JP2004205232A - Ultrasonic wave length measuring apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To measure the length of a long metal of which the periphery is restrained by concrete, or earth and sand or the like, and cannot be conventionally measured. <P>SOLUTION: This ultrasonic wave length measuring apparatus drives a probe by using the burst wave so as to improve transmission/reception sensitivity and resonates the probe. This ultrasonic wave length measuring apparatus matches a probe exciting frequency with an anti-resonance point containing a cable, and increases Q of the probe to several dozen. A transmission circuit is cut off from a reception circuit in transmission time so as to use the transmission energy effectively. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to measuring the length of a structure buried in concrete, soil, or the like.
[0002]
[Prior art]
Lock bolts used to increase the strength of tunnels are often used as the Natomo method, and it is necessary for management to check the length after construction and burial.
In addition, since there is no data on the length of steel in the foundation concrete after a considerable time in the past, it is extremely useful when reusing the foundation.
[0003]
In measuring the length of a metal object, a method of measuring the reflection time of an elastic wave or an ultrasonic wave from an end face and obtaining the length from the sound velocity of a propagating substance is a well-known method.
[0004]
However, long objects such as steel materials used for building foundations have a limited measurable length.
[0005]
That is, it is a method using an ultrasonic pulse reflection method used for a metal flaw detector, or a method using reflection from an end face of an elastic wave using an impact hammer as a transmitting means and an AE sensor as a receiving element.
[0006]
Although these methods seem reasonable at first glance, they have significant shortcomings in terms of length measurement.
[0007]
The reason is that the propagation speed differs depending on the type of generated elastic wave.
Elastic waves in solids can be broadly classified into longitudinal waves, transverse waves, and surface waves. Even if the propagation medium is the same, the speed of the waves is different. In addition, since these waves are generated simultaneously at the same time, it is difficult to select and use them.
[0008]
In particular, elastic waves due to mechanical impact have low particle velocities and therefore have low frequencies, and most of them propagate as surface waves.
For this reason, the reflection from the long metal end face of Muku can be easily obtained, but if it is covered with concrete or buried in the soil, the generation of surface waves will be hindered, the reflected signal will be extremely reduced and measurement will be impossible. Fall into.
This phenomenon is because the surface wave disappears, and only the longitudinal wave component catches the one that propagated in the metal.
[0009]
The metal flaw detector applied an impulse voltage, just like hitting a bell with a splinter. Alternatively, a resonance circuit by free vibration is formed.
Assuming that the time width of the impulse voltage is W, the half width of the included frequency component is T = 1 / W, and a time width pulse determined by the bandwidth of the vibrator is transmitted.
[0010]
In general, a wide-band vibrator is manufactured to increase the distance resolution, and it is desired to reduce the Q of the vibrator as much as possible. Depending on the elastic wave attenuation rate of the measurement medium and the required distance resolution, Thus, the frequency, that is, the wavelength of the generated elastic wave is selected.
[0011]
In the case of a long measurement, the frequency is reduced to reduce the attenuation of the medium.
[0012]
[Problems to be solved by the invention]
There is a difference between the length of the lock bolt after burial and the length stipulated in the design specifications and the actually constructed length, and it is required to ensure the safety of social capital.
[0013]
In addition, the measurement of the length of an old buried structure, for which no data remains, has attracted particular attention recently because of the effective use of social capital by reusing the foundation.
[0014]
The length that can be measured, such as a long steel material, is determined by the transmission energy, the efficiency of the electroacoustic transducer, the amplification factor of the receiving amplifier, and the signal-to-noise ratio. Was not enough.
According to the present invention, it is possible to measure the length of a long buried or covered long structure that could not be detected conventionally.
[0015]
[Means to solve the problem]
The probe was driven by a burst wave to resonate the probe.
[0016]
The probe excitation frequency was adjusted to the anti-resonance point including the cable.
[0017]
The Q of the probe was increased to 20-30.
[0018]
In order to make effective use of the transmission energy, the receiving circuit was disconnected from the transmitting circuit during the transmission time.
[0019]
BEST MODE FOR CARRYING OUT THE INVENTION
In the present invention, the ultrasonic pulse reflection method is optimally configured for measuring the length of a long metal constrained.
[0020]
While maximizing the transmission and reception efficiency of the probe, it was possible to effectively generate longitudinal waves and to measure the length of a constrained long metal structure.
[0021]
【Example】
Hereinafter, an embodiment of an ultrasonic length measuring apparatus according to the present invention will be described with reference to FIGS.
[0022]
As the driving waveform of the burst wave, it is first conceivable to use a linear power amplifier such as a power operational amplifier, but it is not easy to obtain a high-frequency, high-frequency burst sine wave.
Further, since the driving waveform is limited by the bandwidth of the vibration, it does not need to be a sine wave, and a square wave is sufficient.
For this reason, the method of driving a burst wave to obtain a high output is based on this method, since continuous driving of a square wave by a switch element generates little heat, is small and lightweight, and is economical.
[0023]
In a probe used as the electroacoustic conversion means, a piezoelectric ceramic is usually used as a transducer element.
[0024]
FIG. 3 is an equivalent circuit of the piezoelectric ceramic.
The resonance point refers to a frequency at which the impedance becomes minimum, that is, a point at which the induction components L0 and L2 and the capacitor components C0 and C3 cause series resonance, and only the resistance components R0 and R4 are obtained.
The anti-resonance point refers to the frequency at which the impedance becomes maximum, that is, the parallel resonance of L0, 2 and Cd, 5.
[0025]
The transmission sensitivity is at the resonance point, and the reception sensitivity is at the anti-resonance point. Therefore, it is conceivable to arrange two types of transducers in a coaxial structure. However, since the axes are shifted and the area of each transducer is reduced by half, the overall sensitivity does not increase.
[0026]
Cd and 5 are the capacitances of the piezoelectric ceramic, and the dynamic resistance R contributes to the actual transmission and reception of energy.
[0027]
Therefore, L and 1 are added in parallel so that the phase at the operating frequency is as small as possible and close to zero.
[0028]
In the present invention, the Q is made larger than the oscillator used in the pulse reflection method so that the total transmission and reception sensitivity is maximized, and the anti-resonance point which is the maximum point of the reception sensitivity is set as the operating point, and several tens of cycles Excitation is performed with the above burst waves.
[0029]
For this reason, it is a characteristic of the present invention that the resonance state occurs at the frequency including the capacitance of the cable connected to the probe, and the overall transmission / reception sensitivity is significantly increased in a narrow band.
[0030]
The reflected signal time width that determines the accuracy of position detection from the target steel material end depends on the number of cycles of the transmission burst wave. However, in consideration of the detection sensitivity and the position detection accuracy, the gain shown in FIG. It is increased or decreased by the control STC circuit.
[0031]
The transmission / reception switching circuit will be described.
When the voltage is very low, a diode having a characteristic of increasing the resistance is combined and the conventional configuration shown in FIG. 4 is used. However, when high voltage excitation of a long cycle burst wave is performed at an anti-resonance point, The transmission / reception switching circuit acting as a load becomes a load and consumes transmission energy. For this reason, as shown in FIG. 5, the receiving circuit is disconnected during the transmission time, and the controlled switch element 8 connected only during the required reception time is provided.
[0032]
FIG. 1 is a circuit block diagram.
The circuit configuration is basically similar to the conventional pulse reflection method. The signal waveform shown by the gain monitor in FIG. 2 is output as the gain signal in FIG. 1 and the gain control amplifier is proportional to the voltage. The gain is controlled.
[0033]
A burst transmission signal is applied to the probe in synchronization with the transmission synchronization signal, and a gain control signal that changes with time is generated after a delay time that has been controlled to increase or decrease. This is a technique well known as an STC circuit.
[0034]
The features of the present invention are a transmission / reception separation circuit, a transmission burst wave generation circuit, and a transmission / reception switching signal shown in FIG.
[0035]
Further, the bandpass filter is set to have a narrower band than in the case of impulse transmission in order to match the narrowband characteristic of the transmission signal.
[0036]
In the case of a lock bolt having a diameter of 10 to 25 mm and a length of 3 to 6 m, the use frequency is optimally 3 to 5 MHz.
[0037]
【The invention's effect】
It is possible to measure long metal lengths whose surroundings were constrained by concrete, earth and sand, which could not be measured conventionally.
[Brief description of the drawings]
FIG. 1 is a block diagram showing an embodiment of an ultrasonic length measuring apparatus according to the present invention.
FIG. 2 is a control signal diagram of signals.
FIG. 3 is a diagram showing an equivalent circuit of a probe.
FIG. 4 is a diagram showing a conventional transmission / reception switching circuit.
FIG. 5 is a diagram illustrating a transmission / reception switching circuit according to the embodiment;
[Explanation of symbols]
FIG.
1 coil L
2 Induction component L0
3 Condenser component CO
4 Resistance R0
5. Capacitance Cd of piezoelectric ceramic
Figures 4 and 5
REFERENCE SIGNS LIST 1 probe 2 reception diode 3 resistor 4 reception preamplifier 5 transmission diode 6 reception signal 7 transmission signal 8 electronic switch 9 transmission / reception switching signal

Claims (2)

Having electro-acoustic conversion means and burst wave driving means,
A length measuring device wherein the driving frequency is measured at an anti-resonance point of the electroacoustic conversion means. The apparatus as described above, further comprising means for isolating the receiving circuit from the transmitting circuit during the burst wave driving time.

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