GB2080530A - Method of and Apparatus for Ultrasonic Measurement of Rate of Flow - Google Patents

Abstract

A method of ultrasonic measurement of rate of flow for instance of oil passing through a pipeline 6, utilizes simultaneous passage of two auto-circulation pulse trains of opposite directions through a single acoustic channel through the medium to be measured while eliminating instants at which the pulses of the trains coincide. The pulses of one pulse train are used (at 16 or 32) to phase-synchronize a self- excited oscillator (15 or 31) whose frequency is a whole number of times the repetition rate of that pulse train. The coincidence instants (checked at 38) are eliminated by interrupting (via gate 1 or 9) the same pulse train before a certain instant of coincidence and restoring it with the help of a pulse produced by the self-excited oscillator, said pulse being held out of coincidence with a pulse of the other pulse train. The rate of flow is determined at 56 as the difference between the repetition rates of the pulses of the trains by comparing the repetition rate of the pulses of the other train with the frequency of the self-oscillator. <IMAGE>

Description

SPECIFICATION Method of and Apparatus for Ultrasonic Measurement of Rate of Flow The invention relates to the field of ultrasonic measurements, and more particularly to a method of and apparatus for ultrasonic measurement of rate of flow. Such a method and apparatus may be used in the measurement of the rate of flow of petrol and its products, chemical products, food products, and water in melioration systems.

The term "tlowmeter" as used herein applies to apparatus designed to measure both the velocity of flow and the rate of flow, as measurements based on acoustic waves deal with the velocity of flow which is a function of the rate of flow.

When a flow running, for example, through a pipeline is to be measured, it is desirable that its movement is not disturbed during measurement.

Another requirement is concerned with the availability of a relatively cheap apparatus which can provide highly accurate measurements and long service life and which cannot be influenced by the temperature and other changes of the physical properties of the medium under control.

Taken as a first approximation are the results provided by ultrasonic frequency-pulse measurement methods in which the influence of the physical properties of the medium under control is eliminated. These methods are realized by ultrasonic flowmeters based on a synchronization ring-like arrangement which constitutes a pulsed generating system with a delayed accoustic feedback. Such an arrangement is operated in a pulse autocirculation mode.

To measure the rate of flow, use is made of apparatus with one or two acoustic channels in which case an acoustic channel is a space intended to pass the medium under control and to separate two electro-acoustic transducers.

According to one aspect of the invention, there is provided a method of ultrasonic measurement of rate of flow utilizing simultaneous passage of two auto-circulation pulse trains of opposite directions through a single acoustic channel and through a medium being measured so that the instants at which the pulse of the trains are brought into coincidence are eliminated and the rate of flow is determined as the difference between the repetition rates of the pulses of the trains, the method comprising the steps of: utilizing the pulses of one of the pulse trains for phase synchronization of a self-excited oscillator whose frequency is a whole number of times the repetition rate of that pulse train; eliminating the instants of coincidence by interrupting the pulse train before a certain instance of coincidence and restoring it by means of a pulse produced by the self-excited oscillator, the pulse being held out of coincidence with a pulse of the other pulse train; and determining the difference between the repetition rates of the pulses of the trains by comparing the repetition rate of the pulses of the other train with the frequency of the self-excited oscillator.

According to another aspect of the invention, there is provided an apparatus for performing the method according to the invention, comprising two synchronization ringlike arrangements, each of which include, in series, an inhibitory gate, an excitation pulse former, electroacoustic transducers, and an amplifier-pulse former, the transducers and the amplifier-pulse former being common to the two synchronization ring-like arrangements, the transducers being separated from each other by a space, through which a medium to be measured is passed, and having a relative orientation allowing for the transmission and reception of acoustic signals passing between them in a direction which makes an angle different from 900 with the direction in which the medium moves, the apparatus further comprising trigger pulse units coupled to the corresponding synchronization ring-like arrangements and each comprising an adjustable self-excited oscillator whose input is corrected to output of a search/automatic phase control network, and whose output is connected, via a frequency divider, to an input of an AND gate, to an input of the search/automatic phase control network, and to an input of a storage element which has an output coupled to the other input of the search/automatic phase control network and to the AND gate, the apparatus further comprising a measuring unit common to the synchronization ring-like arrangements and having its inputs coupled to outputs of the self-excited oscillators, the trigger pulse units being provided with working pulse formers, the working pulse former of the first trigger pulse unit being coupled serially between the output of the first frequency divider and a common point used to join together respective inputs of the first AND gate, first storage element and first search/automatic phase control network, the working pulse former of the second trigger pulse unit having its input coupled to the output of the second frequency divider, and having its outputs coupled to respective inputs of a unit arranged to check for the coincidence of the pulses generated by the ring-like arrangements and to control the instants at which the ring-like arrangements receive blocking and unblocking pulses, the check/control unit having an input coupled to a second output of the first working pulse former, having an output coupled to the other input of the respective excitation pulse former, and having another output coupled to respective inputs of the second AND gate, second search/automatic phase control network and second storage element.

Preferably the check/control unit comprises a frequency divider having its output coupled to an input of a first AND gate which has its output coupled to an input of a second AND gate and to an input of a third AND gate which has its output coupled to an input of a first storage element which has an output coupled to a data input of a second storage element which has its output coupled to an input of a fourth AND gate, and has the other output coupled to an input of a fifth AND gate and to the other input of the first storage element which has the other output coupled to the other input of the fifth AND gate having its output coupled to a set input of the frequency divider, the other input of the frequency divider, joined together with the other input of the first AND gate and coupled to a clock input of the second storage element as well as the other input of the second AND gate and the other input of the fourth AND gate constitute respective inputs of the check!control unit, the other input of the third AND gate being used as another input of the check/control unit, and the outputs of the fourth and second AND gates, respectively, being used as the first and second outputs of the checkicontrol unit.

In comparison with prior art methods, such a method can provide for higher accuracy of measurement of the rate of flow and does not require a proionged frequency storage. Such an apparatus can be simple to carry out using commercially available measuring units, has means for automatically triggering and restoring the operation of the ring-like arrangements, and offers good operational reliability.

The invention will now be described in more detail, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a block diagram of an apparatus for ultrasonic measurement of rate of flow, constituting a preferred embodiment of the invention; Figure 2 is a block diagram of a unit arranged to check for the coincidence of pulses generated by ring-like arrangements and to control the instants at which the ring-like arrangements of the apparatus receive blocking and unblocking pulses; Figures 3a, b, c, d, e, fare voltage diagrams iliustrating operation of one of the ring-like arrangements of the apparatus of Fig. 1 in trigging mode; and Figures 4a, h, C, d, e, f, g, h, ii, k, I, m are voltage diagrams illustrating operation of the apparatus of Fig. 1 in measuring mode.

A method constituting a preferred embodiment of the invention comprises the following steps.

Two auto-circulation pulse trains of opposite direction are passed through a medium under control and through a single acoustic channel.

The pulses of one of the pulse trains (hereinafter referred to as a slave pulse train) are employed for phase synchronization of a self-excited oscillator, which provide for complete data on the slave pulse train. The self-excited oscillator frequency is a whole number of times the frequency of the slave pulse train. The other pulse train propagating in the opposite direction (hereinafter referred to as a master pulse train) is a continuous pulse train. The instants at which the pulses of the master and slave pulse trains are brought into coincidence are eliminated by interrupting the slave pulse train before the instant of coincidence and restoring it with the help of a pulse produced by the self-excited oscillator and held out of coincidence with a pulse of the master pulse train.

Since the slave pulse train is restored with a phase accuracy, the synchronization of the selfexcited oscillator by the restored pulse train does not cause a transient to occur. This means that the self-excited oscillator provides data on the continuous (quasi-continuous) operation of the slave pulse train. The difference between the repetition rates of the pulses of the both pulse trains, which is a measure of the rate of flow, is determined by comparing the repetition rate of the master pulse train with the self-excited oscillator frequency.

An apparatus constituting a preferred embodiment of the invention used to measure rate of flow is shown in Fig. 1, and comprises two synchronization ring-like arrangements. The first arrangement hereinafter referred to as a master arrangement includes an inhibitory gate 1 (Fig. 1) coupled to an input 2 of an excitation pulse former 3, electroacoustic transducers 4, 5 separated from each other by a space 6 through which the medium whose flow is to be measured is passed, and an amplifier-pulse former 7 which is coupled to an input 8 of the inhibitory gate 1.

The second synchronization ring-like arrangement hereinafter referred to as a slave arrangement includes an inhibitory gate 9 coupled to an input 10 of an excitation pulse former 11, the electroacoustic transducers 5, 4 separated by the space 6 through which the medium under control is passed, and the amplifier-former 7 which is coupled to an input 12 of the inhibitory gate 9.

The transducers 4, 5 are mounted at the opposite sides of a pipeline and are oriented with respect to each other so as to allow for the transmission and reception of acoustic signals passing between them. The angle a between the direction of velocity V in the pipeline and the direction in which acoustic waves pass between the transducers 4, 5 is made different from 900.

The apparatus also comprises trigger pulse units 13, 14 which are coupled, respectively, to the master and slave ring-iike arrangements. The trigger pulse unit 1 3 comprises an adjustable selfexcited oscillator 1 5 whose input is coupled to the output of a search/automatic phase control network 1 6. The output of the self-excited oscillator 1 5 is coupled, via a frequency divider 17, to the input of a working pulse former 1 8 whose output 19 is coupled to a common point 20 which is used to join together an input 21 of an AND gate 22, an input 23 of a storage element 24 and an input 25 of the search/automatic phase control network 1 6. An output 26 of the storage element 24 is coupled to an input 27 of the search/automatic phase control network 1 6 and to an input 28 of the AND gate 22 which has its output coupled to a trigger input 29 of the excite pulse former 3 and to a control input 30 of the inhibitory gate 1. The gate 1 has an output coupled to an input of the storage element 24.

The trigger pulse unit 1 4 comprises a selfexcited oscillator 31 having its input coupled to the output of a search/automatic phase control network 32. The output of the self-excited oscillator 31 is coupled, via a frequency divider 33, to the input of a working pulse former 34 whose outputs 35, 36, 37 are connected to a unit 38 arranged to check for the coincidence of the pulses generated by the ring-like arrangements and to control the instants at which the ring-like arrangements receive blocking and unblocking pulses. An output 39 of the check/control unit 38 is coupled to a trigger input 40 of the excitation pulse former 11, while an output 41 is coupled to a common point 42 used to join together an input 43 of an AND gate 44, an input 45 of a storage element 46 and an input 47 of the search/automatic phase control network 32.An output 48 of the storage element 46 is coupled to an input 49 of the search/automatic phase control network 32 and to an input 50 of the AND gate 44 whose output is coupled to a trigger input 51 of the excitation pulse former 11 and to a control input 52 of the inhibitory gate 9. The gate 9 has its output coupled to an input 53 of the storage element 46. An input 54 of the checkicontrol unit 38 is coupled to an output 55 of the working pulse former 1 8. The outputs of the self-excited oscillators 1 5, 31 are coupled to respective inputs of a measuring unit 56.

A preferred check/control unit 38 is shown in Fig. 2, and comprises a frequency divider 57 having its output coupled to an input 58 of an AND gate 59 which has its output coupled to an input 60 of an AND gate 61 and to an input 62 of an AND gate 63. The gate 63 has its output coupled to a set input 64 of a storage element 64 having its output 66 coupled to a data input of a storage element 68 whose output 69 is coupled to an input 70 of an AND gate 71. A complement output 62 of the storage element 68 is coupled to an input 73 of an AND gate 74 and to an erase input 75 of the storage element 65 whose complement output 76 is coupled to an input 77 of the AND gate 74 which has its output coupled to a set input 78 of the frequency divider 57.An input 79 of the frequency divider 57, coupled to an input 80 of the AND gate 59 and to a clock input 81 of the storage element 68, as well as an input 82 of the AND gate 61 and an input 83 of the AND gate 71 constitute, respectively, inputs 35, 36, 37 of the check/control unit 38. The outputs of the AND gates 71,61 constitute, respectively, outputs 39,41 of the check/control unit 38.

NAND-gates may be used, for example, for the inhibitory gates 1, 9 (Fig. 1). The storage elements 24, 46 (Fig. 1) and the storage element 65 (Fig. 2) may be R--S flip-flops. The frequency divider 57 may be a D flip-flop with a set input, while a clock-type D flip-flop may be used for the storage element 68.

Each of the search/automatic phase control networks 1 6, 33 (Fig. 1) is an element having a discharger, for example, a capacitor.

The measuring unit 56 comprises a frequency changer and an indicator.

The method is carried out by the corresponding apparatus whose operation according to two modes, triggering and measuring, is described below.

In the triggering mode, the voltage from the search/automatic phase control network 1 6 is applied to the input of the self-excited oscillator 1 5 with the result that its frequency is changed.

When the supply voltages are applied, the voltage across the output of the search/automatic phase control network 1 6 is equal to zero. The repetition cycle or period of the pulses produced by the selfexcited oscillator 1 5 is a minimum and is equal to Tmin (Fig. 3a). In addition, a condition must be satisfied that the repetition cycle Tmin K of the pulses from the output of the frequency divider 1 7 having a division factor K is less than a minimum time in which the signal is propagated through the acoustic channel.The period T of the adjustable self-excited oscillator 1 5 is selected so that the maximum repetition cycle of the pulses at the output of the frequency divider 17, Tmax, exceeds the maximum time required for the passage of the signal through the acoustic channel. Thus, the following conditions are to be satisfied.

where L is the distance covered by the acoustic waves passing in the medium under control between the electro acoustic transducers; Cmax is the maximum velocity of propogation of ultrasonic waves in the medium under control, which depends on the medium properties and surrounding; and Vmax is the projection of the vector of the maximum possible velocity in the medium, as referred to the direction of the acoustic wave beam.

where Cumin is the minimum velocity of propagation of ultrasonic waves in the medium under control, which depends on the medium properties and surrounding.

At the moment when supply voltages are applied there is no pulse at the output of the adjustable self-excited oscillator 1 5 and, therefore, no pulses are present at the outputs of the frequency divider 1 7 and the working pulse former 1 8. A low level is present in this case at the output 19 of the working pulse former 1 8.

Said low level is supplied to the storage element 24 whose output 26 produces a high level. In the initial state, the inhibitory gate 1 produces a high level. Since the output 26 of the storage element 24 is coupled to the input 28 of the AND gate 22, then a first positive pulse 85 (Fig. 3b) from the output 19 of the working pulse former 18 is applied to the input 21 of the AND gate 22 and the pulse 86 (Fig. 3c) is applied to the input 30 of the inhibitory gate 1, so that the gate 1 is made conductive, and to the input 29 of the former 3 which is thus triggered by the trailing edge of the positive pulse 86.

A pulse 87 (Fig. 3d) from the former 3 is applied to the electroacoustic transducer 4 and is converted therein to an ultrasonic signal which is passed through the medium under control and is accepted by the electroacoustic transducer 5 which converts that signal into an electrical one.

The electrical pulse is supplied to the amplifierformer 7 which produces a square pulse 88 (Fig.

3e) after amplification and this pulse is applied to the input 8 of the inhibitory gate 1. The pulse 88 at the output of the amplifier-former 7 is delayed relative to the pulse 87 from the output of the former 3 by a time interval t. Since the period of pulses from the output 1 9 of the working pulse former 18 is minimal and is less than t1, then the next pulse 89 (Fig. 3c) from the output of the AND gate 22 is applied to the input 30 of the inhibitory gate 1 some time before the pulse from the output of the amplifier-former 7 arrives at the input 8 of the inhibitory gate 1. The latter, at the moment of arrival of the pulse 88 from the amplifier-former 7, is made non-conductive.In spite of this, the pulse 89 from the output of the AND gate 22 passes through the acoustic channel in a manner analogous to that for the first pulse and so on.

At the same time the positive pulses from the output 1 9 of the working pulse former 1 8 are applied to the input 25 of the search/automatic phase control network 1 6 so that its output voltage is increased (Fig. 3f). The period of the adjustable self-excited oscillator 1 5 is increased until the inhibitory gate 1 becomes conducting by means of the pulse 91 (Fig. 3b) obtainable from the output 19 of the working pulse former 18.

This occurs at the moment when the pulse 90 (Fig. 3e) from the amplifier-former 7 is applied to the inhibitory gate 1. After that, the pulse 90 from the amplifier-former 7 passes to the input 2 of the former 3 and triggers it by the leading edge. As a result the master synchronization ring-like arrangement is activated (sync pulse 92 in Fig.

3d). At the same time, a negative pulse from the output of the inhibitory gate 1 is applied to the input of the storage element 24 so that the output 26 of the latter provides a low level. Thus, the AND gate 22 receives an inhibitating pulse, with the result that the length of the pulse 93 (Fig. 3c) at its output is limited (the point in time t2 in Fig.

3). In this case, the trailing edge of the positive pulse at the output of the AND gate 22 coincides with the leading edge of the negative pulse at the output of the inhibitory gate 1. This means that further operation of the oscillator 1 5 does not influence the operation of the master synchronization ring-like arrangement. As a result, the oscillator 1 5 is automatically switched off and the master arrangement is then operated in a continuous mode.

Now, the search/automatic phase control network 16 is switched from the search mode to the automatic phase control mode in which the phase of the oscillator 1 5 is adjusted with respect to the auto-circulation pulses of the master synchronization ring-like arrangement. A high level at the output 26 of the storage element 24 is set again by the retailing edge of the positive pulse 91 from the output 1 9 of the working pulse former 1 8. The pulses from the output 19 of the - former 18 are applied to the input 25 of the search/automatic phase control network 1 6 whose other input 27 receives pulses from the output 26 of the storage element 24, the leading edge of these pulses being held in coincidence with the leading edge of the master arrangement pulse passed through the inhibitory gate 1.The network 1 6 operates to detect an error characteristic of a time mismatch between the pulse from the output 1 9 of the working pulse former 1 8 and the leading edge of the autocirculation pulse available from the master arrangement, and converts that error to a control signal used to control the frequency and phase of the oscillator 1 5. This adjustment is performed so that the leading edge of the auto-circulation pulse from the master arrangement is held within the pulse from the output 19 of the former 1 8, preferably in the middle of that pulse.Thus, the inhibitory gate 1 and, therefore, the master arrangement will be made conductive by the leading edge of the pulse from the output 1 9 of the former 18 and will assume their nonconductive state according to the leading edge of the pulse from the master arrangement. This means that the time within which the master arrangement is conducting is half the length of the pulse from the output 1 9 of the former 1 8. To provide for better noise immunity, one selects the length of the pulse from the output 1 9 equal to 1 to 2% of the repetition cycle of the autocirculation pulses.

When the electroacoustic channel is disturbed, the pulses from the output 1 9 of the former 1 8 continue to pass to the input 25 of the network 16 so that its voltage output is increased. In this, case, the repetition cycle of the pulses at the output 19 increases. At a maximal voltage at the output of the network 1 6, that repetition cycle reaches a maximum and the network 1 6 causes a discharge from the maximal voltage to zero; thereafter, the apparatus commences an operational cycle analogous to that described above.

The slave arrangement is triggered by means of the trigger pulse unit in a similar way.

Therefore, the pulses from the outputs of the oscillators 1 5, 31 are related In terms of frequency and phase to the pulses of the master and slave arrangements rsp"ect1iy, but have their frequencies exceedi - - exceediit rates of the corresponding arrangement pulses in accordance with the division factors of the frequency dividers 1 7, 33, respectively.

In the measuring mode, the master and slave arrangements of the apparatus are driven into autocirculation and there are the following voltage diagrams for the outputs of certain units.

Figure 4a shows the pulses at the output of the frequency divider 17 of trigger pulse unit 1 3 of the arrangement. The repetition cycle of these pulses is equal to the repetition cycle T1 of the pulses of the master arrangement. Figure 4b shows the pulses at the output 55 of the working pulse unit 1 8. These pulses are referred to as the master arrangement inhibit pulses herein. They are necessary in order that the instants at which the pulses from the master and slave arrangements coincide are eliminated. More detailed description of these pulses will be given hereinafter. Figure 4c shows the pulses at the output 1 9 of the working pulse former 18, Figure 4d shows the pulses delivered from the master arrangement to the transducer 5, and Figure 4e shows the pulses at the output of the former 3.

Referring to Figs. 4d, 4e, the master arrangement operates in a continuous mode and has a period T1.

The division factor of the frequency divider 33 is selected so that the repetition rate at its output (Fig. 4f) is a whole number of times that of the pulses of the slave arrangement (two times in Fig.

4f). The working pulse former 34 of the trigger pulse unit 14 of the slave arrangement is used to form, from the pulses obtainable from the output of the frequency divider 33, the master arrangement inhibit pulses (Fig. 4g) which are applied to the input 35 of the check/control unit 38 and also the pulses (Fig. 4h) applied to the input 36 of the check/control unit 38. These two trains represent, respectively, the master arrangement inhibit pulses and the pulses at the output 19 of the former 18.

Since a fixed coupling is established, in terms of frequency and phase, between the oscillators 15, 31 and the trains of pulses available from the respective ring-like arrangements, one can easily maintain a condition in which the inhibit pulses involve the signals received by the electroacoustic transducers 4, 5.

In addition, a fixed coupling between the oscillator 31 and the pulses of the slave arrangement, in terms of the frequency and phase, allows the working pulse former 34 to form the pulses (Fig. 4i) applied to the input 37 of the check/control unit 38, the leading edges of these pulses being held in coincidence with the leading edges of the pulses of the slave arrangement, the latter being the pulses at the output of the former 11 (Fig. 4i) hereinafter referred to as the stored phase pulses.

Since the repetition rate of the pulses from the output of the frequency divider 33 is a whole number of times that of the pulses from the slave arrangement, the working pulse former 34 produces the trains of pulses representing the inhibit pulses (Fig. 4g), the stored phase pulses (Fig. 4i) and the pulses applied to the input 36 (Fig. 4h) of the check/control unit 38 and having their repetition rate which is a whole number of times that of the pulses of the slave arrangement (two times in the given example). Thus, each of the pulse trains may be considered as one obtained by superposing two pulse trains (an even one and an odd one) having their frequencies equal to the frequency of the slave arrangement but phase-shifted relative to each other by a value equal to the half-period of the slave arrangement.

Due to phase adjustment available, the edges of the stored phase pulses, belonging, for example, to an even pulse train, coincide with the edges of the pulses provided by the former 11 and therefore are maintained in synchronism with the pulses of the slave arrangement. The inhibit pulses for the even pulse train involve the signal received by the transducer 4. The pulses belonging to the even pulse train only are applied from the output 41 of the check/control unit 38 to the AND gate 44, the storage element 46, and the search/automatic phase control network 32.

During the passage of the measured flow through the pipeline section under control, there is a frequency difference between the master and slave arrangements and their signals tend to gradually approach each other. To eliminate the instant of which these signals would coincide with each other, the master arrangement is given a priority by means of the check/control unit 38 and is thus operated in a continuous mode. In addition, the check/control unit 38 checks for the coincidence of the even pulse train inhibit pulses (pulse 94 in Fig. 4j) with the inhibit pulses from the former 1 8 (pulse 95 in Fig. 4b).

After such a coincidence has occurred (pulse 96 of Fig. 4j coincides with pulse 97 of Fig. 4b), the check/control unit 38 works out a half-period phase shift for the auto-circulation pulses of the slave arrangement. To this end, the check/control unit 38 blocks the even train of pulses to the input 43 of the AND gate 44 (pulse 98 of Fig. 4h) and begins to pass the odd train of pulses (pulse 99 of Fig. 4h), the odd pulse train being shifted by a half-period relative to the even pulse train. The inhibitory network 9 does not pass in this case the slave arrangement pulses belonging to even pulse trains, but does so in the case of such pulses belonging to odd pulse trains.

At the same time, the check/control unit 38 passes from the output 39 a stored phase pulse 100 (Fig. 4k) belonging to an odd pulse train, which pulse is applied to the input 40 of the former 11 and restores the operation of the slave arrangement with a half-period shift. Further pulse adjustment applies to odd pulses.

The check/control unit 38 begins to check for the coincidence of the master arrangement inhibit pulses with the slave arrangement inhibit pulses in the case of odd pulse train (pulse 101 in Fig.

4j). When the arrangement signals tend to approach each other again, a half-period phase shift of the auto-circulation pulses occurs in the master arrangement and so on.

Figure 41 shows the slave arrangement signals received by the transducer 4, whereas Figure 4d shows the master arrangement signals received by the transducer 5. As is shown by these figures, the signals are not brought into coincidence. To provide for normal operation of the apparatus, the length T of the inhibit pulses is given by

where T is the minimal repetition cycle of the arrangement pulses; and N is the ratio of the frequency of pulses at the output of the frequency divider 33 to the frequency of pulses of the slave arrangements.

With N=2 in the given example, the value of T is given by

Referring to Fig. 4m, which shows the pulses provided by the former 11, the slave arrangement restores its operation after a half period (pulse 102 in Fig. 4m). At greater values of N, the restore time can be decreased and the minimum value of T is selected in this case on the basis of the parameters of the acoustic transducers 4, 5.

Figures 4f, g, h, ishow continuous pulse trains, since they are obtained from the pulses of the oscillator 31 which is phase-related to the pulses of the slave arrangement. By comparing the repetition rate of the pulses of the master arrangement, one can obtain data on the rate of flow. To obtain a unitary scale, the data on the arrangement pulse frequencies is preferably taken from the oscillators 1 5, 31. In this case, the measuring unit 56 will provide continuous data on the velocity of flow according to the following relation

where Af is the difference between the frequencies of the oscillators 1 5, 31; D is the diameter of the measured pipeline; n is the division factor of the frequency dividers 17, 33, into which the value of a scale factor is introduced; and V is the velocity of the medium under control.

For the apparatus of the invention shown in Fig. n=100.

A detailed description of the check/control unit 38 follows.

The master arrangement inhibit pulses (Fig. 4g) having a frequency which exceeds by a factor of 2 the frequency of this arrangement are passed from the input 35 of the check/control unit 38 to the input 79 of the frequency divider 57 and to the input 80 of the AND gate 59. Since the input 58 of the AND gate 59 is coupled to the output of the frequency divider 57, the output of the AND gate 59 will produce every second inhibit pulse for the slave arrangement (for example, an even pulse train). The repetition rate of these pulses is equal to that of the pulses of the slave arrangement and they are applied to the input 60 of the AND gate 61. Applied to the input 82 of the AND gate 61 are the pulses (Fig. 4h) from the input 36 of the check/control unit 38. The repetition rate of these pulses is two times the frequency of the slave arrangement.Since these pulses are within the inhibit pulses, the output of the AND gate 61 will produce every second pulse from those applied to the input 82 of the AND gate 61, and the pulses so selected are delivered to the output 41 of the check/control unit 38. The pulses from the output of the AND gate 59 are also applied to the input 62 of the AND gate 63 whose input 84 receives the master arrangement inhibit pulses (Fig. 4b) from the input 54 of the check/control unit 38. When the arrangement inhibit pulses do not coincide in the AND gate 63, a low level is present at the output 66 of the storage element 65 and is delivered tithe data input 67 of the storage element 68. As a result, a low level is always held at the output 69 of the storage element 68.That low level blocks the AND gate 71 through the input 70 and the stored phase pulses applied to the input 83 of the AND gate 71 from the input 37 of the check/control unit 38 do not pass to the output 39 of the check/control unit 38.

When the arrangement inhibit pulses 96, 97 are brought into coincidence in the AND gate 63, the output of the latter produces a pulse applied to the set input 64 of the storage element 65 whose output 66 thus accepts a high level. That high level is delivered to the data input 67 of the storage element 68 which is made ready for writing data acknowledging the coincidence of the inhibit pulses. The data is placed in the storage element 68 using the leading edge of the slave arrangement inhibit pulse 101 (Fig. 4j) which is applied to the clock input 81 of the storage element 68 from the input 35 of the check/control unit 38. To restore the operation of the slave arrangement, the store phase pulse 102 (Fig. 4m) is passed from the input 37 of the check/control unit 38 via the AND gate 71.

At the instant when the arrangement inhibit pulses are brought into coincidence, a low level from the output 76 of the storage element 65 is delivered via the AND gate 74 to the set input 78 of the storage element 57 whose output produces a low level too. Now, the output of the AND gate 59 stops even inhibit pulses from being produced for the slave arrangement. According to the leading edge of the pulse 101 (Fig. 4j), a low level from the output 72 of the storage element 68 is applied to the erase input 75 of the storage element 65. In the element 65, data on the arrangement inhibit pulses coincidence is erased and the data input 67 of the storage element 68 accepts a low level again. The present pulse from the input 35 of the pulse control unit 38 causes the storage element 68 to assume the other state.

This in turn makes the AND gate 71 nonconductive through the input 70 and the AND gate 74 becomes conductive through the input 73. A low level is removed from the set input 78 of the storage element 57 and the output of the AND gate 59 produces again inhibit pulses shifted by a half-period and representing, therefore, the pulses of an odd pulse train, and so on.

Claims (5)

Claims

1. A method of ultrasonic measurement of rate of flow utilizing simultaneous passage of two auto-circulation pulse trains of opposite directions through a single acoustic channel and through a medium being measured so that the instants at which the pulses of the trains are brought into coincidence are eliminated and the rate of flow is determined as the difference between the repetition rates of the pulses of the trains, the method comprising the steps of: utilizing the pulses of one of the pulse trains for phase synchronization of a selfexcited oscillator whose frequency is a whole number of times the repetition rate of that pulse train; eliminating the instants of coincidence by interrupting the pulse train before a certain instant of coincidence and restoring it by means of a pulse produced by the self-excited oscillator, the pulse being held out of coincidence with a pulse of the other pulse train; and determining the difference between the repetition rates of the pulses of the trains by comparing the repetition rate of the pulses of the other train with the frequency of the self-excited oscillator.

2. An apparatus for performing the method as claimed in claim 1, comprising two synchronization ring-like arrangements each of which include, in series, an inhibitory gate, an excitation pulse former, electroacoustic transducers, and an amplifier-pulse former, the transducers and the amplifier-pulse former being common to the two synchronization ring-like arrangements, the transducers being separated from each other by a space, through which a medium to be measured is passed, and having a relative orientation allowing for the transmission and reception of acoustic signals passing between them in a direction which makes an angle different from 90 with the direction in which the medium moves, the apparatus further comprising trigger pulse units coupled to the corresponding synchronization ring-like arrangements and each comprising an adjustable self-excited oscillator whose input is connected to output of a search/automatic phase control network, and whose output is connected via a frequency divider, to an input of an AND gate, to an input of the search/automatic phase control network, and to an input of a storage element which has an output coupled to the other input of the search/automatic phase control network and the AND gate, the apparatus further comprising a measuring unit common to the synchronization ring-like arrangements and having its inputs coupled to outputs of the self-excited oscillators, the trigger pulse units being provided with working pulse formers, the working pulse former of the first trigger pulse unit being coupled serially between the output of the first frequency divider and a common point used to join together respective inputs of the first AND gate, first storage element and first search/automatic phase control network, the working pulse former of the second trigger pulse unit having its input coupled to the output of the second frequency divider, and having its outputs coupled to respective inputs of a unit arranged to check for the coincidence of the pulses generated by the ring-like arrangements and to control the instants at which the ring-like arrangements receive blocking and unblocking pulses, the check/control unit having an input coupled to a second output of the first working pulse former, having an output coupled to the other input of the respective excitation pulse former, and having another output coupled to respective inputs of the second AND gate, second search/automatic phase control network and second storage element.

3. An apparatus as claimed in claim 2, wherein the check/control unit comprises a frequency divider, a first AND gate having a first input coupled to the output of the frequency divider, a second AND gate having a first input coupled to the output of the first AND gate, a third AND gate having a first input coupled to the output of the first AND gate, a first storage element having a first input coupled to the output of the third AND gate, a second storage element having a first input coupled to a first output of the first storage element, a fourth AND gate having a first input coupled to a first output of the second storage element, a fifth AND gate having a first input coupled to a second output of the first storage element, having a second input joined to a second input of the first storage element and coupled to a second output of the second storage element, and having an output coupled to a second input of the frequency divider whose first input, together with a second input of the first AND gate and with a second input of the second storage element as well as a second input of the second AND gate and a second input of the fourth AND gate are used as first inputs of the check/control unit, a second input of the third AND gate being used as the second input of the check/control unit, and the outputs of the second and fourth AND gates being used as first and second outputs of the check/control unit, respectively.

4. A method of ultrasonic measurement of rate of flow substantially as hereinbefore described with reference to the accompanying drawings.

5. An apparatus tor ultrasonic measurement of the rate of flow substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.