JPS592524Y2 - Automatic distance sensitivity correction device for electromagnetic induction flaw detection - Google Patents

Description

[Detailed description of the invention] The present invention relates to a detection device that detects various flaws existing on the outer surface of metal materials using electromagnetic induction flaw detection. The present invention relates to an automatic distance sensitivity correction device that automatically corrects the variation in detection output caused by the change in detection output.

There is an electromagnetic induction flaw detection device as a device for detecting various kinds of flaws scattered on the outer surface of a metal material, directly below the outer surface, or even on the inner surface of a tubular object.

This device is equipped with one or more magnetically sensitive detectors for non-destructive testing, installed parallel to and close to the surface of a test object such as a steel pipe. The test object is inspected by exciting the magnetic field and detecting changes in the magnetic field, that is, eddy currents that occur in the flawed area.

In this device, in order to increase detection accuracy or improve reproducibility, it is necessary to keep the distance between the detection surface of the detector and the subject strictly constant.

However, the surface of the test object usually has minute irregularities, and when the surface of a tubular test object such as a steel pipe is inspected while rotating, the test object's bending, vibration, and rotational axis may occur. It is difficult to maintain a constant distance between the detection surface and the surface of the subject due to separation from above (eccentricity) and the like.

For this reason, it has been considered to automatically correct the variation in detection spread caused by this interval variation to ensure detection accuracy.

For example, Japanese Patent Application Laid-Open No. 48-56488 discloses that the device described in this publication detects the interval variation as a change in the excitation current of the flaw detector, and uses the detected value to adjust the amplification factor of the defect signal amplifier to compensate for defect detection sensitivity. is being carried out.

However, with this method, it is difficult to accurately correct the nonlinearity of detection sensitivity change with respect to interval variation.

The sensitivity characteristics of a flaw detection detector are non-linear as shown in Figure 1a.

In general, when the probe coil of a flaw detection detector and the object to be inspected are at a close distance, there is a relationship between the detection output and the distance as a cube, and when the probe coil is a little further away, there is a relationship as a square.

Therefore, it is not possible to simply correct the sensitivity of the flaw detection detector using the detection output proportional to the distance from the displacement measurement detector as shown in Figure 1.
A signal that is inversely functional to the curve in Figure a is required.

Linearizers are generally used to convert linear output to non-linear output.

A linearizer here refers to a device that produces an output that changes non-linearly when a certain signal voltage is input.It is mainly used in the process industry, and is generally used for semiconductor diodes, transistors, etc. Many of them focus on the nonlinearity of input/output characteristics, and a typical example is an operational amplifier that can perform logarithmic compression and width expansion.

In the case of flaw detection detectors, the relationship between the detector output and the distance shown in FIG. 1a varies depending on the individual detector and is not constant.

This is because the distribution shape and degree of magnetic field lines, that is, the degree of intensity attenuation, is affected by the structure, shape, and dimensions of the probe coil of the detector, and the relative relationship with respect to changes in the distance between the sensing surface of the detector and the surface of the object to be examined. This is because the sensitivity characteristics vary depending on the method and structure of the detector.

In addition, there is a recent demand for accurate detection of even smaller and shallower flaws, so the linearizer used in electromagnetic induction flaw detection equipment cannot directly utilize the non-linear characteristics of the input/output characteristics of transistors, etc. mentioned above. Not enough,
Can be adapted to the detection characteristics of individual detectors.

Moreover, a linearizer that is easy to adjust is required.

Figure 2 shows the non-linear characteristics necessary to compensate for the output characteristics of the flaw detection detector shown in Figure 1a.However, in order to give the linearizer the characteristics of the flaw detection shown in Figure 1a, conventionally it was necessary to (maximum value and minimum value), and this adjustment is 2
Repeatedly operate the two regulators several times,
Since it had a predetermined curved shape, it had the disadvantage of being very time-consuming.

The present invention has been made to eliminate these drawbacks of the prior art, and aims to provide an automatic distance sensitivity correction device whose characteristics can be easily adjusted and changed.

The present invention will be described in detail below along with examples. FIG. 3 is an explanatory diagram of the apparatus of the present invention, in which a group of detectors is opposed to the surface of the metal object 1.

This detector group consists of flaw detection detectors (probe coils) 2□~
2n and a variation measurement detector 3, the rain detectors 2 and 3 have a fixed positional relationship, and form a mechanically movable structural unit by an auxiliary mechanism (not shown), and this movable structure The unit performs tracking tracing on the object 1, detects flaws on the object 1 by relative movement of the object 1 and the flaw detection detector 2 and the displacement measurement detector 3, and performs a flaw detection test.

In this case, the cross-sectional shape of the outer surface of the subject 1 may be round, hexagonal, square, or other shape.

Although a single flaw detection detector 2 may be used, in order to detect small and shallow flaws, the probe coil of the detector should be made small in proportion to the size of the flaw to be detected, and multiple detectors should be arranged. It is desirable to increase the resolution and quickly scan the entire surface of the object 1 for flaw detection.

Each of the flaw detection detectors 2 and 2n outputs an output according to the distance variation as shown in FIG.

The outputs of the flaw detection signal amplifiers 4 are individually input to analog multipliers 5 provided as many as the number of detectors.

On the other hand, the displacement measuring detector 3 is composed of, for example, an electromagnetic induction type probe coil, and its output does not pass through the origin O of the graph due to the presence of an offset, as shown in FIG.

A detection output corresponding to the distance d from the subject 1 obtained by the displacement measuring detector 3 is applied to the signal conditioner 6.

The signal conditioner 6 is composed of, for example, an oscillator, an amplifier, and a rectifier, and can thereby obtain a DC voltage output proportional to the distance d.

This DC voltage output is then input to a linearizer 7 which corrects the proportional relationship to the distance d.

As mentioned above, the linearizer device is a device that linearizes a non-straight line, and in the present invention, the inclination adjuster 8, the offset adjuster 9, the polygonal line approximation circuit network 10, and the polygonal line approximation value setting regulators 111 to 11. Consists of.

The slope adjuster 8 changes the amplitude of the signal obtained from the signal conditioner 6 by adjusting the gain of the amplifier.
This allows the proportionality coefficient between the input signal and the output signal to be changed.

This means that an output signal whose slope is arbitrarily changed with respect to the input signal can be obtained.

Therefore, this slope adjuster adjusts the input slope as a linearizer, but when using a voltage amplifier,
It has the role of an amplification gain adjuster for this amplifier.

The inclination adjuster 8 is provided with an offset adjuster 9, a specific example of which is shown in FIG. 4a.

In this figure, amplifier AMP, resistors R1 and R2 are slope adjusters 8
The portion of the variable resistor VR1 and the resistor R3 is the offset adjuster 9.

The amplifier AMP consists of a differential amplifier, as shown in FIG.

As is clear from FIG. 4a, if the slider A of the variable resistor VR is moved, the bias voltage added to or subtracted from the input voltage Vi changes.

The output voltage characteristic curve is shifted in the input voltage axis direction, and the slope of the characteristic curve is changed by changing the feedback resistor R2.

In this offset adjuster, the distance d between the subject 1 and the detectors 2 and 3 is a reference distance when using the device.

, that is, when the reference gap is present, the input signal is adjusted to the reference DC voltage level.

That is, the offset adjuster 9 is located at a distance d approximately at the offshore point of the range of variation of the distance d.

The input signal from the displacement measuring detector 3 is set at approximately the center position within the usable range of the nonlinear curve obtained by the linearizer.

These two circuits 8 and 9 as a whole serve as a signal initial adjustment circuit, and their operation will be explained with reference to FIGS. 5 and 8.

FIG. 8 is a graph showing the final characteristics of the linearizer 7, in which the horizontal axis shows the distance d, and the vertical axis shows the output with respect to this distance change.

In the figure, point A on the curve indicates approximately the center position of the curved portion to be used, and the reference gap d is located at this point A.

Reference output voltage e.

correspond, and the slope of the curve is arbitrarily adjusted.

To do this, first operate the slope adjuster 8 to adjust the slope of the curve to an appropriate value.

In FIG. 5, straight lines B, B', and B'' show examples in which the slope has been converted.

Assuming that the inclination is adjusted as shown in, for example, a straight line B, then the offset adjuster 9 moves this in the horizontal axis direction as shown in straight lines c and c'.

And when point A is located on a straight line like straight line C',
Adjustment ends.

After the initial adjustment has been made in this way, the signal obtained as a result of distance measurement is transmitted to a polygonal line approximation network 10 having m systems.
is input.

The polygonal line approximation circuit network 10 has m polygonal line approximation value setting regulators 11 arranged, and by adjusting the bias voltages of the clamp diodes of these regulators individually using semi-fixed regulators, the curve shown in FIG. A curve approximated to can be obtained.

FIG. 6 shows details of the broken line approximation network 10.

As shown in this figure, this circuit consists of six similarly configured circuit parts U1 to U6, one of which, Ul, is an amplifier A1.
□～A14. Resistance R5~R15, diode d1~d4
Consisting of

Of these, the amplifier A14 is an inverter, which inverts the voltage Vd2 corresponding to the 42 points in FIG. 7 to create -vd2, which is input to the input terminal of the amplifier A1□ via a resistor R6.

FIG. 7 is a diagram illustrating the output voltage characteristics of the broken line approximation network 10, and curves B...A...C correspond to the characteristic curves in FIG.

The amplifiers An and AI□ correspond to the amplifier AMP shown in Fig. 4, and the amplifier All receives the input voltage Vi and the previous voltage -V d 2 and outputs a voltage with the characteristic DBEF shown in Fig. 7. .

Since the output terminal of this amplifier A1□ includes a diode d2 that extracts only a negative voltage, the output voltage does not increase beyond point E.

Also, the amplifier A12 has a voltage ■d corresponding to the point d1 in FIG.
1 is input as the bias voltage, and therefore the lower limit of the output voltage is the voltage e1 corresponding to point B, which is the voltage e1 of the amplifier A.
When a voltage DBEF is input from the 1□ side, a voltage elBE is output.

Amplifier A13 is a kind of adder, and these amplifiers A10 . It receives the output voltage of A□2 and outputs a voltage with a characteristic of elBEF.

The same applies to the other circuit parts U2 to U6, except for the bias voltages Vd2 and Vd3. vd3. Vd4. ■d4t■d5.
Since Vd5 and Vd6 are different, each circuit part U2. U3
The output voltage characteristics of ...... are e2EGH9e3GAI
It will be like...

These output voltages are added together by the amplifier A 70, and finally the circuit 10 obtains an output voltage e having the characteristics of e 1BEGA...CJ.

The slope of each portion BE, EG... is determined by the variable resistor 11.
．． It can be changed by adjusting 11□...
Each point d,, d, . . . has a voltage vd1. vd2...
It can be set by...

In this example, point d. Since it is based on , each voltage ■d1
~■d6 is point d.

Positive mainly. It will take a negative value.

In this broken line approximation network, as described above, the point d1. d2...
Since curve approximation is performed by determining ... and changing the slope of each part, there is an advantage that the approximation operation is extremely easy to perform.

For adjustment, first, a flaw detection detector 2 and a displacement measurement detector 3 are installed on the test object 1, and a predetermined flaw is artificially made on the test object 1.

Next, the distance d between the detector and the subject is dl, d2...
..., the operating point of the device is successively changed, and the output voltage for each operating point is adjusted by the semi-fixed regulators 11□, 11□, etc. of the polygonal line approximation value setting regulator 11. Just adjust it to approximate the ideal curve.

In this way, the linearizer 7 as a whole can approximate the distance d vs. output voltage characteristic curve as shown in FIG. 9 obtained from the signal conditioner 6 to the distance vs. output voltage curve as shown in FIG. .

In this way, the output voltage of a predetermined shape corresponding to the distance d obtained from the linearizer is applied to the analog multiplier 5, and the detection signal voltage containing the flaw detection signals obtained by the flaw detection detectors 21 to 3o is Adjust the amplitude.

In this way, the output voltage of the analog multiplier 5 is a detected voltage corrected for the distance d, and has a substantially flat output characteristic within the operating range of the device, as shown in FIG.

Through this output signal processing amplifier 12, it functions as a general flaw detector.

As described above, in the present invention, the linearizer is equipped with a polygonal line approximation circuit network, and the output voltage at each operating point of the device can be adjusted as desired using the polygonal line approximation value setting regulator as explained in FIG. We also installed an initial adjustment circuit to adjust the inclination and offset amount.
The correction curve can be made into a desired shape more easily than in the past, and the characteristics of the flaw detection apparatus can also be easily changed by changing the detector and the object to be inspected.

In addition, the adjustment device can be easily handled and the reliability of the flaw detection device is improved, making it possible to provide this fruiting device at a low price, resulting in a cost-effective system.

[Brief explanation of the drawing]

Figures 1a and 1) are output characteristic diagrams of the detector, Figure 2 is a diagram showing a correction curve for a flaw detection detector, Figure 3 is a block diagram of an embodiment of the present invention, and Figures 4 and 5. 6 is a circuit diagram of the initial adjustment circuit, and FIG. 6 is a circuit diagram of the broken line approximation circuit network. FIGS. 7 and 8 are diagrams illustrating its operation. FIG. FIG. 10 shows an output characteristic diagram of an analog multiplier whose distance sensitivity has been corrected. In the figure, 1 is a specimen, 2 is a flaw detection detector, 3 is a displacement measurement detector, 4 is an amplifier for flaw detection signal, 5 is an analog multiplier, 6 is a signal conditioner, 7 is a linearizer, and 8 is a tilt 9 is an offset adjuster, 10 is a broken line approximation circuit network, 11 is a broken line approximation value setting regulator, d is a reference gap, c
o is the reference voltage.

Claims (1)

[Scope of utility model registration request] A displacement measurement detector that is placed in parallel with a flaw detection detector placed opposite to the surface of the specimen and that measures the distance to the surface of the specimen, and a distance detection output from the displacement measurement detector is inputted;
a signal conditioner that outputs a DC voltage proportional to the distance; an initial adjustment circuit that adjusts the slope and offset of the output voltage curve of the signal conditioner; a polygonal line approximation circuit network for modifying the output voltage curve of the initial adjustment circuit into a curve shape necessary to compensate for the change in detection output due to the distance change; and a polygonal line approximation circuit network for modifying the detection output of the flaw detection detector. An automatic distance sensitivity correction device for electromagnetic induction flaw detection, comprising: an analog multiplier that multiplies the outputs of the two to produce an output that corrects fluctuations in the detection output due to the distance fluctuations.