DE2530114B1 - Circuit arrangement for determining physical quantities of flowing media, in particular the flow velocity, according to the ultrasonic method - Google Patents

Description

The invention relates to a circuit arrangement for determining physical quantities flowing Media such as the amount of flow, the direction of flow or the speed of sound, but especially the flow velocity, according to the ultrasonic method, in which the arrival time of an ultrasonic signal is determined, with an arrival delay device, which defines an arrival delay time following the measured signal start and at the end of which emits an arrival delay signal, with a zero-crossing selection device that selects from a square-wave signal derived from the received ultrasonic signal that of the arrival delay signal following zero crossing of the one transit direction

device, in particular with a rising edge, selects with a timer, in particular one Oscillator with a downstream counter, which compared to the transmission time around the expected Transit time of the ultrasonic signal displaced reference signal S emits, with a reference delay device which defines a reference delay time following the point in time of the reference signal and at its end emits a time comparison signal, and with a time of arrival detector, which compares the zero crossing with the point in time of the time comparison signal

From DT-OS 23 22 749 and DT-OS 23 33 971 devices for ultrasonic measurement of the flow velocity of flowing media and the speed of sound in flowing media are known in which ultrasonic signals alternate upstream and downstream via one provided with two ultrasonic transducers, at least one Component are sent in the measuring section running in the direction of flow. In the transmit timing of the transmit-side converter is briefly energized and simultaneously triggered a timer to write to the expected life of a reference signal can be, for timing, a voltage controlled oscillator include the f with the downward measurement at a frequency \ and during the upward measurement with a frequency £ is operated. A downstream counter counts a predetermined number of output pulses, for example 256, after the time of transmission. If the expected running time is shorter than the actual running time, the frequency of the oscillator is reduced by means of a control loop; If the expected transit time is longer than the actual transit time, the frequency of the oscillator is increased by means of the control loop.As a result of this tracking, the oscillator frequencies correspond to the reciprocal values of the downward and upward transit times and can be evaluated to obtain the flow velocity and the speed of sound.

In such a device, if the transducer on the transmission side is excited at the time of transmission, it gives it high-frequency ultrasonic signal, which has a frequency of 1 MHz, for example, does not immediately reach maximum Amplitude from; rather, the amplitude increases gradually. This has the consequence that the end of the term, so the beginning of the ultrasonic signal on the receiver side, which can only be determined from the fact that the receiver side Transducer is acted upon by an ultrasonic oscillation that differs only slightly from zero an exact measurement is not possible. Therefore, in the known cases, you have the actual comparison time delayed compared to the start of the signal. This is done on the receiver side by means of an arrival delay device, in which the received ultrasonic signal is rectified at least the first part of the Envelope of the rectified ultrasonic signal is converted into an approximately linearly increasing signal and this is fed to a threshold value detector which, when the threshold value is reached, is compared to the actual Arrival delayed arrival delay signal emits In a second channel that is The received ultrasonic signal is amplified and clipped in such a way that a square-wave signal in phase results. The zero crossing of this square-wave signal following the arrival delay signal with increasing Edge is used as a corrected arrival signal. At the same time, there is a reference delay device a reference delay time has been added at the time of the actual reference signal, the just like the arrival delay time is constant but slightly greater than this. At the end of this Reference delay time, a time comparison signal is output as a corrected reference signal, which is compared with the aforementioned zero crossing is compared. It does not matter whether the The beginning of the incoming ultrasonic signal is determined very precisely. Because by a slightly Delayed determination of the start of the signal is only the arrival delay time and thus the arrival delay signal shifted, but not the selected zero crossing used for the measurement. This results in a very high measurement accuracy.

Difficulties arise, however, when the onset of the incoming ultrasonic signal is so late it is determined that the arrival delay signal is immediately before the zero crossing to be selected appears. Then it can happen that instead of this the next zero crossing for the measurement used and the measurement result is falsified. One was therefore forced to work very precisely To use components on the receiving side that enable the start of the signal to be determined as quickly as possible, preferably within the first half period.

The invention is based on the object of specifying a device of the type described above, in which an exact determination of the arrival time is possible without having to worry about the exact determination of the At the beginning of the incoming ultrasonic signal, the requirements that must be met are as high as before.

According to the invention, this object is achieved by a phase detector which determines the phase position of the arrival delay signal with reference to a zero crossing of the other passage direction, in particular with a falling edge, of the square-wave signal, and by a control device which acts on the arrival delay device and which is dependent on from the phase position the arrival delay time in the sense of a shift of the arrival delay signal in the direction of the last-mentioned zero crossing changes.

In this embodiment, the arrival delay time is no longer constant, but can be changed. she the zero crossing of the square wave signal, which is the zero crossing to be selected, is determined by a control loop advanced by a half period, tracked. This ensures that, on the one hand, the arrival delay signal occurs so in time that the following zero crossing, which is used for measurement, also occurs Certainness can be selected and that on the other hand a late detection of the start of the signal is permitted within wider limits than before, because the arrival delay time automatically corresponds accordingly is shortened. This also allows simpler, commercially available circuit elements to be used, because the control loop compensates for errors that depend on this.

It is also favorable if the control device also acts on the reference delay device and the reference delay time changes in the same direction as the arrival delay time. With this you can make further corrections. In particular, it can be used without manual setting or adjustment automatically ensure that the reference delay time of the respectively determined zero crossing following edge is adapted.

In the case of a device in which the arrival

delay device the received ultrasonic signal rectified, at least the first part of the envelope curve of the rectified ultrasonic signal approximately linearly increasing signal is converted and this is fed to a threshold value detector which, when of the threshold value causes the delivery of the arrival delay signal, it is recommended that the Phase detector if the arrival delay signal occurs too early and early signals if it is too late Occurrence of late signals emits that the early signals with one and the late signals with the opposite Signs can be fed to an integrator and that a control voltage which can be taken off at the output of the integrator is used to change the arrival delay time. When the phase position of the arrival delay signal coincides exactly with the zero crossing of the other direction of passage, occur alternately Early and late signals so that the integrator outputs a constant control voltage. Predominate Early signals or late signals, the control voltage decreases or increases.

In particular, the phase detector can have a D flip-flop whose preparation input or data input is supplied with the square-wave signal and whose clock input is supplied with the arrival delay signal and at one output of which the early signals and the other output of which the late signals are output.

The control voltage is particularly advantageous for one input and the envelope for the other input linearly increasing signal generating differentiating amplifier can be fed. If the difference between Control voltage and envelope increase, if the threshold value is reached earlier, the difference decreases, the threshold is reached later. Instead, the control voltage can also influence it in other ways take, for example by changing the threshold value itself.

In a preferred embodiment, the reference delay device includes a monostable multivibrator which is triggered by means of the reference signal and has an RC element that determines the breakover time, the capacitor charging voltage of which is dependent on the control voltage, and a flip-flop that can be reset after each measurement and that is operated by the multivibrator is set at the end of the tilting time and then emits the time comparison signal. The rising edge of the time comparison signal is used to precisely determine the end of the reference delay time. It is a binary continuous signal that only ends when it is reset.

Furthermore, the threshold value transmitter can send a threshold value signal when the threshold value is reached output, which sets a resettable flip-flop after each measurement, which in turn sets the arrival delay signal gives away. The arrival delay signal is therefore also a binary continuous signal that only starts with the Resetting of the flip-flop ends and its rising edge exactly the end of the arrival delay time designated.

The zero-crossing selection device advantageously has a Z? -Flip-flop that can be reset after each measurement whose preparation input is the reference delay signal and whose clock input is the square-wave signal is supplied and which emits the zero-crossing signal at an output. The zero crossing signal is therefore a binary continuous signal which ends when the flip-flop is reset and whose rising edge is the exact point in time of the zero crossing indicates.

In a favorable embodiment, the arrival time detector has a Z> flip-flop, whose The preparation input is supplied with the time comparison signal and its clock input is supplied with the zero crossing signal is an early measurement signal at its one output and an early measurement signal at its other output Emits late measurement signal, depending on whether the zero crossing signal is before or after the time comparison signal occurs. The early and late measurement signals can then be in Usually evaluated for measurement and display purposes, for example, the frequency of the Adjust the timer oscillator to the actual running time.

Furthermore, a display device with two light-emitting diodes can be provided, each of which has one of the inverters controlled by the early and late signals are fed. If the control loop is functioning correctly these LEDs must light up alternately.

The invention is explained in more detail below with reference to an exemplary embodiment shown in the drawing. It shows
1 shows a block diagram of an ultrasonic measuring device with the device according to the invention,

F i g. 2 shows the circuit structure of an embodiment of the device in a simplified representation,

Fig. 3 Transmission signal, ultrasonic signals, counting signals and reference signals in their time course and

F i g. 4 different signals occurring in the device in their time course.

According to FIG. 1 is in a channel 1 an ultrasonic measuring section 2, which is carried out by two ultrasonic transducers 3 and 4 is limited and at an angle to the direction of flow 5 of the channel 1 flowing through Medium is arranged. A transmitting device 6 is able to send an excitation signal S 7 to the line 7 Transmitter 3 output, which thereupon through the medium in channel 1 an ultrasonic signal with a resonance frequency of, for example, 1 MHz. This signal is picked up by the converter 4 at the end of the running time and converted into an electrical ultrasonic signal 58, which is transmitted via a line 8 to a receiving device 9 is fed. The lines 7 and 8 are interchangeable via a switch 10, so that the transducers 3 and 4 can alternately serve as an ultrasonic transmitter and an ultrasonic receiver. In the In the receiving device, the ultrasonic signal 58 is amplified and then processed further in two channels.

In the first channel there is an amplifier 11, on whose output line 12 a square-wave signal 512 with the frequency of the ultrasonic signal 58 occurs. An arrival delay device is located in the second channel 13, at whose output 14 an arrival delay signal at the end of an arrival delay time 514 occurs. In a phase detector 15, the arrival delay signal 514 with the neighboring trailing edge of a pulse of the square wave signal 512 compared. The phase detector gives Early signals 516 or late signals 517, depending on whether the arrival delay signal 514 is earlier or later than the trailing edge of the pulse of the square wave signal 512 had occurred. As a function of this, a control device 18 is controlled, which a Output 519 to the arrival delay device 13 outputs in such a way that the arrival delay time is shortened or lengthened until the Arrival delay signal 514 exactly with that

Trailing edge coincides. This means that there is a defined zero crossing with a falling edge of the square-wave signal 512 determined.

The arrival delay signal 514 continues to be a zero crossing selection device 20, which is also fed by the square-wave signal S12 will. A zero crossing signal 521 occurs at output 21 when the first rising edge of the Square wave signal 512 after occurrence of the arrival delay signal 514 appears. This establishes a defined zero crossing.

The zero crossing signal 521 is compared with a time comparison signal 523 in an arrival time detector 22. If the zero crossing signal 521 occurs earlier than the time comparison signal 523, an early measurement signal 524 is emitted, and if it arrives late, a late measurement signal 525 is emitted. By integrating all early measurement signals with a sign and all late measurement signals with the opposite sign in a voltage level transmitter 26, a main signal 527 can be obtained which is a direct measure of the speed of sound c . In a second signal level transmitter 28, the early and late measurement signals are evaluated, taking into account the upward signals 529 and downward signals 530 indicating the transmission direction. By integrating all the downward-advance measurement signals with one sign and all upward-advance measurement signals with the opposite sign, an auxiliary signal 531 is obtained which is a measure of the flow velocity ν . The late measurement signals or both the early and late measurement signals can also be processed in a similar manner.

The main signal 527 is fed directly to a summing circuit 32, while the auxiliary signal 531 is fed via a switch 33, which is dependent on the transmission direction, alternately with a positive and negative sign. As a result, control signals 535 and 536 alternately appear at the output of the summing circuit, which influence a voltage-controlled oscillator 37 in such a way that it emits pulse trains 538 at its output 38 with a frequency f \ for downward measurement and a lower frequency ft for upward measurement.

These pulse trains are fed to a counter 39 which, after counting 256 pulses, provides a reference signal 540, some time later a reset signal 541, then a transmission direction switchover signal 542 and, simultaneously with the start of counting, emits a transmission signal 543 to the transmission device 6. The reference signal 540 becomes a reference delay device 44, in which, upon arrival of the reference signal 540, a Reference delay time is started, at the end of which the time comparison signal 523 is output. In addition, the control signal 519 is introduced via the input 45, with the aid of which the reference delay time is changeable. The transmission direction switchover signal 542 is fed to a direction transmitter 46, the the switches 10 and 33 toggles and the signal level transmitter 28 the corresponding downward and Feeds upward signals.

From Fig. 2 there is an embodiment for the devices 9, 11, 13, 15, 18, 20, 22 and 44 of FIG. 1. The receiving device 9 has an amplifier 47 in the output stage, the inverting input of which is the electrical ultrasonic signal 58 is supplied. With this amplifier, the gain can be regulated will. By means of a circuit that is not illustrated, regulation is carried out by supplying a regulating voltage at a terminal 48 such that the amplitude of the occurring at the output 49 of an amplifier 50 Envelope signal 549 remains constant. The output of this amplifier 47 can be via an LC filter circuit 51 be cleaned of interfering frequencies that do not correspond to the ultrasonic frequency. The so The signal values obtained are amplified and clipped in the amplifier 11 in such a way that on the line 12

ίο the square wave signal 512 appears. That amplified Ultrasonic signal is also two field effect transistors 52 for the purpose of two-way rectification and 53 so that a rectified ultrasonic signal 554 appears at the output 54 thereof. This The rectified signal is smoothed in the amplifier 50, which acts as a low-pass filter, so that at the output 59 the envelope 549 occurs.

The envelope curve 549 is fed to a differentiator 55 which, in a preferred exemplary embodiment, is a ramp amplifier whose slew rate (rate of rise of the output signal) is limited. At the output 56 of the differentiator, a signal 556 with a constant slew rate is emitted, which is determined by the slew rate of the amplifier as long as the slew rate of the input envelope 549 is greater than the slew rate of the amplifier. This output signal 556 is compared in a threshold value detector 57 with a fixed threshold value supplied via the input 58 by a voltage divider 58 '. When this threshold value is reached, a threshold value signal 559 is applied to the set input C of a D flip-flop 60, which accordingly emits the arrival delay signal 514 at its output Q until the reset signal 541 is reset.

The arrival delay signal 514 is fed to the clock input of a Z> flip-flop 61, the preparation input D of which is supplied with the square-wave signal 512. As a result, an early signal 516 occurs at output Q or a late signal 517 occurs at output Q , which are linked in NAND gates 62 and 63 with arrival delay signal 514 and can therefore be fed to an integrator 64 as pulses of approximately constant charge.

The early signals are used for the inverting input and the late signals for the non-inverting input of the integrator 64 is supplied. When the arrival delay signal 514 does not exactly match the trailing edge of a pulse of the square wave signal 512 coincides, outweighs the number of early or late signals and the size of the control voltage 519 at the output of the Integrator 64 changes. This output voltage becomes the non-inverting input of the ramp amplifier 55 fed with the consequence that the output voltage 556 parallel to itself upwards or is moved down. This changes the point of intersection with the threshold value and therefore the Time of the threshold value signal 559 and the arrival delay signal 514 until the last-mentioned signal again coincides with the falling edge in the square-wave signal 512.

The regulated in this way arrival delay signal 514 is fed to the input D of a preparation serving as zero-selection device D flip-flop 65, whose clock input C the square wave signal is supplied to the 512th As a result, it occurs at the next zero crossing, i.e. at the leading edge of the next following pulse

609 553/438

in the square-wave signal 512 at the output Q, the zero-crossing signal S 21, which persists until the initial state of the flip-flop 65 is restored by the reset signal 541.

The control voltage 519 acts via a voltage divider 66 on a 7-C element 67 of a monostable multivibrator 68, which is flipped by the reference signal 540 and flipped back again after a time determined by the RC-GXiQa 67. Over the duration of the flip time, which also serves as a reference delay time, produces a signal 569 at the output Q of the multivibrator 68. This signal is the set input C fed to a further flip-flop 70, which thus at its Q output, the time comparison signal 523 outputs until a The reset signal 541 is reset.

A D flip-flop 71 is used as the arrival time detector 22, the preparation input D of which is supplied with the time comparison signal 523 and the clock input C of which is supplied with the zero crossing signal 521. The rising edges of the two signals serve as a time measurement point. Depending on the phase position of these two rising edges, an early measurement signal 524 occurs at output Q or the late measurement signal 525 occurs at output Q.

The early signal 516 is via an inverter 72, the late signal 517 via an inverter 73 each one Light-emitting diode 74 and 75, respectively, which have a common series resistor 76. When the arrival delay signal 514 as desired with the trailing edge of a pulse of the square-wave signal 512 im is essentially synchronous, the diodes 74 and 75 light up alternately.

In FIGS. 3 and 4, different signals are plotted over time. When the transmission signal 543 (line 1) is emitted, the transducer 3 generates an ultrasonic signal 53, which is received by the transducer 4 after a transit time t _z and is detected as an electrical ultrasonic signal 58. At the same time as the transmission signal 543 is output, the counter 39 begins to count the pulses 538 output by the oscillator 37. After 256 pulses or some other predetermined number, the reference signal 540 is output. This corresponds to an expected transit time ie, which decreases with increasing frequency of pulse train 538 and increases with decreasing frequency. The expected transit time t _e is tracked to the actual transit time t _z in the control loop of the device, so that the main signal 527 and the auxiliary signal 531 exactly simulate the speed of sound or the flow speed. It can also be seen that the ultrasonic signal 58 begins with a small amplitude and therefore the beginning of the signal is difficult to use for establishing the actual transit time tz.

From Figure 4 there is initially an enlarged Representation of the ultrasonic signal 58. The rectified signal 554 and 554 results from rectification by smoothing the envelope 549. The signal 554 and the envelope 549 are negative in the illustrated embodiment, as shown in FIG. 2 illustrates is. In addition, by amplifying and clipping the ultrasonic signal 58, the square-wave signal 512 won.

The envelope curve 5 49 generates the output signal 556 in the ramp amplifier 55. This signal is compared with the constant threshold value 558. As soon as the threshold value is reached, the flip-flop 60 is toggled and emits the arrival delay signal 514. The adjustment carried out via the phase detector 15 and the control device 18 has the effect that the arrival delay time f _a thus determined ends at the point in time at which a zero crossing a occurs with the falling edge of the square-wave signal 512. If it is determined in the phase detector 15 that the arrival delay time f _{a is} too short, the output signal 556 is shifted downward with the aid of the control voltage 519, whereby the delay time t _{a is} lengthened. If the delay time t _{a is} too long, the output signal 556 is raised, which shortens the delay time. In the zero crossing selection device 20, the subsequent zero crossing b of the square-wave signal 512 is determined with a rising edge and the zero crossing signal 521 is output as a function thereof. With the arrival delay time f _a regulated, this happens exactly half a period pll of the ultrasonic signal 8 after the arrival of the arrival delay signal 514. This results in a precisely defined delay time, even if the start of the ultrasonic signal 58 cannot be determined exactly.

The reference signal 540 is emitted at the expected time of arrival, which in the regulated state corresponds to the actual time of arrival. In the reference delay device 44, with the aid of the reference delay signal 569, a reference delay time tb is added, at the end of which the time comparison signal 523 appears. The rising edge of the zero crossing signal 521 is compared with the rising edge of the time comparison signal 523 with regard to its phase position and is evaluated in such a way that the zero crossing is determined earlier or later than the time comparison signal and, depending on this, the time at which the time comparison signal occurs is changed in such a way that the essentially with is in synchronism with the zero crossing.

The voltage-controlled oscillator 37 can be of conventional design or as an integrated circuit, z. B. ICL 8038 formed. The frequency divider 39 can also be of conventional design or a Number of individual logical components, e.g. B. Integrated Circuits 7474 have. The direction giver 46 can be through a bistable element, e.g. B. a flip-flop formed. The summing circuit 32 can an operational amplifier, e.g. B. of the type 301A, whose switch 33, which is dependent on the transmission direction be designed electronically and can for example consist of an integrated circuit CA 4016. As far as in Fig. 2 amplifiers have been described in detail, they can be operational amplifiers. In particular, the amplifier 47 can be an integrated circuit MC 159Oe, and the amplifier 11 can be an integrated circuit Circuit MC 1414L, amplifier 50 an integrated circuit 301A, ramp amplifier 55 an integrated circuit HA 2605 and the amplifier of the threshold value detector 57 an integrated circuit MC 1414L, while flip-flops 60, 61, 65, 70 and 71 are formed by logic elements of the 7400 series can.

For this purpose 3 sheets of drawings

Claims (10)

Patent claims: 1. Circuit arrangement for determining physical quantities of flowing media, in particular the flow velocity, according to the ultrasonic method, in which the arrival time of an ultrasonic signal is determined, with an arrival delay device which defines an arrival delay time following the measured signal start and an arrival delay signal at the end emits, with a zero crossing selection device which, from a square-wave signal derived from the received ultrasound signal, selects the zero crossing of the one passage direction following the arrival delay signal, in particular with a rising edge, with a timer, in particular an oscillator with a downstream counter, which has an opposite Emits a reference signal offset approximately by the expected transit time of the ultrasonic signal, with a reference delay device which has a reference delay time fes following the point in time of the reference signal and emits a time comparison signal at the end, and with an arrival time detector which compares the zero crossing with the point in time of the time comparison signal, characterized by a phase detector (15) which determines the phase position of the arrival delay signal (S 14) with reference to a zero crossing (a ) of the other passage direction, in particular with a falling edge, of the square-wave signal (S 12) , and by a control device (18) acting on the arrival delay device (13) which, depending on the phase position, determines the arrival delay time (U) in the sense a shift of the arrival delay signal (SI4) in the direction of the last-mentioned zero crossing (modified. 2. Apparatus according to claim 1, characterized in that the control device (18) also acts on the reference delay device (44) and changes the reference delay time (tb) in the same direction as the arrival delay time (U) . 3. Device according to claim 1 or 2, in which the received ultrasonic signal is rectified in the arrival delay device, at least the first part of the envelope curve of the rectified ultrasonic signal is converted into an approximately linearly increasing signal and this is fed to a threshold value detector which, when the threshold value is reached, the dispensing the arrival delay signal causes, characterized in that the phase detector (15) in to early occurrence of the arrival delay signal (S 14) early signals (S 16) and (17 S) emits at about late onset late signals that the early signals with the one and the late signals with the opposite sign can be fed to an integrator (64) and that a control voltage (S 19) decreasing at the output of the integrator is used to change the arrival delay time (U) . 4. Apparatus according to claim 3, characterized in that the phase detector (15) has a Z> flip-flop (61), the preparation input or data input (D) the square wave signal (S 12) and the clock input (C) the arrival delay signal (S 14) is fed and the early signals (S 16) are emitted at one output (Q) and the late signals (S 17) are emitted at the other output (Q). 5. Apparatus according to claim 3 or 4, characterized in that the control voltage (S 19) can be fed to the one and the envelope curve (S 49) to the other input of a differentiating amplifier (55) generating the linearly increasing signal. 6. Device according to one of claims 3-5, characterized in that for the reference delay device (44) a monostable multivibrator (68) which is triggered by means of the reference signal (S 40) and an RC element (67 ), the capacitor charging voltage of which is dependent on the control voltage (S 19) , and a flip-flop (70) that can be reset after each measurement, which is set by the multivibrator at the end of the tilting time and then emits the time comparison signal (S 23). 7. Device according to one of claims 3-6, characterized in that the threshold value transmitter (57) emits a threshold value signal (S 59) when the threshold value is reached, which sets a resettable flip-flop (60) after each measurement, which in turn sets the arrival delay signal (SH) releases. 8. Device according to one of claims 1-7, characterized in that the zero crossing selection device (20) has a D-flip-flop (65) which can be reset after each measurement, the preparation input (D) of which the arrival delay signal (S 14) and its Clock input (C) the square-wave signal (S 12) is fed and which emits the zero-crossing signal (S21) at an output. 9. Device according to one of claims 1-8, characterized in that the arrival time detector (22) has a D-flip-flop (71) whose preparation input (D) the time comparison signal (S 23) and whose clock input (C) the zero crossing signal (S 21) and which emits an early measurement signal (S24) at its one output and a late measurement signal (S 25) at its other output, depending on whether the zero crossing signal occurs before or after the time comparison signal. 10. Device according to one of claims 4-9, characterized by a display device with two light-emitting diodes (74, 75) which are each fed via an inverter (72, 73) controlled by the early or late signals (S 16, S 17) are.