JP2017134013A - Method and apparatus for measuring non-contact stress by complex resonance method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the accuracy of measurement by detecting minute variation of magnetic properties accompanying the variation of stress such the tension of a wire, such as a PC wire as a large variation value.SOLUTION: A method for measuring a non-contact stress by a complex resonance method comprises: exciting a wire w by a primary coil (an excitation coil) 1; inducing a voltage in a secondary coil (a feedback coil) 2 by magnetic properties of the excited wire w; forming a parallel resonant circuit 5 by the secondary coil (the feedback coil) 2 and a capacitor 4; operating a self-exited oscillator by inputting an appropriate positive feedback amount of the signal into an amplifier 6; operating an oscillation loop so that the resonance voltage value of the secondary coil (the feedback coil) 2 is constant in the output of the amplifier 6; correcting the deviation of phase due to the hysteresis loss of the excitation current since a potential between both ends of the primary coil (the excitation coil) 1 is proportional to an excitation current; and measuring the stress of the wire w.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a non-contact stress measurement method by a composite resonance method and a measurement apparatus thereof capable of detecting a minute change in magnetic characteristics accompanying a change in stress of a wire such as a PC wire on which stress is applied.

  PC wires are called PC steel wires and prestressed concrete wires, and are used in various fields from bridges to buildings in order to compensate for the weak points of concrete and increase the strength. This PC wire is a tendon having a large tensile strength and a large elongation at break. As described above, the tensile strength or the like of a wire such as a PC wire used in a structure may be reduced due to corrosion or other causes. Then, the safety | security of structures, such as a bridge and a building, is improved by measuring the tension | tensile_strength of wire materials, such as PC wire.

  Wires such as PC wires function safely to ensure safety of bridges and buildings. It is an important member especially related to load bearing performance. When such deformation of the wire material such as PC wire becomes obvious, it becomes impossible to perform reliable construction management and maintenance management. Therefore, it is necessary to measure the tension acting on the wire such as the PC wire. For example, it is necessary to check the initial state at the time of start of tension management and operation during construction. Next, during operation, it is necessary to check changes over time at the time of inspection.

As a typical measuring method for measuring the tension acting on a wire such as a PC wire, there are two methods of “measuring method using strain gauge” and “measuring method using load cell” described below.
The measurement method using a strain gauge is a method of measuring a tension value by attaching a strain gauge to a wire (steel material), measuring the strain value, and multiplying the strain value by a Young's modulus and a cross-sectional area. This measurement method is a method in which the measurement accuracy of tension becomes very high by using a high-precision measuring instrument called a strain gauge. However, in order to attach the strain gauge, the surface of the wire material (steel material) needs to be cut even though it is minute, and for the existing steel material, only the incremental tension from the time when the strain gauge was applied could be measured.

  The measuring method using a load cell is a method of measuring a tension by inserting a load cell (compression load measuring instrument) at a fixing end of a wire (steel material). This method has very high measurement accuracy like the above-described strain gauge, and further has an advantage that the surface of the wire (steel) need not be cut. However, since the load cell is a center-hole type measuring instrument, it is necessary to insert the measuring instrument through the steel material when installing the wire (steel material), and it cannot be used for existing steel materials. Since the measuring device is interposed at the fixing end, there is a disadvantage that the fixing end becomes large.

  As a technique for solving the disadvantages of the measurement method using the strain gauge or the measurement method using the load cell, for example, as disclosed in Japanese Patent Application Laid-Open No. 2003-270059 “Reinforced Concrete Stress Reinforced Stress Measurement System” of Patent Document 1, a magnetostriction method is used. There has been proposed an apparatus for measuring stress using a change in magnetic permeability associated with a change in stress of a magnetic material by using a measurement principle called “stress”. This measuring device includes a coil disposed inside and outside a cylindrical hollow member, and further includes a thermometer, and performs measurement by inserting a magnetic material into the hollow portion. The measurement principle is that a pulse current is applied to the outer coil (primary coil), the change in the induced current value is detected in the inner coil (secondary coil), and the stress is determined from the relational expression of the induced current value, temperature, permeability, and stress It is the composition which calculates.

  In addition, as disclosed in Japanese Patent Application Laid-Open No. 2009-265003 “Tension Measuring Device” of Patent Document 2, the measuring instrument is composed of a cylindrical magnetizer that performs direct current magnetization up to a saturation asymptotic magnetization range, and a magnetic sensor disposed inside the cylinder. In addition, there has been proposed a tension measuring device that performs measurement by inserting a magnetic material into a hollow portion. This measurement principle is a configuration in which tension is calculated using a change in spatial magnetic field intensity detected by a magnetic sensor.

JP 2003-270059 A JP 2009-265003 A

  The existing stress measurement system for reinforced concrete structures in Patent Document 1 avoids partial shaving of the wire (steel) and enables measurement at an arbitrary position, and further splits the measuring instrument into two. It can be applied to steel materials. However, the system disclosed in Patent Document 1 has a problem in that there is a limit to the improvement in measurement accuracy because the change in magnetic properties of the magnetic material accompanying the change in stress is a very small change.

  Moreover, the tension measuring device of Patent Document 2 uses DC magnetization to solve the influence of eddy currents on the magnetic permeability and conductivity due to AC magnetization, and more particularly improves the applicability to line structures. However, the apparatus of Patent Document 2 also has a problem that the change in the magnetic properties of the magnetic material accompanying the change in stress is a very small change, and there is a limit to the improvement in measurement accuracy.

  The inventor of the present invention uses a parallel resonance circuit and a series resonance circuit in a positive feedback loop to oscillate the stress such as tension by using it for measuring the stress change of the steel material without using other amplification means. We paid attention to the fact that a small change in the magnetic properties associated with the stress change of the magnetic material can be directly detected as a large change value for the wire such as a working wire.

  The present invention has been developed to solve such problems. That is, an object of the present invention is to detect a minute change in magnetic characteristics accompanying a stress change of a wire as a large change value, thereby improving the measurement accuracy of the stress change, and a non-contact stress measurement method by a composite resonance method And providing a measuring device thereof.

The measurement method of the present invention is a non-contact stress measurement method by a composite resonance method that detects a change in magnetic properties accompanying a stress change of a wire (w) such as a wire and measures the stress of the wire (w),
The wire (w) is excited by a primary coil (excitation coil) (1) through a capacitor (9) near the series resonance frequency, and the secondary coil ( A voltage is induced in the feedback coil) (2),
A parallel resonance circuit (5) is formed by the secondary coil (feedback coil) (2) and the capacitor (4), and this signal is passed through an attenuator (12) of positive feedback (β) to provide an appropriate positive feedback amount. Is input to the amplifier (6) to operate as a self-excited oscillator,
The output of the amplifier (6) excites the wire (w), and simultaneously stabilizes the amplifier (6) from a part of the output via the negative feedback (−β) attenuator (13),
The oscillation loop is operated so that the resonance voltage value of the secondary coil (feedback coil) (2) becomes constant. At this time, the potential at both ends of the primary coil (excitation coil) (1) is proportional to the excitation current. The stress of the wire (w) is measured by correcting the phase shift due to the hysteresis loss of the excitation current.
By measuring the temperature of the wire (w), the stress measurement value of the wire (w) can be corrected using the temperature fluctuation.

The measuring device of the present invention is a non-contact stress measuring device based on a composite resonance method that measures the stress of the wire (w) by detecting a change in magnetic properties accompanying the stress change of the wire (w) such as a wire. And
Stresses in which a primary coil (excitation coil) (1) for exciting the wire (w) and a secondary coil (feedback coil) (2) in which a voltage is induced by the magnetic characteristics of the excited wire (w) are provided. A sensor unit (3);
Between the primary coil (excitation coil) (1) and the secondary coil (feedback coil) (2) of the stress sensor part (3), the secondary coil (2) that is magnetically coupled with the magnetic properties of the wire (w) ( A parallel resonant circuit (5) formed by connecting a capacitor (4) in parallel to the feedback coil) (2);
An amplifier (6) for amplifying a measurement signal generated on the secondary coil (feedback coil) (2) side;
A series resonant circuit (7) formed between the amplifier (6) and the primary coil (excitation coil) (1) and formed through a resistor (8) and a capacitor (4),
The signal of the parallel resonant circuit (5) is operated as a self-excited oscillator by inputting an appropriate positive feedback amount to the amplifier (6) via an attenuator (12) of positive feedback (β),
The output of the amplifier (6) excites the wire (w), and simultaneously stabilizes the amplifier (6) from a part of the output via the negative feedback (−β) attenuator (13), The oscillation loop is operated so that the resonance voltage value of the secondary coil (feedback coil) (2) becomes constant. At this time, the potential at both ends of the primary coil (excitation coil) (1) is proportional to the excitation current. A feature is that the phase shift due to the hysteresis loss of the excitation current is corrected and the stress of the wire (w) can be measured.
The stress sensor part (3) has a structure in which the stress sensor part (3) is divided in the longitudinal direction so that the wire (w) can penetrate through the central part and can be detachably joined. can do.
In order to correct the measured value of the wire (w) using the change value of the temperature of the wire (w), it is preferable to provide a temperature sensor (31) for measuring the temperature change of the wire (w).

In the measurement method of the present invention, the voltage difference between both ends of the primary coil (excitation coil) (1) can be detected as a predetermined signal with respect to the hysteresis loss component of the wire (w) that slightly changes due to the tension. Since the present invention does not require any other amplifying means and can obtain a highly reproducible signal, it is possible to detect a minute change in the magnetic properties of the magnetic material accompanying a change in the stress of the wire (w) as a large change value. The measurement accuracy can be improved.
Further, by correcting the phase shift due to loss such as hysteresis loss by the series resonance circuit (7) of the exciting current by the resistor (8) and the capacitor (4) at the output of amplification, it can be measured more accurately.
Since the stress measurement value of the wire (w) is proportional with a specific coefficient as the temperature varies, the stress measurement value of the wire (w) can be corrected with a simple linear equation.

In the measuring apparatus of the present invention, the differential voltage across the primary coil (excitation coil) (1) is detected as a predetermined signal for the hysteresis loss component of the wire (w) that changes minutely due to tension without using a complicated circuit. be able to. Since a highly reproducible signal can be obtained according to the present invention, the measurement accuracy can be improved for a minute change in the magnetic properties of the magnetic material accompanying a change in stress.
In addition, since it is a simple device, only the stress sensor unit (3) can be attached in advance to each of a number of existing wires (w) such as wires in terms of cost.

It is a schematic block diagram which shows the non-contact stress measuring apparatus by the composite resonance method of Example 1. FIG. It is an enlarged front view which shows the state which mounted | wore the stress sensor part to PC wire. It is a graph which shows the principle of operation in an amplifier. It is a front view which shows the tension testing machine which shows the state which mounted | wore the wire which measures with the non-contact stress measuring apparatus by the composite resonance method of this invention. It is a graph which shows the relationship between the voltage (tensile strength) by a tensile tester, and tension. It is a graph which shows the basic data of the tension | tensile_strength measured with the non-contact stress measuring apparatus by the composite resonance method of this invention. It is a graph which shows the tension measurement test result whose cable length measured with the non-contact-stress measuring apparatus by the composite resonance method of this invention is 2.0 m. It is a graph which shows the tension measurement test result whose cable length measured with the non-contact-stress measuring apparatus by the composite resonance method of this invention is 6.7m. It is a schematic block diagram which shows the stress measuring device provided with the temperature sensor of Example 2.

  The present invention is a non-contact stress measurement method by a complex resonance method that can improve the measurement accuracy by detecting a minute change in magnetic properties accompanying a stress change of a wire such as a PC wire as a large change value.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
<Configuration of non-contact stress measurement device by composite resonance method>
FIG. 1 is a schematic configuration diagram illustrating a non-contact stress measuring apparatus according to the composite resonance method of the first embodiment. FIG. 2 is an enlarged front view showing a state in which the stress sensor portion is mounted on the PC wire.
The non-contact stress measuring apparatus of the present invention includes a primary coil (excitation coil) 1 for exciting a wire w such as a PC wire and a secondary coil (feedback coil) 2 for returning the output of the excited wire w. The stress sensor unit 3 and a secondary coil (feedback coil) 2 that is magnetically coupled with the magnetic characteristics of the wire w between the primary coil (excitation coil) 1 and the secondary coil (feedback coil) 2 of the stress sensor unit 3. And a parallel resonance circuit 5 formed by putting a capacitor 4 (C1) in parallel.

  Only this parallel resonance circuit 5 can detect only a very small change in the magnetic characteristics of the magnetic material of the wire rod w due to the change in stress. In the present invention, the parallel resonant circuit 5 is provided with an amplifier 6 for inputting a measurement signal generated on the secondary coil (feedback coil) 2 side. Further, a series resonance circuit 7 is inserted between the amplifier 6 and the primary coil (excitation coil) 1. The series resonant circuit 7 is formed by a resistor 8 and a capacitor 9 (C2). Further, the series resonance circuit 7 is constituted by an internal stress output (DC) and a capacitor 10 (C3), and together with other necessary components, is integrated in a case as a non-contact stress measuring device.

<Configuration of stress sensor section>
As shown in FIG. 2, the primary coil (excitation coil) 1 has a cylindrical bobbin 11 wound in a solenoid shape so as to penetrate a wire w such as a ferromagnetic PC wire to be measured at the center. is there.

  The secondary coil (feedback coil) 2 is also wound around the same bobbin 11 in the form of a solenoid so that the wire w such as a ferromagnetic PC wire of the object to be measured penetrates in the center. A magnetic closed loop is formed by penetrating a ferromagnetic wire to be measured at the center of the primary coil (excitation coil) 1 and the secondary coil (feedback coil) 2. A parallel resonant circuit 5 is formed in the secondary coil 2 by a capacitor 4. The signal of the parallel resonance circuit 5 inputs an appropriate positive feedback amount to the amplifier 6 via the positive feedback (β) attenuator 12 and operates as a self-excited oscillator.

  Since the measuring apparatus of the present invention is a simple apparatus, it becomes possible to previously attach only the stress sensor unit 3 to each of the wire w such as a large number of wires from the cost viewpoint.

  In the schematic configuration diagram of FIG. 1, the stress sensor unit 3 shows a configuration in which a primary coil (excitation coil) 1 and a secondary coil (feedback coil) 2 are arranged. However, the configuration is not limited to such a configuration. Although not shown, a double structure in which a secondary coil (feedback coil) 2 is wound on the upper side of a solenoid-like primary coil (excitation coil) 1 inside the bobbin 11 may be used.

  Further, as shown in the mounted state of FIG. 2, in the present invention, a wire w such as a ferromagnetic PC wire to be measured is penetrated and used at the center. It may be difficult to penetrate the existing wire w later. Therefore, although not shown, the stress sensor unit 3 can be divided into two in the longitudinal direction so that the stress sensor unit 3 can be attached to the wire w later, and the structure can be freely joined thereafter. At this time, both the internal primary coil (excitation coil) 1 and the secondary coil (feedback coil) 2 can be divided into two. The divided coils 1 and 2 are freely sandwiched between the wire rods w.

<Description of measurement principle>
In the non-contact stress measuring apparatus according to the composite resonance method of the first embodiment, when the wire w is excited (magnetized) with the primary coil (excitation coil) 1 via the capacitor 9 near the series resonance frequency (series resonance current), this excitation A voltage is induced in the secondary coil (feedback coil) 2 due to the magnetic characteristics of the wire w. It is slightly larger than the magnetic flux when the wire w is not magnetized. When incorporated in the parallel resonant circuit 5, the inductance of the secondary coil (feedback coil) 2 acts as a mutual inductance when a magnetic flux comes from the wire w.

  Only this parallel resonance circuit 5 can detect only a very small change in the change in the magnetic characteristics of the magnetic material due to the stress change. Therefore, the present invention includes an amplifier 6 for inputting a measurement signal generated on the secondary coil (feedback coil) 2 side. Since the parallel resonance circuit 5 is formed by the capacitor 4 in the secondary coil (feedback coil) 2, this signal inputs an appropriate positive feedback amount to the amplifier 6 via the attenuator 12 of the positive feedback (β), Operate as a self-excited oscillator. The output of the amplifier 6 excites the wire w and simultaneously stabilizes the amplifier 6 from a part of the output via the attenuator 13 of negative feedback (−β).

  That is, the magnetic flux density B varies depending on the shape factor such as the magnetic characteristics of the wire w and the magnetic circuit of the measuring device. For example, the open gain of the amplifier 6 is about 80 db, and it is used with a gain of 26 db by negative feedback, so that a very stable amplification degree can be obtained. A series resonance circuit 7 and a primary coil (excitation coil) 1 are connected in series to the output of the amplifier 6 to excite the wire rod w. A secondary coil (feedback coil) 2 is similarly wound on the primary coil (excitation coil) 1, and a parallel resonant circuit 5 is formed by a capacitor 4 in parallel (F0280 Hz). This signal is sent to the amplifier 6 via an ATT. Connect to the + input to form a positive feedback loop.

  The oscillation loop operates so that the resonance voltage value of the secondary coil 2 (feedback coil) becomes constant. It operates similarly between the no load and the maximum load of the wire rod w. At this time, the potential across the primary coil (excitation coil) 1 is proportional to the excitation current. This can be output as a change in the magnetic properties of the magnetic material accompanying a change in the stress of the wire w, and the change in the tension of the wire w can be measured.

  The measured values measured by the non-contact stress measuring apparatus according to the composite resonance method of Example 1 are as follows: no-load voltage P-P 14 V, current P-P 0.7 A, maximum load voltage P-P 30 V, current P-P 1. 4A, Z = impedance 20Ω-21.4Ω was obtained.

FIG. 3 is a graph showing the principle of operation in the amplifier.
The horizontal axis of the graph shows the series resonance frequency of the primary coil (excitation coil) 1 and the parallel resonance frequency of the secondary coil (feedback coil) 2 and each resonance slope with respect to the tensile load. The vertical axis indicates the voltage / current due to the series resonance impedance of the primary coil (excitation coil) 1 and the capacitor 9 (C2) and the parallel resonance voltage of the secondary coil (feedback coil) 2.

  At the parallel resonance frequency f1 of the secondary coil (feedback coil) 2 when no load is applied, a continuous positive feedback oscillation level (written on the right side of the graph) is set, and the process shifts from f1 to f2 as the tensile load increases. That is, the series resonance current of the primary coil (excitation coil) 1 can be automatically controlled by the amplifier 6 so that the load increases and the parallel resonance voltage of the secondary coil (feedback coil) 2 becomes constant. Therefore, the non-contact stress measurement method by the composite resonance method of the present invention enables measurement with high sensitivity and high reproducibility.

Thus, the non-contact stress measuring method and measuring apparatus by the composite resonance method of the present invention can be used for measuring the tension of the wire w such as PC wire.
The wire material w such as PC wire changes minutely depending on the load. Although it was extremely difficult to selectively measure inductance, magnetic permeability, hysteresis loss, and eddy current loss, according to the positive feedback oscillation of the positive feedback amplifier 6 of the present invention, changing inductance, magnetic permeability, hysteresis loss. Parameters such as eddy current loss can be selected. Among the parameters, the hysteresis loss of the real number term cancels the complex term due to resonance and becomes only the real number term, and the hysteresis loss can correspond to the weighted change of the wire w such as PC wire.

  With the composite resonance method of the present invention, the amplitude H increases as the value of −α approaches 0 (oscillation state), as indicated by the mathematical formula 1. The gain of the entire circuit increases rapidly. As the Q value is expressed by the mathematical formula 2 and the bandwidth is expressed by the mathematical formula 3, the bandwidth increases and the bandwidth becomes narrower than the original value. When the value of 1-α is 0.01, the gain is 100 times, and the Q value and selectivity are also 100 times better than the original circuit. That is, highly accurate stress measurement is possible.

<Tension measurement test (tensile tester)>
FIG. 4 is a front view showing a tensile tester showing a state in which a wire to be measured by a non-contact stress measuring apparatus using the composite resonance method of the present invention is mounted.
Basic data of the non-contact stress measuring device of the present invention was collected using a tensile tester 21. A load detector (load cell) 22 is fixed to the upper part of a tensile tester 21 as shown in the figure, and the upper part of a wire w (steel wire) to which a test piece gripping tool (chuck) 23 is connected is fixed thereto. On the other hand, the lower part of the wire rod w is grasped by the gripping tool 23 and fixed to the rigid frame lower part 24. By rotating the screw rods 26 in the frames 25 on both sides with a motor, the wire rod w is stretched at a constant speed. A wire w (steel wire) was attached to the upper and lower test piece gripping tool 23 of the tensile tester 21 and tested. At this time, the stress sensor unit 3 of the non-contact stress measuring device of the present invention was attached to the wire w.

<Tension measurement test (relationship between tension and voltage)>
FIG. 5 is a graph showing a relationship between voltage (tensile strength) and tension by a tensile tester. FIG. 6 is a graph showing the relationship between tension and voltage measured by a non-contact stress measuring apparatus using the composite resonance method of the present invention.
As shown in FIG. 5 and FIG. As shown in the test result table of Table 1, this test result was a relationship between the voltage (tensile strength) and tension by the tensile testing machine 21. The test was performed three times (Voltage 1, Voltage 2, Voltage 3). FIG. 5 shows a graph of the test results.

  As shown in FIG. 6, the voltage increased as the tension increased. A voltage change of about 13 V could be output with a tension change of 170 kN, and the tension change could be detected as a relatively large voltage change. In addition, the history remains almost unchanged even when measured repeatedly, and has extremely high reproducibility. In addition, it was confirmed that the voltage was slightly higher during loading than when unloading. The reason for drawing a slightly different history between loading and unloading is considered to be the effect of magnetic hysteresis.

  As shown in the graph of FIG. 6, the measurement results are mechanically pulled, and the voltage (V) at that time is shown on the vertical axis and the tension (kN) is shown on the horizontal axis. The mathematical formula at this time was calculated by the regression equation shown in Equation 4. In this regression equation, T: tension (kN) and e: output voltage (V). Although the influence of various factors such as temperature has not been taken into account, this formula was derived from this result by the least square method. This mathematical formula is a polynomial, and is a cubic formula with the degree of freedom adjusted coefficient of determination closest to 1. In this experiment, the test was performed three times using a PC steel stranded wire. The measurement temperature was 14.5 ° C.

<Tension measurement test (tension estimation)>
FIG. 7 is a graph showing a tension measurement test result when the length of the wire measured by the non-contact stress measuring apparatus according to the composite resonance method of the present invention is 2.0 m. FIG. 8 is a graph showing the result of a tension measurement test in which the length of the wire measured by the non-contact stress measuring apparatus according to the composite resonance method of the present invention is 6.7 m.
Similarly, the basic data of the non-contact stress measuring device of the present invention are shown in FIGS. A load detector (load cell) 22 is fixed to the upper part of the tensile tester 21, and a test piece gripping tool (chuck) 23 is connected to the tensile tester 21 to fix the upper part of the steel wire as a wire rod w. On the other hand, the lower part of the wire rod w is grasped by the gripping tool 23 and fixed to the rigid frame lower part 24. By rotating screw rods 26 on the frames 25 on both sides by a motor, the wire rod w is stretched at a constant speed. A steel wire wire was attached to the upper and lower test piece gripping tool 23 of the tensile tester as a wire w and tested.

<Tension measurement test results (tension estimation)>
As shown in the graph of FIG. 7, as a measurement object, a steel wire having a wire w length of 2.0 m was tested three times. The temperature of the steel was tested in the range of 9.5 ° C to 9.9 ° C. The measurement result shows the load cell measurement value (kN) on the horizontal axis of the graph of FIG. 7, and the measurement value (kN) by the stress measurement device of the present invention on the vertical axis.
Similarly, as shown in the graph of FIG. 8, a steel wire having a wire w length of 6.7 m was also tested three times. The temperature of the steel material at this time was tested in the range of 16.4 ° C to 16.7 ° C. The horizontal axis of the graph of FIG. 8 shows the load cell measurement value (kN), and the vertical axis shows the measurement value (kN) by the stress measurement device of the present invention.
As shown in the accuracy table of the regression equation in Table 2, the coefficient of determination shows a substantially constant value from these test results, indicating that the measurement accuracy of the non-contact stress measuring device by the composite resonance method of the present invention is high. Yes.

A hysteresis loss component that changes minutely due to the tension can be obtained by using the differential voltage across the primary coil as a predetermined signal and without requiring other amplifying means. The change in the magnetic properties of the magnetic material accompanying the change in stress can improve the measurement accuracy for very small changes.
In addition, it is possible to measure accurately by correcting the phase shift due to loss such as hysteresis loss by the series resonance circuit 7 of the excitation current by the resistor and the capacitor at the output of amplification.

<Configuration of stress measuring device with temperature sensor>
FIG. 9 is a schematic configuration diagram showing a stress measuring device provided with the temperature sensor of the second embodiment.
In the stress measuring device of Example 2, the temperature sensor 31 for measuring the temperature change of the wire w was provided. This is to correct the stress measurement value of the wire w using the change value of the temperature of the wire w. The wire w such as PC wire that is actually used should be used in harsh conditions such as a climate where the temperature is +50 to + 60 ° C or a climate where the temperature is -20 to -30 ° C. There is.

  In such a case, the measurement value in the high temperature condition or the low temperature condition is collected in advance by the temperature sensor 31, and the stress measurement value of the wire w is corrected using the change value of the temperature of the wire w. Measured values can be obtained. Since other devices and measurement methods are the same as those in the first embodiment, description thereof is omitted.

  Note that the present invention is not limited to the above-described embodiment of the present invention, as long as the measurement accuracy can be improved by detecting a minute change in magnetic characteristics accompanying the stress change of the wire rod w as a large change value. Of course, various changes can be made without departing from the scope of the present invention.

  The present invention is not limited to the measurement of the tension of the wire w such as a PC wire, and can be used for measurement as long as it is a metal material accompanied by other stress changes.

1 Primary coil (excitation coil)
2 Secondary coil (feedback coil)
DESCRIPTION OF SYMBOLS 3 Stress sensor part 4 Capacitor 5 Parallel resonance circuit 6 Amplifier 7 Series resonance circuit 8 Resistance 9 Capacitor 10 Capacitor 12 Attenuator 13 Attenuator 31 Temperature sensor w Wire material (PC wire)

Claims (5)

A non-contact stress measurement method by a composite resonance method for detecting a change in magnetic properties accompanying a stress change of a wire (w) such as a wire and measuring the stress of the wire (w),
The wire (w) is excited by a primary coil (excitation coil) (1) through a capacitor (9) near the series resonance frequency, and the secondary coil ( A voltage is induced in the feedback coil) (2),
A parallel resonance circuit (5) is formed by the secondary coil (feedback coil) (2) and the capacitor (4), and this signal is passed through an attenuator (12) of positive feedback (β) to provide an appropriate positive feedback amount. Is input to the amplifier (6) to operate as a self-excited oscillator,
The output of the amplifier (6) excites the wire (w), and simultaneously stabilizes the amplifier (6) from a part of the output via the negative feedback (−β) attenuator (13),
The oscillation loop is operated so that the resonance voltage value of the secondary coil (feedback coil) (2) becomes constant. At this time, the potential at both ends of the primary coil (excitation coil) (1) is proportional to the excitation current. A non-contact stress measurement method by a composite resonance method, wherein the stress of the wire (w) is measured by correcting a phase shift due to hysteresis loss of an excitation current.   The non-contact stress measurement method by a composite resonance method according to claim 1, wherein the temperature of the wire (w) is measured, and the stress measurement value of the wire (w) is corrected using the temperature fluctuation. . A non-contact stress measuring device based on a composite resonance method for measuring the stress of the wire (w) by detecting a change in magnetic properties accompanying a stress change of the wire (w) such as a wire,
Stresses in which a primary coil (excitation coil) (1) for exciting the wire (w) and a secondary coil (feedback coil) (2) in which a voltage is induced by the magnetic characteristics of the excited wire (w) are provided. A sensor unit (3);
Between the primary coil (excitation coil) (1) and the secondary coil (feedback coil) (2) of the stress sensor part (3), the secondary coil (2) that is magnetically coupled with the magnetic properties of the wire (w) ( A parallel resonant circuit (5) formed by connecting a capacitor (4) in parallel to the feedback coil) (2);
An amplifier (6) for amplifying a measurement signal generated on the secondary coil (feedback coil) (2) side;
A series resonant circuit (7) formed between the amplifier (6) and the primary coil (excitation coil) (1) and formed through a resistor (8) and a capacitor (4),
The signal of the parallel resonant circuit (5) is operated as a self-excited oscillator by inputting an appropriate positive feedback amount to the amplifier (6) via an attenuator (12) of positive feedback (β),
The output of the amplifier (6) excites the wire (w), and simultaneously stabilizes the amplifier (6) from a part of the output via the negative feedback (−β) attenuator (13), The oscillation loop is operated so that the resonance voltage value of the secondary coil (feedback coil) (2) becomes constant. At this time, the potential at both ends of the primary coil (excitation coil) (1) is proportional to the excitation current. A non-contact stress measuring apparatus using a composite resonance method, wherein a phase shift due to hysteresis loss of an exciting current is corrected and the stress of the wire (w) can be measured.   The stress sensor part (3) has a structure in which the stress sensor part (3) is divided in the longitudinal direction so that the wire (w) can be penetrated through the central part and can be detachably joined. The non-contact stress measuring apparatus by the composite resonance method according to claim 3, wherein the apparatus is a non-contact stress measuring apparatus.   In order to correct the measured value of the wire (w) using the change value of the temperature of the wire (w), a temperature sensor (31) for measuring the temperature change of the wire (w) is provided. The non-contact stress measuring apparatus by the composite resonance method according to claim 3 or 4.