RU2227896C2 - Displacement-to-time interval conversion method - Google Patents

Abstract

FIELD: automatics, measuring technique, possibly conversion of displacements to time intervals with use of wave guide converters. SUBSTANCE: method comprises steps of elastically exciting in wave guide of displacement to time interval converter at distance equal to spacing measured from reception zone; receiving elastic wave reflected from end of wave guide; measuring in time period (equal to period of elastic wave passing from one end of wave guide until its another end) distribution time interval of elastic wave along wave guide beginning from time moment of exciting it. EFFECT: enlarged range of conversion due to lowered minimum value of converted displacement. 2 dwg

Description

The invention relates to automation and measuring equipment and can be used in mechanical engineering and instrumentation when converting displacements into a time interval based on waveguide transducers.

It is known that the influence of intrinsic interference is one of the most important factors limiting the minimum measurable movement of acoustic and waveguide devices, due to the proximity of their sources to the receiving elements, [Gorbatov AA, Rudashevsky G.E. Acoustic methods for measuring distances and control. 2nd ed., Revised. and add. - M .: Energoizdat, 1981 - 208 p.].

The closest technical solution to the invention is a method for converting displacements into a time interval when an elastic wave is excited in the waveguide, a reflected wave is received, and the time interval from the moment of excitation to reception is measured. [Domrachev V.G. et al. Circuit design of digital displacement transducers. / Domrachev VG, Matvievsky VR, Smirnov Yu.S. - M .: Energoetomizdat, 1987, p. 67-72].

The disadvantage of this method is the limited conversion range of small displacements due to the "dead zone" formed due to the occurrence of a transient oscillatory process in the excitation element circuit after the end of the excitation pulse, finite duration of the excitation pulse, and recovery time from the saturation state of the receiver amplifier to the initial active mode of operation.

To achieve a technical result - expanding the conversion range by reducing the minimum convertible movement - an elastic wave in the waveguide is excited at a distance equal to that measured from the receiving point, an elastic wave reflected from the end of the waveguide is received, the propagation time of the elastic wave is measured, and the measurement is carried out after a period of time equal to the time the elastic wave travels from one end of the waveguide to the other from the time of excitation.

Regardless of the distance between the excitation and reception elements, an elastic wave arises in the waveguide during excitation, which propagates along it in both directions from the place of excitation at a speed of C.

At the same time, at the end of the action of the excitation pulse, a transient oscillatory process occurs in the circuit of the excitation element, which in the form of electromagnetic interference penetrates the input circuit of the receiver amplifier and puts the input, most sensitive cascade of it, into a saturation state. The duration τ _{P of} this transient is determined by the parameters of the circuit of the excitation element and the receiver amplifier.

After the end of the transition process, it is still necessary for some time τ _y for the receiver amplifier to return to its original active mode of operation.

For a time equal to:

from the moment of excitation, the elastic wave travels along the waveguide a distance equal to:

which determines the minimum possible transformable displacement X _min - the "dead zone", because the measurement of the wave propagation time from the moment of excitation for a period of time t _{In is} impossible.

In formula (2), τ is the duration of the excitation pulse.

In real displacement transducers with an excitation pulse duration of the order of 1 μs, the “dead zone" is several tens of mm.

Measurement of the transit time of an elastic wave from the moment of excitation to the reception of the reflected wave after a period of time

equal to the propagation time of an elastic wave from one end of the waveguide to the other, it allows you to convert small displacements, including those located inside the "dead zone".

Here X _m is the maximum translatable displacement.

So, if the excitation element is located inside the "dead zone" at a distance X from the receiving element, then the receiver amplifier will enter the input of the amplifier after a period of time

from the moment of excitation, the emf pulse corresponding to the moment of arrival of an elastic wave reflected from the end of the waveguide to the receiving element.

According to the method, a period of time

will uniquely determine the measured displacement of X.

In all other cases, when X> X _min , two emf pulses will be received sequentially from the moment of excitation at the input of the amplifier of the receiver: first, after time t _x and second, after time t ₀ , corresponding to the moments of arrival of the input element at the input direct and reflected elastic waves.

Since the first impulse of the emf arrives at the input of the converter of the time interval of the time interval meter Δt earlier than the last one begins to function (t _X <t _m ), then the measurement result in these cases will also be determined by expression (5).

In the proposed method of converting displacements into a time interval, the minimum displacement is limited only by the sizes of the excitation and reception elements and is of the order of 2-5 mm, which is an order of magnitude smaller than with the known method.

Figure 1 shows a variant of the structural diagram of a transducer of displacements on torsional waves during the formation of a time interval by a single reflection method that implements the method, and figure 2 shows the time diagrams:

a) pulses of the excitation current I ₆ ;

b) the processes of excitation of the elastic wave in the waveguide at time t ₁ and t _i and the formation of time intervals t _x1 , t _m , t ₀ and t _xi ;

c) and d) voltages acting respectively at the input and output of the amplifier-former 7;

e) and f) the voltage at the outputs of the delay element 8 and the shaper of the time interval 9.

The time-domain displacement transducer contains a ferromagnetic waveguide 1, one end of which is placed in the damper 5 and the other 3 is rigidly pinched, the excitation element 2 connected to the object, the displacement X of which relative to the stationary reception element 4 is measured, the excitation current pulse generator 6, with a period repeating T≥2H _m / C amplifier driver 7 readout pulses, a delay element 8, whose delay time t _{3 = X m / C = t m} , and a driver 9 interval Δt, and the output-driver amplifier 7 is connected to the input R Settings shaper 9 in state "0", and the output of the delay element 8 is connected to the input S Fitting shaper 9 to "1".

The waveguide 1 is made of a material with high saturation magnetostriction.

The element of excitation 2 is a permanent magnet magnetized along the axis of the waveguide, and a torsional elastic wave to emf converter is used as the receiving element 4.

The receiving element 4 and the amplifier-driver 7 of the read pulses form the receiver of the Converter.

Before starting work, the shaper 9 is set to the state "0" (the installation circuit is not shown in the diagram).

The transducer movements in the time interval works as follows. The excitation current pulse I ₆ from the output of the generator 6 (figure 2), due to the direct Wiedemann effect, excites an elastic wave in the waveguide 1 under the excitation element 2, which propagates in both directions from the place of occurrence at a speed of C.

At the output of reception element 4 from a transient oscillatory process, an emf occurs interference, the duration of which t _B.

After a period of time t _x = X / C from the moment of excitation, an elastic wave that propagates to the left passes under reception element 4 and an emf occurs at its output reading out. This emf together with the emf the interference is amplified by the amplifier-former 7 and the pulses from the emf are formed at the output of the latter reading and emf interference (U ₇ ), which are received at the R-input of the former 9, which is already in the state "0". In figure 2. for the moment of excitation time t ₁ this impulse e.m.s. reading is not shown, since it is located inside the interval of the emf interference. Propagating further, the elastic wave is absorbed by the damper 5.

After time t ₃ at the output of the delay element 8 there will be a voltage pulse (U ₈ ), which will translate the former 9 in the state "1".

достигнет жестко защемленного конца 3 волновода, отразится от него и через время t₀=t₂+t_m=2t_m - t_X дойдет до элемента приема 4, наведет в последнем э.д.с. считывания и затем, достигнув демпфера 5, поглатится им.Elastic wave, which propagates from the place of excitation to the right, after a period of time

will reach the rigidly clamped end 3 of the waveguide, will be reflected from it and after a while t ₀ = t ₂ + t _m = 2t _m - t _X will reach reception element 4, it will guide in the last emf reading and then, having reached the damper 5, it will be swallowed by it.

This emf reading in the form of a pulse from the output of the amplifier-former 7 (U ₇ ) is fed to the input R of the former 9 and puts it in the state "0". In this case, at the output of the shaper 9, a pulse (U ₉ ) of duration

proportional to the transformed movement X.

In figure 2, for the time t _i at the input of the receiving element 4 induces two pulses of the emf readings shifted relative to the moment of excitation of the elastic wave by the time t _Xi and t _0i, respectively (U ₄ ), therefore, the voltage pulses (U ₇ ) at the output of the amplifier-former 7 will be shifted by the same time.

The first pulse of this voltage is supplied to the input R of the shaper 9, which is already in the state "0".

By the time of the arrival of the second pulse of this voltage t ₀ to the input of the former 9, the last voltage pulse from the output of the delay element 8 (U ₈ ) was transferred to the state "1". Therefore, the second voltage pulse from the output of the amplifier-former 7, after a time Δt _i = t _0i -t ₃ from the moment of excitation of the elastic wave in the waveguide, returns the former 9 to its initial state "0", and a time interval of Δt proportional to it will be generated at its output transformable displacement X.

Claims (1)

A method of converting displacements into a time interval including excitation at a distance equal to that converted from one end of the waveguide, an elastic wave in the waveguide, receiving a reflected elastic wave from the end of the waveguide, measuring the propagation time of an elastic wave, characterized in that the measurement is carried out after a period of time equal to time the passage of an elastic wave distance from one end of the waveguide to the other from the moment of excitation.

Images