates the evaluation of the sound speed in the test sample from the measured resonance frequency and Qm. Experimental results are presented for several materials, with the measured sound speeds given as a function of prestress and temperature.

Investigations of horizontal contact resonance of vibration pickup

Investigations of horizontal contact resonance of vibration pickup

Horizontal resonant frequencies of vibration pickup on soil surfaces

A vibration pickup set on a soil surface has a resonant frequency caused by the mass of the pickup and the contact compliance of a setting point. The resonant frequency produced in the measurement system causes the errors in measurement and places restrictions on the measurement frequency range. This paper gives the characteristics of the horizontal resonant frequency and also derives expressions for a coupled motion of the vibration pickup model set on an elastic half-space. It is shown graphically, by an example, that the height of the center of gravity and the contact areas of the pickup have considerable effects upon the horizontal resonant frequency. The derived solutions, which are approximately represented as the function of resonant frequency and the frequency of an exciting force, provide adequate accuracy for engineering analysis to the footings of little bodies.

Effect of pressurization by an internal pressure on the cyclic strength of welded cryogenic pipelines

As a result of x-ray monitoring of the seams, samples of tubes with from 6 to 20% nonfusion were selected for the tests. The actual dimensions of the nonfusion zones were determined after fracture. The criterion for evaluation of nonfusion was the ratio of the total area of the defects in the welded seam to the rated area of the tube. The static pressure in the samples was set up at normal temperature. The value of the pressure of the pressurization was selected from the condition of the attainment of plastic deformations in the welded joint in a nonfusion zone, and the assurance of the relaxation of the residual welding stresses. The plastic deformations in the welded joint were monitored by the strain-gage method using PKB-5-100 strain-gage pickups. Under these circumstances, the deformation in the axial direction after pressurization was 0.2-0.3%. For tubes with a diameter of 103  3 ram, the pressurization pressure was 132 kg/cm 2, and, for tubes with a diameter of 38 x 3 ram, 412 kg/cm 2. The holding time of the samples under the load did not exceed 2 min. For the testing of tubes with cyclic loading by bending and elongation, special attachments were built for mass-produced testing machines. Tests of tubes with a diameter of 38 x 3 mm with simple cyclic bending were made in a VU 70/100 vibration test stand. At cryogenic temperatures, liquid nitrogen was fed into the cavity of the sample during the tests. The frequency of the cyclic loads with testing in the stand was 16-40 Hz. Tests of tubes with a diameter of 103  3 mm with axisymmetric loading were made in a PDM-100Pu pulsation machine, equipped with a cryogenic chamber for low-temperature tests. The frequency of the loading (elongation) of the samples in these tests was 10 Hz. The adopted criterion of fracture of the samples was the moment of the appearance of a through fatigue crack with a length of 10-15 ram. As the tests showed, with the appearance of a through microcrack, it grows considerably. With tests in a VU 70-100 test stand, this moment is characterized by a change in the frequency of the vibrations of the sample-vibration test-stand table system. The change in the frequency of the vibrations was recorded by a special vibration pickup, connected into the control circuit and shutting down the test stand. With tests in a TsDM-100Pu vibration machine, the moment of the appearance of a through fatigue crack coincided with a lowering of the reading of the load according to a dynamic manometer, which was recorded by an operator. With both kinds of cyclic loading with a frequency up to 16-20 Hz, the temperature of the samples rose only very slightly. With the testing of samples with a high frequency of the loading, there was a considerable increase in the temperature. The fatigue limits of the welded joints of the tubes were determined using the method of accelerated tests [1-3] of ten samples, and were verified experimentally on five samples, on a base of 5 x 106 cycles.

Contact Resonance of Vibration Pick-up and its Control

Contact Resonance of Vibration Pick-up and its Control

Calibration of vibration pick-ups used in seismic method in mines. In Polish : Przegl. Gorn. V31, N10, 1975, P421–424

Calibration of vibration pick-ups used in seismic method in mines. In Polish : Przegl. Gorn. V31, N10, 1975, P421–424

浮選スラリー用オンストリーム粒度測定装置

An On-stream size measuring equipment has been developed for flotation pulp. It uses both vibrational output and light absorption. Sample flows into the vibration detection cell and next into the light absorption cell.The vibration pickup detects very weak signals that are produced by collisions of particles and the cell. Effective signals are separated through an acoustic filter from noises.The cross section area of light absorption cell is 1.3 cm2 and light pass length is 3 mm. Suitable pulp density for this cell is about 4 wt%.Several kinds of closed circuit tests have been done using SiO2 and complex sulphide ore particles. From these tests the following results were obtained.1) When n value of Rosin-Rammler distribution function of samples remained nearly constant, it is possible for this equipment to measure the size distributed samples as well as size sorted samples2) When the variation of pulp density is limited in narrow range, an on-stream size measurement is attainable by the vibrational output only.At the pilot plant tests, -200 mesh% of flotation pulp were measured by this equipment. The results of on-stream measured size, compared with screen analysis, were as follows.Number of samples 109-200mesh%(mean value) 73.91%Mean square root error 2.03%Correlation coefficient 0.923

Mounting of Vibration Pickup of Vibration Level Meter on the Surface of Ground Soil

Mounting of Vibration Pickup of Vibration Level Meter on the Surface of Ground Soil

Some specific characteristics of vibration pickup type auditory canal microphones

In high‐noise environments, we cannot sufficiently transmit voice signals by the usual transducers. Therefore, we have developed a vibration pickup‐type microphone (acceleration type) and propose that communications be exchanged using this method. We chose the auditory canal in order to equip this microphone easily. In this investigation, we (1) compared a vibration pickup‐type auditory canal microphone with a noise‐canceling microphone focusing on their ability to shut noise out; and (2) compared an air‐conduction spectrum caught by a handy microphone with a bone‐conduction spectrum caught by the vibration pickup‐type used in Experiment 1. When subjets pronounced the vowel /a/ with a vibration pickup‐type microphone, the ability to shut noise out increased 5 to 9 dB when compared with a noise‐canceling microphone. If the subjects put on earmuffs, the ability to shut noise out increased 6–10 dB. According to the results of Experiment 2, the response decreased in the high frequency beyond 1 kHz. This might be caused by the dumping of bone conduction, We then tried to make an equalizer in order to produce a more natural voice by revising the high‐range dumping.

ねじり受振器の固有周期伸長のための電磁装置

A simple electromagnetic device is developed for lengthening the natural period of torsional vibration pickup, utilizing a conventional eddy-current damper which is one of the essential elements of the seismic pickup of long natural period. A rectangular coil of small number of turn, connected to a DC source, is bonded on a surface of the plate conductor of the damper in such a way that two facing sides of the coil intersect respectively leakage fluxes existing symmetrically on both sides of the permanent magnet of the damper. By proper dimensioning of the coil, each of two facing sides travels inside a range within which the leakage-flux density varies with respect to the travel of coil as linearly as possible; thus a controllable negative restoring torque is electrodynamically generated to lengthen the natural period, and the resulting natural period can be pasily controlled by adjusting the coil current. The principle of operation of the device and limiting factors for lengthening the natural period are discussed in detail. Under a laboratory condition, the natural period Of 1 s can be lengthened to as long as 7 s.

Optimum allocation of vibration pickups on randomly vibrating structures on the basis of information theory

Optimum allocation of vibration pickups on randomly vibrating structures on the basis of information theory

大形歯切盤の伝達誤差の測定

A seismic instrument for measuring the hob-to-table cyclic error of large gear hobbing machine is described in which a large and heavy torsional vibration pickup, currently in use for detecting the non-uniformity of rotation of the machine table, is replaced by a pair of small and light rectilinear vibration pickups mounted tangentially on a periphery of the machine table, 180 apart. Two differential-transformer seismic pickups of 1.6 s natural period are connected so as to be additive for the rotational vibration and null each other for the rectilinear vibration of the machine table. The sensitivity for rotational vibration increases in proportion to the table diameter, the minimum measurable angular displacement being 0.0025 sec of arc for the table diameter of 6 m.From theoretical analysis of the motion of the seismic system under working condition, it is shown that the equality of the sensitivities and frequency responses and the parallelism of the sensitive axes of both pickups, and the accuracy of the machine alignment are important factors in determining the measurement error; and these factors are examined in detail. The operating principle of the instrument and the adjustment and calibration of pickups, together with the test results on the bobbing machines of 2 m and 6 m in table diameter, are outlined.

変位形ねじり受振器の試作

This paper describes the design and performance of a torsional vibration pickup which has been newly developed for measurements of the transmission errors of gears. The pickup described consists of a seismic inertia suspended between two units of cross-spring pivots, a differential transformer, an eddy-current damping device, and a slip-ring assembly, and has the following characteristics; size 130 φ 182 mm : weight 3.2 kg : natural frquency 1 Hz or 0.62 Hz : fraction of critical damping 0.55.The variation of natural frequency, one of the principal disadvantages of the pickups currently used for the above-mentioned applications, can be eliminated by placing the center of gravity of the seismic inertia at the mid-point of the axis of rotation of the seismic system and by mounting the pivots in such a way that each unit of pivot is in the opposed angular position. The theory and practical performance limit of the elimination of this disadvantage is discussed, together with the static angular rotation of seismic inertia resulting from the elastic deformation of pivot caused by the weight of seismic inertia.

PROBLEMS CONCERNING MOUNTING OF PICKUPS FOR VIBRATION LEVEL METER

A vibration level meter with weighting network corresponding to human vibra- tion sensation has recently been planned by the Acoustic Society of Japan to assess vibration pollution. However, weight, size and position of a sensing element of a vibration pickup of the vibration level meter have not been standardized. To determine optimum values for them, the contact resonance was examined on combinations of eleven mounting materials and seven vibration pickups on a vibration table of electro- dynamic type in vertical and horizontal directions.It was found that the vibration pickup which had weight of 300 g was desirable for vertical and horizontal vibrations under almost all mounting conditions except in the case of some special materials. The contact resonance frequency between the pickup and the mounting material was able to be elevated to a considerably high frequency for vertical vibration, but for horizontal vibration it was lowered until near half the value in vertical vibration. Therefore, vibration occurring in human environment is desirable to be measured by a VL range of the vibration level meter, in which the weighting circuit of the amplifier has the same frequency characteristics as those of human vibration sensation below 90 Hz and above it the cut-off frequency nature is -18 dB/oct. Vibration pickup of the vibration level meter was able to be calibrated without bolting on the vibration table below 90 dB (0 dB=10-3 cm/sec2).

Using a Computer Display to Model a Complex Vibrating Surface

Vibration waveforms are taken at several points on a vibrating surface and then combined, using a computer with a cathode-ray-tube display, to produce several representations of the movement of the surface. An important advantage of this method is that the forms of the data and representations lend themselves readily to manipulation by the computer. A noncontact vibration pickup, developed especially for this application, is briefly described.

High-sensitivity capacitive vibration pickup

High-sensitivity capacitive vibration pickup

Vibration-Isolation Treatment of a Railroad Track Bed

A few years ago, a half-mile section of railroad track was given a vibration-isolation treatment under several new buildings in Boston. The treatment consisted of welding all rail joints, inserting molded rubber rail seats under the lower flange of the rail, and installing an extra-deep ballast bed under the ties. Recently, a simple measurement was made of the earthborne vibration reduction provided by this treatment. A vibration pickup was mounted on a concrete wall inside the track, and the signal was tape recorded for passages of several short passenger trains. At one position, the vibration pickup was located beside the welded and isolated track. On the following day, the same passenger trains were recorded with the vibration pickup located beside conventional unwelded and unisolated track, approximately 200 yd from the first position. Train speed, train makeup, wheel loads, earth conditions, and the geometry of the measurement conditions were quite similar for both locations, so it is believed that the measured 10 dB difference was due to the vibration reduction provided by this treatment.