JPH04248427A - Strain detector - Google Patents

Abstract

PURPOSE:To exclude the effect of a disturbance magnetic field by one sensor by taking out an external magnetic field component to feed back the same and cancelling the external magnetic field component. CONSTITUTION:An exciting core and a detection core arranged so as to cross each other at a fight angle have two magnetic legs 2,3 parallel to each other and, with respect to a magnetic anisotropic sensor wherein windings 7a,2b and windings 3a,3b are wound around the respective magnetic legs in cumulative connection, winding 3c being third winding is wound around the Hall element 6 provided to the leading end surface of one magnetic leg 3 and the detection core and the output signal of the Hall element 6 is used as a feedback signal and the winding 3c is excited by an error amplifier 5 so as to cancel an external magnetic field component.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a stress detector for non-destructively testing stress on steel materials and the like.

0002

2. Description of the Related Art There is a strong need for stress detection in monitoring the condition of steel materials or detecting deterioration. As a sensor most suitable for detecting this stress, for example, a magnetic anisotropy sensor (Magnetic Anisotropy sensor) is used.
y Sensor (hereinafter referred to as MAS). This sensor is described in, for example, Japanese Patent Publication No. 61-31828, and measures the distribution and changes in the magnetic anisotropy (the difficulty of magnetization varies depending on the direction of the material) of the object to be measured. Its unique feature is that it can detect stress, defects, etc. in a non-contact manner.

FIG. 2 is a schematic perspective view showing the basic structure of a magnetic anisotropy sensor. MAS has two horseshoe-shaped magnetic legs 2
, 3 are disposed perpendicularly to each other, and windings 2a and 2b are wound around each leg of the magnetic legs 2 forming the excitation cores E1 and E2, and both are connected in series. Similarly, detection cores D1, D
Winding wires 3a and 3b are wound around the magnetic leg 3 forming 2.
Both are connected in series. In this case, the distance between both legs is set equal.

In the above configuration, during measurement, the magnetic legs 2 and 3 are placed on the object to be measured (a steel plate in this example) 4 (in reality, the magnetic legs 2 and 3 are A gap is formed between the tip end surface of the test object 4 and the surface of the object to be measured 4). In this state, an alternating current voltage (for example, 400 Hz) Ve is applied between the windings 2a and 2b. The magnetic flux from the magnetic legs E1 to E2 of the excitation core passes through the measurement object, but when no stress is applied to the measurement object, the magnetic flux distribution within the measurement object is symmetrical about the E1 - E2 axis, and the magnetic flux of the detection core passes through the measurement object. Points D1 and D2 are at the same potential level. However, when stress is applied to the object to be measured, magnetic anisotropy occurs due to the opposite effect of magnetostriction, a difference is created between the magnetic potentials of the magnetic legs D1 and D2, and a voltage is induced in the windings 3a and 3b. This detected output voltage Vd is synchronously rectified and
By outputting to the recorder, a voltage proportional to the torque or stress of the object to be measured 4 can be obtained. In addition, MAS
When measuring the stress of the object to be measured, the sensitivity is highest when the angle between the stress direction and the E1-E2 direction of the excitation core is θ=45°.

By the way, in the above-mentioned MAS, since the magnetic path of the detection core is open, it is affected by an external magnetic field. When measuring stress with MAS, we consider the two typical cases where a magnetic field is applied: the shaft current flowing in the shaft of a dynamo, etc., and the power or communication shaft current flowing in the rails of a railway track. will be a little different. First, when measuring the torque of a shaft such as a dynamo, the stress applied to the shaft surface is in the direction of 45 degrees with respect to the axial direction, and when a shaft current flows, the direction of the magnetic field due to the current and the direction of the detection core are 90 degrees. It becomes °. Next, in the case of measuring the rail axial force of a railway track, the angle between the direction of the magnetic field due to the axial current and the detection core is 45°, which is more susceptible than in the case of torque measurement. When an external magnetic field is superimposed, the operating point of the MAS's detection core changes. The amplitude and phase of the voltage induced in the sensing core are determined by the nonlinearity and hysteresis of the sensing core. Therefore, it is necessary to take measures to reduce the effects of external magnetic fields.

As one of these methods, for example, "Non-destructive Testing" Vol. 35 No. 12 (December 1986), 861
As shown in "Influence of disturbance magnetic field on output signal of magnetic anisotropy sensor and method for reducing the same" on pages 867 to 867, a dual type magnetic anisotropy sensor has been proposed. This dual type magnetic anisotropy sensor is constructed using two magnetic anisotropy sensors with the same specifications, and the windings of the excitation cores of the two sensors each consisting of a pair of magnetic legs are connected in parallel. The windings of the detection core are connected differentially. Then, a voltage that is the sum of the signal and the disturbance is created at the output of one sensor, a voltage that is the sum of the antiphase signal and the disturbance is created at the output of the other sensor, and the disturbance noise is canceled out by subtracting the latter from the former. This reduces the influence of magnetic fields.

[0007]

[Problems to be Solved by the Invention] However, although the dual type magnetic anisotropy sensor described above is excellent as a measurement system because theoretically the influence of the disturbance magnetic field is already reduced at the input stage of the amplifier, , since two sensors with the same specifications are required, there is a problem that the sensor becomes larger, heavier, and costs increase. The present invention has been made in view of the above-mentioned actual state of the prior art, and it is an object of the present invention to provide a stress detector that can eliminate the influence of a disturbance magnetic field using a single sensor.

[0008]

[Means for Solving the Problems] In order to achieve the above object, the present invention provides an excitation core and a detection core that are arranged orthogonally to each other and have two parallel magnetic legs. A stress detector using a magnetic anisotropic sensor in which a coil is wound around each of the coils in a harmonic connection, the Hall element being attached to the tip end surface of the detection core, and the third coil being wound around the detection core. and an error amplifier that excites the third winding using the output signal of the Hall element as a feedback signal.

[0009]

[Operation] According to the above means, the external magnetic field component is detected by the Hall element, and this is used as a feedback signal to excite the third winding of the detection core so as to cancel the external magnetic field component, thereby reducing stress. Measured values can be made free of errors. Therefore, the influence of external magnetic fields can be eliminated with a simple configuration without increasing the size of the sensor.

0010

Embodiments Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a schematic perspective view showing an embodiment of a stress detector according to the present invention. Note that in this embodiment, the same reference numerals are used for the same parts as in FIG. 2, and therefore, redundant explanations of the configuration and operation will be omitted below.

In this embodiment, the arrangement relationship between the magnetic legs 2 and 3 is as shown in FIG.
In addition to windings 3a and 3b, there is a third winding, winding 3.
c is wound around the core base. The output of the error amplifier 5 is applied to this winding 3c. A Hall element 6 is attached to the tip end surface of the magnetic leg D1, and a low-pass filter 7 is connected to this Hall element 6. The output of the low-pass filter 7 is connected to a subtracter 8, and its output is applied to the input of an error amplifier (DC amplifier) 5. Note that the low-pass filter (LPF) 7 may be replaced with a band-eliminating filter that extracts components other than the frequency of the excitation voltage Ve.

The influence on the MAS output is caused by the fact that the operating point of the B-H characteristic of the detection core is biased by the magnetic flux that enters the detection core. The MAS synchronously detects voltages induced in the windings 3a and 3b (detection coils) to reduce the influence of disturbance factors such as noise. However, as the magnetic operating point of the detection core is biased, the amplitude and phase of the detection voltage change slightly. The amplitude depends on the core nonlinearity and the phase depends on the hysteresis bulge.

Therefore, in the present invention, as a means for reducing the influence of the external magnetic field, a Hall element 6 is provided to detect the magnetic field component of a frequency other than the excitation frequency that enters the detection core, and performs feedback so that this becomes zero. There is. That is, the signal obtained by removing unnecessary parts in the output signal of the Hall element 6 by the low-pass filter 7 is input to the negative input side of the error amplifier 5, and the difference component from the target value 0V is input to the error amplifier 5.
, and excites the winding 3c. In this way, magnetic field components other than the excitation frequency in the detection core can be reduced to zero. With this method, only one sensor is required compared to the above-mentioned dual type, so it is possible to deal with the bias of the external magnetic field. As a result of being able to eliminate the influence of external magnetic fields, it has become possible to use it for stress and torque measurements in the field.

[0014]

As is clear from the above, according to the present invention, the excitation core and the detection core, which are arranged orthogonally to each other, both have two parallel magnetic legs, and each of the magnetic legs has a coil. is a stress detector using a magnetic anisotropy sensor wound in a harmonic connection, comprising: a Hall element attached to the tip end surface of the detection core; a third winding wound around the detection core; , and an error amplifier that excites the third winding using the output signal of the Hall element as a feedback signal, thereby eliminating the need to use two sensors.
A simple configuration can eliminate the influence of external magnetic fields.

[Brief explanation of the drawing]

FIG. 1 is a schematic perspective view showing an embodiment of a stress detector according to the present invention.

FIG. 2 is a schematic perspective view showing an example of a conventional stress detector.

[Explanation of symbols]

2 Magnetic legs 2a, 2b Winding wire 3 Magnetic legs 3a, 3b, 3c, 3d Winding 4 Object to be measured 5 Error amplifier 6 Hall element 7 Low pass filter 8 Subtractor

Claims (1)

[Claims] Claim 1: A magnetic anisotropic device in which an excitation core and a detection core arranged orthogonally to each other both have two parallel magnetic legs, and a coil is wound around each of the magnetic legs in a harmonic connection. A stress detector using a stress sensor, which uses a Hall element attached to the tip end surface of the detection core, a third winding wound around the detection core, and an output signal of the Hall element as a feedback signal. and an error amplifier that excites the third winding.