JPS6310795B2 - - Google Patents

Description

Detailed Description of the Invention This invention is an ultrasonic measurement method in which an ultrasonic pulse is emitted onto a measurement surface, the reflected wave is received, and the distance and level to the object to be measured are measured from the round trip time of the ultrasonic pulse. The present invention relates to an ultrasonic measuring apparatus, and more particularly to an ultrasonic measuring apparatus that makes it possible to easily adjust the minimum measurable time from the emission of ultrasonic pulses, the so-called dead zone, to an appropriate value.

As the principle of a conventional ultrasonic measuring device, an ultrasonic level meter will first be explained with reference to FIG. A repeated start pulse 12 from a terminal 11 is applied to an ultrasonic pulse generation circuit 13 to generate an ultrasonic signal. The ultrasonic signal passes through the signal switching circuit 14 and reaches the transducer 15, from which ultrasonic pulses 16 are radiated into the air. The ultrasonic pulse reflected from the measurement surface 17 is received again by the transducer 15, generating a weak reception signal. The received signal passes through the signal switching circuit 14 and then passes through the received signal amplification detection circuit 18.
guided by. The repeated start pulse 12 and the received signal detection signal from the received wave amplification detection circuit 18 are guided to the time width voltage conversion circuit 19, and the time difference between the two, that is, the ultrasonic pulse 16 is changed between the transducer 15 and the measurement surface 17. A voltage proportional to the time required to go back and forth between the two is generated in the conversion circuit 19. This voltage is subjected to zero and span calculations in the output circuit 21,
converted into a predetermined output.

Incidentally, since the transducer 15 continues to vibrate at the ultrasonic frequency even after emitting the ultrasonic pulse 16, the received signal output of the signal switching circuit 14 changes to the ultrasonic pulse as shown at 22 in FIG. 2A. A voltage is generated for some time after radiation. This is called residual vibration. The radiation wave 23 can be detected when the signal voltage due to the residual vibration 22 becomes sufficiently small. In other words, even if the received wave 23 returns while the residual vibration 22 remains, the received wave amplification detection circuit 18 cannot identify the received wave 23. Therefore, the received signal amplification detection circuit 18 must prevent the residual vibration 22 from being mistaken for the received signal 23.

Therefore, conventionally, as shown in Figure 2B, a monostable multivibrator with a fixed time width is driven in synchronization with ultrasonic pulse emission, and detection of the received signal is prohibited during the output pulse, and the subsequent received signal is is taken out as a detection output as shown in FIG. 2C. The time width T _i during the operation of the monostable multivibrator or the distance required for the ultrasonic pulse to travel back and forth during this time is called the dead zone, and is the minimum measurable distance between the transducer 15 and the measurement surface 17. becomes.

In order to prevent malfunctions due to residual vibrations being mistaken for received signals, it is preferable to make the dead zone T _i of the monostable multivibrator as long as possible.
However, since it is necessary to install the transducer 15 above the highest position of the measurement surface 17 by the amount of the dead zone, it is better to make the dead zone as short as possible when considering the space for installing the transducer 15. Given these two conflicting conditions, it is difficult to set the output pulse width of the monostable multivibrator so that the dead zone is as short as possible while avoiding malfunctions.
Furthermore, it is very difficult to set the optimum value of the dead zone when considering variations in the period of residual vibration caused by the transducer 15 and changes in the way the residual vibration is damped due to fluctuations in ambient temperature.

An object of the present invention is to provide an ultrasonic measuring device in which it is easy to create an appropriate dead zone.

According to this invention, when the residual vibration becomes below a predetermined level, it is detected, and after the residual vibration becomes below a predetermined level, it is detected that the received output becomes above a predetermined level, and the subsequent detected output is corrected. Used as a received wave for reflected waves.
By doing this, even if the length of the residual vibration is different for any transducer, the influence of the residual vibration can be avoided without being affected by the magnitude of the received signal, and the dead zone can be avoided. It becomes possible to significantly shorten the time.

For example, as shown in FIG. 3 by assigning the same reference numerals to the parts corresponding to those in FIG. The signal is supplied to the amplifier 26 in the received signal amplification and detection circuit in FIG. As the amplified output, for example, a residual vibration 22 and a reflected wave 23 as shown in FIG. 4A are obtained. This amplified output is supplied to the shaping circuit 27.

In the shaping circuit 27, the signal is rectified and smoothed by, for example, a diode 28 and a capacitor 29, and a residual vibration envelope output 31 and a radiated wave envelope output 32 as shown in FIG. 4B are obtained. This is supplied to one end of a comparison circuit 33 and compared with a predetermined level 35 from a reference power supply 34 . Predetermined level 35
When the input to the comparator circuit 33 is greater than , a high level (first level) is output from the comparator circuit 33,
If it is small, a low level (second level) is output. This output is due to residual vibration 2 as shown in Figure 4C.
The result is a square wave 36 representing two parts and a pulse 37 representing the 23rd part of the reflected wave.

The output of this comparison circuit 33 is supplied to the clock terminal of a JK flip-flop 38. The JK flip-flop 38 is reset in advance by a start pulse from the terminal 11, and its Q output is at a low level. When the output of the comparator circuit 33 changes from high level to low level, the flip-flop 38
The Q output becomes high level as shown in FIG. 4D. In this way, the fact that the residual vibration 22 has fallen below a predetermined level is detected by the Q output of the flip-flop 38 becoming a high level.

After the end of the residual vibration is detected by the output of the JK flip-flop 38, a signal of a predetermined level or higher is detected from the received wave by the signal detection circuit 39. The signal detection circuit 39 is composed of, for example, a JK flip-flop, and the reset terminal has a JK flip-flop.
The output of flip-flop 38 is supplied;
When the end of the residual vibration 22 is not detected, the Q output of the flip-flop 39 is at a low level as shown in FIG. 4E. On the other hand, the comparison circuit 3 is connected to the clock terminal of the flip-flop 39.
The output of No. 3 is inverted in polarity and supplied to the inverter 41, and a low level is given to the K terminal. Therefore, when the end of the residual vibration is detected in the JK flip-flop 38 and the reset of the flip-flop 39 is released, that is, in _FIG . When the signal supplied to the clock terminal of the flip-flop falls, that is, when the rectified output 37 of this reflected wave rises in FIG. 4, the Q output of the flip-flop 39 at time _t2 becomes as shown in FIG. 4E. It becomes high level and reception of the signal is detected.

The rise of this Q output is the time width voltage conversion circuit 19
The time from the start pulse 12 until the signal is detected by the signal detection circuit 39 is converted into a voltage, and the voltage is output from the time width voltage conversion circuit 19.
In the signal detection circuit 39, while residual vibration exists, it is reset by the JK flip-flop 38, so even if the input supplied to the clock terminal becomes a low level, the output of the flip-flop 39 does not go to a high level. , it rises only after the residual vibration ends and responds only to correct reflected waves. In addition, the flip-flop 39 is activated only by the first falling signal after the end of the residual vibration.
Since the Q output becomes high level and this state is maintained, it is not affected by multiple reflections.

FIG. 5 shows a main part of another example of the ultrasonic measuring device according to the present invention, in which the flip-flop of the signal detection circuit 39 is reset by the start pulse from the terminal 11 during the pulse width τ. By selecting the pulse width τ, the overall configuration becomes simple. That is, this pulse width τ is selected to be the same as the shortest residual vibration of the transducer used, that is, to be slightly longer than the time during which the residual vibration is saturated in the receiving input limiter in the signal switching circuit 14. be done. In this embodiment, flip-flop 38 in FIG. 3 is omitted. In this configuration, the clock terminal input of the flip-flop 39 falls at the rising edge of the residual vibration, but at this point the starting pulse 1
Since the flip-flop 39 is held in reset by the inverter 2, the Q output of the flip-flop 39 never rises, and when the output of the inverter 41 falls thereafter, the flip-flop 39
The output rises and is detected as a correct reflected wave 23.

For example, as shown in FIG. 6, the shaping circuit 27 supplies the output of the amplifier 26 directly to a comparator circuit 33 without rectifying it, compares it with a predetermined level of the reference voltage source 34, and produces an output as shown in FIG. 4G. get the waveform,
This output drives the retriggerable monostable multivibrator 43. The time constant of the retriggerable monostable multivibrator 43 is selected to be slightly longer than the period _T1 of ultrasonic vibration, for example, 1.5 periods. Therefore, the output of the multivibrator 43 has a waveform similar to that shown in FIG. 4C, as shown in FIG. 4H. Therefore, the shaping circuit 27 of FIG. 6 can be used in the same way as the shaping circuit 27 of FIG. 3 or 5.

As described above, the ultrasonic measuring device of the present invention detects the state in which the residual vibration has fallen below a predetermined level, and then detects the signal that is higher than the predetermined level as a correct signal, thereby removing the residual signal. There is no need to manually adjust the monostable multivibrator each time, and the dead zone will automatically be set to the most appropriate value. In an ultrasonic measuring device, the amplitude of the received wave decreases as the propagation distance of the ultrasonic wave increases, so the gain of the received wave amplification circuit is controlled to increase over time compared to the transmission of the ultrasonic wave. Increasing the gain of the amplifier circuit increases the amplitude of the residual vibration at the output of the amplifier circuit, and in the device of this invention, the period of residual vibration becomes longer; however, in long-distance measurements, even if the dead zone becomes longer, no measurement can be made. has no effect.

[Brief explanation of the drawing]

Fig. 1 is a principle diagram showing the general configuration of an ultrasonic level meter, Fig. 2 is a waveform diagram for explaining its operation, and Fig. 3 is a block diagram showing an example of an ultrasonic measuring device according to the present invention. FIG. 4 is a time chart for explaining the operation of the ultrasonic measuring device according to the present invention, FIG. 5 is a block diagram showing a part of a modification of the ultrasonic measuring device according to the present invention, and FIG. 6 is a shaping circuit 27. FIG. 3 is a block diagram showing another example. 11: Start pulse input terminal, 14: Signal switching circuit, 15: Transducer/receiver, 19: Time width voltage conversion circuit, 27: Shaping circuit, 39: Signal detection circuit.

Claims (1)

[Claims] 1. An ultrasonic pulse is transmitted from a transducer for each start pulse, and the distance to the measurement surface is measured from the round trip time of the ultrasonic pulse between the transducer and the measurement surface. In an ultrasonic measurement device, a received signal is supplied, outputs a first level when it is above a predetermined level, outputs a second level when it is below a predetermined level, and outputs a first level when the residual vibration of the transducer is above a predetermined level. a shaping circuit that continues to output a level; a signal detection circuit that is supplied with the output of the shaping circuit and outputs a signal detection output when triggered by a change in the output from a second level to the first level; An ultrasonic measuring device comprising: means for resetting at least during the start pulse width.