JPH0117090B2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention amplifies an ultrasonic signal having a plurality of peaks, and outputs an output when the wave height of a signal detection peak in the amplified signal reaches a reference level. , relates to an ultrasonic signal detection device, particularly suitable for use in an ultrasonic flowmeter, detecting an ultrasonic signal with automatic gain control applied so that the wave height of the signal detection peak is maintained within a certain range. Regarding equipment.

[Conventional technology]

In general, in measuring instruments that utilize ultrasound, ultrasound signals are propagated within an object to be measured, and physical properties of interest are often detected from changes in the propagation time. The waveform of the ultrasonic signal, especially the ultrasonic pulse, that has propagated within the object to be measured is considerably disturbed due to mutual interference due to multiple reflections, so it is necessary to shape the waveform by some means. However, in the past, there was no suitable waveform shaping method, so if the waveform changed significantly, an error would occur in the measured propagation time, making it impossible to accurately determine the physical property being measured.

FIG. 1 shows the configuration of an ultrasonic flowmeter that measures the flow rate of a fluid 12 flowing through a pipe 10 from the propagation time of an ultrasonic signal. In the figure, 14 and 1
Reference numeral 6 denotes an ultrasonic transducer 21 that serves as a transmitter and a receiver, which are attached to the surface of the pipe 10 so as to face each other via shoes 18 and 20, respectively.
2 is a circuit section, 22 and 24 are changeover switches that are automatically switched in conjunction with each other at regular intervals, 26 is a drive circuit that excites the ultrasonic vibrator, and 28 is an ultrasonic beam 30 propagated through the fluid 12. 32 is a reception pulse generation circuit that outputs a pulse when the amplifier 28 receives an ultrasonic beam of a certain level; 34 is a drive circuit 26 that applies a pulse signal to one ultrasonic transducer; , a time difference measuring circuit that measures the time interval until a received pulse is detected via the other ultrasonic transducer.

When the changeover switches 22 and 24 are in the position shown in FIG. into amplifier 28; When the changeover switches 22 and 24 are switched to the positions opposite to those shown in FIG. , into amplifier 28. When the fluid 12 is flowing in the pipe 10 and the ultrasonic beam is emitted in the downstream direction of the fluid flow as in the first case, the propagation time is the same as the propagation time when the fluid 12 is stationary. On the other hand, when the ultrasonic beam is emitted in the upstream direction of the fluid flow as in the second case, its propagation time is longer than the propagation time when the fluid 12 is stationary. . The difference in propagation time when changing the propagation direction of this ultrasonic beam is
Since the value is proportional to the flow velocity v of the fluid, the flow velocity can be determined from this time difference.

In an ultrasonic flowmeter with such a configuration, the ultrasonic reception signal is basically a resonant waveform with the natural vibration frequency of the ultrasonic vibrator, but it also depends on temperature, fluid flow rate, and ultrasonic pulses passing through different paths. Due to mutual interference, etc., the waveform is not beautiful, and generally has a plurality of peaks as shown by the solid line A or the broken line B in FIG. In the reception pulse generation circuit 32, the level when no ultrasonic signal is input is
If l ₀ is set, another reference level l ₁ is set at a certain value away from l ₀ , and the output is output when the peak wave height of the input waveform reaches the reference level l ₁ . . Therefore, it is desirable that the input to the reception pulse generation circuit 32 always have a constant waveform, but in reality, due to changes in fluid flow velocity, the peak wave height and The relative height of the peak wave height changes. When an ultrasonic signal as shown by the solid line A is input, an ultrasonic reception pulse is generated at the first peak, and when an ultrasonic signal as shown by the broken line B is input, it is generated at the second peak. When the signal detection peak changes in this way, a large error occurs in the measured propagation time, making it impossible to accurately measure the flow velocity.

In order to prevent measurement errors in reception time due to changes in the waveform of the ultrasonic signal as described above, conventionally, the amplifier 28 is controlled so as to keep the wave height of the peak having the maximum wave height in the ultrasonic signal within a certain range. A method of varying the gain is being used. FIG. 3 shows a receiving amplifier circuit of an ultrasonic flowmeter to which such conventional automatic gain control is added. In the figure, 36 is an amplifier whose gain can be controlled by an electric signal applied from a control terminal, and ₃₈ is an amplifier whose gain can be controlled by an electric signal applied from _a control terminal. A first comparator, 42, outputs a voltage E ₂ provided by a DC power supply 44.
A second comparator 46 is disposed between the second comparator 42 and the amplifier 36, and outputs an output when the input signal is greater than the gain control level l ₂ (l ₂ >l ₁ ) set by This is a gain control circuit. the amplifier 36
is connected to the output side of the changeover switch 24, and the first
The output of the comparator 38 is connected to the input side of the time difference measuring circuit 34. Other points are the same as those in FIG. 1, so explanations will be omitted.

The gain control circuit 46 has a reset terminal connected to a second
a flip-flop circuit 4 whose set terminal is connected to the output of the comparator 42 and whose set terminal is connected to the drive circuit 26;
8, changeover switches 50 and 52 operated by the output of the flip-flop circuit 48, a positive power supply 54 connected to the changeover switch 50, a negative power supply 56 connected to the changeover switch 52, and the changeover switch 50, The integrator 58 receives a positive voltage or a negative voltage from a positive power source or a negative power source selected by 52.

In the reception amplifier circuit of such an ultrasonic flowmeter, upon receiving a signal from the ultrasonic transducer, the amplifier 36 amplifies the signal with a gain determined by the control signal from the integrator 58, and comparator 3
Give input to 8,42. The first comparator 38 generates a receive pulse when the received signal exceeds the reference level l ₁ and the second comparator 42 generates a receive pulse when the received signal exceeds _{the reference level l 1 .} 1 comparator 38, the received signal reaches the gain control level.
When _l2 is exceeded, a pulse signal X is output as shown in FIG. The flip-flop circuit 48 of the gain control circuit 46 is set for each measurement period by a pulse signal Y having the same period as the transmission timing taken out from the drive circuit 26 for each measurement period. When a pulse signal X is input here, its output Z is reset, so that a rectangular wave as shown in FIG. 4 is output. The output has a waveform that is the inversion of the output Z. Since the changeover switches 50 and 52 are controlled by this Z, the output U of the integrator 58 moves in the direction of decreasing voltage when the changeover switch 50 is on, and in the direction of increasing the voltage when the changeover switch 52 is on. This voltage output U becomes the output of the gain control circuit 46 and becomes a control signal for the amplifier 36. When the control signal becomes large, the gain of the amplifier 36 decreases, and when the control signal becomes small, the gain of the amplifier 36 increases. Therefore, when the peak value of the received signal decreases, the second comparator 42 outputs a pulse. Signal X no longer appears, Z remains high level, voltage output U decreases,
Since the gain of amplifier 36 increases, the output of amplifier 36 increases. Conversely, when the peak value of the received signal increases, the second comparator 42 outputs a pulse signal X at every measurement period, Z alternately repeats high and low levels, and the voltage output U increases. amplifier 36
Since the gain of the amplifier 36 decreases, the output of the amplifier 36 decreases. In this way, even if the peak value of the received signal fluctuates, the output of the amplifier 36 is maintained within a certain range.

[Problems to be Solved by the Invention] The reception amplifier circuit of an ultrasonic flowmeter equipped with such a conventional automatic gain control circuit has the following problems. That is, in the conventional configuration, automatic gain control operates and the output becomes constant at the highest peak value among the peaks of the received waveform.
However, the first comparator 38, which normally determines the ultrasound reception time, operates at the first peak or second peak of the received waveform. The peak with the maximum wave height value in the received waveform is as shown in Figure 2.
It is normal for it to be quite far back, so the first
This is different from the peak at which the comparator 38 operates. Therefore,
Even with automatic gain control, the height of the signal detection peak at which the first comparator 38 operates cannot be made constant. Therefore, if the relative height of the peak waveform changes significantly, the possibility of comparing received signals at different peaks remains unresolved.

[Purpose of the invention]

An object of the present invention is to provide an ultrasonic signal detection device that can reliably detect ultrasonic signals by keeping the wave height of a signal detection peak within a certain range.

[Means for solving problems]

In order to achieve the above object, the present invention includes a variable gain amplifier that amplifies an ultrasonic signal having multiple peaks, a first comparator that outputs an output when the output wave height of the amplifier reaches a reference level, Similarly, the second comparator outputs an output when the output wave height reaches a gain control level higher than the reference level, and a gain control circuit that changes the gain of the amplifier according to the output of the second comparator. In the ultrasonic signal detection device, the time width signal output circuit operates when the output wave height of the amplifier reaches the time width signal output level, and the second comparator output is activated only when the time width signal is output. A gate circuit for transmitting information to the gain control circuit is provided, and the amplification degree of the amplifier is changed according to the ultrasonic signal within the signal detection peak reception time, so that the wave height of the signal detection peak is maintained within a certain range. It is characterized by the fact that

[Embodiments of the invention]

Embodiments of the present invention will be described in detail below with reference to the drawings. As shown in FIG. 5, the first embodiment of the present invention includes a time width signal output circuit operated by the output of a first comparator 38 in a receiving amplifier circuit of an ultrasonic flowmeter equipped with a conventional gain control circuit. 60, and the output of the second comparator 42 is sent to the gain control circuit 46 only when the output of the time width signal output circuit 60 is output.
An AND circuit 62 that transmits the information is provided.
Other points are the same as those of the conventional example shown in FIG. 3, so explanations will be omitted.

The time width signal output circuit 60 is configured to output an output for a certain period of time τ after the output V of the first comparator 38 is output. This time width τ can be set to the time from when the signal detection peak reaches the reference level until the next peak also reaches the reference level, for example, within about 1 μs for an ultrasonic signal with a fundamental frequency of 1 MHz. .

The operation will be explained below with reference to FIG. The amplifier 36 inputs the received signal from the ultrasonic transducer and sends its output to the first and second comparators 38 and 42.
give to The first comparator 38 produces an output V when the input signal exceeds the reference level _l1 . This output V is not only given to the time difference measuring circuit 34 as in the conventional case, but also inputted to the time width signal output circuit 60. The time width signal output circuit 60 outputs the time width signal W only for a certain period of time τ after receiving the input. On the other hand, the second comparator 42 generates an output X when the input signal exceeds the gain control level _l2 , as in the prior art. This output X is not immediately input to the gain control circuit 46, but is sent to
After passing through, it is applied to the gain control circuit 46. Therefore, the pulse signal X' transmitted to the gain control circuit 46 is
Of the pulse signals X, only those within the time period during which the output W of the time width signal output circuit 60 is output. The operation of the gain control circuit 46 is the same as that of the conventional example, so a description thereof will be omitted.

In this embodiment, the reference level is the time width signal output level, and the time width signal output circuit is the first
After the output of the comparator 38, a time width signal is output for a certain period of time τ, so automatic gain control can be applied to the wave height of the first peak in the ultrasonic signal, and the first peak is It can be used as a detection peak.

In this embodiment, since the reference level is also used as the time width output level for operating the time width output circuit, the circuit configuration is extremely simple.

A second embodiment of the invention is shown in FIG. In this embodiment, a third comparator 64 disposed on the output side of the amplifier 36, a time width signal output circuit 66 operated by the third comparator 64, and an output of the first comparator 38 This embodiment differs from the first embodiment in that an AND circuit 68 that performs an AND with the output of the time width signal output circuit 66 is provided.

The third comparator 64 outputs T when the input signal becomes larger than a time width signal output level l ₃ (l ₃ <l ₁ ) determined by the voltage E ₃ set by the DC power supply 70.
occurs.

The time width signal output circuit 66 outputs a time width signal with a time width τ ₂ after τ ₁ hour has passed since the input is applied.
It is designed to produce W′. The delay time τ ₁ and the time width τ ₂ are selected so that the target signal detection peak is received within the time width τ ₂ . For example, when the second peak in the ultrasound signal is the peak for signal detection, τ ₁ and τ ₂ can each have a time width corresponding to one peak cycle of the ultrasound signal.

The operation will be explained below with reference to FIG. When an ultrasound signal is input and the output of the amplifier 36 first exceeds the duration signal output level _l3 , the third comparator 64 produces an output T. Then, the time width signal output circuit 6
6 operates, and after a delay time τ ₁ has elapsed, output W' having a time width of τ ₂ is generated. Even if the first peak exceeds the reference level _l1 , the AND circuit 62,
Since one input of the AND circuit 68 is off, the outputs X'' and V' of the AND circuits 62 and 68 are never turned on.When the second peak, that is, the peak for signal detection, is input, the time width signal output circuit 66 is on, AND circuits 62 and 68 both output V', when the other input X or V is input.
Give W′. For the third and subsequent peaks, the time width signal output circuit 66 is turned off again, and the AND
Because one input of circuits 62 and 68 is turned off
The outputs of the AND circuits 62 and 68 are never turned on.

In this embodiment, since the time width signal output circuit outputs the output after the delay time τ ₁ has elapsed from the time when the output wave height of the amplifier reaches the time width signal output level, the second peak is output as the signal. It can be used as a detection peak.

Also, using the time width signal output circuit 66, the first
Since only the peak for signal detection is extracted from the output of the comparator 38, the configuration of the subsequent time difference measuring circuit can be simplified.

In the above embodiment, the second peak was used as the peak for signal detection, but it is clear that by changing the length of the delay time τ ₁ of the time width output circuit, any peak can be used as the peak for signal detection. It is.

In each of the embodiments described above, the present invention is applied to a receiving amplifier circuit having an automatic gain control circuit using a comparator, but the scope of application of the present invention is not limited thereto.

Further, in all of the above embodiments, the present invention was applied to detecting ultrasonic signals in ultrasonic flowmeters, but the scope of application of the present invention is not limited to this, and the present invention is applicable to ultrasonic level meters and ultrasonic flaw detection devices. It is obvious that the present invention can be applied to other ultrasonic application devices such as the present invention.

〔Effect of the invention〕

As explained above, the present invention includes a variable gain amplifier that amplifies an ultrasonic signal having multiple peaks, a first comparator that outputs an output when the output wave height of the amplifier reaches a reference level, and a first comparator that outputs an output when the output wave height of the amplifier reaches a reference level. An ultrasonic wave comprising: a second comparator that outputs an output when the wave height reaches a gain control level higher than the reference level; and a gain control circuit that changes the gain of the amplifier according to the output of the second comparator. The signal detection device includes a time width signal output circuit that operates when the output wave height of the amplifier reaches the time width signal output level, and a time width signal output circuit that operates when the output wave height of the amplifier reaches the time width signal output level, and a time width signal output circuit that operates when the output wave height of the amplifier reaches the time width signal output level. A gate circuit is provided to transmit information to the control circuit, and the amplification degree of the amplifier is changed according to the ultrasonic signal within the signal detection peak reception time, so that the wave height of the signal detection peak is maintained within a certain range, It has the excellent effect of stably detecting ultrasonic signals.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the configuration of an ultrasonic flowmeter to which the present invention is applied, FIG. 2 is a diagram showing the received waveform of an ultrasonic signal in the ultrasonic flowmeter, and FIG. 3 is a diagram showing a conventional ultrasonic flowmeter. FIG. 4 is a block diagram showing the reception amplifier circuit portion of an ultrasonic flowmeter to which the automatic gain control circuit of FIG. FIG. 6 is a block diagram showing the configuration of the first embodiment of the reception amplifier circuit portion of the ultrasonic flowmeter; FIG. 6 is a diagram showing the waveforms of each part of FIG.
FIG. 7 is a block diagram showing the configuration of a second embodiment of the present invention, and FIG. 8 is a diagram showing waveforms of various parts in FIG. 10...Pipe, 12...Fluid, 14,16...
...Ultrasonic transducer, 30... Ultrasonic beam, 32...
... Reception pulse generation circuit, 34 ... Time difference measurement circuit, 36 ... Amplifier, 38, 42, 64 ... Comparator, 46 ... Gain control circuit, 60, 66 ... Time width signal output circuit, 62, 68 ... ...AND circuit.

Claims (1)

[Claims] 1. A variable gain amplifier that amplifies ultrasonic waves having multiple peaks; a first comparator that outputs an output when the output wave height of the amplifier reaches a reference level; a second comparator that provides an output when a gain control level higher than the reference level is reached;
A time width signal output circuit that operates when the output wave height of the amplifier reaches a time width signal output level in the ultrasonic signal detection device comprising a gain control circuit that changes the gain of the amplifier according to the output of the comparator. and,
A gate circuit is provided that transmits the output of the second comparator to the gain control circuit only when a time width signal is output, and the amplification level of the amplifier is adjusted according to the ultrasonic signal within the peak reception time for signal detection. 1. An ultrasonic signal detection device characterized in that the wave height of the signal detection peak is maintained within a certain range by changing the wave height of the signal detection peak. 2. The time width signal output circuit is configured to set the reference level to the time width signal output level and output the time width signal for a certain period of time after the output of the first comparator, and the first peak in the ultrasonic signal 2. The ultrasonic signal detection device according to claim 1, wherein the wave height of the ultrasonic signal is maintained within a certain range. 3. The time width signal output circuit is configured to output a time width signal for a certain period of time after a certain period of time has elapsed since the output wave height of the amplifier reaches the time width signal output level, and the second time width signal in the ultrasonic signal is The ultrasonic signal detection device according to claim 1, wherein the wave height of subsequent peaks is maintained within a certain range.