JP2772477B2 - Rebar detector using resonance - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to a rebar exploration device utilizing resonance for nondestructively exploring rebar buried in a concrete wall, and in particular,
With high sensitivity, it is possible to detect rebar at a considerably deep part with high resolution.

[Prior Art] A conventional probe of this type uses a coil as a search probe, and when the coil approaches a reinforcing bar, the inductance of the coil changes. Therefore, the change is detected to detect the presence of the reinforcing bar. It is.

[Problems to be Solved by the Invention] The simplest method for improving the sensitivity for this purpose is to increase the magnetic field of the coil. A large current needs to flow, and when the coil is enlarged, its magnetic field distribution range is expanded, making it impossible to search for the exact position of the buried reinforcing bar. This type of device, which is large and originally used as a handy type, has inconvenient use such as an independent power supply unit, so that the magnetic field cannot be unconditionally strengthened.

Therefore, it should be considered that the use of a resonance system is indispensable for such a kind of spacecraft, and it is rather preferable to add another compensation circuit to the resonance system to eliminate the above-mentioned disadvantage.

[Object of the Invention] Accordingly, an object of the present invention is to eliminate the above-mentioned drawbacks and to provide a highly sensitive rebar searcher.

[Means for Solving the Problems] For this reason, in the present invention, a constant-frequency oscillator for supplying power to the resonance circuit, a variable phase shifter capable of appropriately adjusting the phase of the output from the oscillator, Differential amplifier that compares the output from the oscillator with the output from the oscillator, and a lock-in amplifier that differentiates based on a constant frequency output from the oscillator and amplifies the output of the differential amplifier. Combine with
Needless to say, the output frequency of the oscillator is slightly shifted from the resonance frequency of the resonance circuit, and the oscillator is operated in a sharply rising curve toward a peak in a resonance curve of a general resonance circuit.

[Operation] At first, power is supplied to the coil constituting the resonance circuit of the probe of the present invention at a frequency slightly shifted from the resonance point of the resonance circuit as described above. And a second output, which is the output of the oscillator that is the power supply for the resonance circuit and does not pass through the resonance circuit, is compared in phase with a differential amplifier. ,
It is first prepared so that the second output becomes equal, that is, the output of the differential amplifier becomes zero.

Next, in the exploration operation, when the coil approaches the metal body, the output of the first output rises almost proportionally to the resonance point along the resonance curve, and the differential output from the differential amplifier is obtained. However, since this difference output may include an unnecessary frequency due to a distortion component, this difference output is filtered by a filter, and further, the lock-in amplifier fixed by the original frequency signal from the oscillator is used. Output to instrument through instrument.

This instrument output is the difference between the output signal when the rebar is not near the rebar coil and the output signal when the rebar is nearby, and is data on the degree of proximity of the rebar to the coil, i.e., the burial depth, without repairing. .

Next, the basic operation of the probe of the present invention using a resonance system will be described with reference to FIGS.

In the second 5 is assumed to current of a certain frequency than this becomes V ₁ by the oscillator is flowed in the coil L, also now V _O output terminal of the ends seam capacitor C spans the output end of the L
And

In FIG. 2, the output voltage V _O across the capacitor C is Now, ωL = 1 / ωC to be between occur resonance of L and C, and the frequency and omega _R. Output voltage at resonance
V _o Next maximum output is obtained in the third is as shown in FIG. Frequency omega _R.

That is, the maximum current flows through the coil at the time of resonance. Therefore, the magnetic field generated from the coil is strengthened accordingly, and the possibility that the coil can be used for exploring deeper reinforcing bars will appear.

When actually operating the apparatus, a frequency ω ₁ or ω ₂ which is only slightly shifted from a perfect resonance state is used.

The reason for this is that when the coil there were not a close to the rebar, it occurs that the inductance of the coil L is changed deviate from the resonance point ω _R. In this case, when operating at the resonance point, when the frequency is shifted, the output voltage drops to the same degree regardless of which of ω ₁ and ω ₂ the coil L is connected to, and it is possible to distinguish whether the inductance of the coil L has increased or decreased. Not stick. In addition, L
The same is true even if the inductance of the 変 化 changes. However,
By setting slightly to omega ₁ or omega ₂ away from the resonance from the beginning, the output voltage even if the inductance is changed rapidly increases almost monotonically proportional to the frequency. Also, compared to the change in the frequency at the resonance point near the very changes in the output voltage with respect to omega ₁ or omega ₂ If the frequency is large. This serves to increase the sensitivity.

It is a matter of course that the resonance circuit can be applied to the present invention regardless of whether it is a series resonance circuit or a parallel resonance circuit.

Embodiment FIG. 1 shows a circuit of a typical embodiment of the present invention, which will be described.

Reference numeral 5 denotes an oscillator for driving a resonance system having a certain frequency, for example, about 30 KHZ, and a coil L and a capacitor C constitute a resonance circuit. The coil L is provided in an exploration probe and is closely swept to a wall where a reinforcing bar may be embedded. And provide for exploration.

The output from the oscillator 5 is fed to the resonant circuit via the buffer circuit 1, and output detected by the coil L is subjected to impedance conversion through the buffer circuit 2 of high input resistance, and then is Zohaba in Zohaba unit 3 outputs V _L Sine wave output

On the other hand, the sine wave output from the oscillator 5 is also guided to the amplifier 4 to be amplified to an appropriate amplitude and to reduce the output impedance. By passing the sine wave output of the amplifier 4 through the variable phase shifter 6, the phase can be changed without changing the amplitude. After passing through the variable phase shifter 6, the variable gain amplifier 7
Obtain the output V _D through.

The sensor coil L by adjusting the variable phase shifter 6 as V _L and V _D oven away far from reinforcing bars are in phase, Fuhaba also adjust the variable gain increase width vessel 7 to be identical. Ideally, the output of the differential amplifier 8 is adjusted to be zero. In reality
V _L and V _D are unnecessary signal to the output of the differential increase width unit 8 misalignment occurs appears by distortion of negligible waveform. Therefore, by using the band-pass filter 9 that allows only a certain frequency from the oscillator 5 to pass, the output voltage due to waveform distortion can be reduced. When a large distortion waveform is input to the high-sensitivity lock-in amplifier 10, the input may be saturated with an unnecessary signal, but this is avoided. Since the lock-in amplifier 10 guides the signal of the oscillator 5 to its ref terminal, the lock-in amplifier 10 functions as a synchronous detector that matches the fixed frequency of the oscillator 5 but only shows the signal. Since the sensitivity of the input of the lock-in amplifier 10 can be increased even to the noise level, the amplitude of the difference from the original frequency component can be read by the meter 11 connected to the output. This output signal is data relating to the degree of approach or depth of the reinforcing bar.

[Effects of the Invention] The features and effects of this device can be summarized as follows: 1) The operating frequency is higher than that of the conventional type, and the sensitivity is high because of the use of the resonance phenomenon.

2) Since the frequency is slightly shifted without using the frequency at the resonance point, the change in V _O with respect to the change in the inductance of the coil L increases, and high sensitivity can be achieved.

3) The signal that has passed through the coil L in the output from the oscillator 5
Since V _L and the signal V _O that does not pass through the coil L are balanced before the start of measurement, only a change when the rebar approaches is detected, so that the discrimination degree is good.

In the probe of the present invention, a high-frequency ferrite core (about 10 mm in diameter) is inserted in the coil L in order to improve the resolution with respect to the reinforcing bar position.

As a result, all the magnetic fields generated from the coil L are collected in the core, and the lines of magnetic force exiting from the end of the core are much higher in density than the air core. Can be improved.

[Brief description of the drawings]

FIG. 1 is a block circuit diagram of an embodiment of the probe of the present invention, FIGS. 2 and 3 are diagrams for explaining the basic operation of the probe of the present invention, FIG. 2 is a circuit diagram of a resonance system, and FIG. The figure is a resonance curve diagram. 5 ... Oscillator, L: Probe coil, C ... Resonant capacitor, 1,2 ... Buffer circuit, 3,4,7,10 ... Amplifier, 6 ... Phase device, 8 ... Difference Dynamic amplifier, 9 ... Filter, 11 ... Meter

Claims (2)

(57) [Claims] 1. A rebar detector for detecting the presence of a buried rebar based on a change in inductance caused by forming a resonance circuit with a coil and a capacitor and bringing the coil closer to a rebar, and supplying power to the resonator circuit. oscillator having a constant frequency, variable phase shifter that varies the phase of the output of the oscillator, the differential increase width for comparing the output V _D from the output V _L and the variable phase shifter from the resonant circuit, difference Dozo A lock-in amplifier that receives the output of the amplifier and operates using a constant frequency from the oscillator as a reference signal, and a meter that indicates the output of the lock-in amplifier. Spacecraft. 2. The rebar exploration device according to claim 1, wherein the constant frequency is a frequency slightly deviated from a resonance frequency of the resonance circuit.