DE2229224A1 - Device for determining the resonance frequency of magnetostrictive material - Google Patents

Description

The invention relates to a device for determining the resonance frequency magnetostriction material in which a Test specimen length of the material is pre-magnetizable and magneto « ßtrikti-vc vibrations of the test object an electrical signal in a transducer encompassing one end of the test object length - Generate coil as well as an excitation coil da.s the other end of the test specimen length includes, with the coils an amplifier connected to the electrical signal from the pickup coil amplifies and gives the amplified signal to the excitation coil and a device that measures the oscillation frequency is provided.

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With the help of such a device, the resonance frequency of a test piece made of carbon steel can be determined, the test piece being an integral part of a magnetostrictive Oscillator forms during the test.

The possibility of the drawability, of carbon steel-Blechon and determining the tendency of these sheets to form ears or spikes during deformation is greatly facilitated the selection of carbon steel sheets for their respective later use. These properties can be determined from the permanent dimensional change ratio of the sheet, however This requires carefully carried out voltage tests on carefully prepared test objects to identify the small differences in the elongation properties to determine the corresponding differences in drawability and tendency to form tips or ears.

However, since the permanent change in size ratio is related to the modulus of elasticity, this can also be used as a mitigation value for the drawability and the tendency to form lobes. Although the differences in the modulus of elasticity between sheet metal are small and the corresponding modulus values must be determined with great accuracy, the use of the modulus of elasticity to determine the drawability of sheet metal is more suitable for quality tests for the control of rolling mills than the measurement of the permanent dimensional change ratio. Highly accurate measurements of the modulus of elasticity can be obtained in a short period of time for test specimens produced in a simple manner by using the resonance frequency technique. So far, however

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accurate values of the modulus of elasticity mainly Scientific studies of the properties of solid substances are needed, so that, accordingly, resonance frequency devices are useful scientific apparatus for a variety of applications.

The dependence of the resonance frequency on the modulus of elasticity has been known for many years and many methods have been given for measuring the resonance frequency. This procedure has in common that, firstly, a test object is synchronized with an adjustable frequency driver source in mechanical vibrations secondly, the frequency of the driver source is changed until the amplitude of the test object oscillation occurs Maximum reached, which can be displayed on an oscilloscope, for example, to which the output signal of a device under test coupled vibration transducer, and thirdly, the frequency at which the maximum vibration amplitude occurs, i.e. the resonance frequency, is determined by an exact counter. There were both mechanical and electromagnetic Couplings for connecting the driver source and the vibration pickup used with the test item. However, this conventional technique uses devices that are high quality and expensive, whereby even commercially available resonance frequency devices have considerable expertise in the arrangement of the test object Operation of the control organs and those to be carried out with the eye Require choice of the amplitude maximum. Obviously, such techniques are only a little popular in the Rolling mills, especially if this process is also sensitive to ground vibrations.

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The object of the invention is to create a new device of the type mentioned at the outset, with which the resonance frequency of a test object can be measured with miniiual ^ m specialist knowledge of an operator. is to be determined, whereby the facility should be red and requires only minimal maintenance. In addition, this device is intended to automatically prevent the oscillation signaling c; on and overheating of the test object «

In a device of the type mentioned, this object is achieved according to the invention in that between the amplifier and a band limiting circuit to the pickup coil and a line limiter between the amplifier and the excitation coil are switched.

'- ^:: -''In the inventive device, the output signal of a comprehensive the DUT pickup coil having a band limiting circuit So is connected, in turn, Blindfolded with a preamplifier i, which has a tuning capacitor which consists of cooking. ■ - · The preamplifier is fed to an excitation coil encompassing the DUT via an amplifier and a limiter The test object will then usually vibrate at its resonance frequency, which is indicated by the limiter, while a precise counter indicates the frequency be to the

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Reverse bias.

The invention is illustrated by means of one in the drawing Embodiments explained in more detail;

In the drawing, a test piece 5 is shown a «low carbon steel sheet metal, in which the longibudinalo fundamental wave of the mechanical resonance frequency is to be determined. The test item 5 is shown arranged in a measuring module 2. The arrangement 2 has an excitation coil 4 that encompasses the test object, a premagnetization field coil 6 that encompasses the test object, and a pick-up coil 8 that also encompasses the test object. The excitation coil 4 consists of 130 turns of a 24-wire copper wire, which is inserted into
three layers tightly over a winding egg shape, not shown here
is waved, which is 6 _V 4 mm high, 11.2 mm wide and 24 mm long and an impedance of about 18 ohms at 25 KHz. having. The pick-up coil 8 consists of approximately 1800 turns of a 34 mm copper wire, which is tightly wound in approximately 14 layers over a coil shape (not shown here) that is 6.4 mm high,
11.2 mm wide and 24 mm long and has an impedance of approximately 5.5 KOhm at 25 KHz. The bias field coil 6 'consists of 237 turns of a 30 copper wire tightly wound in three layers over a coil shape not shown here that is 4.7 mm high, 11.2 mm wide and 22.3 mm long. The coils 4, 6 and 8 are aligned with each other with Abs tape so that, when the test specimen is arranged with the desired dimensions within the coils, the hitbe of the test specimen rests on the coil frame of the coil 6, one end of the test specimen

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eich extends to near the outer end of the coil 8, the the other end of the test item extends over the outer end of the coil 4 outstretched b and the test-inr-; the coil ahne η of the coils. 4 and 8 are not affected. Ferromagnetic shield caps 10 surround the coils, with openings 12 for receiving; the test item are provided »The pick-up coil δ eats with a band.begreii7, ungs circuit 1''I- connected via a shielded © line 16.

The band limiting circuit 1'I- has three resistors 18, 20 and 22 in series with an output coupling capacitor are connected to the pickup coil 8 with a preamplifier circuit 34 connects. A first capacitor 24 and a first inductor 28 are in parallel between the connection point of resistors 18 and 20 and earth connected. A second capacitor 26 and a second inductor 30 are also in parallel between the junction of resistors 20 and 22 and ground switched. The components of the band limit circuit can be printed in a conventional manner on a not shown here Formwork panel be attached, this being powered by an electrical

see and ferromagnetic shield 36 is included. In the preferred embodiment of the invention, the components of the band limiting circuit are as follows chosen:

18th - 220 above 24 - 0 , 0068 mf 28 - mh 20th - 390 Χλ 26th - 0 , 004 mf 30 - mh 22nd - 100 Ω. 32 - 2 mf - 10 - 10

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A feed circuit, designated as a whole by 58 ", comprises a Power supply unit W, which has a switch 5? -? a fuse 44 with a Speisespaimungsanücliluß of 110 Y and 60 Hsvex-bundon i.'jt and to which an indicator lamp 46 is connected in parallel: “That Spoisegerilt 40 can be a model T-270-28-1.5R modulator Povjcr Unit manufactured by the Modular Power Incorporate ^ 15302 Oak Canyon Road, Poway, California with en 92 064, be the one DC voltage output 48 of minus 28 Y, an equalization output 50 of plus 28 Y and a ground output 52. That Power supply 40 is via a shielded .Leitung 5 ^ with the Preamplifier circuit 34 connected. The preamp circuit 34 can be a modified, broadband 'ionfreguens' amplifier circuit in Bulletin DS 909 3R1, Harz 1969, and the model MC 13O3L one from Motorola Semiconductors, Phoenix, Arizona. The one described in Bulletin DS 9093R1 Circuit was made by removing a 1.0 mf coupling capacitor0 and by replacing one 100E - & - resistor with two in series switched 47KU resistors 56 and 58 modified. Additionally the connection between resistors 56 and 58 was over a 910XL resistor 60 and one between 75 pf to 750 pf adjustable capacitor 62 connected to ground. One consisting of a 5 mf capacitor 64 and a 1KXL resistor 66 The filter is connected via the input of the amplifier circuit 34-.

The output 48 is with a four pole H, three position Double changeover switch 68 connected via resistors 70 and 72, as he as a switch ITr. 25312 from Switchcraft, Inc. , will be produced. The output 50 is also with the switch

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tied together". The resistor 70 causes a suitable voltage for indicator lamp 74. Resistor 72 gives a suitable one Voltage on connection 76 between switch 68 and the Bias field coil 6. Switch 68 also has a shielded feed line 78 leading to an amplifier circuit 80.

The output of the preamplifier circuit 34 is connected to the input the amplifier circuit 80 is connected. The amplifier circuit 80 may be a power amplifier designed for a grounded Consumer and an input switched according to the bootstrap principle is modified and in Bulletin 85.29 »February 1969, which specifies the model PA 246 of a 5 watt integrated power amplifier manufactured by Semiconductor Products Department, General Electric Corporation, Electronics Park, Syracuse, New York. The one in the bulletin 8 ^ .29 has been modified by changing the Input coupling capacitor 82 to 0.15 mf and the output coupling ! capacitor s 84 modified to 35 mf. The exit of the Amplifier 80 is via a shielded line 86 via a variable resistance lamp 88, which is preferably is a lamp no: 1446, with the excitation coil 4 tied together. The preamplifier circuit 34 and the amplifier circuit 80 can conventionally not be based on one here be attached to the printed circuit shown. A frequency counter 90, such as the Faratron Corporation Model 410-4P, 290 Lodi Street, Hackensack, New Jersey, is also with the Output of amplifier 80 connected.

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The modulus of elasticity can be determined according to the following formula will:

E a 4pL ² f ² .. (1) ■■ -.-

where E = modulus of elasticity, ρ = mass density of the test object, -L = Length of the test item and f = resonance frequency for one over the length

of the test object are longitudinal waves.

This expression can be shortened to:

E = f £ _ (2)

where E = modulus of elasticity in 0.07 ^ 2 and f ~ resonance frequency in Hz for a longitudinal wave running over the length of the test object.

These details relate to a test piece 10.4650 cm in length with a density of 7 »9 g / cm, the typical density of a Low carbon steel sheet. The standardized A test piece length of 10.4-630 cm is chosen to simplify the calculation of the modulus of elasticity after determining the frequency. At this length, the resonance frequency of the longitudinal fundamental wave is about 25,000 Hz.

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The test specimen is preferably made from the sheet to be tested made using a conventional die punch. A test object width of up to 6.4 mm can be used well within, the 1.6 mm thick insulated coil forms, which are dimensioned and arranged to easily accommodate sheet metal thicknesses to be able to accommodate up to about 1.8 mm. While the width and thickness can be changed as long as the specimen is still good fits into the insulated coil shapes, the length should be like this should be as close to 10.4630 cm as possible so that simplified formula (2) can be used. A simple nomogram becomes then used to convert the frequency into the modulus of elasticity.

To switch on the oscillator, the switch 42 is closed in order to switch on the power supply unit. This in turn feeds the preamplifier 34. Then a standard test specimen is introduced into the coils 4, 6 and 8 and, as shown in the drawing, shifted slightly so that the end of the test specimen is the shield or a suitable stop of the pick-up coil not touched. In this position the test object rests on the bobbin of the coil ^: 6, but does not touch the bobbins of coils 4 and 8 and protrudes about 3 »2. mm from a protective plate beyond the shield 10. The switch 68 is then closed either in its upper or lower position and the capacitor 62 adjusted until the frequency counter 90 indicates the desired frequency, let the oscillator be tuned to the use of a standard test item or a group of test items, so none further coordination or adjustment required. The behavior of the selected components and circuits is such that no drift occurs and the components have wide tolerance ranges.

Resistor 70 creates a bias voltage of about 1 to 0.5 volts on the coil 6. This causes a sufficient premagnetization so that the magnetic field in the test object 5 does not reverse can when the test object vibrates. The bias does not need to be changed.

If the oscillator is tuned, an unknown device under test can 'in are inserted into the coils in the same way as a standard specimen. If switch 68 is closed, observe the operator the lamp 88. If the lamp lights up with its typical, full brightness, this indicates that the The test object oscillates at the resonance frequency of the longitudinal fundamental wave. If the lamp lights up, but only weakly, there is this indicates that the test item is not oscillating at the desired frequency. If the lamp does not light up, this indicates that the device under test does not vibrate at all and the device under test should be bumped or moved slightly with the switch 68 turned on remains .. If the lamp still does not light up at full brightness, the switch should be switched to its other position, which in a simple manner the bias at the coil 6 reverses. As a result, any residual magnetization be eliminated in the test item. If the lamp still does not light up with the correct brightness, then the DUT removed and grounded with its other end into the coils to be introduced. Should neither this nor a toast or Moving the test object to cause the desired oscillation, the test object should be eliminated.

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The band limiting circuit 14 strongly attenuates both the second harmonic and semi-harmonic and also effects a phase rotation sufficient to prevent the test specimen from being de-excited. The band limiting circuit is shielded in order to prevent electrical stray signals or magnetic stray flux from influencing the components of the band limiting circuit. In addition to its display of the oscillation of the test object at the resonance frequency of the longitudinal fundamental wave, the lamp 88 also acts as a power limiter and promotes the oscillation. The low resistance of the lamp, as long as it is not heated to incandescent heat, allows instabilities to easily reach the excitation coil, whereby an oscillation is initiated. If an oscillation is initiated, the excitation power increases until the lamp reaches incandescent heat, as a result of which the resistance of the lamp has risen so far and limits the power given to the excitation coil. This prevents overexcitation of the test object and the resultant heating of the test object, which would lead to incorrect resonance frequencies.

Capacitor 64 and resistor 66 are in the preamplifier circuit 34 additionally provided to the band limiting circuit to improve. The capacitor 62 and the resistor 60 increase the gain of the preamplifier circuit 34 from about 100 to about 200. The coupling capacitor 82 is selected so that it is matched to the impedance of the amplifiers 34 and 80 is, and the coupling capacitor 84 is chosen so as to respond to the amplifier 80 at undesirably low frequencies to eliminate.

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The counter 90 is a conventional electronic frequency counter and may be appropriately set to have a. Indicates counting every second or every 0.1 second. Usually the third reading of the counter is already a fixed value after the start of oscillation.

The supply device 40 can be any desired supply device generating the required voltages. As the feeder 40 contains a power transmitter and although this transmitter is shielded, -so-it should be at least about 15 cm away from coils 4, 6 and 8 of the operational oscillator be arranged.

Through the careful use of standard components and impedance matching between the components of the oscillator a very robust and accurate oscillator for determining the resonance frequency is obtained, with simple operations such as the arrangement of the test object in a slot of suitable depth, the adjustment of a spring-loaded switch, the observation a lamp and then reading five digits on a display tube.

- patent claims -

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Claims (8)

~ 14 - Claims f1. / Device for determining the resonance frequency magnetostrictive Material in which a test piece length of the material can be pre-magnetized and magnetootrictive vibrations of the Device under test an electrical signal in one end of the device under test length Generate comprehensive transducer coil and an excitation coil covers the other end of the test piece length, wherein an amplifier is connected to the coils, which amplifies the electrical signal of the pick-up coil and the amplified signal to the excitation coil gives, and a die Sctwing frequency measuring device is provided, thereby characterized in that between the amplifier and the pick-up reel a band limiting circuit and between the amplifier and the excitation coil a power limiter are switched. 2. Device according to claim 1, characterized in that the * power limiter one, incandescent lamp is that the lamp has a small resistance before the start of oscillation and when oscillations are low, so that circuit instabilities are easily transferred from the amplifier to the Excitation coil can arrive, and a growing resistance when the vibrations increase the magnitude of the amplified electrical signal around the lamp wire heat up to incandescent so that the power given to the excitation coil can be limited and the vibrations caused by the white glow can be displayed. 209853/0801 3. Device according to claim 1 or 2, characterized that the booster has an udder connected to the band limiting circuit, with which the size of unwanted frequencies in the electrical signal can be attenuated, and that a preamplifier with the filter and connected to the amplifier which is connected to the preamplifier and the power limit limiter. In that a feedback path is 4. The device according to claim 5, characterized in that in the preamplifier provided which aiifweist a ^v resistor and a variable capacitor, whereby the gain of the preamplifier is increased and a change of the capacitor to the phase angle of the amplified electrical signal for frequency tuning at a Test specimen of a desired, predetermined length and desired, predetermined density changes. - - ■ 5. Device according to at least one of claims 1 to 4-, characterized in that the electrical signal in addition to the fundamental wave of the longitudinal <wave of the resonance frequency has other components that the band-limiting circuit attenuates the size and the Phase angle changes of each component of the electrical signal that has a lower frequency than a first frequency and has a higher frequency than a second frequency, so that the first and second frequencies delimit a frequency band, which contains the fundamental wave of the resonance frequency of a device under test of predetermined length and density, and that the band-limiting circuit is electrically and ferromagnetically shielded from external influences. 209853/0801 6. Device according to claim 5, characterized that a bias field coil "Provision is made for the device under test to be connected to a direct current source with the preamplifier is connected that the amplifier and the direct current source from the field coil, the pickup coil and the excitation coil is arranged remotely and that a switch is connected between the direct current source and the field coil, so that the current flow through the field coil is reversible. 7 device according to claim 6, characterized z e i c h η et that the field coil in the test object is a magnetic one Field generated that is sufficient to prevent a reversal of the magnetic field in the test object when the bias field with the generated by the limited, amplified electrical signal that passes through the excitation coil Field is summarized, and that the DUT on a single Vibration node is supported. 8. Device according to claim 7, characterized in that the test piece is a carbon steel sheet is about 10 cm (4 inches) in length and that the frequency band lies approximately between 24 · EHz and 27 KHz. 209853/0801