JP2010048723A - Reinforcing bar corrosion inspection method and reinforcing bar corrosion inspection apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a highly stable inspection result by reducing the influence of an individual difference between members and variations in the equipment arrangement of an inspection apparatus when inspecting the degree of corrosion of a reinforcing bar included in a reinforced concrete member by an eddy current method. <P>SOLUTION: An AC current having a plurality of frequencies is supplied to a differential coil composed of a first coil 3 wound around the reinforced concrete member 10 and a second coil 4 wound around a prescribed reference member 20. The difference level of the impedance of the first coil to the difference in the frequency of an AC current supplied to the first coil 3 is detected as an index value indicating the degree of corrosion of a reinforcing bar 12. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a reinforcing bar corrosion inspection method and apparatus for inspecting the degree of corrosion of reinforcing bars contained in a concrete member by an eddy current method.

In general, a telephone pole, an elevated road column, and the like are concrete members (hereinafter referred to as reinforced concrete members) in which reinforcing bars are contained. Such a reinforced concrete member may corrode internal reinforcement due to secular change and usage environment, and the strength may decrease. In non-destructive inspection of reinforced concrete members used as support members for heavy objects, it is important to replace or reinforce them at appropriate times and prevent serious accidents.
Conventionally, eddy current inspection is known as an effective technique for nondestructive inspection of reinforced concrete members. The inspection of reinforced concrete members by the eddy current method, as shown in Patent Document 1, supplies alternating current to a coil wound around a reinforced concrete member, and uses the coil impedance as an index value indicating the degree of corrosion of the reinforcing bar. This is an inspection method to detect. When an alternating current flows through a coil wound around a reinforcing bar that is a conductor, an eddy current is generated in the reinforcing bar. This eddy current generates Joule loss, and the Joule loss becomes a resistance component of the coil impedance. Therefore, the greater the Joule loss, the smaller the coil impedance. Further, since the corroded reinforcing bar has a lower electrical conductivity than the non-corroded reinforcing bar, the more the corrosion of the reinforcing bar, the greater the Joule loss and the lower the impedance of the coil. Therefore, the impedance of the coil obtained in advance by inspection of a reinforced concrete member with a known degree of corrosion of the reinforcing bar is used as a reference value, and by comparing the reference value with the impedance of the coil obtained for the reinforced concrete member to be inspected, It is possible to determine the degree of corrosion of the reinforcing bar at the portion where the coil is wound.
Japanese Patent Laid-Open No. 9-21786

However, in the inspection of reinforced concrete members by the eddy current method, the impedance of the coil is not only the degree of corrosion of the reinforcing bars, but also the individual differences in the reinforced concrete members, such as the outer shape, the material of the concrete, the location of the reinforcing bars, and the coil and reinforced concrete members. It also changes depending on the relative positional relationship. Therefore, the conventional inspection method that evaluates the degree of corrosion based on the absolute value of the impedance of the coil detected by the eddy current method has a problem that it has instability due to individual differences of members and variations in the position of the coil with respect to the members. There was a point.
Therefore, the present invention has been made in view of the above circumstances, and the object of the present invention is to examine the individual differences of members and the inspection device when inspecting the degree of corrosion of the reinforcing bars contained in the concrete member by the eddy current method. It is an object of the present invention to provide a reinforcing bar corrosion inspection method and apparatus capable of obtaining a highly stable inspection result that is less affected by variations in equipment arrangement.

In order to achieve the above object, a reinforcing bar corrosion inspection method according to the present invention is a method for inspecting the degree of corrosion of reinforcing bars contained in a reinforced concrete member by an eddy current method, and is shown in the following (1) and (2). It is a method of performing each process.
(1) An alternating current supply step of supplying alternating currents having a plurality of frequencies to a coil wound around the reinforced concrete member.
(2) An impedance difference detection step of detecting a magnitude of a difference in impedance of the coil with respect to a difference in frequency of the alternating current supplied to the coil.
In the reinforcing bar corrosion inspection method according to the present invention, the detection result of the impedance difference detection step is used as an index value of the degree of corrosion of the reinforcing bar.

As described above, when an alternating current flows through a coil wound around a reinforcing bar as a conductor, Joule loss due to eddy current occurs, and the greater the Joule loss, the smaller the impedance of the coil. Here, corrosion of reinforcing bars occurs mainly on the surface of the reinforcing bars.
On the other hand, the Joule loss increases as the frequency of the alternating current of the coil, that is, the frequency of the eddy current generated in the reinforcing bar increases. Joule loss occurring at the surface layer becomes more dominant.
FIG. 4 is a graph showing the relationship between the frequency of the supply current and the Joule loss in the eddy current method. In FIG. 4, the graph marked with a black circle represents the Joule loss when there is no corrosion (rust) of the reinforcing bar, and the graph marked with a white circle is when the range of 1 mm of the surface layer of the reinforcing bar is the corrosion part (magnetite) Represents the joule loss. In both graphs, the conditions are the same except for the presence or absence of corrosion of the reinforcing steel surface.
As shown in Fig. 4, the greater the degree of corrosion of the reinforcing bars, the greater the difference in Joule loss when the frequency of the alternating current flowing through the coil is low (the frequency of the eddy current). As a result, the difference in coil impedance also increases. The tendency is particularly remarkable when the frequency of the supply current is 100 kHz or more.
In addition, the impedance of the coil is similarly affected by the individual difference of the reinforced concrete member and the variation of the equipment arrangement of the inspection device regardless of the frequency of the eddy current.
Therefore, the difference in the impedance of the coil caused by the difference in the frequency of eddy current is less affected by the individual differences of the reinforced concrete members and the variation in the equipment arrangement of the inspection device, and the highly stable inspection result (index value of the degree of corrosion) It becomes.

More specifically, it can be considered that the alternating current supply step is a step of changing the frequency of the alternating current supplied to the coil. In this case, the impedance difference detection step is a step of detecting the impedance of the coil by a detection circuit every time the alternating currents having different frequencies are supplied to the coil, and calculating the magnitude of the difference by the calculation means. is there.
Thus, the inspection can be performed by a simple inspection apparatus employing an oscillator having a variable oscillation frequency, a circuit for detecting the impedance of the coil, or the like.
In addition, it is conceivable that the alternating current supply step is a step of supplying the coil with the alternating current on which currents of a plurality of frequency components are superimposed. In this case, the impedance difference detection step detects the impedance of the coil to which the alternating current is supplied by a detection circuit and performs frequency analysis of the detection signal by an analysis device to cope with the difference in frequency components of the alternating current. Detecting the magnitude of the difference in impedance of the coil.
As a result, the inspection time can be shortened because only one detection of the impedance of the coil is required for each inspection point.
Further, it is conceivable that the alternating current supply step is a step of supplying a pulse current to the coil. It is known that the pulse current can be regarded as an alternating current on which a large number of frequency component currents are superimposed. In this case, the impedance difference detection step detects the impedance of the coil to which the alternating current is supplied by a detection circuit and performs frequency analysis of the detection signal by an analysis device to cope with the difference in frequency components of the alternating current. Detecting the magnitude of the difference in impedance of the coil. The detection signal of the coil impedance obtained when the pulse current is supplied is a distortion waveform signal including a harmonic component, which is a signal that can be analyzed in frequency.
In this case as well, the inspection time can be shortened because it is only necessary to detect the impedance of the coil once per inspection location.

Moreover, this invention can also be grasped | ascertained as a reinforcement corrosion inspection apparatus which detects the index value of the degree of corrosion of the reinforcement contained in the reinforced concrete member by an eddy current method.
The reinforcing bar corrosion inspection apparatus according to the present invention is an apparatus including each component shown in the following (A1) to (A3).
(A1) A coil wound around the reinforced concrete member (hereinafter referred to as a first coil).
(A2) AC current supply means for supplying AC currents having a plurality of frequencies to the first coil.
(A3) The magnitude of the difference in impedance of the first coil relative to the difference in frequency of the alternating current when the alternating current is supplied to the first coil is detected as an index value of the degree of corrosion of the reinforcing bar. Impedance difference detection means.
The difference in impedance of the first coil detected by the impedance difference detection means is less affected by individual differences in the reinforced concrete members and variations in the equipment arrangement of the inspection apparatus, and results in highly stable inspection results (an index of the degree of corrosion). Value).
Further, it is conceivable that the reinforcing bar corrosion inspection apparatus according to the present invention further includes a component shown in the following (A4).
(A4) A second coil that is wound around a reference member other than the reinforced concrete member to be inspected and forms a differential coil in a pair with the first coil.
In this case, the impedance difference detecting means is configured to change the alternating current based on a difference between voltages generated in the first coil and the second coil when the alternating current is supplied to the differential coil by the alternating current supply means. The magnitude of the difference in impedance of the first coil with respect to the difference in current frequency is detected.
As a result, noise components and offset components due to the variation in the ambient temperature are removed from the detection signal of the impedance difference detection means, and a detection signal with higher accuracy can be obtained.

  According to the present invention, when inspecting the degree of corrosion of the reinforcing steel contained in the reinforced concrete member by the eddy current method, the influence of individual differences of members and the variation of the equipment arrangement of the inspection device is small, and a highly stable inspection result is obtained. Obtainable.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings so that the present invention can be understood. The following embodiment is an example embodying the present invention, and does not limit the technical scope of the present invention.
FIG. 1 is a block diagram showing a schematic configuration of the reinforcing bar corrosion inspection apparatus X1 according to the first embodiment of the present invention. FIG. 2 shows a schematic configuration of the reinforcing bar corrosion inspection apparatus X2 according to the second embodiment of the present invention. FIG. 3 is a block diagram showing a schematic configuration of a reinforcing bar corrosion inspection apparatus X3 according to a third embodiment of the present invention, and FIG. 4 is a graph showing the relationship between the frequency of a supply current and Joule loss in the eddy current method. .

First, a reinforcing bar corrosion inspection apparatus X1 according to the first embodiment of the present invention will be described with reference to FIG.
The reinforcing bar corrosion inspection apparatus X1 is an apparatus that detects an index value of the degree of corrosion of the reinforcing bars 12 included in the reinforced concrete member 10 by an eddy current method. The reinforced concrete member 10 is one in which one or a plurality of reinforcing bars 12 are embedded in a columnar (cylindrical or prismatic) concrete member 11, such as a telegraph pole or an elevated road post. is there.
As shown in FIG. 1, the reinforcing bar corrosion inspection device X1 includes an oscillator 1, a constant current source 2, a first coil 3 and a second coil 4, a differential amplifier 5, a phase detector 6 and a computer 7. .
The oscillator 1 outputs an AC signal (sine wave), and is a device whose frequency of the AC signal is variable in accordance with a command from the computer 7.
The constant current source 2 is a power supply circuit that outputs an alternating current (sine wave current) synchronized with an alternating signal supplied from the oscillator 1. The constant current source 2 includes two output terminals that output the same alternating current.

The first coil 3 and the second coil 4 are paired to constitute a differential coil. That is, the first coil 3 and the second coil 4 are the same coil, one end is connected to each of the two output ends of the constant current source 2, and the other end is grounded. And the said 1st coil 3 is wound around the reinforced concrete member 10 which is a test object. The second coil 4 is wound around a predetermined reference member 20 other than the reinforced concrete 10. The reference member 20 is, for example, a reinforced concrete member having the same size and material as the reinforced concrete member 10 to be inspected and having no corrosion of the reinforcing bar.
The calculator 7 is provided with a control signal output interface (not shown) for designating an oscillation frequency to the oscillator 1 and sequentially changes the designated value of the oscillation frequency in accordance with preset contents. That is, the calculator 7, the oscillator 1 and the constant current source 2 sequentially change the frequency of the alternating current supplied to the differential coil (the first coil 3 and the second coil 4), An alternating current supply step for supplying alternating currents having a plurality of frequencies to the differential coil is executed.

The differential amplifier 5 is a device that detects a voltage difference (potential difference) generated in each of the first coil 3 and the second coil 4 and amplifies the detection signal. Specifically, each time the differential amplifier 5 is supplied with alternating currents having different frequencies from the constant current source 2 to the differential coils (the first coil 3 and the second coil 4). The potential difference is detected.
The phase detector 6 is a device that detects the amplitude (voltage amplitude) and phase of the output signal of the differential amplifier 5 using the output signal of the oscillator 1 as a reference signal. Specifically, each time the phase detector 6 is supplied with alternating current having a different frequency from the constant current source 2 to the differential coil (the first coil 3 and the second coil 4). The amplitude and phase of the output signal of the differential amplifier 5 are detected. The detected amplitude and phase information is taken into the computer 7.
The supply of alternating current to the differential coil changes the voltage generated in each of the first coil 3 and the second coil 4 in synchronization with the change (frequency) of the alternating signal. Here, if the amplitude of the alternating current output from the constant current source 2 is constant, the amplitude of the voltage generated in each of the first coil 3 and the second coil 4 is also constant. Therefore, the amplitude and phase of the output signal of the differential amplifier 5 represent the difference between the impedance of the first coil 3 and the impedance of the first coil 4. Here, since the reference member 20 is a member that is common to all inspection objects or is common to each type of inspection object, the output signal of the differential amplifier 5 represents the impedance of the first coil 4. It represents the impedance of the first coil 3 normalized to a reference.
Accordingly, the differential amplifier 5 and the phase detector 6 are circuits for detecting the impedance of the first coil 3 each time an alternating current having a different frequency is supplied to the first coil 3 and the second coil 4. It is an example. The impedance is determined by the difference in voltage generated between the first coil 3 and the second coil 4 when the alternating current is supplied to the differential coils 3 and 4 (the output signal of the differential amplifier 5). Detected.

The computer 7 inputs the detection result of the phase detector 6 every time an alternating current having a different frequency is supplied to the differential coils 3 and 4 through the oscillator 1 and the constant current source 2. The result is converted into an impedance detection value. Further, the computer 7 (an example of a calculation means) is configured to detect the impedance detection value (equivalent to the detection value of the impedance of the first coil 3) obtained every time AC currents having different frequencies are supplied to the coils 3 and 4. Is calculated as an index value of the degree of corrosion of the reinforcing bars 12. Hereinafter, ΔY calculated by the computer 7 is referred to as a reinforcing bar corrosion index value.
As the reinforcing bar corrosion index value ΔY, the following may be considered.
For example, it is conceivable that the ratio of the two detected impedance values obtained at the time of supplying alternating currents of two types of frequencies is the reinforcing bar corrosion index value ΔY.
Further, linear fitting processing is performed based on three or more impedance detection values obtained by supplying alternating currents of three or more frequencies, and the slope of the linear expression obtained thereby is defined as the reinforcing bar corrosion index value ΔY. It is also possible to do.
In addition, a non-linear fitting process is performed based on three or more impedance detection values obtained by supplying an alternating current of three or more types of frequencies, and the average value or representative value of the tangent slope in the curve equation obtained thereby. Is considered to be the reinforcing bar corrosion index value ΔY. As the non-linear fitting process, for example, an Nth-order equation (N ≧ 2), an exponential function fitting process, or the like can be considered.
The reinforcing bar corrosion index value ΔY may be derived from the phase detection value corresponding to the impedance detection value.

In addition, the storage unit (hard disk drive or the like) of the computer 7 is obtained by measuring in advance a sample of reinforced concrete member in a maximum state in which the degree of corrosion of the reinforcing bar is allowed by the reinforcing bar corrosion inspection apparatus X1. The rebar corrosion index value ΔY or the value corresponding thereto is stored as the allowable limit detection value ΔYs.
Then, the computer 7 compares the rebar corrosion index value ΔY obtained for the reinforced concrete member 10 to be inspected with the allowable limit detection value ΔYs, and the corrosion of the rebar 12 in the reinforced concrete member 10 to be inspected. It is determined whether or not the degree is within an allowable range, and the determination result is notified by display on the display, lamp lighting, alarm sound output, or the like.
It is also conceivable that the storage unit of the computer 7 stores the past reinforcing bar corrosion index value ΔYo obtained by the past inspection and the inspection date of the reinforced concrete member 10 to be inspected. In this case, it is possible for the computer 7 to perform processing for estimating the time when the reinforcing bar corrosion index value ΔY exceeds the allowable limit detection value ΔYs, that is, the time when the degree of corrosion of the reinforcing bar 12 exceeds the allowable range. is there. The estimation of the time is performed by extrapolation based on the past reinforcing bar corrosion index value ΔYo, the reinforcing bar corrosion index value ΔY obtained by the current inspection, and the interval between both inspection days.

In the inspection using the reinforcing bar corrosion inspection apparatus X1, as shown in FIG. 4, the higher the degree of corrosion of the reinforcing bar 12, the lower the frequency of the alternating current flowing through the first coil 3 (the frequency of the eddy current). The difference in Joule loss increases when the same frequency is high, and accordingly, the difference in impedance of the first coil 3 also increases.
In addition, the impedance of the first coil 3 is not dependent on the frequency of the eddy current, but may vary depending on individual differences such as the material of the concrete member 11, the arrangement position of the reinforcing bars 12, and variations in the position of the first coil 3 relative to the member. Similarly affected.
Therefore, the difference in impedance of the first coil 3 (the reinforcing bar corrosion index value ΔY) caused by the difference in the frequency of eddy current is less affected by the individual difference of the concrete member 11 and the variation in the equipment arrangement at the time of inspection. Test result (index value of the degree of corrosion).
Further, by using the differential coil, noise components and offset components due to fluctuations in the ambient temperature are removed from the output signal of the differential amplifier 5, and the corrosion index value of the rebar 12 with higher accuracy is removed. Is obtained.

Next, a reinforcing bar corrosion inspection apparatus X2 according to a second embodiment of the present invention will be described with reference to FIG. In FIG. 2, the same components as those shown in FIG. 1 are denoted by the same reference numerals.
The object and principle of the inspection by the reinforcing bar corrosion inspection apparatus X2 are the same as those of the reinforcing bar corrosion inspection apparatus X1, but the reinforcing bar corrosion inspection apparatus X2 omits the second coil 4, and the first coil 3 by a balanced bridge circuit. Is supplied with an alternating current. The frequency of the alternating current is changed manually.

As shown in FIG. 2, the reinforcing bar corrosion inspection apparatus X2 includes the oscillator 1, the constant current source 2, and the first coil 3 similar to those included in the reinforcing bar corrosion inspection apparatus X1. However, the frequency of the output signal of the oscillator 1 is changed manually.
Furthermore, the reinforcing bar corrosion inspection apparatus X2 includes a first resistance element 5a, a second resistance element 5b, an ammeter 6a, and a bridge circuit 4x. The bridge circuit 4x is a circuit in which a variable resistor 4a and a variable capacitor 4b are connected in parallel.
An alternating current (sine wave current) output from the constant current source 2 is supplied to the first coil 3 through the first resistance element 5a, and the second resistance element 5b and the series connected to the second resistance element 5b. It is also supplied to the bridge circuit 4x.
The ammeter 6a connected between the current path from the first resistance element 5a to the first coil 3 and the current path from the second resistance element 5b to the bridge circuit 4x has a bridge circuit balance. This is for detecting a point.
The resistance value of the variable resistor 4a in the bridge circuit 4x is such that the indicated value of the ammeter 6a becomes a stable equilibrium point when an alternating current of a predetermined frequency is supplied from the constant current source 2. The capacitance of the variable capacitor 4b is manually adjusted.

The resistance R and the inductance L in the impedance Z of the first coil 3 at the equilibrium point are known resistance values R1, R2, R3 of the first resistance element 5a, the second resistance element 5b, and the variable resistor 4a, respectively. , And the following equation based on the capacitance C1 of the variable capacitor 4b.
R = R1 / R2 / R3, L = C1 / R1 / R2
Therefore, in the inspection using the reinforcing bar corrosion inspection apparatus X2, the bridge circuit 4x is adjusted so as to be the equilibrium point every time the set frequency for the oscillator 1 is changed (that is, every time the alternating current frequency is changed). Then, based on the resistance value R3 of the variable resistor 4a which is the adjustment result, the impedance Z of the first coil 3 is calculated using a calculator (not shown), and the calculation result is recorded.
Further, the computer calculates the reinforcing bar corrosion index value ΔY based on the impedance Z of the first coil 3 obtained according to the change in the frequency of the alternating current, and the calculation result and the allowable limit detection value ΔYs Based on the comparison, it is determined whether or not the degree of corrosion of the reinforcing bars 12 in the reinforced concrete member 10 to be inspected is within an allowable range.

Reinforcing bar corrosion inspection device X2 for a 10 mm diameter rebar sample where rust occurs in the surface layer of 0.1 mm (corrosion) and where no rust occurs (non-corrosion) I tried the inspection (measurement).
For a telephone pole to be actually measured, it is sufficient to detect whether or not rust is present in a surface layer of about 1 mm of a reinforcing bar having a diameter of 10 mm, for example. On the other hand, in the sample in which the presence or absence of rust on the surface layer of 0.1 mm of the reinforcing bar having a diameter of 10 mm is inspected, the presence or absence of rust cannot be determined by the conventional inspection based on the absolute value of impedance Z of the first coil 3. It is a sample.
The first coil 3 used at this time is a 100-turn cylindrical shape, and the length in the direction of the central axis of the cylinder is 10 mm. The frequency of the alternating current was changed between 1 MHz and 4 MHz.
Further, as the reinforcing bar corrosion index value ΔY, in the impedance Z2 of the first coil 3 when the same frequency with respect to the resistance R1 in the impedance Z1 of the first coil 3 when the frequency of the alternating current is 1 MHz is 4 MHz. The ratio of resistance R2 (R2 / R1) was calculated.
As a result, the rebar corrosion index value ΔY (= R2 / R1) obtained for each of the plurality of corrosion sites was about 21, whereas it was obtained for each of the plurality of non-corrosion sites. The reinforcing bar corrosion index values ΔY (= R2 / R1) were all about 19, and an inspection result capable of sufficiently identifying the presence or absence of rust was obtained.

Next, a reinforcing bar corrosion inspection apparatus X3 according to a third embodiment of the present invention will be described with reference to FIG. In FIG. 3, the same components as those shown in FIG. 1 are denoted by the same reference numerals.
The inspection target and the basic principle of the rebar corrosion inspection apparatus X3 are also the same as those of the rebar corrosion inspection apparatus X1. The reinforcing bar corrosion inspection apparatus X3 is different from the reinforcing bar corrosion inspection apparatus X1 in that the first coil 3 and the second coil 4 are supplied with an alternating current having a different frequency and the first coil according to the difference in frequency. 3 is different from the detection method of impedance difference.

As shown in FIG. 3, the rebar corrosion inspection apparatus X3 is similar to the rebar corrosion inspection apparatus X1 in that the constant current source 2, the first coil 3, the second coil 4, the differential amplifier 5, and the A computer 7 is provided.
Furthermore, the reinforcing bar corrosion inspection apparatus X3 includes a plurality of oscillators 1a and 1b that output alternating signals (sine wave signals) having different frequencies, and a multiplexer 1c that superimposes these output signals. Then, a signal in which a plurality of AC signals having different frequencies are superimposed is supplied to the constant current source 2 by the multiplexer 1c. The calculator 7 controls the output timing of the AC signal from each of the oscillators 1a and 1b.
Thereby, the plurality of oscillators 1a, 1b, the multiplexer 1c, and the constant current source 2 supply the first coil 3 and the second coil 4 with an alternating current on which a plurality of frequency component currents are superimposed. It is a circuit that takes charge of the process.
The example shown in FIG. 3 is an example in which two oscillators 1a and 1b are used to generate an alternating current in which two types of frequency components are superimposed, but three or more types are used by using three or more oscillators. It is also conceivable to generate an alternating current on which the frequency component is superimposed.

The reinforcing bar corrosion inspection apparatus X3 includes a signal analysis apparatus 8 to which the output signal of the differential amplifier 5 is input instead of the phase detector 6.
The signal analysis device 8 performs a frequency analysis process on the output signal of the differential amplifier 5, thereby generating a plurality of frequency component signals in the alternating current, that is, a plurality of signals, from the output signal of the differential amplifier 5. Signals of oscillation frequency components of the oscillators 1a and 1b are extracted. In the frequency analysis process, a Fourier transform process is performed on the input signal, and signals of components of the oscillation frequencies of the plurality of oscillators 1a and 1b are individually extracted from the frequency domain signals obtained thereby, and the extracted individual signals are extracted. Is subjected to inverse Fourier transform processing, so that each frequency component signal is returned to a time domain signal.
Further, the signal analysis device 8 detects a phase difference between signals of a plurality of frequency components extracted by frequency analysis processing, and outputs the detection result to the computer 7. It is conceivable that the signal analyzer 8 uses the signals of the oscillators 1a and 1b as reference signals in order to detect the initial phase of each frequency component.
Then, the computer 7 determines the rebar corrosion index value ΔY, that is, the rebar corrosion index value ΔY, that is, similar to the rebar corrosion inspection device X1, based on the phase difference of the signals of the plurality of frequency components obtained from the signal analysis device 8. The magnitude of the difference in impedance of the first coil 3 corresponding to the difference in frequency of the alternating current is calculated.
According to the reinforcing bar corrosion inspection apparatus X3, it is only necessary to detect the impedance of the first coil 3 once per inspection location, so that the inspection time can be shortened. However, the configuration of the apparatus is slightly more complicated and expensive than the reinforcing bar corrosion inspection apparatus X1 in that the number of oscillators is increased and an expensive signal analysis apparatus with high signal processing capability is employed.

In the reinforcing bar corrosion inspection apparatus X3, a pulse current is supplied to the first coil 3 and the second coil 4 instead of the oscillators 1a and 1b, the multiplexer 1c and the constant current source 2. An inspection apparatus provided with a pulse current circuit is also conceivable. The pulse current circuit generates a pulse current (pulse current) having a pulse width of about 0.1 μsec, for example. It is known that such a pulse current can be regarded as an alternating current in which a large number of frequency component currents are superimposed.
The output signal of the differential amplifier 5 (the detection signal of the impedance of the first coil 3) obtained when the pulse current is supplied becomes a distortion waveform signal including a harmonic component, which has a frequency of It is a signal that can be analyzed.
Therefore, as described above, the signal analysis device 8 performs frequency analysis processing on the output signal of the differential amplifier 5, and outputs a plurality of frequency component signals in the alternating current from the output signal of the differential amplifier 5. Can be extracted.
In this case as well, the inspection time can be shortened because it is only necessary to detect the impedance of the coil once per inspection location.

  INDUSTRIAL APPLICABILITY The present invention is applicable to a reinforcing bar corrosion inspection method and apparatus for inspecting the degree of corrosion of reinforcing bars contained in a concrete member by an eddy current method.

The block diagram showing the schematic structure of the rebar corrosion inspection apparatus X1 which concerns on 1st Embodiment of this invention. The block diagram showing schematic structure of the rebar corrosion inspection apparatus X2 which concerns on 2nd Embodiment of this invention. The block diagram showing the schematic structure of the rebar corrosion inspection apparatus X3 which concerns on 3rd Embodiment of this invention. The graph showing the relationship between the frequency of the supply current in a eddy current method, and a Joule loss.

Explanation of symbols

X1, X2, X3: Rebar corrosion inspection apparatus 1, 1a, 1b: Oscillator 1c: Multiplexer 2: Constant current source 3: First coil 4: Second coil 4x: Bridge circuit 4a: Variable resistor 4b: Variable capacitance Capacitor 5: Differential amplifier 5a: First resistance element 5b: Second resistance element 6: Phase detector 6a: Ammeter 7: Computer 8: Signal analysis device 10: Reinforced concrete member 11: Concrete member 12: Reinforcing bar 20: Reference member

Claims (6)

A rebar corrosion inspection method for inspecting the degree of corrosion of rebar contained in a reinforced concrete member by the eddy current method,
An alternating current supply step of supplying alternating currents of a plurality of frequencies to a coil wound around the reinforced concrete member;
An impedance difference detection step of detecting a magnitude of a difference in impedance of the coil with respect to a difference in frequency of the alternating current supplied to the coil;
A reinforcing bar corrosion inspection method in which the detection result of the impedance difference detection step is used as an index value of the degree of corrosion of the reinforcing bar. The alternating current supplying step is a step of changing a frequency of the alternating current supplied to the coil;
The impedance difference detecting step is a step of detecting the impedance of the coil by a detection circuit each time the alternating currents having different frequencies are supplied to the coil, and calculating the magnitude of the difference by a calculation means. 2. The reinforcing bar corrosion inspection method according to 1. The alternating current supplying step is a step of supplying the coil with the alternating current on which a plurality of frequency component currents are superimposed;
In the impedance difference detection step, the coil corresponding to the difference in frequency components of the alternating current is detected by detecting the impedance of the coil to which the alternating current is supplied by a detection circuit and analyzing the frequency of the detection signal by an analyzer. The reinforcing bar corrosion inspection method according to claim 1, wherein the method is a step of detecting the magnitude of the impedance difference between the bars. The alternating current supplying step is a step of supplying a pulse current to the coil;
In the impedance difference detection step, the coil corresponding to the difference in frequency components of the alternating current is detected by detecting the impedance of the coil to which the alternating current is supplied by a detection circuit and analyzing the frequency of the detection signal by an analyzer. The reinforcing bar corrosion inspection method according to claim 1, wherein the method is a step of detecting the magnitude of the impedance difference between the bars. A rebar corrosion inspection device for detecting an index value of the degree of corrosion of a rebar contained in a reinforced concrete member by an eddy current method,
A first coil wound around the reinforced concrete member to be inspected;
AC current supply means for supplying AC current of a plurality of frequencies to the first coil;
Impedance difference detection for detecting the magnitude of the difference in impedance of the first coil relative to the difference in frequency of the alternating current when the alternating current is supplied to the first coil as an index value of the degree of corrosion of the reinforcing bar. Means,
Reinforcing bar corrosion inspection apparatus characterized by comprising. A second coil that is wound around a reference member other than the reinforced concrete member to be inspected and forms a differential coil in a pair with the first coil;
The impedance difference detecting means is configured to determine the frequency of the alternating current based on a difference in voltage generated in each of the first coil and the second coil when the alternating current is supplied to the differential coil by the alternating current supply means. The reinforcing bar corrosion inspection apparatus according to claim 5, wherein a magnitude of a difference in impedance of the first coil with respect to a difference is detected.

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