JPH0312509A - Method and device for measuring internal gap in concrete using ultrasonic wave - Google Patents

Abstract

PURPOSE:To improve measurement accuracy as to the thickness of a concrete specimen and the position of the internal gap by varying the oscillation frequency of ultrasonic pulses, using a low-frequency longitudinal-wave probe which provides high damping as a probe, and further sending modulated pulses. CONSTITUTION:A variable frequency transmitting means 11 is provided in order to send ultrasonic wave pulses of frequency corresponding to the quality of concrete from the probe 12. Therefore, the ultrasonic wave pulses are prevented from being scattered and attenuated in a concrete slab. The ultrasonic wave pulses 14 sent out of the probe 12 are reflected by the bottom surface of the concrete slab and internal gap and the reflected wave 15 is detected by the probe 12 and a displayed as a waveform on a display means 13 such as an oscilloscope. Further, the sent pulses 14 are modulated and the low-frequency, longitudinal-wave probe which provides high damping is used as the probe 12 to shorten the pulse width of the sent pulses. Therefore, the sent pulses and reflected wave are prevented from overlapping with each other.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is applicable to ultrasonic measurement used for quality control and deterioration testing of concrete IJ-contact structures, or non-destructive testing of timber, reinforced plastic FRP, etc. In particular, the present invention relates to a measuring method and apparatus using ultrasonic waves for measuring the thickness and internal voids of a concrete specimen by a probe method.

[Prior Art] In the fields of architecture and civil engineering, the thickness and internal voids of concrete slabs are usually measured by ultrasonic measurement. An example is shown in FIG. What is shown in Fig. 4 is the so-called -probe method, in which the reflected wave of the ultrasonic pulse emitted from the probe 1 is received by the probe 1, and the received signal is The waveform is displayed on a display means such as an oscilloscope (not shown). However, when attempting to measure the thickness of the concrete slab 2 and the position of the internal void 3 using the -probe method, the reflected waves from the slab bottom and the internal void 3 overlap with the transmitted pulses, making it difficult to clearly distinguish the reflected waves. That was difficult.

Therefore, as shown in FIG. 5, two probes, a transmitting probe 5 and a receiving probe 6, are placed on the surface of the concrete slab 7, and the transmitting probe 5 generates an ultrasonic pulse. The bottom surface of the concrete slab 7 and the internal void 8
The receiving probe 6 detects the reflected wave from the concrete slab, displays the reflected waveform on a display means such as an oscilloscope (not shown), and reads the propagation time of the ultrasonic pulse from the reflected waveform to determine the thickness and internal voids of the concrete slab. measure the position of
The so-called two-probe method has been adopted.

[Problems to be Solved by the Invention] However, the two-probe method also had the following problems. In other words, in conventional ultrasonic measuring devices and probes,
Since the frequency components of the ultrasonic waves used are uniquely determined by the performance of the device, depending on the material of the concrete, the ultrasonic pulses may be scattered or attenuated, making measurement impossible. Also, probe 5.6
Since no special measures were taken, such as using a damper material, there was a phenomenon in which the transmitted pulse vibrated for a long time, as shown in FIG. 6, and the measurement accuracy was poor. Furthermore, in the two-probe method, how to arrange the two probes is a troublesome problem.

The present invention solves the above-mentioned problems, and aims to provide a measuring method and apparatus using ultrasonic waves that can improve the measurement accuracy of the thickness of a concrete specimen and the position of internal voids. be.

[Means for Solving the Problems] In order to achieve the above object, the method for measuring internal voids in concrete using ultrasound according to the present invention includes transmitting and receiving ultrasonic pulses with one probe. In a measurement method using ultrasonic waves, the probe uses high damping low frequency◆
It is a longitudinal wave probe 1, the ultrasonic pulse is a modulated pulse, and the ultrasonic pulse is emitted from the probe while changing its frequency, and the echo of the reflected wave received by the probe is The device for measuring internal voids in concrete using ultrasonic waves according to the present invention is characterized by selecting a frequency that is approximately the maximum. A probe that is a frequency φ longitudinal wave probe, variable frequency transmitting means for continuously varying the transmitting frequency of the ultrasonic pulse, and display means for displaying the waveform of the signal received by the probe. It is characterized by comprising:

[Function] In the present invention, since the transmission frequency of the ultrasonic pulse is made variable, measurement can be performed using an ultrasonic pulse of an optimum frequency depending on the properties of the test specimen. In addition, since a high-damping, low-frequency fist longitudinal wave probe is used as the probe, and the emitted pulse is a modulated pulse, the vibration time of the emitted pulse can be shortened, making it possible to clearly separate the emitted pulse and the reflected wave. It is something that can be done.

[Example] Examples will be described below with reference to the drawings.

FIG. 1 is a diagram showing the configuration of one embodiment of the present invention, and as is clear from the figure, a single probe method is adopted in the present invention. In FIG. 1, reference numeral 11 denotes a variable frequency transmitting means, which is provided to enable the probe 12 to transmit ultrasonic pulses having a frequency corresponding to the material of the concrete. This makes it possible to prevent scattering and attenuation of ultrasonic pulses within the concrete slab, which conventionally occurs. The ultrasonic pulse 14 emitted from the probe 12 is reflected by the bottom surface and internal voids of the concrete slab (not shown), and the reflected wave 15 is detected by the probe 12 and displayed as a waveform on a display means 13 such as an oscilloscope. be done.

In addition, as mentioned earlier, in the case of the -probe method, there is a problem in which the reflected wave and the transmitted pulse overlap, but this is because the vibration time of the transmitted pulse is long in conventional longitudinal wave probes. Therefore, in the present invention, the transmitted pulse 14 is a modulated pulse as shown in FIG. 2, and the probe 12 is a highly damped low frequency/longitudinal wave probe. The width is shortened. In other words, by using a modulated pulse instead of the conventional damped oscillation type pulse as the transmission pulse, harmonic components can be reduced and broadband ultrasonic waves with one center frequency component can be transmitted. By using the probe 12 as a low frequency/longitudinal wave probe with high damping, the pulse width can be reduced to about 1/100 of the conventional one.As a result, the emitted pulse width can be shortened, and the emitted pulse and reflected wave can be It is possible to prevent them from overlapping.

Next, a method for measuring internal voids in concrete using the configuration shown in FIG. 1 will be described.

First, similar to the one shown in Fig. 4, the probe 12 is placed on the surface of a concrete slab as a test specimen, and ultrasonic pulses are emitted into the concrete to detect reflected waves from the bottom surface and internal voids of the concrete slab. is received by the probe 12. At this time, the variable frequency transmitting means 11 continuously changes the transmitting frequency from about 100 kHz to about 500 kHz, and selects the frequency at which the height of the echo of the reflected wave is the highest. An example of the received waveform at this time is shown in FIG.

In FIG. 3, the wave indicated by A is a reflected wave of the transmitted pulse, and the wave indicated by B is a wave reflected by the bottom surface or internal void. It can be seen from the figure that the transmitted pulse and reflected wave do not overlap. Now, let T be the time from when the ultrasonic pulse is transmitted until the rise of the reflected wave B, and let V be the predetermined standard velocity of the ultrasonic wave within the concrete of the frequency, then the reflection source, the bottom surface or The position of the internal void from the concrete slab surface can be determined by D=VXT.

Although one embodiment of the present invention has been described above, the present invention is not limited to the above embodiment, and various modifications are possible. For example, the frequency range of the ultrasonic pulse can be changed as appropriate depending on the properties of the object being measured. Further, in the above embodiment, an example was given of measuring the thickness of a concrete slab and the position of internal voids, but the present invention is applicable not only to concrete but also to non-destructive inspection of wood, FPR, etc.

[Effects of the Invention] As is clear from the above explanation, according to the present invention, ■ The transmission frequency of the ultrasonic pulse is made variable, so that ultrasonic pulses with the optimal frequency depending on the properties of the test specimen can be used. A high-damping, low-frequency longitudinal wave probe is used as the probe, and the emitted pulse is a modulated pulse, so the vibration time of the emitted pulse can be shortened, and the emitted pulse and reflected wave can be It has excellent effects such as being able to clearly separate the two, and as a synergistic effect of these, measurement accuracy can be improved.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the configuration of an embodiment according to the present invention, FIG. 2 is a diagram showing an example of a transmitted pulse, FIG. 3 is a diagram showing an example of a received waveform according to the present invention, and FIG. Diagram showing the tactile method, No. 5
The figure shows the two-probe method, and FIG. 6 shows the vibration of a conventional transmitted pulse. 11... Variable frequency transmitting means, 12... Probe, 1
3...Display means. Fig. 3 Fig. 4 Fig. 17 Section / Fig. 5 Fig.

Claims (2)

[Claims] (1) In a method for measuring internal voids in concrete using ultrasonic waves in which one probe transmits and receives ultrasonic pulses, the probe is a high damping low frequency/longitudinal wave probe. , the ultrasonic pulse is a modulated pulse, and is transmitted from the probe while changing the frequency of the ultrasonic pulse, and selects a frequency at which the echo of the reflected wave received by the probe is approximately maximum. A method for measuring internal voids in concrete using ultrasonic waves. (2) A probe that is a high damping low frequency/longitudinal wave probe that transmits and receives ultrasonic pulses made into modulated pulses, and a variable frequency probe that continuously varies the transmission frequency of the ultrasonic pulses. An apparatus for measuring internal voids in concrete using ultrasonic waves, comprising a transmitting means and a display means for displaying a waveform of a signal received by the probe.