CN114001636A - Reinforced concrete protective layer thickness detection method, detection device and use method - Google Patents
Reinforced concrete protective layer thickness detection method, detection device and use method Download PDFInfo
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- 239000011150 reinforced concrete Substances 0.000 title claims abstract description 95
- 239000011241 protective layer Substances 0.000 title claims abstract description 66
- 238000001514 detection method Methods 0.000 title claims abstract description 63
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- 230000005291 magnetic effect Effects 0.000 claims abstract description 67
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- 239000010959 steel Substances 0.000 claims description 46
- 238000006073 displacement reaction Methods 0.000 claims description 18
- 238000012805 post-processing Methods 0.000 claims description 18
- 229910001294 Reinforcing steel Inorganic materials 0.000 claims description 17
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- 230000007547 defect Effects 0.000 description 2
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
- G01B7/00—Measuring arrangements characterised by the use of electric or magnetic techniques
- G01B7/02—Measuring arrangements characterised by the use of electric or magnetic techniques for measuring length, width or thickness
- G01B7/06—Measuring arrangements characterised by the use of electric or magnetic techniques for measuring length, width or thickness for measuring thickness
- G01B7/10—Measuring arrangements characterised by the use of electric or magnetic techniques for measuring length, width or thickness for measuring thickness using magnetic means, e.g. by measuring change of reluctance
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Abstract
本发明公开了一种钢筋混凝土保护层厚度检测方法、检测装置及使用方法，该检测方法以涡流效应理论为基础，采用具有初级线圈和次级线圈的传感器，并使得传感器工作于磁耦合谐振状态，利用传感器分别在不同提离高度下对裸筋进行检测，并得到次级线圈上的电压数据U1，同时利用传感器对待测钢筋混凝土的表面进行检测，并得到次级线圈上的电压数据U2，通过将电压数据U1和电压数据U2进行比较以判断待测钢筋混凝土保护层厚度，实现对待测钢筋混凝土保护层厚度的检测。本方案检测成本低、检测精度高且不会对钢筋混凝土结构产生损害。
The invention discloses a thickness detection method, detection device and use method of a reinforced concrete protective layer. The detection method is based on the eddy current effect theory, adopts a sensor with a primary coil and a secondary coil, and makes the sensor work in a magnetic coupling resonance state , use the sensor to detect the bare bars at different lift-off heights, and obtain the voltage data U 1 on the secondary coil, at the same time use the sensor to detect the surface of the reinforced concrete to be tested, and obtain the voltage data U on the secondary coil 2. By comparing the voltage data U1 and the voltage data U2 to determine the thickness of the reinforced concrete protective layer to be measured, the detection of the thickness of the reinforced concrete protective layer to be measured is realized. The scheme has low detection cost, high detection accuracy, and will not cause damage to the reinforced concrete structure.
Description
Technical Field
The invention relates to the technical field of civil engineering structure monitoring, in particular to a reinforced concrete protective layer thickness detection method, a detection device and a use method.
Background
At present, a reinforced concrete structure is one of the most widely used structural forms in the field of civil engineering. The thickness of the concrete protective layer is an important design index of a reinforced concrete structure, and plays a crucial role in the structure: the reinforcing steel bars and the surrounding concrete can work together to give full play to the strength of the reinforcing steel bars; the protection reinforcing bar prevents it and takes place the corruption, ensures that the member does not appear reducing the holistic reliability of structure because of the reinforcing bar corrodes in design life. Therefore, in order to avoid the defects of concrete carbonization, steel bar corrosion, structural cracks and the like caused by the fact that the thickness of the concrete protective layer does not meet the requirement in the using process of the reinforced concrete structure, and further reduce the bearing capacity, durability and safety of the structure, the effective detection and control of the thickness of the concrete protective layer are very important.
At present, the detection of the thickness of the reinforced concrete protective layer is divided into two categories, namely destructive detection and nondestructive detection. The destructive detection method is that an electric hammer drill or a water drill is adopted for drilling and coring, an endoscope can be used for observing the internal steel bar structure after hole cleaning treatment, and the thickness of the protective layer can be directly measured through a vernier caliper; this method has the advantage that the thickness of the protective layer can be detected more accurately, but at the same time irreversible damage to the structure is also produced. The nondestructive testing method mainly adopts a radar detection method, wherein a transmitting antenna is used for transmitting sound waves to a target object, and the thickness of the concrete protective layer can be calculated by analyzing the components of the returned sound waves received by a receiving device according to the difference of the rebound feedback quantity of the reinforcing steel bars and the concrete to the sound waves.
Disclosure of Invention
Aiming at the defects in the prior art, the technical problems to be solved by the invention are as follows: how to provide a reinforced concrete protective layer thickness detection method which has low detection cost and high detection precision and does not damage a reinforced concrete structure.
In addition, the invention also provides a device for detecting the thickness of the reinforced concrete protective layer and a using method thereof, so as to realize the purposes of low cost and high precision detection of reinforced concrete and no damage to the reinforced concrete structure.
In order to solve the technical problems, the invention adopts the following technical scheme:
a method for detecting thickness of reinforced concrete protective layer is based on eddy current effect theory, and comprises adopting a sensor with a primary coil and a secondary coil, enabling the sensor to work in a magnetic coupling resonance state, detecting bare bars at different lift-off heights by utilizing the sensor working in the magnetic coupling resonance state, and obtaining voltage data U on the secondary coil when the sensor detects the bare bars at different lift-off heights1Simultaneously, the sensor working in the magnetic coupling resonance state is used for detecting the surface of the reinforced concrete to be detected, and the condition that the sensor is used for detecting the reinforced steel bar to be detected is obtainedVoltage data U on the secondary coil when the concrete surface is detected2Voltage data U on the secondary coil when the sensor detects the bare rib1And voltage data U on the secondary coil when the sensor detects the surface of the reinforced concrete to be detected2And comparing to judge the thickness of the reinforced concrete protective layer to be detected, so as to detect the thickness of the reinforced concrete protective layer to be detected.
The working principle of the invention is as follows: the eddy current effect indicates that a primary coil fed with a sinusoidal voltage or current will generate a varying magnetic field B due to electromagnetic induction phenomena1The measured metal test piece (steel bar) is in the changing magnetic field B1Will generate induced eddy current I0Induced eddy currents I0Will in turn generate an and B in space1Eddy magnetic field B with opposite direction2When a varying magnetic field B exists in the space1And an eddy current magnetic field B2When one factor is changed, the superposed magnetic field is also changed, so that the magnetic flux of the coil is changed, and finally the induced voltage on the secondary coil is changed, and under the condition that other parameters are not changed, the relative position d between the sensor and the metal test piece (steel bar) to be detected is changed, at the moment, the induced voltage of the secondary coil is only related to the relative position d between the sensor and the metal test piece (steel bar) to be detected, and at the moment, the thickness of the protective layer of the reinforced concrete can be detected.
This scheme is utilizing above-mentioned eddy current effect principle to examine time measuring, utilizes the sensor to carry earlier and detects naked muscle under the height from the difference, carries to carry and is the relative position d between sensor and the naked muscle from the height promptly, and the difference is carried to change from the relative position d between the height promptly between sensor and the naked muscle from the height, can obtain the voltage data U that the sensor corresponds on the secondary coil when carrying out the detection to naked muscle under the height at this moment in the difference, and the difference is carried to the difference1Then, the surface of the reinforced concrete to be detected is detected by using a sensor, and the method is used for detecting the surface of the reinforced concrete to be detectedThe thickness of the protective layer on the reinforced concrete can be regarded as the lift-off height d when the sensor detects, and the voltage data U on the secondary coil when the sensor detects the surface of the reinforced concrete to be detected is obtained2Finally, voltage data U detected by the sensor twice1Sum voltage data U2Comparing voltage data U1Sum voltage data U2And the corresponding lift-off height d is the thickness of the reinforced concrete protective layer to be detected at the moment, so that the thickness of the reinforced concrete protective layer to be detected is detected.
In conclusion, the invention provides a method for detecting the thickness of the concrete protective layer based on the magnetic coupling resonance eddy current by combining the eddy current effect and the magnetic coupling resonance effect, and the linearity and the detection depth of the thickness detection of the concrete protective layer can be effectively improved; the detection cost is low, the detection precision is high, and the damage to the reinforced concrete structure can be avoided.
Preferably, the relationship between the lift-off height d of the sensor from the surface of the steel bar and the voltage U of the secondary coil is as follows:
U＝U(σ,μ,A,f,d)
in the formula: sigma is the conductivity of the steel bar; mu is the magnetic conductivity of the steel bar; a is the amplitude of the excitation voltage of the sensor; f is the excitation frequency of the sensor; d is the lifting height of the sensor from the surface of the steel bar; u is the voltage of the secondary winding.
Preferably, the sensor detects a current I 'of the secondary coil when the reinforcing bar is detected'2Eddy current I 'generated by steel bar eddy effect'0The relationship between them is:
wherein:
in the formula: i'2The current of a secondary coil is detected by a sensor when the sensor detects the steel bar; i'0For producing eddy current effect of reinforcing steel barThe eddy current of (2); u shapesIs the excitation voltage of the sensor; z1Is the primary coil loop impedance; z2Is the secondary loop impedance; omega is angular frequency; m12Is the mutual inductance between the primary coil and the secondary coil; m13Is mutual inductance between the primary coil and the reinforcing steel bar; m23Is the mutual inductance between the secondary coil and the reinforcing steel bar; z3Is the eddy current short circuit loop impedance.
Thus, the eddy current I 'generated by the steel bar eddy effect can be known from the above formula'0Term makes induced current I 'on secondary coil'2Become small, I'0The effect of (c) is manifested as a reduction in the secondary coil induced voltage; meanwhile, the magnetic effect of the steel bar can influence the magnetic field distribution of the medium around the sensor coupling system, and the coupling degree of the system is weakened, so that the mutual inductance M between the primary coil and the secondary limit of the sensor12The reduction will also result in a current I 'of the secondary coil'2A decrease in; moreover, the presence of the steel bars can also change the equivalent impedance Z of the primary coil and the secondary coil1And Z2The resonance frequency is shifted, which causes detuning and decoupling of the system and reduction of energy transmission efficiency. Therefore, as long as the excitation frequency is adjusted to enable the double-coil eddy current sensor to generate magnetic coupling resonance, the system energy transmission efficiency will be the highest, the induced voltage on the secondary coil will also be the largest, after the steel bar is intervened, the induced voltage of the secondary coil is reduced due to the eddy current effect of the steel bar, the induced voltage of the secondary coil is reduced due to the magnetic effect of the steel bar and the decoupling offset of the magnetic coupling resonance system, the induced voltage change amplitude of the secondary coil is increased due to the intervention of the steel bar, and therefore the eddy current effect of the steel bar is enhanced.
Preferably, an excitation current having an excitation frequency equal to a natural frequency of the primary coil is supplied to the primary coil of the sensor, so that the primary coil generates a high-frequency changing magnetic field, and the natural frequency of the secondary coil is equal to the frequency of the high-frequency changing magnetic field generated by the primary coil, so that coupling resonance occurs between the primary coil and the secondary coil, and the sensor operates in a magnetic coupling resonance state.
Thus, by making the excitation frequency of the excitation current the same as the natural frequency of the primary coil and the natural frequency of the secondary coil the same as the frequency of the high-frequency varying magnetic field generated by the primary coil, the sensor can be made to operate in a magnetically coupled resonance state in which the primary coil and the secondary coil are most strongly magnetically coupled.
The detection device comprises an excitation assembly, a sensor and a displacement controller, wherein the sensor comprises a primary coil and a secondary coil, the displacement controller is connected with the sensor to drive the sensor to move along reinforced concrete, the output end of the excitation assembly is electrically connected with the primary coil to provide excitation current for the primary coil, the input end of the signal acquisition device is electrically connected with the secondary coil to acquire the induced voltage of the secondary coil, and the input end of the post-processing device is connected with the output end of the signal acquisition device to acquire the induced voltage data of the secondary coil.
Therefore, when the detection device is used for detecting the thickness of the protective layer of the reinforced concrete to be detected, the detection device, the signal acquisition device and the post-processing device are connected firstly; then, the exciting assembly provides exciting current for the primary coil, the signal acquisition device acquires voltage signals of the secondary coil, and the frequency of the exciting current provided by the exciting assembly is changed until the voltage signals of the secondary coil acquired by the signal acquisition device reach a maximum value, and the frequency of the exciting current provided by the exciting assembly is the resonance frequency of the sensor.
The exciting assembly provides exciting current of resonant frequency for the primary coil, and the displacement controller drives the sensor to move, so that the sensor is lifted from the height at different heights to detect the bare rib, and the signal acquisition device acquires voltage data U on the secondary coil when the sensor is lifted from the height at different heights to detect the bare rib1(ii) a Then the sensor detects different positions of the reinforced concrete to be detected, and the signal acquisition device acquires the sensor on the reinforced concrete to be detectedVoltage data U on secondary coils at different locations of the concrete2(ii) a Post-processing device acquires voltage data U acquired by signal acquisition device1Sum voltage data U2And by applying voltage data U1Sum voltage data U2Comparing voltage data U1Sum voltage data U2And if the lifting heights d are the same, the corresponding lifting heights d are the thickness of the reinforced concrete protective layer to be detected at the moment, so that the thickness of the reinforced concrete protective layer to be detected is judged, and the thickness of the reinforced concrete protective layer to be detected is detected.
Preferably, the excitation device includes a signal generator and a power amplifier, an output terminal of the signal generator is connected to an input terminal of the power amplifier to input the excitation current generated by the signal generator into the power amplifier for amplification, and an output terminal of the power amplifier is connected to the primary coil to input the amplified excitation current into the primary coil.
In this way, the signal generator is used for generating exciting current, and the power amplifier is used for amplifying the exciting current and outputting the amplified exciting current to the primary coil, so that the primary coil can generate a larger exciting magnetic field.
Preferably, the primary coil and the secondary coil are coaxially arranged and fixed on a rigid support, and the movement controller is connected with the rigid support so as to drive the sensor to move through the rigid support.
Therefore, the coaxial design of the secondary coil and the primary coil can achieve the best coupling effect, is favorable for picking up magnetic field signals generated by the steel bars, and simultaneously plays a supporting effect on the primary coil and the secondary coil by utilizing rigid support to ensure the stable use of the primary coil and the secondary coil in the moving process.
Preferably, the rigid support is made of a non-metallic material which is non-conductive and has a relative magnetic permeability of 0.9-1.1.
Thus, the rigid support is made of non-metal materials with the relative permeability of 0.9-1.1, on one hand, the influence of an external magnetic field can be prevented, and on the other hand, the outward diffusion of an induced magnetic field generated by the sensor can be reduced.
Preferably, the signal acquisition device comprises an oscilloscope, an input end of the oscilloscope is electrically connected with the secondary coil to acquire the voltage on the secondary coil, and the post-processing device is a PC terminal.
Therefore, the voltage of the secondary coil is collected by the oscilloscope, and the collected voltage data is transmitted to the PC terminal for further processing.
The use method of the reinforced concrete protective layer thickness detection device comprises the following steps:
step 1) connecting the detection device, the signal acquisition device and the post-processing device;
step 2) the excitation assembly provides an excitation current for the primary coil, the signal acquisition device acquires a voltage signal of the secondary coil, and the frequency of the excitation current provided by the excitation assembly is changed until the voltage signal of the secondary coil acquired by the signal acquisition device reaches a maximum value, and at this time, the frequency of the excitation current provided by the excitation assembly is the resonance frequency of the sensor;
step 3) the excitation assembly provides excitation current with resonant frequency for the primary coil, the displacement controller drives the sensor to move, so that the sensor detects bare bars at different lifting heights, and the signal acquisition device acquires voltage data U on the secondary coil when the sensor detects bare bars at different lifting heights1；
Step 4) the excitation assembly provides excitation current with resonant frequency for the primary coil, the displacement controller drives the sensor to move along the surface of the reinforced concrete to be detected, the sensor detects different positions of the reinforced concrete to be detected, and the signal acquisition device acquires voltage data U of the sensor on the secondary coil at different positions of the reinforced concrete to be detected2；
Step 5) the post-processing device acquires the voltage data U adopted by the signal acquisition device in the step 3)1And the signal acquisition device in the step 4)Voltage data U used2And by applying voltage data U1Sum voltage data U2And comparing to judge the thickness of the reinforced concrete protective layer to be detected, so as to detect the thickness of the reinforced concrete protective layer to be detected.
Compared with the prior art, the magnetic coupling resonance double-coil structure sensor has the advantages of simple structure, novel method, high response speed and wide application range, can convert detection signals into electric signals which are easy to measure and analyze by utilizing the magnetic coupling resonance double-coil structure sensor, effectively improves the detection distance and the linearity, and is very beneficial to the detection of the thickness of the concrete protective layer.
Drawings
FIG. 1 is a sensor equivalent circuit model;
FIG. 2 is a model of an equivalent circuit of a sensor with a metallic conductor (steel bar);
FIG. 3 is a connection block diagram of a reinforced concrete protective layer thickness detection apparatus;
fig. 4 is a schematic diagram of the reinforced concrete protective layer thickness detection device during detection of reinforced concrete.
Description of reference numerals: the sensor 1, the primary coil 11, the secondary coil 12, the rigid support 2, the displacement controller 3, the signal generator 4, the power amplifier 5, the oscilloscope 6 and the PC terminal 7.
Detailed Description
The invention will be further explained with reference to the drawings and the embodiments.
A method for detecting thickness of reinforced concrete protective layer is based on eddy current effect theory, and includes using sensor with primary coil and secondary coil, making sensor work in magnetic coupling resonance state, using sensor working in magnetic coupling resonance state to detect bare bar at different lift-off heights, and obtaining voltage data U on secondary coil when sensor detects bare bar at different lift-off heights1Simultaneously, the sensor working in the magnetic coupling resonance state is used for detecting the surface of the reinforced concrete to be detected, and voltage data U on the secondary coil when the sensor detects the surface of the reinforced concrete to be detected is obtained2By passing throughVoltage data U on secondary coil when sensor detects bare rib1And voltage data U on the secondary coil when the sensor detects the surface of the reinforced concrete to be detected2And comparing to judge the thickness of the reinforced concrete protective layer to be detected, so as to detect the thickness of the reinforced concrete protective layer to be detected.
The working principle of the invention is as follows: the eddy current effect indicates that a primary coil fed with a sinusoidal voltage or current will generate a varying magnetic field B due to electromagnetic induction phenomena1The measured metal test piece (steel bar) is in the changing magnetic field B1Will generate induced eddy current I0Induced eddy currents I0Will in turn generate an and B in space1Eddy magnetic field B with opposite direction2When a varying magnetic field B exists in the space1And an eddy current magnetic field B2When one factor is changed, the superposed magnetic field is also changed, so that the magnetic flux of the coil is changed, and finally the induced voltage on the secondary coil is changed, and under the condition that other parameters are not changed, the relative position d between the sensor and the metal test piece (steel bar) to be detected is changed, at the moment, the induced voltage of the secondary coil is only related to the relative position d between the sensor and the metal test piece (steel bar) to be detected, and at the moment, the thickness of the protective layer of the reinforced concrete can be detected.
This scheme is utilizing above-mentioned eddy current effect principle to examine time measuring, utilizes the sensor to carry earlier and detects naked muscle under the height from the difference, carries to carry and is the relative position d between sensor and the naked muscle from the height promptly, and the difference is carried to change from the relative position d between the height promptly between sensor and the naked muscle from the height, can obtain the voltage data U that the sensor corresponds on the secondary coil when carrying out the detection to naked muscle under the height at this moment in the difference, and the difference is carried to the difference1Then, the sensor is used for detecting the surface of the reinforced concrete to be detected, the thickness of the protective layer on the reinforced concrete can be regarded as the lift-off height d during the detection of the sensor, and the lift-off height d is obtainedVoltage data U on secondary coil when sensor detects reinforced concrete surface to be detected2Finally, voltage data U detected by the sensor twice1Sum voltage data U2Comparing voltage data U1Sum voltage data U2And the corresponding lift-off height d is the thickness of the reinforced concrete protective layer to be detected at the moment, so that the thickness of the reinforced concrete protective layer to be detected is detected.
In conclusion, the invention provides a method for detecting the thickness of the concrete protective layer based on the magnetic coupling resonance eddy current by combining the eddy current effect and the magnetic coupling resonance effect, and the linearity and the detection depth of the thickness detection of the concrete protective layer can be effectively improved; the detection cost is low, the detection precision is high, and the damage to the reinforced concrete structure can be avoided.
In this embodiment, the relationship between the lift-off height d of the sensor from the surface of the steel bar and the voltage U of the secondary coil is:
U＝U(σ,μ,A,f,d) (1)
in the formula: sigma is the conductivity of the steel bar; mu is the magnetic conductivity of the steel bar; a is the amplitude of the excitation voltage of the sensor; f is the excitation frequency of the sensor; d is the lifting height of the sensor from the surface of the steel bar; u is the voltage of the secondary winding.
Specifically, the sensor includes a primary coil and a secondary coil, and an equivalent circuit model thereof is shown in fig. 1.
In fig. 1: u shapeSIs an excitation voltage; l is1、L2Primary coil and secondary coil inductance; r1、R2Internal resistance of the primary coil and the secondary coil; c1、C2A capacitance for resonance compensation of the primary coil and the secondary coil; m12The mutual inductance of the coils reflects the coupling strength of the two coils.
Primary coil loop impedance Z1And secondary coil loop impedance Z2Respectively as follows:
according to kirchhoff's law, there is a system of equations:
the following formula (2) and formula (3) can be obtained:
magnetically coupled resonance means: when the excitation frequency of the high-frequency voltage excitation source is the same as the natural frequency of the primary coil, a high-frequency variable magnetic field is generated, and when the high-frequency variable magnetic field generated by the primary coil is the same as the natural frequency of the secondary coil, the primary coil and the secondary coil are in coupling resonance. At resonance, the circuit is purely resistive, with:
jωL1+1/jωC1＝jωL2+1/jωC2＝0 (5)
in the formula, ω0Called the resonance angular frequency, corresponding to f0Called resonant frequency, when the operating frequency is the resonant frequency f0When the eddy current sensor generates magnetic coupling resonance, the maximum value of the induced voltage at the two ends of the secondary coil occurs.
And when there is a metal conductor (steel bar) around the coupled resonant system, the equivalent circuit model of the whole system is shown in fig. 2: in fig. 2: u shapeSIs an excitation voltage; l is1、L2Is equivalent inductance of primary coil and secondary coil, L3Is an eddy current short circuit loop inductor; r1、R2Is the equivalent resistance of the primary coil and the secondary coil, R3Is an eddy current short circuit loop resistor; c1、C2A capacitance for resonance compensation of the primary coil and the secondary coil; m12、M13、M23Respectively a primary coil and a secondary coil, a primary coil and a reinforcing steel bar, a secondary coil and a reinforcing steel barMutual inductance of (2), reaction coupling strength.
From FIG. 2, the primary loop impedance Z1Secondary coil loop impedance Z2Eddy current short circuit loop impedance Z3Respectively as follows:
likewise, from kirchhoff's law:
finishing to obtain:
current I 'of secondary coil when sensor detects steel bar'2Eddy current I 'generated by steel bar eddy effect'0The relationship between them is:
wherein:
in the formula: i'2The current of a secondary coil is detected by a sensor when the sensor detects the steel bar; i'0Eddy currents generated for the eddy current effect of the reinforcing steel bars; u shapesIs the excitation voltage of the sensor; z1Is the primary coil loop impedance; z2Is the secondary loop impedance; omega is angular frequency; m12Is the mutual inductance between the primary coil and the secondary coil; m13Is mutual inductance between the primary coil and the reinforcing steel bar; m23Is the mutual inductance between the secondary coil and the reinforcing steel bar; z3Is the eddy current short circuit loop impedance.
Thus, the eddy current I 'generated by the steel bar eddy effect can be known from the above formula'0Term makes induced current I 'on secondary coil'2Become small, I'0The action results ofA reduction in induced voltage for the secondary coil; meanwhile, the magnetic effect of the steel bar can influence the magnetic field distribution of the medium around the sensor coupling system, and the coupling degree of the system is weakened, so that the mutual inductance M between the primary coil and the secondary limit of the sensor12The reduction will also result in a current I 'of the secondary coil'2A decrease in; moreover, the presence of the steel bars can also change the equivalent impedance Z of the primary coil and the secondary coil1And Z2The resonance frequency is shifted, which causes detuning and decoupling of the system and reduction of energy transmission efficiency. Therefore, as long as the excitation frequency is adjusted to enable the double-coil eddy current sensor to generate magnetic coupling resonance, the system energy transmission efficiency will be the highest, the induced voltage on the secondary coil will also be the largest, after the steel bar is intervened, the induced voltage of the secondary coil is reduced due to the eddy current effect of the steel bar, the induced voltage of the secondary coil is reduced due to the magnetic effect of the steel bar and the decoupling offset of the magnetic coupling resonance system, the induced voltage change amplitude of the secondary coil is increased due to the intervention of the steel bar, and therefore the eddy current effect of the steel bar is enhanced.
In this embodiment, an excitation current having an excitation frequency equal to the natural frequency of the primary coil is applied to the primary coil of the sensor, so that the primary coil generates a high-frequency variable magnetic field, and the natural frequency of the secondary coil is equal to the frequency of the high-frequency variable magnetic field generated by the primary coil, so that coupling resonance occurs between the primary coil and the secondary coil, and the sensor operates in a magnetic coupling resonance state.
Thus, by making the excitation frequency of the excitation current the same as the natural frequency of the primary coil and the natural frequency of the secondary coil the same as the frequency of the high-frequency varying magnetic field generated by the primary coil, the sensor can be made to operate in a magnetically coupled resonance state in which the primary coil and the secondary coil are most strongly magnetically coupled.
As shown in fig. 3, a device for detecting the thickness of the reinforced concrete protective layer includes a detection device, a signal acquisition device and a post-processing device, the detection device includes an excitation assembly, a sensor 1 and a displacement controller 3, the sensor 1 includes a primary coil 11 and a secondary coil 12, the displacement controller 3 is connected to the sensor 1 to drive the sensor 1 to move along the reinforced concrete, an output end of the excitation assembly is electrically connected to the primary coil 11 to provide an excitation current to the primary coil 11, an input end of the signal acquisition device is electrically connected to the secondary coil 12 to acquire an induced voltage of the secondary coil 12, and an input end of the post-processing device is connected to an output end of the signal acquisition device to acquire induced voltage data of the secondary coil 12.
Therefore, when the detection device is used for detecting the thickness of the protective layer of the reinforced concrete to be detected (as shown in figure 4), the detection device, the signal acquisition device and the post-processing device are connected firstly; then, the exciting assembly provides exciting current to the primary coil 11, the signal acquisition device acquires the voltage signal of the secondary coil 12, and the frequency of the exciting current provided by the exciting assembly is changed until the voltage signal of the secondary coil 12 acquired by the signal acquisition device reaches a maximum value, and at the moment, the frequency of the exciting current provided by the exciting assembly is the resonance frequency of the sensor 1.
The exciting assembly provides exciting current of resonant frequency for the primary coil 11, the displacement controller 3 drives the sensor 1 to move, so that the sensor 1 is lifted from different heights to detect bare bars, and the signal acquisition device acquires voltage data U on the secondary coil 12 when the sensor 1 is lifted from different heights to detect the bare bars1(ii) a Then the sensor 1 detects different positions of the reinforced concrete to be detected, and the signal acquisition device acquires voltage data U of the sensor 1 on the secondary coil 12 at different positions of the reinforced concrete to be detected2(ii) a Post-processing device acquires voltage data U acquired by signal acquisition device1Sum voltage data U2And by applying voltage data U1Sum voltage data U2Comparing voltage data U1Sum voltage data U2And if the lifting heights d are the same, the corresponding lifting heights d are the thickness of the reinforced concrete protective layer to be detected at the moment, so that the thickness of the reinforced concrete protective layer to be detected is judged, and the thickness of the reinforced concrete protective layer to be detected is detected.
In the present embodiment, the excitation device includes a signal generator 4 and a power amplifier 5, an output terminal of the signal generator 4 is connected to an input terminal of the power amplifier 5 to input the excitation current generated by the signal generator 4 to the power amplifier 5 for amplification, and an output terminal of the power amplifier 5 is connected to the primary coil 11 to input the amplified excitation current to the primary coil 11. Specifically, the signal generator 4 is required to be able to output a sinusoidal voltage signal of an arbitrary frequency within 10 MHz.
Thus, the signal generator 4 is used to generate an excitation current, and the power amplifier 5 is used to amplify the excitation current and output the amplified excitation current to the primary coil 11, so that the primary coil 11 can generate a larger excitation field.
In the present embodiment, the primary coil 11 and the secondary coil 12 are coaxially disposed and fixed on the rigid support 2, and the movement controller is connected to the rigid support 2 to move the sensor 1 through the rigid support 2. Specifically, the primary coil 11 and the secondary coil 12 may be further externally connected with a high-frequency capacitor, a resistor, and other elements of a certain size to adjust the resonant frequency.
Therefore, the coaxial design of the secondary coil 12 and the primary coil 11 can achieve the best coupling effect, is beneficial to picking up magnetic field signals generated by the reinforcing steel bars, and simultaneously, the rigid support 2 is utilized to play a supporting effect on the primary coil 11 and the secondary coil 12, so that the stable use of the primary coil 11 and the secondary coil 12 in the moving process is ensured.
In the embodiment, the rigid support 2 is made of non-conductive non-metallic material with relative permeability of 0.9-1.1; such as plastic, glass, etc.
Thus, the rigid support 2 is made of non-metallic material with relative permeability of 0.9-1.1, which can prevent the influence of external magnetic field and reduce the outward diffusion of induced magnetic field generated by the sensor 1.
In the embodiment, the signal acquisition device comprises an oscilloscope 6, an input end of the oscilloscope 6 is electrically connected with the secondary coil 12 to acquire the voltage on the secondary coil 12, and the post-processing device is a PC terminal 7.
Thus, the voltage of the secondary coil 12 is collected by the oscilloscope 6, and the collected voltage data is transmitted to the PC terminal 7 for further processing.
In this embodiment, the displacement controller 3 includes a step motor and a step motor controller, the step motor controller is electrically connected to the step motor to enable the step motor controller to drive the step motor to move, and the step motor is connected to the rigid support 2 to enable the step motor to drive the rigid support 2 to move.
Thus, the displacement controller 3 adopts a stepping motor and a stepping motor controller, and the linear displacement output by the stepping motor is in direct proportion to the input pulse number, so that the sensor 1 can be conveniently controlled to move along the reinforced concrete.
The use method of the reinforced concrete protective layer thickness detection device comprises the following steps:
step 1) connecting a detection device, a signal acquisition device and a post-processing device;
step 2) the excitation assembly provides excitation current for the primary coil 11, the signal acquisition device acquires a voltage signal of the secondary coil 12, and the frequency of the excitation current provided by the excitation assembly is changed until the voltage signal of the secondary coil 12 acquired by the signal acquisition device reaches the maximum value, and the frequency of the excitation current provided by the excitation assembly is the resonance frequency of the sensor 1;
step 3) the exciting assembly provides exciting current with resonant frequency for the primary coil 11, the displacement controller 3 drives the sensor 1 to move, so that the sensor 1 detects bare bars at different lifting heights, and the signal acquisition device acquires voltage data U on the secondary coil 12 when the sensor 1 detects bare bars at different lifting heights1；
Step 4) the exciting assembly provides exciting current with resonant frequency for the primary coil 11, the displacement controller 3 drives the sensor 1 to move along the surface of the reinforced concrete to be detected, the sensor 1 detects different positions of the reinforced concrete to be detected, and the signal acquisition device acquires voltage data U of the sensor 1 on the secondary coil 12 at different positions of the reinforced concrete to be detected2；
Step 5) the post-processing device acquires the voltage data U adopted by the signal acquisition device in the step 3)1And voltage data U adopted by the signal acquisition device in the step 4)2And by applying voltage data U1Sum voltage data U2And comparing to judge the thickness of the reinforced concrete protective layer to be detected, so as to detect the thickness of the reinforced concrete protective layer to be detected.
Compared with the prior art, the magnetic coupling resonance double-coil structure sensor 1 has the advantages of simple structure, novel method, high response speed and wide application range, can convert detection signals into electric signals which are easy to measure and analyze, effectively improves the detection distance and the linearity, and is very beneficial to the detection of the thickness of the concrete protective layer.
Finally, it should be noted that the above embodiments are only used for illustrating the technical solutions of the present invention and not for limiting the technical solutions, and those skilled in the art should understand that modifications or equivalent substitutions can be made on the technical solutions of the present invention without departing from the spirit and scope of the technical solutions, and all that should be covered by the claims of the present invention.
Claims (10)
1. The reinforced concrete protective layer thickness detection method is characterized in that based on the eddy current effect theory, a sensor with a primary coil and a secondary coil is adopted, the sensor works in a magnetic coupling resonance state, the sensor working in the magnetic coupling resonance state is used for detecting bare bars at different lift-off heights respectively, and voltage data U on the secondary coil when the sensor detects the bare bars at different lift-off heights is obtained1Simultaneously, the sensor working in the magnetic coupling resonance state is used for detecting the surface of the reinforced concrete to be detected, and voltage data U on the secondary coil when the sensor detects the surface of the reinforced concrete to be detected is obtained2Voltage data U on the secondary coil when the sensor detects the bare rib1And voltage data U on the secondary coil when the sensor detects the surface of the reinforced concrete to be detected2And comparing to judge the thickness of the reinforced concrete protective layer to be detected, so as to detect the thickness of the reinforced concrete protective layer to be detected.
2. The method for detecting the thickness of a reinforced concrete protective layer according to claim 1, wherein the relationship between the lift-off height d of the sensor from the surface of the reinforcing steel bar and the voltage U of the secondary coil is as follows:
U＝U(σ,μ,A,f,d)
in the formula: sigma is the conductivity of the steel bar; mu is the magnetic conductivity of the steel bar; a is the amplitude of the excitation voltage of the sensor; f is the excitation frequency of the sensor; d is the lifting height of the sensor from the surface of the steel bar; u is the voltage of the secondary winding.
3. The method for detecting the thickness of a protective layer of reinforced concrete according to claim 1, wherein the sensor detects the current I 'of the secondary coil when the sensor detects the reinforcing steel bar'2Eddy current I 'generated by steel bar eddy effect'0The relationship between them is:
wherein:
in the formula: i'2The current of a secondary coil is detected by a sensor when the sensor detects the steel bar; i'0Eddy currents generated for the eddy current effect of the reinforcing steel bars; u shapesIs the excitation voltage of the sensor; z1Is the primary coil loop impedance; z2Is the secondary loop impedance; omega is angular frequency; m12Is the mutual inductance between the primary coil and the secondary coil; m13Is mutual inductance between the primary coil and the reinforcing steel bar; m23Is the mutual inductance between the secondary coil and the reinforcing steel bar; z3Is the eddy current short circuit loop impedance.
4. The method for detecting the thickness of a reinforced concrete protective layer according to claim 1, wherein an excitation current having an excitation frequency equal to the natural frequency of the primary coil is supplied to a primary coil of the sensor so that the primary coil generates a high-frequency changing magnetic field, and the natural frequency of the secondary coil is equal to the frequency of the high-frequency changing magnetic field generated by the primary coil so that coupling resonance occurs between the primary coil and the secondary coil, and the sensor operates in a magnetic coupling resonance state.
5. The reinforced concrete protective layer thickness detection device according to claim 1 is realized by comprising a detection device, a signal acquisition device and a post-processing device, wherein the detection device comprises an excitation assembly, a sensor and a displacement controller, the sensor comprises a primary coil and a secondary coil, the displacement controller is connected with the sensor to drive the sensor to move along reinforced concrete, an output end of the excitation assembly is electrically connected with the primary coil to provide excitation current for the primary coil, an input end of the signal acquisition device is electrically connected with the secondary coil to acquire induced voltage of the secondary coil, and an input end of the post-processing device is connected with an output end of the signal acquisition device to acquire induced voltage data of the secondary coil.
6. The reinforced concrete protective layer thickness detection device according to claim 5, wherein the excitation device includes a signal generator and a power amplifier, an output terminal of the signal generator is connected to an input terminal of the power amplifier to input the excitation current generated by the signal generator to the power amplifier for amplification, and an output terminal of the power amplifier is connected to the primary coil to input the amplified excitation current to the primary coil.
7. The reinforced concrete protective layer thickness detection device according to claim 5, wherein the primary coil and the secondary coil are coaxially disposed and fixed to a rigid support, and the movement controller is connected to the rigid support to move the sensor through the rigid support.
8. The reinforced concrete protective layer thickness detection device as claimed in claim 7, wherein the rigid support is made of a non-metallic material which is non-conductive and has a relative magnetic permeability of 0.9-1.1.
9. The reinforced concrete protective layer thickness detection device of claim 5, wherein the signal acquisition device comprises an oscilloscope, an input end of the oscilloscope is electrically connected with the secondary coil to acquire the voltage on the secondary coil, and the post-processing device is a PC terminal.
10. The method for using the reinforced concrete protective layer thickness detection device according to claim 5, characterized by comprising the following steps:
step 1) connecting the detection device, the signal acquisition device and the post-processing device;
step 2) the excitation assembly provides an excitation current for the primary coil, the signal acquisition device acquires a voltage signal of the secondary coil, and the frequency of the excitation current provided by the excitation assembly is changed until the voltage signal of the secondary coil acquired by the signal acquisition device reaches a maximum value, and at this time, the frequency of the excitation current provided by the excitation assembly is the resonance frequency of the sensor;
step 3) the excitation assembly provides excitation current with resonant frequency for the primary coil, the displacement controller drives the sensor to move, so that the sensor detects bare bars at different lifting heights, and the signal acquisition device acquires voltage data U on the secondary coil when the sensor detects bare bars at different lifting heights1；
Step 4) the excitation assembly provides excitation current with resonant frequency for the primary coil, the displacement controller drives the sensor to move along the surface of the reinforced concrete to be detected, the sensor detects different positions of the reinforced concrete to be detected, and the signal acquisition device acquires the transmissionVoltage data U of sensor on secondary coils at different positions of reinforced concrete to be measured2；
Step 5) the post-processing device acquires the voltage data U acquired by the signal acquisition device in the step 3)1And the voltage data U acquired by the signal acquisition device in the step 4)2And by applying voltage data U1Sum voltage data U2And comparing to judge the thickness of the reinforced concrete protective layer to be detected, so as to detect the thickness of the reinforced concrete protective layer to be detected.
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