JPH0249187A - Reinforcing steel survey machine utilizing resonance - Google Patents

Abstract

PURPOSE:To detect the presence of reinforcing steel embedded in a concrete wall with high sensitivity and high resolution by comparing the output of a resonance circuit which shifts slightly from the frequency of an oscillator with the output of said oscillator and detecting their difference output. CONSTITUTION:The oscillator 5 feeds electricity to a probe coil L constituting a resonance circuit at a frequency shifting slightly from the resonance point of the resonance circuit, a differential amplifier circuit 8 compares the output VL of the resonance circuit with the output VD of said oscillator which is not passed through the resonance circuit, and adjustments are made previously so that the output is zero. When the probe constituting said coil L comes close to the reinforcing steel position in survery operation, the output VL of the resonance circuit increases and a difference output is obtained from the differential amplifier 8. Unnecessary frequency components contained in the difference output are removed by a filter 9. The signal is amplified by a lock-in amplifier 10 with the original frequency signal from said oscillator 5 and outputted to an instrument 11.

Description

Detailed Description of the Invention "Industrial Application Field 1 The present invention relates to a reinforcing bar probe using resonance for non-destructive exploration of reinforcing bars buried in concrete walls. Reinforcing bars can also be detected with good resolution.

r Conventional technology 1 Conventional probes of this kind use a coil as a probe, and when this coil approaches a reinforcing bar, the inductance of the coil changes, and this change is detected to know the presence of a reinforcing bar. It is.

"Problem to be Solved by the Invention 1 The simplest way to improve the sensitivity is to strengthen the magnetic field of the coil, but in the conventional example, in order to strengthen the magnetic field, the probe coil must be enlarged, It becomes necessary to flow a large current, and when the coil is made larger, the magnetic field distribution range expands, making it impossible to probe the exact location of the buried reinforcing steel.In addition, the power supply equipment is required to flow a large current through the coil. Since this type of device is large and is originally used as a handheld device, it is inconvenient to use it, such as having to have an independent power supply section, so it is not possible to unconditionally strengthen the magnetic field.

Therefore, the use of a resonant system should be considered indispensable for this type of probe, and it is preferable to eliminate the above drawbacks by adding another compensation circuit to this resonant system.

OBJECT OF THE INVENTION J Therefore, an object of the present invention is to eliminate the above-mentioned drawbacks and provide a highly sensitive reinforcing bar probe.

``Means for Solving Problems'' For this reason, the present invention provides an oscillator with a constant frequency that feeds power to a resonant circuit, a variable phase shifter that allows the phase of the output from the oscillator to be adjusted appropriately, and this phase. a differential amplifier that compares the output from the oscillator with the output from the oscillator; a lock-in amplifier that operates based on the constant frequency output from the oscillator and amplifies the output of the differential amplifier; However, the output frequency of the oscillator is slightly shifted from the resonant frequency of the resonant circuit, so that the resonant circuit operates in a sharp curve rising toward the peak of the resonant curve of a general resonant circuit.

r effect J The coil constituting the resonant circuit of the probe of the present invention is initially supplied with power at a frequency slightly shifted from the resonance point of this resonant circuit as described above, and in this state, from the resonant circuit. The first output of the resonant circuit and the raw second output of the oscillator which is the power supply for the resonant circuit, which does not pass through the resonant circuit, are matched in phase and are compared by a differential amplifier. 1. First, prepare so that the second outputs are equal, that is, the differential amplifier output is zero.

Next, in the exploration operation, when the coil approaches a metal object, the output of the first output increases almost proportionally to the resonance curve up to the resonance point, and the differential amplifier outputs a differential output. However, since this difference output may contain unnecessary frequencies due to distortion components, this difference output is filtered using a filter, and then a lock-in amplification fixed with the original frequency signal from the oscillator is applied. output to the meter through the device.

This instrument output is the difference between the output signal when the reinforcing bar is not near the coil and the output signal when the reinforcing bar is near the coil, and is essentially data about the degree of proximity of the reinforcing bar to the coil, that is, the burial depth. be.

Next, the basic operation of the probe of the present invention using a resonance system will be explained in the second section. FIG. 3 will be explained.

In Figure 2, 5 is an oscillator, from which a current with a frequency of
. shall be.

In Figure 2, the output voltage V across capacitor C. is now ωL
By setting =1/ωC, resonance between L and C occurs, and this frequency is set as ωR. Output voltage when resonance ■. ■. = j″′”C■1, as shown in FIG. 3, and the maximum output is obtained at the frequency ω□.

In other words, the maximum current flows through the coil during resonance. As a result, the magnetic field generated by the coil becomes stronger, opening the possibility of using it to explore reinforcing bars in deeper locations.

When actually operating this device, a frequency ω, or ω2, which is slightly shifted from a perfect resonance condition is used.

The reason for this is that when the coil approaches the reinforcing steel, the inductance of the coil L changes and deviates from the resonance point ωR. In this case, if it is operated at the resonance point, when the frequency shifts, the output voltage will drop to the same extent whether it is shifted toward ω or ω2, and it will be difficult to distinguish whether the inductance of the coil L has increased or decreased. do not have. Further, the same applies even if the inductance of L changes due to temperature change. However, if ω1 or ω2 is set slightly away from resonance from the beginning, even if the inductance changes, the output voltage will rise rapidly in almost monotonous proportion to the frequency. Also, compared to the change in frequency near the resonance point, ω1 or ω
If it is 2, the change in output voltage with respect to frequency is large. This serves to increase sensitivity.

Note that it is a matter of course that the present invention can be applied to both series and parallel resonant circuits.

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

5 is a certain constant frequency that drives the resonance system, for example, 30KH2
The oscillator, the coil L, and the capacitor C constitute a resonant circuit, and the coil is installed in the exploration probe and is closely swept against the wall surface where reinforcing bars may be buried for exploration.

The output from the oscillator 5 is fed to the resonant circuit through the buffer circuit 1, and the output detected by the coil is subjected to impedance conversion through the buffer circuit 2 with high human resistance.
The signal is then amplified by an amplifier 3 to obtain a sine wave output.

Part of the sine wave output from the oscillator 5 is also guided to the amplifier 4,
The amplitude is increased to an appropriate amplitude and the output impedance is lowered. By passing the sine wave output of the amplifier 4 through a variable phase shifter 6, the phase can be changed while the amplitude remains the same. After passing through the variable phase shifter 6, the output ■ passes through the variable gain amplifier 7.

get.

Keep the sensor coil L far away from the reinforcing steel and connect V5 and vo.
The variable phase shifter 6 is adjusted so that they are in phase, and the variable gain amplifier 7 is adjusted so that the amplitudes are also the same. Ideally, the output of the differential amplifier 8 is adjusted to be flat. In reality, ■5 and VI are shifted due to very slight waveform distortion, and an unnecessary signal appears at the output of the differential amplifier 8. Therefore, by using a bandpass filter 9 that passes only a certain frequency from the oscillator 5, it is possible to reduce the output voltage due to waveform distortion. If a large distorted waveform is input to the highly sensitive lock-in amplifier 10, the input may be saturated with unnecessary signals, 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 in which only a signal matching the constant frequency of the oscillator 5 appears. Since the input of the lock-in amplifier 10 can be sensitive to the noise level, the amplitude of the difference from the original frequency component can be read by a meter 11 connected to its output. This output signal becomes data related to the proximity of the reinforcing bars, that is, the depth.

``Effects of the Invention'' To summarize the features and effects of this device, 1) The frequency used is higher than that of conventional types, and the sensitivity is high because it uses a co-occurrence phenomenon.

2) Since the frequency was shifted by a small amount without using the frequency at the resonance point, V was affected by the change in the inductance of the coil L. The change in value becomes large, resulting in high sensitivity.

3) Among the outputs from the oscillator 5, the signal vL that passes through the coil L and the signal V0 that does not pass through the coil L are balanced before starting the measurement, so only the change when the reinforcing bar approaches is detected, so it is easy to discriminate. Furthermore, in the probe of the present invention, a high-frequency ferrite core (diameter of about 10 mmΦ) is inserted into the coil L in order to improve the resolution of the reinforcing bar position.

As a result, the magnetic field generated from the coil L is all concentrated in the core, and the lines of magnetic force coming out from the end of the core have a higher density than when using an air-core coil, which improves the performance of determining the location of reinforcing bars compared to when using an air-core coil. It can be improved.

[Brief explanation of the drawing]

Figure 1 is a block circuit diagram of an embodiment of the probe of the present invention, Figures 2 and 3 are diagrams explaining the basic operation of the probe of the present invention, Figure 2 is a circuit diagram of a common system, and Figure 3 The figure is a communal curve diagram. 5... Oscillator L... Coil for probe
C... Common capacitor 1.2... Buffer circuit 3, 4, 7.10... Amplifier 6...
・Phase shifter 8...Differential amplifier 9...Filter 11...Meter 1 m Representative Person ω1 ωU Procedural Amendment≠ Indication of the case 1988 Patent Application No. 200373 2゜Name of the invention Relationship with the case of a person who makes 3° correction of a reinforcing bar probe using resonance

Claims (2)

[Claims] (1) In a reinforcing bar probe that detects the presence of buried reinforcing bars by forming a resonant circuit with a coil and a capacitor and detecting the presence of buried reinforcing bars based on changes in inductance when the coil is brought close to the reinforcing bars, a fixed frequency is used to supply power to the resonant circuit. an oscillator, a variable phase shifter that changes the phase of the output of the oscillator, a differential amplifier that compares the output V_L from the resonance circuit and the output V_D from the variable phase shifter, and the output of the differential amplifier. 1. A rebar probe utilizing resonance, comprising: a lock-in amplifier that operates using a constant frequency from the oscillator as a reference signal; and a meter that indicates the output of the lock-in amplifier. (2) The reinforcing bar probe according to claim 1, wherein the constant frequency is a frequency slightly different from the resonant frequency of the resonant circuit.