JPS6044626B2 - Ultrasonic measuring device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an ultrasonic measuring device that measures the round trip time of an ultrasonic pulse between a transducer and an object to be measured, and particularly to a gain control section in an amplifying section of a received wave.

For example, in an ultrasonic level meter that measures the height of a liquid level using ultrasonic pulses, repeated pulses from a terminal 11 are supplied to an ultrasonic pulse generation circuit 12 as shown in FIG. The sonic pulse electric signal excites the transmitter 13 and emits ultrasonic pulses toward the liquid surface 14 that is the object to be measured.

The reflected wave from the liquid surface 14 is received by the receiver 15, and the received pulse is detected by the received wave amplification detection circuit 16. On the other hand, the activation pulse from the terminal 11 is supplied to a time width voltage conversion circuit 17, and the time width from this activation pulse until an output is obtained from the received wave amplification detection circuit 16 is converted into a voltage. The converted voltage is output to the output circuit 18
and output as a standardized signal if necessary, or displayed on a display. In this way, when measuring the round trip transmission time of ultrasonic waves, the longer the transmission distance, the more the received waves are attenuated.

That is, as shown in FIG. 2A, the longer the distance to the surface to be measured 14, and therefore the longer the round trip time of the ultrasonic pulse, the smaller the amplitude of the received wave becomes. For this reason, a time-variable gain amplification circuit is provided in the received wave amplification detection circuit 16 to increase the gain with time after the ultrasonic pulse is emitted. Increase as time passes. In this way, the received output was made to have a constant amplitude regardless of the distance to the reflecting surface and therefore the round trip time of the ultrasonic waves, as shown in FIG. 2C. Even if such a time-variable gain amplification circuit is provided, the amplitude of the received wave will not be constant because the reflectance of the ultrasonic wave reflecting surface varies depending on, for example, bubbles or waves.

Therefore, as mentioned above, in addition to the so-called TVG control, which increases the amplification gain as time passes, so-called automatic gain control (AGC) is also performed, regardless of the distance to the object to be measured or the reflectance of the object. This ensures that an output with a constant amplitude is always obtained and that the received waves are detected correctly. Furthermore, according to the time variable gain amplification control, that is, TVG control, residual vibrations remaining in the transmitter during ultrasonic emission leak and become noise, but the gain of the received wave amplification detection circuit is small during the residual vibrations. It is possible to detect weak reflected waves from a long distance with a large gain without being affected by such noise.

By the way, when the distance between the transducer and the object to be measured is short and the reflectance of the reflecting surface is high, so-called multiple reflections occur, which occur back and forth between the ultrasonic pulse transducer and the reflecting surface many times. occurs.

That is, this multiple reflection causes a transmitted pulse P, for example, as shown in FIG. 3A. On the other hand, the first reflected pulse P1, the second reflected pulse P2, and the third reflected pulse P3 are generated sequentially at regular intervals according to their round trip distance, and as the number of round trips increases, the propagation distance becomes longer, and the distance is longer. The amplitude of the reflected wave will be weak, similar to when it is received from a reflecting surface. Even for such multiple reflections, the multiple reflection waves are received with a constant amplitude as shown in FIG. 3B by the time variable gain amplification effect. Generally, an ultrasonic level meter performs a measurement operation by detecting the first received pulse P1 after emitting an ultrasonic pulse, and is not affected by subsequent reflected waves or noise.

However, when automatic gain control is combined with the effect of equalizing the amplitudes of multiple reflections, the average value of the received wave becomes large in the waveform shown in FIG. 3B. Therefore, the ideal peak value A
If the amplitude is not controlled by GC, the overall output amplitude is likely to decrease. Furthermore, the manner in which each reflected wave of multiple reflections is attenuated differs depending on various conditions.

Therefore, in some cases, as shown in Figure 3C, the gain is too small at the time of the first reflected wave P1 due to the effect of the TVG, and the amplitude of the second reflected wave P2 becomes larger than that of the first reflected wave P1. There is. In other words, the first reflected wave P1 has a detection level of 1
1 or less, but there is a possibility that the second reflected wave P2 exceeds the detection level 11 and the second reflected wave P2 is mistakenly detected as the first reflected wave. In this state, when the N°C circuit operates at the peak value of the second reflected wave P2, the first reflected wave P1 is at the detection level 1.
1), resulting in a large error in the measured value. In such cases, the characteristics of time variable gain control are not appropriate, and
This is because the gain was increased too much when receiving the second reflected wave P2 compared to when receiving the first reflected wave P1.

Therefore, the control characteristics may be changed so that the rate at which the gain increases over time, as shown by the dashed line in FIG. 2B, is lower than that shown by the solid line in FIG. 2B. However, if the distance between the reflective surface and the transducer becomes short, multiple reflections will occur as shown in Figure 3A, but if the reflectance of the reflective surface is low, multiple reflections will not occur and only The amplitude of one reflected wave also becomes smaller. Therefore, the automatic gain control works to increase the overall gain, and the overall gain increases.In this state, as shown by the dashed line in Figure 2B, if the gain increase rate of the time variable gain control is small, , the residual vibration part or radiation pulse P. The noise component immediately after is also sufficiently amplified, which may exceed the detection level 11 and cause a large error.
In such a case, it is better for the time variable gain control to have a large voltage change rate as shown by the solid line in FIG. 2B. In short, time-variable gain control needs to be set to preferable control characteristics depending on the environment in which the ultrasonic level meter is placed and various conditions, and conventionally, making adjustments for this purpose required extremely sophisticated technology and time. Moreover, it was not always possible to make good adjustments, which sometimes caused malfunctions.

An object of the present invention is to provide an ultrasonic measuring device in which time-variable gain control automatically adjusts to preferable characteristics according to various conditions, thereby allowing accurate measurements.

According to the present invention, when the gain of the control amplifier is small, the increase time change rate of the gain of the time variable gain amplifier that increases the gain over time with respect to the received wave is controlled to be small or O. do.

Therefore, when the level of the received wave is small, the temporal change rate of the time variable gain control becomes large, and when the received wave j is large at a short distance, that is, in a state where multiple reflections occur, the temporal change in gain increase increases. The ratio becomes small or the state becomes O, that is, the gain becomes constant. Such control can be automatically performed using the gain control signal of the automatic gain amplifier circuit.

That is, when the time variable gain control signal is controlled by the gain control signal of the automatic gain control amplifier circuit and the gain of the AGC is small,
Set the TVG gain increase rate to small or O. In this way, the characteristics of the time variable gain control are automatically adjusted to the optimum value without having to be obtained. Next, the main parts of an embodiment of the ultrasonic measuring device according to the present invention will be explained with reference to FIG. The received signal from terminal 21 is supplied to time variable gain amplifier 22 . The gain of this amplifier 22 is controlled by a control signal from a terminal 23 so that it increases as the ultrasound pulse is emitted. This control signal is generated, for example, as follows. That is, in the time variable gain control signal generation circuit 30, the power supply terminal 24 is connected to one end of the capacitor 25, the other end of the capacitor 25 is connected to one end of the resistor 26, and the connection point between the capacitor 25 and the resistor 26 is connected to the control terminal 23. connected to.

A switch 27 is connected across the capacitor 25 .
Ultrasonic radiation pulse P shown in FIG. 5A. In synchronization with this, the switch 27 changes from the on state to the off state as shown in FIG. 5B. Therefore, for example, if the other end of the resistor 26 is connected to a common potential point as shown by the dotted line in the figure, the control terminal 23 will be at the voltage of the power supply terminal 24, for example 5, from the moment the switch 27 is turned off. , the potential gradually decreases to the common potential point according to the time constants of the capacitor 25 and resistor 26 (FIG. 5C). Amplifier 22 has its control terminal 2
The larger the voltage applied to 3, the smaller the gain is used.

Therefore, the gain of the amplifier 22 is the ultrasonic pulse P. It reaches its lowest level at the time of radiation, and starts to increase gradually over time. The output of this time variable gain control amplifier 22 is fed to an automatic gain amplifier 28, and the output of this amplifier 28 is held at a constant level.

The received wave, which has been made to a constant level by the amplifier 28, is compared with the detection level 11 of the reference power supply 31 in a comparator 29, for example, and a level higher than this is detected. The gain for automatic gain amplifier 28 is controlled by a control signal at terminal 33.

This control signal is generated by the automatic gain control signal generation circuit 40, for example, as follows. The output side of the amplifier 28 is connected to a common potential point through a rectifying diode 34 and further through a capacitor 35, and a switch 36 is connected between both ends of the capacitor 35. The switch 36 activates the ultrasonic radiation pulse P as shown in FIG. 5D. The residual vibration period is turned on, and the other periods are turned off. During this off period, the output of the amplifier 28 is subjected to peak value detection by the diode 34. When the first reflected pulse P1 is received, the pulse is subjected to peak value detection, and a voltage corresponding to the peak amplitude value of the pulse P1 is stored in the capacitor 35 as a negative voltage as shown in FIG. 5E. The voltage obtained at the capacitor 35 is subtracted from the set voltage Va of the amplitude setting power supply 38 in a subtraction circuit 37.

The subtraction output is sampled by the switch 39 (FIG. 5F) which is temporarily turned on after receiving the reception pulse P1, and is supplied to the integration circuit 41, and only while the switch 39 is on, the output of the subtraction circuit 37 is It is integrated by an integrating circuit 41. The positive output from the integrating circuit 41 is supplied to the terminal 33 as a control signal. The gain of the amplifier 28 is controlled depending on whether the amplitude of the received pulse is larger or smaller than the amplitude setting voltage Va, so that the amplitude of the output pulse of the amplifier 28 is controlled to match the setting voltage Va. This automatic gain control amplifier 28 is also controlled such that the larger the control signal at its terminal 33, the smaller the gain. For example, if the amplitude of the received pulse is larger than the set voltage Va, the output of the subtraction circuit 37 becomes negative, and therefore the integrated output of the integration circuit 41 is integrated in the positive direction, resulting in a decrease in the gain of the amplifier 28. controlled. In this embodiment, the opposite side of the resistor 26 of the circuit 30 which generates the control signal for the time variable gain amplifier 22 from the capacitor 25 is connected to the control terminal 33 of the automatic gain control amplifier.

In this way, the time variation characteristics of the time-variable gain control signal are automatically changed in accordance with the automatic gain control signal. The change is made so that when the gain of the automatic gain control amplifier 28 is small, the time rate of change of the gain of the time variable gain amplifier 22 becomes small. When switch 27 is turned off in this embodiment, the voltage at control terminal 23 decreases toward the voltage at automatic gain control terminal 33, as shown in FIG. 5C. Therefore, if the voltage of the control signal at the automatic gain control terminal 33 is small and the gain of the automatic gain control amplifier 28 is large, the control signal at the terminal 23 will be lower than the voltage 5 of the power supply 24, as shown by the solid line in FIG. 5C. It decreases at a relatively large rate of change. The gain of amplifier 22 thus increases at a large rate. However, if the gain of the automatic gain amplifier 28 is small,
In other words, when the amplitude of the received signal is large, that is, when the distance to the reflecting surface is short and the reflectance is high, in other words, when multiple reflections occur frequently, the automatic gain control signal, that is, the signal at terminal 33 is The voltage will be relatively large.

Therefore, switch 2 of time variable gain control signal generation circuit 30
7 is turned off, the voltage at the control terminal 23 is, for example, 5th.
As shown by the dash-dotted line in FIG. The increase rate of the gain of the amplifier 22 over time becomes smaller. Therefore, unnecessary reflected waves such as the second reflected wave are not amplified to a large extent, and there is no risk of misjudging them as the first reflected wave. The waves will be detected correctly. In addition, even if the reflecting surfaces are close to each other, if the reflectance of the reflecting surface is small and multiple reflections are difficult to occur, the amplitude of the first reflected wave is small and the gain of the automatic gain control amplifier 28 is large, and the terminal 33 is Since the control voltage is small, the time-variable gain control signal changes as shown by the solid line in Figure 5C, and the rate of change over time is large, so the gain is not sufficient while the transmitter is generating residual vibration. Moreover, when the first reflected wave is received, the gain is sufficiently increased so that it can be detected without being affected by residual vibration. In the above description, the rate of increase in the gain of the time variable gain amplifier 22 is controlled according to the gain of the automatic gain amplifier 28, but when the gain of the automatic gain control amplifier 28 becomes smaller than a certain value, the gain of the time variable gain amplifier 22 is controlled. A constant value, that is, the rate of change of the gain may be set to O.

For example, as shown in FIG.
4, and when the voltage at this terminal 33 becomes larger than this set voltage, that is, when the gain of the automatic gain control amplifier 28 is smaller than a certain value, the comparator 43
The switch 45 is switched from the output side of the time variable gain control signal generation circuit 30 to the fixed control signal generation circuit 46 side by the output of the fixed control signal generation circuit 46, and a constant voltage from the fixed control signal generation circuit 46 is supplied to the control terminal 23. Time variable gain amplifier 2
2 is held at a constant gain determined by its fixed control signal. Therefore, in the multiple reflection reception state, the level of the reflected waves after the second reflected wave does not increase, and the first reflected wave can be reliably detected. However, the amplitude of the received signal is small,
When the automatic gain control signal at the terminal 33 is small, the output of the comparator 43 switches the switch 45 to the time variable gain control signal generation circuit 30, and the output of the circuit 30 changes the gain of the amplifier 22 over time. It is controlled so that it rises relatively rapidly.

Therefore, the residual vibration can be sufficiently suppressed, and the first reflected wave relatively close to the residual vibration can be detected. In this way, when the gain of the amplifier 22 is changed to a constant gain, the fixed control signal generating circuit 46 is configured as a voltage holding circuit, and when switching the switch 45 to the output side of the fixed control signal generating circuit 46, the fixed control signal generating circuit 46 is configured as a voltage holding circuit. As shown by the dotted line in FIG. 6, the switch 47 is controlled to cause the fixed control signal generation circuit 46 to sample and hold the current control signal of the time variable gain control signal generation circuit 30, and to supply this holding voltage to the control terminal 23. It can also be done. In this case, the gain of amplifier 22 is set to a preferable value. Moreover, in this case, even if the second reflected wave is mistakenly detected as the first reflected wave, if the switch 45 is switched to the fixed control signal generation circuit 46 side,
During the next measurement using ultrasonic radiation, the first reflected pulse is always received at a higher level than the second reflected pulse. That is, even if the change characteristics in the time-variable gain control are too large and the second reflected wave is mistakenly detected, it is immediately switched to reception of the correct first reflected wave. In the above description, the configurations of the time variable gain control signal generation circuit 30 and the automatic gain control signal generation circuit 40 are not limited to the example shown in FIG. 4, and various configurations can be used.

Furthermore, in the above description, the change characteristics of the gain control signal for the time variable gain amplifier 22 are controlled by the control signal of the automatic gain control signal generation circuit 40. For example, if the measured distance becomes less than a predetermined value due to the measurement output, Depending on the distance, the time-variable gain control signal can be controlled to change from the solid line to the dashed line in FIG. 5C, or it can be switched to a fixed value. Also, as the amplifiers 22 and 28, amplifiers whose gain becomes smaller as the gain control voltage becomes higher are used, but it is not necessarily necessary to use amplifiers whose gain becomes larger as the voltage becomes larger. All you have to do is create a control signal. The present invention can be applied not only to ultrasonic level meters but also to various ultrasonic measurement devices such as ultrasonic distance meters, sonars, and ultrasonic flaw detectors. As described above, according to the present invention, the gain change characteristic of the time variable gain amplifier is automatically adjusted to the optimum value, or is automatically changed to a fixed gain to prevent malfunction. Adjustments are painless and accurate measurements are made.

[Brief explanation of the drawing]

Figure 1 is a configuration diagram showing the ultrasonic level meter, Figure 2 is a curve diagram showing the relationship between the measurement distance, the round trip time of the ultrasonic pulse, the gain of the time variable gain amplifier, and the output amplitude, and Figure 3 is a curve diagram showing the relationship between the measurement distance, the round trip time of the ultrasonic pulse, the gain of the time variable gain amplifier, and the output amplitude. Waveform diagram showing the relationship between the reflected wave and its received output signal, No. 4
The figure is a circuit diagram showing the main parts of the ultrasonic measuring device according to the present invention, FIG. 5 is a waveform diagram for explaining its operation, and FIG.
The figure is a block diagram showing the main parts of another example of the ultrasonic measuring device according to the present invention. 13: Transmitter, 14: Reflective surface of reflective object, 15: Receiver,
22: Time variable gain amplifier, 23: Gain control terminal, 28
: automatic gain control amplifier, 29: comparator, 30: time variable gain control signal generation circuit, 40: automatic gain control signal generation circuit, 43: comparator, 46: fixed control signal generation circuit.

Claims (1)

[Claims] 1. In an ultrasonic measurement device that measures the round trip time of an ultrasonic pulse between a transducer and an object to be measured, a time variable gain amplifier whose gain increases over time in synchronization with ultrasonic pulse emission is installed in the received wave amplification section. and an automatic gain control amplifier that controls the gain so that the output amplitude is constant; small or 0
1. An ultrasonic measuring device characterized by comprising means for controlling so that