JPS6044624B2 - Ultrasonic measuring device - Google Patents

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention relates to an ultrasonic measuring device using ultrasonic waves, such as an ultrasonic level meter, an ultrasonic concentration meter, an ultrasonic flaw detector, etc. The present invention relates to an ultrasonic measuring device that is intended to prevent malfunctions due to multiple reflection phenomena.

<Prior Art> FIG. 1 is a system diagram showing an example of an ultrasonic level meter that has been commonly used in the past.

In FIG. 1, an ultrasonic oscillator 1 excites a transducer 3 at certain time intervals using timing pulses output from a timing pulse generator 2.

Thereby, the transducer 3 intermittently transmits ultrasonic waves toward the object to be measured, for example, the liquid surface 4. The time width measuring circuit 5 starts measuring the time width when a measurement start signal is supplied from the timing pulse generator 2, and inputs a reception signal of the reflected wave from the liquid surface 4 detected by the wave reception circuit 6. The time width measurement is completed and the measurement result is output to the display 7. Here, the wave receiving circuit 6 includes a preamplifier 8 that amplifies the received signal of the reflected wave from the liquid surface 4 captured by the wave transmitter/receiver 3 to a predetermined level, and a preamplifier 8 that amplifies the received signal of the reflected wave from the liquid surface 4 captured by the wave transceiver 3 to a predetermined level. The distance correction circuit 9 is constructed of a distance correction circuit 9 that operates to increase the gain, an automatic gain control circuit 10, and a control circuit 11 that controls the gain of the distance correction circuit 9 to gradually increase as time passes.

Next, the reason for installing the distance correction circuit 9 and the control circuit 11 will be described.

Since the liquid level 4 generally changes freely, the distance between the transducer 3 of the ultrasonic level meter and the liquid level 4 changes freely.

By the way, it is known that the magnitude of the reflected wave that returns to the transducer 3 is approximately inversely proportional to the square of the distance between the transducer 3 and the liquid surface 4. Therefore, the magnitude of the received signal obtained at the output side of the preamplifier 8 changes depending on the position of the liquid level 4. In other words, as the distance between the transducer 3 and the liquid surface 4 becomes longer, the level of the received signal becomes smaller. For this purpose, the distance correction circuit 9 and the control circuit 1
1 is provided. The distance correction circuit 9 can use, for example, a multiplication circuit, receives a control signal that gradually increases over time from the control circuit 11, and multiplies this control signal by the received signal from the preamplifier 8. . By doing this, the received signal that arrives after a longer time from the time of transmission can be amplified more greatly, and the received signal can be kept at a constant amplitude regardless of the distance from the liquid level 4 to the automatic gain control circuit 10. can be supplied. Problems to be Solved by the Invention> However, this conventional ultrasonic measuring device has the following problems.

Incidentally, FIGS. 2 to 4 show waveform diagrams for explaining the operation of FIG. 1. By providing the distance correction circuit 9, the transducer 3 and the liquid level 4 operate normally while the distance between the transducer 3 and the liquid level 4 is a certain distance. When the distance becomes short, a multiple reflection phenomenon occurs, resulting in malfunction.

That is, when the liquid surface 4 approaches the transducer 3, the force of the ultrasonic wave reflected from the liquid surface 4 is large, so it is reflected again from the surface of the transducer 3, and it is directed toward the liquid surface 4 again, and from the liquid surface 4. The reflected wave returns again. Repeating this several times, following the transmission signal C, the first reception signal A1, the second reception signal A2, and the third reception signal A
3. A plurality of received signals such as the n-th received signal An are generated continuously. As shown in FIG. 2, the plurality of received signals are eventually adjusted to a constant amplitude by the distance correction circuit 9 and supplied to the automatic gain control circuit 10. Two problems may occur here.

As one of these, a plurality of received signals Al, A2, A3, .
...An is continuously supplied to the automatic gain control circuit 10, so the automatic gain control circuit 10 operates based on the average value of the plurality of received signals, and its gain is unnecessarily narrowed down.

Therefore, as shown in FIG. 3, the output signal from the receiving circuit 6 has a low level and does not reach the received signal detection level P, and the first received signal A1 is detected by the time width measuring circuit 5. It becomes impossible to stop the time width measurement operation. As a result, measurement may become impossible. Second, by providing the distance correction circuit 9, the amplitudes of the successively arriving received signals Al, A2, A3, . . . An are gradually increased as shown in FIG. There is a risk that it will happen.

As a result, a plurality of received signals Al, A2, A3,...M
Since an automatic gain control signal is formed by For example, the second received signal A2 or the third received signal ~ which follows this acts as a time width measurement end signal, and therefore there is a possibility that an erroneous measured value may be displayed. An object of the present invention is to provide an ultrasonic measuring device that can avoid malfunctions due to multiple reflection phenomena as in the conventional example and can obtain accurate measurement results.

Means for Solving the Problems In order to achieve the above object, the present invention transmits ultrasonic waves toward an object to be measured using a transducer and receives the reflected waves or passing waves. In ultrasonic measurement equipment that performs various measurements, the gain is controlled by an automatic gain control circuit based on the amplitude of the received signal, and the time width for the maximum distance at which multiple reflections occur after ultrasonic wave transmission. is set, and a detection circuit detects whether or not the first received signal of the above received signal is obtained within a time width shorter than this time width, and when the above first received signal is detected by this detection circuit. The present invention is characterized in that the gain of the automatic gain control circuit is maintained at the current state by a means for holding the gain of the automatic gain control circuit based on a signal from the detection circuit.

<Embodiment> In this invention, when the distance between the transducer and the liquid surface becomes smaller than a certain set value and a multiple reflection phenomenon occurs, the automatic gain control circuit is activated to control the first received signal. By forcibly making it depend only on the amplitude, even if a multiple reflection phenomenon occurs, the operation of the time width measurement circuit can be reliably stopped by the first received signal, thereby reducing the influence of multiple reflections. The present invention provides an ultrasonic measuring device that is not subjected to

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below in detail with reference to the drawings, taking an ultrasonic level meter as an example, similar to the description of the prior art. FIG. 5 is a system diagram showing an embodiment of the present invention.

In FIG. 5, parts corresponding to those in FIG. 1 are designated by the same reference numerals, and redundant explanation thereof will be omitted. In FIG. 5, the automatic gain control circuit (hereinafter abbreviated as 1AGC circuit) 10 of the present invention has a keyed M° circuit configuration. That is, in this example, the M°C circuit 10 includes a multiplier circuit 10a and an output signal of the multiplier circuit 10a, which is connected to a diode D1.
A switching element 10b supplies an AGC signal at a level proportional to the amplitude of the received signal to the storage capacitor C1 through the switch element 10b, and amplifies and multiplies the difference between the AGC signal stored in the storage capacitor C1 and the voltage value from the set voltage source 10c. circuit 10a
It can be configured by a differential amplifier 10d that feeds back to the In this AGC circuit 10, when the liquid level 4 approaches the transducer 3 to the extent that a multiple reflection phenomenon may occur, the switch element 10b is turned on only while the first received signal A1 is generated, and the first received signal A1 is turned on. It operates to store an AGC voltage proportional to the amplitude of A1 in the storage capacitor C1.
In order to turn on and off the switching element 10b of this AGC circuit 10, a monostable multivibrator (hereinafter referred to as 5
A detection circuit is provided which includes monostable multi-channel circuits 12, 13, and 14, an AND gate circuit 15, a flip-flop circuit 16, an OR gate circuit 17, and an inverter 18.

The switch element 10b of the N°C circuit 10 is turned on or off by a signal from this detection circuit. Figure 6 is the 5th
FIG. 4 is a waveform diagram for explaining the operation shown in the figure.

The operation shown in FIG. 5 will be explained below along with this waveform diagram. The switch element 10b is controlled to be turned off during the time when the ultrasonic wave is transmitted from the transducer 3 and a certain time before and after that time.

For this purpose, a signal issued a certain time before the wave transmission timing is extracted from the timing pulse generator 2, and this signal is supplied to the monostable multi 14, as shown in FIG. 6 (1) B. A rectangular wave Pb including the transmitting period of the transmitting signal C is obtained as shown in FIG. The element 10b is connected to the rectangular wave Pg (
7) Make the RO logic hold it off. on the other hand,
In this example, a monostable multi-13
is provided.

The monostable multi 13 is supplied with a wave transmission timing signal from the timing pulse generator 2, and generates a rectangular wave Pc shown in FIG.
Output. The pulse width Tc of this rectangular wave Pc is set to a time width corresponding to the maximum value of the distance at which the multiple reflection phenomenon occurs. The monostable multi 12 is supplied with the time width measurement signal that is the output of the time width measurement circuit 5, and obtains a rectangular wave Pe that maintains the logic for a certain period of time from the fall of the time width measurement signal. The time width measurement circuit 5 can use a flip-flop circuit in this example, and its set terminal S is supplied with the transmitting timing pulse from the timing pulse generator 2, and its reset terminal R is supplied with the transmitting timing pulse from the receiving circuit 6. A received signal is supplied. Therefore, when the first received signal A1 has reached a predetermined level, the time width measuring circuit 5 is reset by the first received signal A1, and the time width measuring circuit 5 is outputted as a time width measuring signal as shown in FIG. (1) A rectangular wave Pd maintained at 11J logic from the time of transmission to the first received signal A1 as shown in D is obtained. Incidentally, since the pulse width of this rectangular wave Pd corresponds to the distance to be measured, for example, the pulse width of the rectangular wave Pd
The clock pulses are counted while the 11J logic is maintained, and the number of clock pulses is displayed on the display 7 to display the distance from the transducer 3 to the liquid level 4.

The operation of the monostable multi 12 will be explained again.

In the monostable multi 12, the time 11. from the fall of the rectangular wave Pd, which is the output of the time width measurement circuit 5, until at least the first received signal A1 ends. Rectangular wave Pe that maintains J logic
occurs. This rectangular wave Pe is supplied to the AND gate circuit 15. Therefore, when the rectangular wave Pe is generated while the rectangular wave Pc output from the monostable multi 13 maintains the logic of r1, the rectangular wave Pe passes through the AND gate circuit 15 and is output to the flip-flop circuit 16. It is led to the set terminal S. Therefore, the flip-flop circuit 16 is set at the falling edge of the rectangular wave Pe. Note that, for example, a wave transmission timing pulse may be supplied to the reset terminal R of the flip-flop circuit 16 to reset the flip-flop circuit 16 at the time of wave transmission. Therefore, the flip-flop circuit 16
As shown in FIG. 6(1), E and F, a rectangular wave Pf is obtained which is held in the 11j logic from the falling point of the rectangular wave Pe to the wave transmission timing. It passes through the circuit 17, has its polarity inverted by the inverter 18, and is supplied to the switching element 10b, so that the switching element 10b eventually converts the rectangular wave Pf from the falling edge of the rectangular wave Pb, as shown in FIG. 6 (1) G. It is turned on until the fall of , and is kept off during the rest of the period. Therefore, in this state, only the first received signal A1 is rectified by the diode D1, and its rectified output is stored in the storage capacitor C1 ( In other words, this storage capacitor C1 has an AGC level that depends only on the amplitude of the first received signal A1.
I get a signal. When the amplitude of the first received signal A1 is large, the positive polarity voltage of the output of the differential amplifier 10d gradually decreases, and this is supplied to the multiplier circuit 10a.
The level of the received signal obtained from a is controlled in the direction of decreasing. Conversely, when the amplitude of the first received signal A1 is small,
The charging voltage of the storage capacitor C1 becomes smaller, the output of the differential amplifier 10d increases in the positive polarity direction, and the gain of the multiplier circuit 10a increases. Therefore, by configuring as described above, as shown in FIG. 6 (■), the first received signal Al
, Al'' are the rectangular waves Pc, Pc'' from the monostable multi 13
Only when the waves are received within the time width Tc of , the switch element 10b is controlled to be turned off after the generation of the first received signals Al, Al'', and the subsequent second received signals A2, ~'', Third received signal A3, A3'', ... nth received signal An, An''
is prevented from being added to the AGC signal component.

Therefore, in a situation where a multiple reflection phenomenon occurs in a short distance, only the amplitude of the first received signals Al, Al'' is detected, and the AGC circuit 1
0 performs a normal amplification operation only for the first received wave signals Al, Al'', and can supply a normal measurement stop signal to the time width measuring circuit 5. By the way, when the liquid level 4 is If the distance is larger, the first received signal A1'' is generated after the fall of the rectangular wave Pc'' from the monostable multi 13, as shown in FIG. The rectangular wave Pe'' from the stable multiplier 12 cannot pass through the AND gate circuit 15, so the flip-flop circuit 16 is not set forever (the output maintains the RO logic as shown in FIG. 6(■)F). Therefore, the switch element 10b is controlled to be OFF only during the period of the rectangular wave Pb'' from the monostable multi 14, and is controlled to be ON during the other periods, so that the received signal reflected from a long distance is transferred to the distance correction circuit. 9 and the AGC circuit 10 work together to enable accurate capture. <Other Examples> By the way, in the above description, it is assumed that the operation is performed in such a state that the period of damped oscillation of the transmitted signal is suppressed to a constant value so that even the slightest amount does not remain after the time width of the rectangular wave Pb. As shown above, the time width of the damped oscillation fluctuates due to power-on, temperature changes, etc., and there are cases where the damped oscillation still remains after the fall of the rectangular wave Pb from the monostable multi 14.

An example of the operation of the detection circuit at this time is shown in Figure 6 (■) immediately after the power switch of the device is turned on and the charging voltage of the storage capacitor C1 of the AGC circuit 10 is zero, that is, the AGC circuit 10 is in the maximum gain state. Explain using. AG like this
When the gain of the C circuit 10 is large, the monostable multi 1
The damped vibration C″″″ remaining after the fall of the rectangular wave Pb2″5 from Pb2″5 can be sufficiently amplified by the AGC circuit 10, so that it is erroneously detected as a received signal.

As a result, the flip-flop circuit 5 is reset and the rectangular wave Pd'''' falls, and this signal outputs the rectangular wave Pe'''' from the monostable multi 12 to the AND gate circuit 15. On the other hand, since the rectangular wave Pc'''' is in the RlJ logic, the AND gate circuit 15 outputs the 01J logic to the flip-flop circuit 16. As a result, the flip-flop circuit 16 is set and the rectangular wave Pr'''' is output. r1 logic, and the rectangular target Pg'''' from the inverter 18 is 1.
The normal first received signal A1 changes from L logic to 10 logic.
The switch element 10b is turned off before ``'''' arrives. Note that the rectangular wave Pg""" first becomes "1L logic" at the falling edge when the rectangular wave Pb""" from the monostable multi 14 becomes "10" logic, and at this time the switch element 10b is turned on. .Therefore, when this situation occurs, AG
Since the gain of the C circuit 10 depends on the point in time of the remaining damped oscillation, it remains at its maximum gain state. Therefore, it operates in the same way for the next transmitted signal. That is, the rectangular wave Pb
If the time width of the damped oscillation becomes larger than ``'''' or is larger from the beginning, the remaining damped oscillation may be mistaken for a received signal, and as a result, the gain of the AGC circuit 10 temporarily returns to the maximum gain state. When this happens, there is a drawback that a phenomenon occurs in which the maximum gain state is locked. Fig. 7 is a system diagram of an embodiment for eliminating this drawback, and Fig. 8 is similar to Fig. 6. AG in FIG. 7 correspondingly represented
FIG. 7 is a waveform diagram for explaining the corresponding operation when the gain of the C circuit becomes large.

In this example shown in FIG. 7, the output of the differential amplifier 10d of the AGC circuit 10 is input to the inverting terminal of the comparator 19 and compared with the set value connected to the non-inverting terminal, and the output of the differential amplifier 10d is When the gain is larger than the set value and the AGC circuit 10 has a gain higher than a predetermined value, the output of the comparator 19 is inverted to RO logic.

The TO logic of the comparator 19 is supplied to the AND gate circuit 15, and the output of the AND gate circuit 15 is fixed to the RO logic. That is, the flip-flop 5 is reset by the residual component of the damped vibration, and as shown in FIG. Even if the output is output to 10, this output is ignored and the output of the AND gate circuit 15 is fixed at 10 logic. Therefore, the output of the flip-flop circuit 46 maintains the RO logic as shown in FIG. At the point when the voltage becomes 10, the rectangular wave Pg from the inverter 18 becomes r1, and is controlled to be turned on. A first received signal A1, a second received signal A2,
...The rectified output of the n-th received signal M is the storage capacitor C1
The gain of the AGC circuit 10 is lowered. The output Pg from the inverter 18 is, as shown in FIG. 8 (1) G, when the output rectangular wave Pb'' of the next monostable multi 14 becomes RlJ logic, that is, when the next transmission is started. de1
It becomes 0J logic. Therefore, at the time of the next transmission, the output of the differential amplifier 10d of the AGC circuit 10 whose gain has decreased is compared with the set value by the comparator 19. As a result of the comparison, if the output of the differential amplifier 10d is still larger than the set value, the above operation is repeated again. As a result of the comparison, when the output of the differential amplifier 10d becomes smaller than the set value of the comparator 19 (when the gain of the AGC circuit 10 is equal to or smaller than the predetermined gain), the output of the differential amplifier 10d is relatively is inverted to Rlj logic and supplied to the AND gate circuit 15.
An operation depending on the logical output of e, that is, an operation for preventing multiple reflections by opening the nest circuit 15, can be configured as shown in FIG. 8 (■, ■-).

By the way, in Fig. 7, the output signal of the comparator 19 is used to detect a state in which the reflected wave does not return due to some reason, and this detection output is used to detect the state in which the reflected wave is not returned. It is also possible to maintain the display by retaining the data value.

<Effects of the Invention> As described above in detail with reference to the embodiments, according to the present invention, malfunctions of, for example, an ultrasonic level meter can be reliably prevented and reliability can be improved.

It should be noted that it will be easily understood that the present invention is not limited to being applied to an ultrasonic level meter, but can also be applied to other measuring instruments that utilize ultrasonic waves.

[Brief explanation of the drawing]

FIG. 1 is a system diagram for explaining a conventional ultrasonic level meter, and FIGS. 2 to 4 are waveform diagrams for explaining its operation.
Fig. 5 is a system diagram showing one embodiment of the invention, Fig. 6 is a waveform diagram for explaining its operation, Fig. 7 is a system diagram showing another embodiment of the invention, and Fig. 8 is a system diagram thereof. FIG. 3 is a waveform diagram for explaining the operation. 1... Ultrasonic transmitter, 3... Transmitter/receiver, 5... Time width measuring circuit, 6... Wave receiving circuit.

Claims (1)

[Claims] 1. In an ultrasonic measuring device that uses a transducer to transmit ultrasonic waves toward an object to be measured and receives the reflected waves or passing waves to perform various measurements, the received signal is and an automatic gain control circuit whose gain is controlled by the amplitude of the received signal. a detection circuit for detecting whether or not the first received signal is obtained; and a signal from the detection circuit when the first received signal is detected by the detection circuit to control the gain of the automatic gain control circuit at that time. An ultrasonic measuring device comprising: means for maintaining the state.