RU2529734C1 - Time-of-flight method of determining sound speed in liquid medium and apparatus therefor - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: procedure of measuring sound speed using a time-of-flight method includes setting a measurement base using a special measure of length in the form of a rectangular parallelepiped with two polished sound-reflecting surfaces. The rectangular parallelepiped is mounted vertically on an adjustable base of the working measurement volume bounded by a cover in the form of plane-parallel plate. Receiving/transmitting piezoelectric transducers are installed opposite the sound-reflecting face of the rectangular parallelepiped and the sound-reflecting base, said transducers being connected to an electric pulse generator and a time interval measuring device. The piezoelectric transducers are mounted on the outer surface of the plane-parallel plate, and adjustment elements are placed on the base, connected to the upper part of the device by squirrel wheel. The measurement procedure includes multiple reflection of sound pulses. Sound speed is estimated based on the time interval from the beginning of generation of sound pulses by the generator to the time of receiving the sound pulses, taking into account adjustment corrections.

EFFECT: increased accuracy of measuring sound speed.

2 cl, 4 dwg

Description

The invention relates to the field of metrology and measuring equipment and can be used in sonar to determine the speed of sound in liquid media.

Known time-of-flight method for determining the speed of sound, which consists in the formation of a measurement base using two opposite piezoelectric transducers - transmitting and receiving sound pulses [Copyright certificate of the USSR, USSR, No. 1483285, class. GOIH 5/00, 1987] [1].

A device for implementing the method is known, comprising a transmitting piezoelectric transducer, a receiving piezoelectric transducer, an electric pulse generator and a time interval meter connected respectively to a transmitting and receiving piezoelectric transducer [1].

A disadvantage of the known method and device is the low accuracy of setting the measurement base, and hence the low accuracy of determining the speed of sound in the medium.

There is a known time-of-flight method for determining the speed of sound in a liquid medium, which consists in the fact that at given temperature and pressure, sound pulses are used to direct sound pulses to two sound reflectors installed in parallel in a liquid medium at a distance L _t , _P from one another, the second of which closest to the shapers of sound pulses, and receive reflected sound pulses, by the time of arrival of which they judge the speed of sound in a liquid medium [I.L. Kuznetsov. AM Molokov, F.P. Schnittman. Analysis of the accuracy of the time of flight transducer of sound velocity in water. Sat Scientific Proceedings of VNIIFTRI. Hydrophysical measurements. M., 1985. P.33-39] [2].

A device for determining the speed of sound in a liquid medium containing a base, which is made sound-reflecting in the form of a plate, a rectangular parallelepiped (hereinafter, a parallelepiped) of length L _t , _P with plane-parallel sound-reflecting ends, fixed with one end on the base, a working measuring volume, electrically connected in series an electric pulse generator and a transceiver piezoelectric transducer (hereinafter referred to as the piezoelectric transducer) mounted opposite the free end of the rod and base, and zmeritel time slots to connection to the piezoelectric transducer [2].

These method and device are taken as prototypes. The disadvantage of the prototypes is the lack of accuracy in determining the speed of sound in a liquid medium, associated with errors due to diffraction (edge) effects of dividing the sound beam into two sections, changes in temperature and pressure of the medium, as well as the absence of alignment elements on which the parallel measurement base depends and directions of movement of sound pulses.

The first type of error is due to the fact that in the prototype one transducer, one half, is located above the parallelepiped that defines the measurement base, and the second half, above the sound-reflecting base of the working measuring volume, which inevitably causes diffraction effects at the edge of the parallelepiped. The second type of error is due to the lack of means for adjusting the sound-reflecting base relative to the direction of the axis of the radiation pattern of the piezoelectric transducer, which leads to inaccurate formation of the length of the measurement base.

In addition, in the prototype, the piezoelectric transducer is in direct contact with a liquid medium, which can be under high pressure and at high temperature. This inevitably affects the characteristics of the piezoelectric transducer and the accuracy of measuring the propagation time of sound pulses, and hence the accuracy of determining the speed of sound.

The technical result obtained from the introduction of inventions is the elimination of these disadvantages, that is, improving the accuracy of determining the speed of sound.

This technical result is achieved by the fact that in the known time-of-flight method for determining the speed of sound in a liquid medium, which consists in the fact that at given temperature and pressure, sound pulses direct sound pulses to two sound reflectors installed in parallel in a liquid medium at a distance L _t , _P one from another and specifying the measurement base, the second of which is the closest to the shapers of sound pulses, and receive reflected sound pulses, along the time of passage of which the measurement base L _t , _P judge the speed of sound in a liquid medium, use the third and fourth sound reflectors located above the above, parallel to the first two, formed by the planes of a plane-parallel plate, the third sound reflector being placed on the lower surface of the plate in contact with the liquid medium, and the fourth in plane of the sound pulses, then measure the time interval τ ₁ from the beginning of the formation of sound pulses generated by the first generator, until the reception of sound pulses reflected s from the first acoustic reflector, the time interval τ ₂ from the beginning of the formation of sound pulses generated by the first generator, until the reception of sound pulses sequentially reflected from the first, third and first acoustic reflector, the time interval τ ₃ from the beginning of the formation of sound pulses generated by the second generator to the time of reception of sound pulses reflected from the first acoustic reflector, the time interval τ ₄ from the beginning of the formation of sound pulses generated by the second generator, until receiving ulcers postglacial pulses sequentially reflected from the first, third and first acoustic reflector, the time interval τ ₅ from the beginning of the formation of sound pulses generated by the third generator to the moment of reception of sound pulses from the second acoustic reflector, the time interval τ ₆ from the beginning of the formation of sound pulses generated by the third generator, until the moment of receiving sound pulses created by the third driver, successively twice reflected from the second sound reflector and once from the third sound reflector, inter tore time τ ₇ from the beginning of the formation of sound pulses generated by the fourth shaper to the moment of receiving sound pulses generated by the fourth shaper from the second reflector, time interval τ ₈ from the start of formation of sound pulses generated by the fourth shaper to the moment of receiving sound pulses generated by the fourth shaper, successively twice reflected from the second sound reflector and once from the third sound reflector, and the speed of sound C is determined from the mathematical expression:

$$C=\frac{2L_{t,P}\pm \Delta L_{tP}}{\left[\frac{\left({\tau }_2-{\tau }_{\mathrm{one}}\right)+\left({\tau }_{\mathrm{four}}-{\tau }_3\right)}{2}\right]-\left[\frac{\left({\tau }_6-{\tau }_5\right)+\left({\tau }_8-{\tau }_7\right)}{2}\right]},\text{(one)}$$

where ± ΔL _{t, P} is the correction for the allowable misadjustment.

In the device part, the technical result is achieved in that in the device containing the base, which is made sound-reflecting in the form of a plate, a parallelepiped of length L _{t, P} with plane-parallel sound-reflecting ends, fixed by one of the ends on the base, the working measuring volume, the electric pulse generator and the piezoelectric transducer, mounted opposite the free end of the rod and the base, interconnected, and a time interval meter connected to the piezoelectric transducer, additionally introduced a parallel plate installed in the upper part of the device, three additional piezoelectric transducers, electrically connected to an electric pulse generator and a time interval meter, as well as a squirrel wheel, while the piezoelectric transducers are mounted on the upper plane of the plane-parallel plate, and the alignment elements are located on the base connected to the upper part devices squirrel wheel.

The invention is illustrated by drawings. Figure 1 shows the main elements of the device, figure 2 - the location of the piezoelectric transducers relative to the plane-parallel plate, figure 3 is a diagram explaining the principle of the method, figure 4 is a timing chart explaining the essence of the method.

The device contains a parallelepiped 1 with plane-parallel polished sound-reflecting ends 2, 3, defining the measurement base L _{t, P.} The parallelepiped 1 is fixed by one of the ends, for example the end 3, on the sound-reflecting base 4 of the working measuring volume 5 with a liquid medium.

The connecting link between the base and the upper parts of the device is the squirrel wheel 6 and the alignment elements (which are the know-how elements in the part of the applicant’s device) of the parallelepiped 1 with respect to the direction of propagation of sound signals. Through the holes of the squirrel wheel 6, the liquid medium penetrates into the zone of measuring the speed of sound. The volume 5 is closed by a lid in the form of a plane-parallel plate 7 mounted on the squirrel wheel 6 parallel to the sound-reflecting base 4. On the plane-parallel plate 7, four piezoelectric transducers 8, ..., 11 are installed outside (Figs. 1, 2). The piezoelectric transducers 8, 9 and 10, 11 are located on the periphery of the plate 7 diametrically opposite, as shown in figure 2.

At the same time, the sound-reflecting surfaces of the end face 2 of the parallelepiped 1 and the base 4 of the working volume 5 are made of one material, for example, stainless steel.

The device also includes an electric pulse generator and a time interval meter (not shown in the drawing) connected to converters 8, ..., 11.

The basis of any time-of-flight method for determining the speed of sound, including the analogue, prototype and the claimed method, is the need for accurate measurement of the measurement base _{Lt, P} and time τ of its passage by sound pulses. The use of a parallelepiped 1 with sound-reflecting ends 2, 3 as a measurement base allows, at given temperature t and pressure P, to set the measurement base with high accuracy using modern standard length measuring instruments. The main types of errors in the measurement of the measurement base in this case will be manifested due to the influence of temperature t and pressure P, as well as due to the device misconfiguration (the directions of the vertical faces of the parallelepiped 1 do not coincide with the direction of movement of the sound pulses). The method for determining the latter type of error in the amount of (± ΔL _{t, P} ) is the know-how of the applicant in terms of the method.

The values of the corrections for the length of the measurement base with changes in temperature t and pressure P are calculated from known dependences [A.A. Alexandrov, D.K. Larkin. Experimental determination of the speed of ultrasound in water over a wide range of temperatures and pressures. Heat engineering, 1976, No. 2, 75-78]. The error due to misalignment of the device is easily eliminated in the proposed technical solution by the introduction of plane-parallel plate 7 and piezoelectric transducers 8, ..., 11.

On the other hand, the location of the piezoelectric transducers 8, ..., 11 on the outer side of the plate 6 with respect to the medium under study allows us to exclude the influence of the medium on the characteristics of the piezoelectric transducers, and hence on the measurement of the base length and sound propagation time.

However, the introduction of these signs leads to the appearance on the propagation path of sound pulses of four (and not two, as in the prototype) sound reflectors “a”, “b”, “c”, “d” (Fig. 1) and, as a consequence of this, to the appearance of two sound pulses reflected from these sound reflectors at the input of each piezoelectric transducer. In this regard, the determination of the time τ of the passage of sound pulses of the measurement base L _{t, P} is more complex than in the prototype, in which time τ is equal to the difference in the arrival times of sound pulses reflected from the boundaries of the measurement base.

In Fig. 1, conventionally, the arrows indicate the sound pulses τ ₁ , τ ₂ , τ ₃ , τ ₄ sequentially received at the input of the piezo transducers 8, 9 after reflections from the sound reflectors “a”, “b”, “a”, as well as the sound pulses τ ₅ , τ ₆ , τ ₇ , τ ₈ , successively reflected from the sound reflectors “b”, “c”, “b” and coming to the input of the piezo transducers 10, 11.

3, 4, for clarity, the reflection data is shown in time sequence.

The pulse τ ₁ conditionally characterizes the time interval from the beginning of the formation of the sound pulse to the moment it is received after reflection from the sound reflector “a” (piezoelectric transducer 8).

The pulse τ ₂ is the time interval from the beginning of the formation of the sound pulse to the moment of its reception after reflection in series from the sound reflectors “a”, “b”, “a”, as follows from the second diagram in figure 2 (piezoelectric transducer 8).

Pulse τ ₃ is the time interval from the beginning of the formation of sound pulses to the moment of receiving pulses successively reflected from the sound reflector “a” (piezoelectric transducer 9).

The pulse τ ₄ is the time interval from the beginning of the formation of sound pulses to the moment of their reception, when they are successively reflected from the sound reflectors “a”, “b”, “a” (piezoelectric transducer 9).

Pulse τ ₅ is the time interval from the beginning of the formation of sound pulses to the moment of receiving pulses reflected from the sound reflector “b” (piezoelectric transducer 10).

Impulse τ ₆ is the time interval from the beginning of the formation of sound pulses to the moment of receiving pulses successively reflected from the sound reflectors “b”, “c”, “b” (piezoelectric transducer 10).

Pulse τ ₇ is the time interval from the beginning of the formation of sound pulses to the moment of receiving pulses sequentially reflected from the sound reflector “b” (piezoelectric transducer 11).

Impulse τ ₈ is the time interval from the beginning of the formation of sound pulses to the moment of receiving pulses successively reflected from the sound reflectors “b”, “c”, “b” (piezoelectric transducer 11).

It is easy to see that for piezoelectric transducers 8, 9, the doubled average time required for the sound pulse to travel from the sound reflector “b” to “a” (Figs. 1–4) will be equal to

$$\frac{\left({\tau }_2-{\tau }_{\mathrm{one}}\right)+\left(\tau {}_{\mathrm{four}}-{\tau }_3\right)}{2}\text{(2)}$$

Similarly, for transducers 10, 11, the doubled average time required for the sound pulse to travel from the sound reflector “c” to “b” (FIGS. 1-4) will be equal to

$$\frac{\left({\tau }_6-{\tau }_5\right)+\left(\tau {}_8-{\tau }_7\right)}{2}\text{(3)}$$

In this case, the sound pulse passage time of the base distance L _{t, P} will be equal to the difference of values (2) and (3). Dividing the measurement base by the obtained time, we obtain equation (1) for determining the speed of sound by the proposed method.

The method is implemented as follows.

First, using piezoelectric transducers 8, ..., 11 (FIG. 2) and alignment elements, the base 4 is aligned with respect to the plate 7 according to the equality of the times the pulse travels through the liquid layer in the measuring volume. The difference between the times in practice should not exceed 10 ns.

Sequentially or simultaneously from the piezoelectric transducers (8, 9) and (10, 11) to the sound reflectors “a” and “b”, respectively, they direct sound pulses using an electric pulse generator and measure the times τ ₁ , ..., τ ₈ and when the base is known measurements of L _{t, P} according to the formula (1) and when using the know-how regarding the method, determine the speed of sound in a liquid medium.

In this method, there are no errors associated with the presence of diffraction effects, since sound pulses do not fall on the edges of the parallelepiped 1, in contrast to the prototype.

The measurement results are not affected by changes in the physical characteristics of the medium, since the piezoelectric transducers 7 and 8 do not contact it.

Using the adjustment elements (know-how regarding the device) and using the correction (know-how regarding the method) using the claimed device determines the speed of sound in a liquid medium with high accuracy (0.01 ... 0.05) m / s the range of sound speeds in a liquid medium (800 ... 2000) m / s.

This achieves the technical result set in the application.

Claims (2)

1. The time-of-flight method for determining the speed of sound in a liquid medium, which consists in the fact that at given temperature and pressure, sound pulses are used to direct sound pulses to two sound reflectors installed in parallel in a liquid medium at a distance L _{t, P} from one another and defining the base measuring the second of which - the closest to the formers acoustic pulses and receiving the reflected sound pulses, the time base measuring passage which L _{t, P} is judged on the sound velocity in a liquid medium, wherein Thu used additionally third and fourth acoustic reflector disposed above said parallel first two formed planes parallel plate, said third acoustic reflector disposed on the lower surface of the plate, in contact with the liquid medium, and the fourth - in the plane of the sound pulses, then measure the time interval τ ₁ from the beginning of the formation of sound pulses created by the first driver, until the moment of receiving sound pulses reflected from the first sound reflector, the interval in Yemeni τ ₂ from the beginning of the formation of sound pulses generated by the first generator, until the reception of sound pulses sequentially reflected from the first, third and first acoustic reflector, the time interval τ ₃ from the beginning of the formation of sound pulses generated by the second generator, until the reception of sound pulses reflected a first acoustic reflector, the time interval τ ₄ from the beginning of the formation of sound pulses generated by the second generator, until the reception of sound pulses sequentially reflected s from the first, third and first acoustic reflector, the time interval τ ₅ from the beginning of the formation of sound pulses generated by the third generator to the moment of reception of sound pulses from the second acoustic reflector, the time interval τ ₆ from the beginning of the formation of sound pulses generated by the third generator to the moment of reception of sound pulses created by the third driver, successively twice reflected from the second sound reflector and once from the third sound reflector, time interval τ ₇ from the beginning of the formation of sound of the pulses generated by the fourth shaper, until the sound pulses generated by the fourth shaper are received from the second reflector, the time interval τ ₈ from the beginning of the formation of sound pulses created by the fourth shaper, until the sound pulses created by the fourth shaper are received, twice reflected from the second one reflector and once from the third reflector, and the speed of sound C is determined from the mathematical expression:
$$C=\frac{2L_{t,P}\pm \Delta L_{tP}}{\left[\frac{\left({\tau }_2-{\tau }_{\mathrm{one}}\right)+\left({\tau }_{\mathrm{four}}-{\tau }_3\right)}{2}\right]-\left[\frac{\left({\tau }_6-{\tau }_5\right)+\left({\tau }_8-{\tau }_7\right)}{2}\right]}$$

,
where ± ΔL _{t, P} is the correction for the allowable misadjustment. 2. Device for determining the speed of sound in a liquid medium, containing a base made sound-reflecting in the form of a plate, a rectangular parallelepiped of length L _t, p with plane-parallel sound-reflecting ends, fixed by one of the ends on the base, a measuring volume, an electric pulse generator and a transceiver piezoelectric transducer mounted opposite the free end of the rectangular parallelepiped and the base, interconnected, and a time interval meter connected to the piezoelectric transducer lu, characterized in that it is equipped with a plane-parallel plate installed in the upper part of the device, three additional receiving and transmitting piezoelectric transducers, electrically connected to an electric pulse generator and a time interval meter, as well as a squirrel wheel, while the piezoelectric transducers are mounted on the upper plane of the plane-parallel plate, and the adjustment elements are located on the base connected with the upper part of the device by a squirrel wheel.

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