JP3935848B2 - Ultrasonic transducer - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an ultrasonic transducer that converts an ultrasonic wave into an electric signal in an audible frequency band. For example, based on ultrasonic detection, detection of a fluid leakage point in a piping system, detection of equipment wear, or detection of an operating state of an equipment. The present invention relates to an ultrasonic transducer used for electrical processing of detected ultrasonic waves in the apparatus.
[0002]
[Prior art]
Conventionally, in this type of ultrasonic transducer, as shown in FIG. 7, the frequency approximates the conversion circuit 2 that converts the ultrasonic wave U into the high-frequency electric signal Zi, and the high-frequency electric signal Zi that is sent from the conversion circuit 2. The local oscillation circuit 15 that generates the electrical signal Zm, the mixing circuit 9A that superimposes the electrical signal Zm generated by the local oscillation circuit 15 on the high-frequency electrical signal Zi that is transmitted from the conversion circuit 2, and the electrical that is transmitted from the mixing circuit 9A The apparatus comprises a detection circuit 9B for detecting the signal Zt ′ and a filter circuit 10 for removing a high-frequency component from the electric signal Zt transmitted from the detection circuit 9B and extracting an electric signal Zo in the audible frequency band. It was.
[0003]
Conventionally, as shown in FIG. 7, in order to constitute the mixing circuit 9A, a buffer B for inputting the high-frequency electric signal Zi sent from the conversion circuit 2 to the non-inverting input terminal via the volume VR1 is provided. An inverting amplifier circuit OP (op-amp) that inputs the high-frequency electrical signal Zi transmitted from the buffer B to the inverting input terminal through the resistor R1 is provided, and an approximate frequency generated by the local oscillation circuit 15 is generated at the inverting input terminal of the inverting amplifier circuit OP. The electric signal Zm is input together with the high-frequency electric signal Zi from the resistor R1.
[0004]
In addition, the detection circuit 9B is configured to detect the electrical signal Zt ′ transmitted from the mixing circuit 9A by a voltage doubler rectifier circuit using two diodes D1 and D2.
[0005]
The non-inverting input terminal of the inverting amplifier circuit OP is grounded, and the output voltage of the inverting amplifier circuit OP is fed back to the inverting input terminal of the inverting amplifier circuit OP through the feedback resistor Rf. Reference numeral 8 denotes an amplifier circuit that amplifies the high-frequency electric signal Zi sent from the conversion circuit 2.
[0006]
In other words, in this conventional apparatus, the electric signal Zm (approximate frequency electric signal) generated by the local oscillation circuit 15 is superimposed on the high-frequency electric signal Zi sent from the conversion circuit 2 in the mixing circuit 9A using the inverting amplifier circuit OP. Thus, a superimposed electric signal Zt ′ having both waveforms as schematically shown in FIG. 8 (a) is generated, and then the superimposed electric signal Zt ′ having both waveforms is generated in the detection circuit 9B comprising a voltage doubler rectifier circuit. By performing the detection process, a superimposed electric signal Zt having a single-wave waveform (detection waveform) as schematically shown in FIG. 8B is generated, and the superimposed electric signal Zt having the single-wave waveform is generated in the filter circuit 10. By performing the removal process of the high frequency component, an electric signal Zo in an audible frequency band as schematically shown in FIG.
[0007]
[Problems to be solved by the invention]
However, the above-described conventional ultrasonic transducer has a large number of parts constituting each of the mixing circuit 9A and the detection circuit 9B, resulting in a high apparatus cost. Further, the consumption of the mixing circuit 9A (particularly the inverting amplification circuit OP) is increased. There was a problem with large power.
[0008]
In addition, the electric signal Zm generated by the local oscillation circuit 15 input to the inverting input terminal of the inverting amplifier circuit OP in the mixing circuit 9A is likely to leak to the converter circuit 2 side of the previous stage through the resistor R1, and the leakage signal causes the operation of the apparatus. For example, in this type of ultrasonic transducer, for example, an amplifier circuit 8 for amplifying a high-frequency electric signal Zi transmitted from the converter circuit 2 is generally provided in front of the mixing circuit 9A. When the leakage signal is mixed into 8, the output signal of the amplifier circuit 8 is likely to be saturated.
[0009]
In addition, in order to avoid the adverse effect caused by the leakage signal as much as possible, the amplification degree of the amplifier circuit 8 is limited to be low, which causes a problem that the S / N ratio of the device is lowered.
[0010]
In view of this situation, the main problem of the present invention is to effectively solve the above problem by rational improvement.
[0011]
[Means for Solving the Problems]
The invention according to claim 1 relates to an ultrasonic transducer, characterized by
A conversion circuit that converts ultrasonic waves into a high-frequency electrical signal, a local oscillation circuit that generates an electrical signal whose frequency approximates that of the high-frequency electrical signal sent from the conversion circuit, and a high-frequency electrical signal sent from the conversion circuit is gated A field effect transistor for mixing and detection that inputs an electric signal generated by the local oscillation circuit to an ungrounded source terminal and an electric signal transmitted from a drain terminal of the field effect transistor that is not connected to a power source. And a filter circuit for removing an electric signal in an audible frequency band by removing a high frequency component.
[0012]
That is, according to this configuration, the mixing process of superimposing the electric signal generated by the local oscillation circuit on the high-frequency electric signal sent from the conversion circuit (that is, the process in the mixing circuit 9A in the above-described conventional apparatus) and the mixing are performed. Both the detection processing applied to the superimposed electrical signal obtained by the processing (that is, the processing in the detection circuit 9B in the above-described conventional device) is performed in the above-described field effect transistor for mixing and detection, and the conversion circuit The frequency approximates the frequency of the high-frequency electrical signal transmitted from the terminal (that is, the high-frequency electrical signal corresponding to the ultrasonic wave input to the conversion circuit) and the generated electrical signal of the local oscillation circuit (that is, the high-frequency electrical signal transmitted from the conversion circuit). Detected superimposed electricity that includes a low frequency component (beat component) with a frequency equal to the frequency difference from the electrical signal) No. is input to the subsequent filter circuit is delivered from the drain terminal of the field effect transistor.
[0013]
Therefore, as in the conventional device, the frequency of the electric signal generated in the local oscillation circuit is set to an appropriate value according to the input ultrasonic wave to the conversion circuit, and is sent from the drain terminal of the field effect transistor in the filter circuit. If the high-frequency component is removed from the electric signal, an electric signal in an audible frequency band corresponding to the input ultrasonic wave to the conversion circuit can be extracted from the filter circuit.
[0014]
And while obtaining the same function as the conventional device for the function of converting the ultrasonic wave into an audible frequency band in this way, according to the above configuration, the mixing circuit 9A and the detection circuit 9B as described above in the conventional device are used. Compared to the above, the number of parts constituting the mixing processing unit and the detection processing unit can be reduced, the device cost can be reduced, and the drain terminal is not connected to the power source, and the power consumption of the field effect transistor is reduced. Therefore, the power consumption of the entire apparatus can be greatly reduced.
[0015]
In addition, the input impedance of the field effect transistor is considerably larger than the input impedance of the inverting amplifier circuit, and a large resistance is allowed to be inserted in the input portion with respect to the gate terminal of the field effect transistor. Therefore, it is possible to effectively avoid the leakage of the electric signal generated by the local oscillation circuit to the conversion circuit side of the previous stage, thereby causing the conventional problem caused by the leakage signal, that is, the leakage signal adversely affects the operation of the device. In order to avoid problems and adverse effects due to leakage signals, the problem that the S / N ratio of the device is lowered by limiting the amplification degree in the amplification process for the high-frequency electrical signal from the conversion circuit to be low can be effectively avoided. In this respect, the device performance can be effectively improved as compared with the conventional device.
[0016]
In the implementation of the invention according to claim 1, the electric signal in the audible frequency band taken out by the filter circuit is not necessarily used for the purpose of generating the audible sound corresponding to the ultrasonic wave by inputting the signal to the speaker or the receiver. However, the present invention may be used for any purpose such as displaying the signal value of the signal for various purposes or performing various controls based on the signal.
[0017]
The conversion circuit is not limited to the one that inputs ultrasonic waves propagating in gas, but the one that inputs ultrasonic waves that propagate as solid mechanical vibrations or one that inputs ultrasonic waves that propagate in liquids. For example, ultrasonic waves may be input in any form.
[0018]
DETAILED DESCRIPTION OF THE INVENTION
1 and 2 show a portable ultrasonic leak detection device using the ultrasonic transducer of the present invention. At the tip of the leak detection device 1, ultrasonic waves generated at a fluid leak point in a piping system are shown. A directional microphone 2 for detecting U and a light beam irradiation light source 3 are arranged, and the intensity of the detected ultrasonic wave U (in this example, the sound pressure level of the detected ultrasonic wave U) is displayed on the rear end portion with a digital display 4a. A bar graph display 4b and a display 4 for displaying the sensitivity level S at each time point as a digital display 4c and various keys 5 are arranged.
[0019]
In addition, the leak detection device 1 is equipped with an earphone 6 that expresses the intensity of the detected ultrasonic wave U with an audible sound having a sound volume (or sound quality) according to the detected strength and recognizes it to the user of the device.
[0020]
As shown in FIG. 3, the microphones 2 are arranged in a distributed manner at the apex positions of the regular polygon K (regular hexagon in this example) in a state where the overlapping portion EE common to the directivity range E is generated as shown in FIG. In addition, the light beam irradiation light source 3 is disposed at the center of gravity of the regular polygon K in a front view of the apparatus so as to irradiate the common overlapping portion EE of the microphone directing range E with the light beam.
[0021]
That is, in this leak detection device 1, the direction of the tip of the microphone 2 is changed by gradually changing the direction of the tip in the direction in which the pipe extends in the state where the tip of the device is directed toward the pipe to be detected as shown in FIG. In this case, the leakage location is detected based on the audible sound output from the earphone 6 and the digital display 4 a and the bar graph display 4 b on the display 4. At this time, the irradiation of the light beam emitted from the light beam irradiation light source 3 is performed. The point P matches the detection target location at each time point, so that the user of the apparatus can clearly grasp the detection target location at each time point by visually observing the irradiation point P.
[0022]
Reference numeral 7 denotes a conical cap having a small opening formed at the tip. When a portion that seems to be a leaked portion is detected, the cap 7 is attached to the tip of the apparatus 1 as necessary, and a plurality of microphones 2 are attached. In a state where the directivity as a whole is strengthened, the leakage location is confirmed in more detail.
[0023]
FIG. 5 shows a detection circuit of the leak detection apparatus 1, and the microphone 2 is connected to a microcomputer via a series connection circuit of an amplification circuit 8, a mixing detection circuit 9, a filter circuit 10, a rectification circuit 11, and a final adjustment circuit 12. The earphone 6 is connected to the portion between the filter circuit 10 and the rectifier circuit 11 in the series connection circuit via the volume control means 14. It is.
[0024]
The microphone 2 (specifically, a series or parallel connection circuit of a plurality of microphones 2) is a conversion circuit that converts the ultrasonic wave U propagating in the air from the leakage location into a corresponding high-frequency electric signal Zi, and the amplification circuit 8 A high-frequency electric signal Zi transmitted from the microphone 2 is amplified at a specified magnification.
[0025]
Reference numeral 15 denotes a local oscillation circuit that generates an electric signal Zm having a set approximate frequency that approximates the frequency of the high-frequency electric signal Zi transmitted from the microphone 2, and the mixing detection circuit 9 is transmitted from the microphone 2 and amplified by the amplifier circuit 8. A mixing process for superimposing the generated electric signal Zm of the local oscillation circuit 15 on the high frequency electric signal Zi is performed, and a detection process is performed in conjunction with the mixing process. Subsequently, the filter circuit 10 sends out from the mixing detection circuit 9 The high frequency component is removed from the detected superimposed electric signal Zt, and the electric signal Zo in the audible frequency band is taken out.
[0026]
That is, in the leak detection apparatus 1, the detected ultrasonic wave U of the microphone 2 is converted into an electric signal Zo in the audible frequency band corresponding to the so-called heterodyne method.
[0027]
The audible frequency band electrical signal Zo transmitted from the filter circuit 10 is full-wave rectified by the rectifier circuit 11 and finally adjusted by the final adjustment circuit 12 and input to the central processing unit 13. The signal value of the input signal Zo is averaged and converted into a predetermined conversion value and displayed on the display 4 by the digital display 4a and the bar graph display 4b.
[0028]
On the other hand, an audible frequency band electrical signal Zo transmitted from the filter circuit 10 is input to the earphone 6 via the volume adjusting means 14, and thereby an audible sound corresponding to the detected ultrasonic wave U is output from the earphone 6. .
[0029]
In addition to the display 4, the central processing unit 13 is connected to the light beam irradiation light source 3, various keys 5, trigger-type activation switch 16, storage unit 17, and communication unit 18. According to the operation of the start switch 16, the power is turned ON / OFF to switch between the operating state and the non-operating state of the device, and the light beam irradiation light source 3 is turned ON / OFF according to the operation of the various keys 5 by the user. Then, various processes such as a sensitivity level S change process, a leakage amount calculation process, and a data recording process are executed.
[0030]
The amplifier circuit 8 includes a first adjustment unit 8A in which an amplifier 19a, a band filter 20a, and an attenuator 21a are connected in series, a second adjustment unit 8B in which the amplifier 19b, a band filter 20b, and an attenuator 21b are connected in series, and the amplifier 19c, a band filter 20c and an attenuator 21c connected in series are connected in series. When the central processing unit 13 is instructed to change the sensitivity level S by a key operation, The attenuation rate of the attenuators 21a to 21c in each of the adjustment units 8A to 8C is changed stepwise by the control signal c, and the magnification of the signal amplification as the entire amplification circuit 8 is changed to a magnification corresponding to the instructed sensitivity level S. To do.
[0031]
In addition, when the central processing unit 13 is instructed to calculate the leakage amount by a key operation, the calculation conditions similarly input by the key operation, the setting information about the leakage amount calculation stored in the storage unit 17 in advance, Based on the detection data of the ultrasonic wave U, the amount of fluid leakage at the leakage point where the ultrasonic detection data is obtained is calculated.
[0032]
Further, when the central processing unit 13 is instructed to record data by key operation, the ultrasonic detection is performed together with ultrasonic detection data such as the display value of the digital display 4a and the sensitivity level S when the display value is obtained. The calculation leakage amount for the leaked location from which data is obtained is stored in the storage means 17 with a management number for each detected leak location.
[0033]
The communication means 18 performs two-way communication with the management computer under communication control by the central processing unit 13 in accordance with a communication command given by key operation or a communication command from the external management computer (not shown). Through this two-way communication, the data (management number, ultrasonic detection data, and calculation leak amount) sequentially stored in the storage means 17 for each leak location in the leak location detection operation is managed from the leak detection device 1. Processing to send to the computer, processing information for the leak amount calculation described above, various initial setting values of the device, etc. are sent from the management computer to the leak detection device 1 and stored in the storage means 17.
[0034]
The mixing detection circuit 9 inputs a high-frequency electric signal Zi transmitted from the microphone 2 and amplified by the amplifier circuit 8 to the gate terminal G through the resistor R1, and an electric signal Zm having a set approximate frequency generated by the local oscillation circuit 15. The field effect transistor 9T for mixing and detection (N-channel FET in this example) is input to the ungrounded source terminal S through the resistor R2, and the drain terminal of the field effect transistor 9T is connected to the power source. The electric signal Zt sent out from D is inputted to the filter circuit 10.
[0035]
The filter circuit 10 is a low-pass filter configured by connecting ground capacitors C3 and C4 between the resistors R5 and R6 and the lower side of the resistor R6 in a series connection row of resistors R5 and R6. The electric signal Zo from which the high frequency component has been removed is taken out from the output terminal connected to the resistor R6 and the ground capacitor C4. The capacitor C5 is for removing a DC component generated at the time of detection.
[0036]
In other words, in this leakage detection apparatus 1, a mixing process of superimposing the electric signal Zm generated by the local oscillation circuit 15 on the high-frequency electric signal Zi transmitted from the microphone 2 and amplified by the amplifier circuit 8 is obtained by the mixing process. Both the detection processing applied to the superimposed electric signal is performed in the field effect transistor 9T for mixing and detection, and the high-frequency electric signal Zi sent from the microphone 2 and the electric signal Zm generated by the local oscillation circuit 15 The detected superimposed electric signal Zt including a low frequency component (beat component) having a frequency equal to the frequency difference is transmitted from the drain terminal D of the field effect transistor 9T not connected to the power source and input to the filter circuit 10.
[0037]
In this filter circuit 10, an audible frequency band corresponding to the input ultrasonic wave U to the microphone 2 is removed by removing a high frequency component from the detected superimposed electric signal Zt transmitted from the drain terminal D of the field effect transistor 9 T. The electric signal Zo is sent from the filter circuit 10 to the subsequent circuit.
[0038]
In addition, when the ultrasonic wave U is converted into the electric signal Zo in the audible frequency band by the heterodyne method in this way, the electric signal Zm generated by the local oscillation circuit 15 leaks to the front stage side through the field effect transistor 9T. The large resistance R1 connected to the 9T gate terminal G effectively prevents the device operation inconvenience caused by such a leakage signal, thereby ensuring high device performance.
[0039]
Reference numerals 15a and 15b denote oscillators and buffers that constitute the local oscillator circuit 15, R3 and R4 denote resistors that constitute the local oscillator circuit 15, C1 and C2 denote capacitors that also constitute the local oscillator circuit 15, and 12a and 12b denote final capacitors. These are a low-pass filter and an amplifier in the adjustment circuit 12.
[0040]
6A to 6D show examples of the waveforms of the electrical signals Zi, Zt, Zm, and Zo at the respective parts A to D in the detection circuit of FIG.
[0041]
[Another embodiment]
Next, another embodiment will be listed.
[0042]
In the implementation of the present invention, the conversion circuit that converts the ultrasonic wave U into the high-frequency electric signal Zi is not limited to the one that inputs the ultrasonic wave propagating in the gas as shown in the above-described embodiment, but in any form. A sound wave may be input, and the specific circuit structure may take various structures depending on the form of the ultrasonic wave to be detected, the application of the apparatus, and the like.
[0043]
In the implementation of the present invention, the specific circuit structure of the local oscillation circuit that generates the electrical signal Zm having a frequency approximate to that of the high-frequency electrical signal Zi transmitted from the conversion circuit, and the power supply unconnected in the field effect transistor 9T The specific circuit structures of the filter circuits for removing the high frequency component from the detected superimposed electric signal Zt transmitted from the drain terminal D and extracting the electric signal Zo in the audible frequency band are the structures as shown in the above embodiments. Not limited to this, various configuration changes are possible.
[0044]
The audible frequency band electrical signal Zo extracted by the filter circuit may be used for any purpose, and the ultrasonic transducer according to the present invention detects fluid leakage in the piping system and tanks based on the ultrasonic detection. Ultrasonic leak detection device that detects the wear of equipment based on ultrasonic detection, or ultrasonic operation that detects the operating state of equipment based on ultrasonic detection The present invention can be applied to various devices such as a state detection device.
[Brief description of the drawings]
FIG. 1 is a perspective view of a leak detection apparatus. FIG. 2 is an enlarged view of a rear part of the apparatus. FIG. 3 is an enlarged view of a front part of the apparatus and a pointing range. FIG. 6 is a block diagram showing the electric signal waveform of each part. FIG. 7 is a block diagram showing the circuit structure of the conventional apparatus. FIG. 8 is a schematic diagram of the electric signal waveform of each part in the conventional apparatus. Graph [Explanation of symbols]
2 Conversion circuit 9T Field effect transistor 10 for mixing and detection Filter circuit 15 Local oscillation circuit D Drain terminal G not connected to power source S Gate terminal S Non-grounded source terminal U Ultrasonic Zi High frequency electric signal Zm sent out by conversion circuit Local oscillation Electric signal Zo of approximate frequency generated by the circuit Electric signal Zt of audio frequency band taken out by filter circuit Electric signal sent from drain terminal

Claims (1)

A conversion circuit that converts ultrasonic waves into a high-frequency electrical signal, a local oscillation circuit that generates an electrical signal whose frequency approximates that of the high-frequency electrical signal sent from the conversion circuit, and a high-frequency electrical signal sent from the conversion circuit is gated A field effect transistor for mixing and detection that inputs an electric signal generated by the local oscillation circuit to an ungrounded source terminal and an electric signal transmitted from a drain terminal of the field effect transistor that is not connected to a power source. An ultrasonic transducer provided with a filter circuit that removes high frequency components and extracts an electric signal in an audible frequency band.

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