SU119003A1 - Device for determining the elastic modulus and the absorption coefficient of free vibrations in the test specimens - Google Patents

Description

The invention relates to devices for determining the elastic modulus and the absorption coefficient of free oscillations for the test specimens, for example, in concrete, or R structural elements.

Commonly used devices of the same designation, including; an electrodynamic vibrator, an audible frequency generator with a power amplifier, a waiting cathode oscilloscope with a wait sweep, a control sensor attached to the input of the oscilloscope that do not provide a constant initial amplitudes of free damping, their vibrations.

To eliminate this drawback, the device described uses a pulse generator with a trigger trigger circuit and a cathode follower that provides synchronization of the start of the oscilloscope's sweep with the moment of power failure of the vibrator and thus a constant initial amplitude of free decaying, vibrating.

FIG. 1 shows a block diagram of the described device; in fig. 2nd circuit diagram; in fig. 3-structure piezometric oscillation receiver.

As can be seen from the diagram in FIG. 1, the concrete sample being tested / is brought into oscillatory motion by the energy supplied to it through an air medium from an electrodynamic excite, 2 oscillations that are powered by a sound pulse generator 3 with an output power amplifier 4. The mechanical vibrations of a concrete sample / are perceived by a piezoelectric receiver 5 and sent to the entrance of the oscilloscope's vertical deflection. b. The change in frequency in the sound pulses

N 119003

; a pathogen 2, is the resonant frequency of the test sample. The natural,;, frequency of oscillations of the fundamental tone is determined by the maximum amplitude of the vertical deflection of the beam. The value of char-shch-8SH: Nity1 (Pc ao limb, located on the front panel of the instrument. Chch4y;,; 1triodes in each pulse of sound frequency, incoming - Electrodynamic causative agent, approximately 25 per second), is sufficient for the excitation of mechanical resonant oscillations maximum amplitude, and the time intervals between pulses are sufficient to damp the amplitude of free oscillations several times.

From the sound pulse generator 3, at the times corresponding to the cessation of the pulse, a synchronizing signal is issued to start the waiting sweep of the beam of the oscilloscope 6, as a result of which an oscillogram of damped natural oscillations of the test sample is displayed on its screen. The frequency of the sound pulses (up to 25 per sec.) Is quite sufficient in order to obtain on the oscilloscope screen a solid stable oscillogram and process it directly or photograph it if necessary.

The audio pulses arriving at the exciter 2 oscillation do not contain amplitude increase and attenuation sections, which ensures the complete stabilization of oscillograms of damped free oscillations of the test element, since it allows to precisely synchronize the beginning of the horizontal scan with the moment of excitation of the exciting oscillations and, moreover, gives constant initial amplitude of free damped oscillations.

Measuring sound RC generator 7 is assembled according to the scheme of a serial device. The output power amplifier is 4-stroke, without corrective devices (it does not require special frequency linearity and some distortion of the waveform during full load operation is allowed).

The pulse generator 3 is used to generate probe pulses applied to the preliminary stage of the power amplifier.

Its action consists in the following (see Fig. 2).

The storage capacitor Cig, included in the anode power of the thyratron Ld, is charged through the resistance Kg and the non-centimeter KzL. As a result, the storage capacitor Cig is discharged, the potential based on the thyratron decreases, and the thyratron goes out. Then the process is repeated again. In addition to a constant negative bias, a pulsating voltage is applied to the thyratron grid from a measuring sound generator with a frequency that has been set as resonant for a given test specimen. The supply of this pulsating voltage to the locking grid of the thyratron ensures that it is ignited continuously in the same phase of oscillation.

Electrical impulses produced by a relaxation-relaxation generator with a repetition rate of 50 pulses per second are fed through a capacitor Ci and two semiconductor diodes to a trigger trigger circuit, assembled on a combined Trigger lamp, for every two signals of the relaxation generator produces one rectangular impulse, equal to the duration of the rectangular pulse between two matching signals. Next, the square pulses pass through the cathode tube assembled on the left side of the lamp Lt, after which the average potential of the pulses decreases due to the application of a constant negative component from the rectifier through the voltage divider 2 and then the pulses are normalized on the diode limiter assembled on the second half of the lamp is Lt. The rectangular negative voltage pulses are sent to the grid of the lamp // s (preliminary stage of the power amplifier) and lock the last one, thereby stopping the oscillating flow ka output terminals. These pulses have a specified duration. With a repetition rate of 25 pulses per second, their duration is 0.02 second; the beginning of each pulse is precisely synchronized with a specific phase of oscillation of the measuring sound generator.

From the grid of the left triode of trigger L, sharp positive pulses are emitted through the capacitor Cjs to the output of synchronization and the waiting sweep of the oscilloscope. These pulses are directed to an external triggering of the oscilloscope and ensure the start of a waiting beam sweep at the moment of sending the locking pulse to the output amplifier.

Lamp L is a cathode follower separating the measuring sound generator and power amplifier. This cathode repeater provides a complete cessation of the supply of electrical oscillations at the output of the device when a negative pulse arrives at the grid of the Lz lamp.

The causative agent 2 oscillations is a conventional dynamic loudspeaker mounted on a stand with displacement supports for sample winding.

The piezoelectric receiver 5 (Fig. 2) consists of a sensing element in the form of a plate of segnetevoy salt 8 with a seismic mass 9 fixed cantilever on the basis of organic glass 10. The sensor is damped using felt strips 11. By carefully damping the sensor element, it is achieved that works essentially like a periodic. This is especially necessary in the study of the absorption coefficient by the method of free-awarder vibrations. To protect against mechanical damage, the entire receiver is placed in a metal casing 12. In the process of testing, the base of the receiver is attached to the surface of the oscillating element, which is perpendicular to the plane of the flexural vibrations.

Subject invention

A device for determining the elastic modulus and the absorption coefficient of free oscillations in the test samples, for example in concrete or in structural elements, including an electrodynamic vibrator, an audio frequency generator with a power amplifier, a waiting scan cathode oscilloscope, a control sensor attached to the element under study and connected to the input of said oscilloscope, characterized in that, in order to provide a constant initial amplitude of free damped oscillations, an impulse is applied in it A trigger generator with a trigger trigger circuit and a cathode repeater, which synchronizes the start of an oscilloscope's pending sweep with the moment the vibrator is powered off.

- 3 - # 119003

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