JPH0226172B2 - - Google Patents

Description

Detailed Description of the Invention The present invention utilizes the fact that when stress acts on a magnetic material, the core loss of the magnetic material changes in relation to the stress, and a magnetic sensor is brought into contact with the surface of the magnetic material. The present invention relates to a stress measuring device that is placed in a magnetic material and measures stress in a magnetic material.

For magnetic materials such as steel used in assembled structures, there is generally a relationship between stress and iron loss acting on the magnetic material, or between stress and iron loss change rate, as shown in Figure 1 or Figure 2. . That is, FIG. 1 shows the relationship between the stress acting on the magnetic material and iron loss, and FIG. 2 shows the relationship between the stress acting on the magnetic material and the rate of change in iron loss. Here, the rate of change in iron loss is defined as (Wi−
It is expressed as Wo)/Wo×100 (%).
Therefore, by measuring the iron loss of the magnetic material from FIG. 1 or 2, the stress acting on the magnetic material can be determined.

As is clear from both figures, there is a nearly linear relationship between compressive stress and iron loss or rate of change in iron loss, so when calculating tensile stress, it is necessary to calculate the A more accurate stress can be obtained by measuring the iron loss in the direction in which the iron is located, first obtaining the compressive stress, and then converting it to tensile stress based on the relationship of the Boisson ratio.

Normally, to measure stress, as shown in FIG. 4, which is an enlarged cross-section of A-A in FIG. A magnetic sensor 2 configured by winding a secondary voltage coil 4 (a magnetic element such as a Hall element may be used in place of the secondary coil 4 of the magnetic sensor 2, but the following explanation is based on the case where the secondary coil 4 is used) As shown in FIG. The magnetic sensor 2 is placed in close contact with the surface of the magnetic material 1 so that the center line is aligned with the direction of the stress whose center line is to be measured. Figure 5 shows that, as mentioned above, the magnetic sensor 2 is placed in close contact with the magnetic material 1, the iron loss is measured, the iron loss change rate is determined from the measured iron loss, and the stress FIG. 2 is a block diagram of a conventional stress measuring device for determining the stress acting on the magnetic material 1 in terms of conversion.
This conventional stress measuring device for magnetic materials using iron loss includes an iron loss measuring device 19, an A/D converter 12, an iron loss indicator 13, an initial value setting device 14, a calculator 15,
It is composed of a stress indicator 16 and an indicator 17, and the iron loss measuring device 19 includes an AC power source 6, a magnetic sensor 2, a first amplifier 7, a second amplifier 8, an ammeter 11,
It is composed of an output secondary voltage setting device 9 and a first operational amplifier 10. That is, the primary coil 3 of the magnetic sensor 2 is connected to the current terminal of the wattmeter 11 via the AC power source 6 and the first amplifier 7, and the secondary coil 4
is connected to a first operational amplifier 10 via a rectifier (not shown) and to a voltage terminal of a power meter 11 via a second amplifier 8. The output secondary voltage setter 9 is connected to the first operational amplifier 10. The output side of the first operational amplifier 10 is connected to the AC power supply 6. The wattmeter 11 is connected to an A/D converter 12 , and the output side of the A/D converter 12 is connected to an iron loss indicator 13 and a calculator 15 . It is obvious that if the data is not converted into digital data, the wattmeter 11 may be connected directly to the arithmetic unit 15 instead of the A/D converter 12. This computing unit 1
5 is also connected to an initial value setter 14 and a stress indicator 16. The indicator 17 is connected to the output sides of the first amplifier 7 and the second amplifier 8 via a switch 18.

Now, when the primary coil 3 of the magnetic sensor 2 of the iron loss measuring device 19 is excited by the AC power supply 6, the magnetic core 5
As shown in Fig. 4, the magnetic flux from flows in the magnetic material 1 parallel to the direction of stress as shown by the arrow,
A closed magnetic path returning to the magnetic core 5 is formed again. At this time, the output secondary voltage induced in the secondary coil 4 of the magnetic sensor 2 is compared and subtracted from the voltage set in the output secondary voltage setting device 9 in the first operational amplifier 10, and the subtraction result is Feedback was given to 6.
The excitation current of the primary coil 3 is controlled so that the output secondary voltage is always a constant voltage, that is, equal to the set voltage of the output secondary voltage setting device 9. This output secondary voltage and the exciting current of the primary coil 3 are introduced into the voltage terminal and current terminal of the wattmeter 11 via the first amplifier 7 and the second amplifier 8, respectively, and are multiplied by the instantaneous values of these voltages and currents. The wattmeter 11 calculates the average value of the values.
Since it is displayed as iron loss, the iron loss of the magnetic material 1 can be measured correctly. The thus measured iron loss is converted into a numerically displayed iron loss Wi by the A/D converter 12, and is indicated to the iron loss indicator 13 and sent to the calculator 15. The calculator 15 calculates the iron loss W ₀ when no stress is applied to the magnetic material 1 sent from the initial value setting device 14 and the iron loss Wi when the stress is applied, as described above. Calculate the iron loss change rate from the iron loss change rate formula, convert the iron loss change rate to stress using the relationship shown in Figure 2,
The stress is indicated to the stress indicator 16. The value of iron loss W ₀ set in the initial value setting device 14 is based on the magnetic material 1.
Iron loss indicator 13 measures the iron loss when no stress is applied to
You can read it more. The indicator 17 also switches the switch 18 to the excitation current side 25 or the output secondary voltage side 26.
By switching to , the excitation current of the primary coil 3 of the magnetic sensor 2 or the output secondary voltage of the secondary coil 4 is indicated, so if necessary, the setting voltage of the output secondary voltage setting device 9 can be checked. can be used.

Since the conventional stress measuring device has the above configuration, the magnetic sensor 2 is placed on the surface of the magnetic material 1.
If they are arranged in close contact with each other so that the If the induced output secondary voltage is made equal to the set voltage of the output secondary voltage setting device 9 and kept constant, the magnetic flux flowing through the magnetic material 1 is kept constant, so as described above, By measuring the core loss of the magnetic material 1, the stress acting on the magnetic material 1 can be accurately determined. However, if the surface of the magnetic material 1 is uneven and the area in contact with the magnetic sensor 2 placed on the surface becomes large, the magnetic resistance increases in proportion to the size of the area. A large magnetomotive force is required, and a large excitation current flows through the primary coil 3 of the magnetic sensor 2, which may burn out the excitation circuit and primary coil of the magnetic sensor 2. In addition, when measuring the stress of a large number of magnetic materials continuously, you can finish the stress measurement of one magnetic material without turning off the power switch.
To move the magnetic sensor to the next magnetic material,
When the closed magnetic circuit formed by the magnetic sensor and the magnetic material is opened, an excessive excitation current flows through the primary coil of the magnetic sensor, resulting in burnout of the primary coil and excitation circuit of the magnetic sensor.

In view of the above points, when a magnetic sensor is placed in contact with the surface of a magnetic material in order to measure the stress of the magnetic material, even if an air gap occurs in the contact area between the magnetic sensor and the magnetic material, A limiting device that limits the excitation current of the primary coil so that an excessive excitation current that could burn out the primary coil or excitation circuit of the magnetic sensor does not flow even if the closed magnetic path formed by the magnetic sensor and magnetic material is opened. a stress measuring device equipped with a
The present invention provides a stress measuring device which is equipped with an alarm and issues an alarm when the excitation current of the primary coil exceeds a limit current value.

An embodiment of the stress measuring device of the present invention will be described below with reference to the drawings.

FIG. 6 is a block diagram of the conventional stress measuring device for magnetic materials using iron loss shown in FIG.
The other configuration is the same as that shown in FIG. 5. The iron loss measuring device 24 includes a limiting current setting device 21 and a second operational amplifier 2 in addition to the iron loss measuring device 19 shown in FIG.
An excitation current limiter 23 consisting of 0 is added. That is, the output side of the first operational amplifier 10 is connected to the second operational amplifier 20 via the limiting current setting device 21.
The second operational amplifier 20 is connected to the primary coil 3. The output side of the second operational amplifier 20 is connected to the AC power supply 6. Other than this, the connections are the same as in the circuit shown in FIG. Now, set the set voltage in the output secondary voltage setting device 9 and the maximum allowable current for the excitation circuit of the magnetic sensor 2 in the limiting current setting device 21, and as shown in FIG. A magnetic sensor 2 is placed on the surface of 1,
When the primary coil 3 of the magnetic sensor 2 is excited by the AC power supply 6, the exciting current of the primary coil 3 is introduced into the second operational amplifier 20 of the exciting current limiter 23,
It is compared and subtracted from the set current of the limit current setting device 21,
The calculation result is fed back to the AC power supply 6, and the excitation current of the primary coil 3 of the magnetic sensor 2 is controlled so as not to exceed the current set by the limit current setting device 21. Further, the output secondary voltage induced in the secondary coil 4 of the magnetic sensor 2 is transmitted through the first operational amplifier 10.
is introduced into the AC power source 6 and compared with and subtracted from the set voltage of the output secondary voltage setting device 9, and the calculation result is fed back to the AC power source 6 via the excitation current limiter 23.
The output secondary voltage of the secondary coil 4 of the magnetic sensor 2 is made equal to the set voltage and held constant. The excitation current and output secondary voltage of the magnetic sensor 2 are introduced into a wattmeter 11 via a first amplifier 7 and a second amplifier 8, respectively, to display the iron loss of the magnetic material 1. Thereafter, the process of determining the stress acting on the magnetic material 1 from this iron loss is the same as that described in the conventional example shown in FIG.

FIG. 7 is a block diagram of the stress measuring device shown in FIG. 6, except that an iron loss measuring device 27 is provided in place of the iron loss measuring device 24, and the first operational amplifier 10 and the excitation current limiter 23 are provided. limit current setting device 21
The structure is the same as in FIG. 6 except that an alarm device 22 is connected between the two.

Therefore, when measuring stress in a magnetic material, the magnetic sensor 2
The excitation current of the primary coil 3 is limited by the current setting device 21
When the set current is exceeded, the second operational amplifier 20 feeds back a signal to the AC power supply 6 to reduce the excitation current of the primary coil 3. Magnetic sensor 2
When the excitation current of the primary coil 3 decreases, the output secondary voltage of the secondary coil 4 decreases, and this decreased voltage is compared and subtracted from the set voltage of the output secondary voltage setting device 9 in the first operational amplifier 10. is outputted from the first operational amplifier 10 so as to increase the output secondary voltage by the difference. When the output voltage from the first operational amplifier 10 reaches a certain value, the alarm 22 is activated and issues an alarm with a buzzer or lamp to notify the measuring person that the excitation current of the magnetic sensor 2 has exceeded the limit value. Stop the measurement. In this way, the excitation current of the primary coil of the magnetic sensor 2 is always controlled to be the set current, so the excitation circuit and the primary coil of the magnetic sensor 2 will not be burnt out.

Furthermore, in FIGS. 6 and 7, if a current limiting device having a fold-back overcurrent protection characteristic is used instead of the output secondary voltage setting device 9 and the first operational amplifier 10, the short circuit current can be reduced. It can be made thermally advantageous.

As described above, by using the stress measuring device of the present invention shown in FIG. 6, the excitation current of the primary coil of the magnetic sensor is controlled so as not to exceed the limiting current value set in the limiting current setting device, Since the excitation current of the sensor is always controlled to be below the set limit current value, the excitation circuit and primary coil of the magnetic sensor will not be burnt out. Furthermore, if the stress measuring device according to another embodiment of the present invention shown in FIG. 7 is used, the sixth
Another advantage of the embodiment shown in the figure is that when the current limit value is exceeded, an alarm is issued by the alarm device, allowing the operator to stop the measurement.

[Brief explanation of drawings]

Figure 1 is a diagram showing the relationship between stress acting on magnetic material and iron loss, Figure 2 is a diagram showing the relationship between stress acting on magnetic material and iron loss change rate, and Figure 3 is a diagram showing the relationship between stress acting on magnetic material and iron loss change rate. The arranged plan view, Figure 4 is A in Figure 3.
- An enlarged cross-sectional view of A; FIG. 5 is a block diagram of a stress measuring device for magnetic materials using a conventional iron loss measuring device; FIG. 6 is a block diagram of a stress measuring device for magnetic materials that is an embodiment of the present invention. 7 are block diagrams of a stress measuring device for magnetic materials according to another embodiment of the present invention. DESCRIPTION OF SYMBOLS 1...Magnetic material, 2...Magnetic sensor, 3...Primary coil, 4...Secondary coil, 5...Magnetic core, 6...
...AC power supply, 7...First amplifier, 8...Second amplifier, 9...Output secondary voltage setter, 10...First operational amplifier, 11...Power meter, 20...Second operational amplifier, 21... Limit current setting device, 22... Alarm device, 23... Excitation current limiter, 24, 27... Iron loss measuring device.

Claims (1)

[Scope of Claims] 1. A magnetic sensor configured by winding a primary coil and a secondary coil around a magnetic core having a substantially U-shaped cross section, an AC power source that excites the primary coil of this magnetic sensor, and a primary coil of the magnetic sensor; A wattmeter that is connected to the secondary coil and displays the iron loss value, an output secondary voltage setting device that can set a predetermined output secondary voltage, and the setting voltage of this output secondary voltage setting device and the secondary coil of the magnetic sensor. a first operational amplifier that compares and subtracts the output secondary voltage of the magnetic sensor; a limit current setter that is connected to the first operational amplifier and sets the maximum allowable current of the primary coil of the magnetic sensor; and a setting of the limit current setter. a second operational amplifier that compares and subtracts the value from the excitation current of the primary coil of the magnetic sensor and feeds back the subtraction result to the AC power supply; when no stress is acting on the magnetic material; An initial value setting device for setting the iron loss value; enter the iron loss value from this initial value setting device and the iron loss value when stress is acting on the magnetic material from the wattmeter, and calculate the iron loss change rate. 1. A stress measuring device comprising: a computing unit that calculates stress based on the rate of change in iron loss; and a stress indicator that displays the output from the computing unit. 2. A magnetic sensor configured by winding a primary coil and a secondary coil around a magnetic core having a substantially U-shaped cross section, an AC power source that excites the primary coil of this magnetic sensor, and a magnetic sensor that is connected to the primary coil and secondary coil of the magnetic sensor. A wattmeter that displays the iron loss value, an output secondary voltage setting device that can set a predetermined output secondary voltage, and the setting voltage of this output secondary voltage setting device and the output secondary voltage of the secondary coil of the magnetic sensor. a first operational amplifier that compares and subtracts a value, a limit current setter that is connected to the first operational amplifier and sets the maximum allowable current of the primary coil of the magnetic sensor, and a limit current setter that sets the maximum allowable current of the primary coil of the magnetic sensor; an iron loss measuring device comprising a second operational amplifier that compares and subtracts the excitation current of the primary coil and feeds back the subtraction result to the AC power supply; and sets an iron loss value when no stress is acting on the magnetic material. Initial value setting device: Input the iron loss value from this initial value setting device and the iron loss value when stress is acting on the magnetic material from the wattmeter, calculate the iron loss change rate, and calculate the iron loss change rate. It is characterized by comprising: a computing unit that calculates stress from the rate of change in loss; a stress indicator that displays the output from the computing unit; and an alarm provided in a feedback circuit that connects the first operational amplifier and the AC power source. Stress measuring device.