HK1082795A - Sensor - Google Patents

Description

Sensor with a sensor element

Technical Field

The present invention relates to a method and an apparatus for sensing and displaying permanent state deviations (permanent state deviations) by detecting temporary internal material oscillations in certain vital parts in real time, for use in, for example, prototyping, hardware design and construction in existing production equipment within the industry, and/or monitoring to maintain previously constructed infrastructure.

Background

In recent years, developments in the field of microelectronics, in particular the development of increasingly powerful memories for computers, have made it possible for different types of transducers or sensors, such as accelerometers, bending/deformation indicators, acoustic emission indicators, etc., which are used to measure the magnitude of significance for the dimensioning of the products in the design, to be found on the market, which, in respect of the increasing demands of modern hardware designs, in particular in respect of modern software permits, have proven to be extremely complex in construction and thus extremely space-consuming and expensive to apply.

Disclosure of Invention

It is therefore a main object of the present invention to achieve a transducer element or sensor and a configuration thereof which is in principle very simple and thus very space-saving in construction, so as to be able to achieve previously unthinkable transducer or sensor configurations, while offering the opportunity to measure with higher sensitivity and accuracy over a wider range than has hitherto been possible, and also being able to measure amplitudes which have previously been barely detectable. Another object of the invention is to achieve a sensor arrangement whose inherent mass is so small that it does not affect the amplitude of the object to be measured it measures.

The above object is achieved by a method and a device consisting of one or more amorphous or nanocrystalline strip elements of at least about 20 μm thickness with high permeability and relatively high magnetostriction, which are incorporated in the relevant components, which strip elements are subjected to a magnetic field heat treatment in order to obtain the desired material structure, which strip elements are at least partly surrounded by a multi-turn coil, so that state deviations, such as any occurring particle movements, are transmitted to the strip element/elements, which either cause a clearly measurable and detectable magnetic flow change (dB/dt) in the coil, which is proportional to the particle movement, or a similar measurable and detectable inductance change in the coil/coils.

Drawings

The invention will be explained in more detail below with reference to the drawings. In the drawings:

fig. 1 shows an acoustic emission sensor photographed on a piece of millimeter paper.

FIG. 2 is a schematic diagram of a sensor for detecting acoustic emissions.

Fig. 3 shows the output signal as a function of load in positive and negative extension when measuring the change in inductance.

Fig. 4 shows the time signals from the sensors P1_1(a. top), P1_2(b. middle) and P1_3(c. bottom).

Fig. 5 shows the frequency spectrum of the output signals of P1_1, P1_2, and P1_3 (a. top, b. middle, and c. bottom, respectively) at the time of breaking glass.

FIG. 6 is a schematic diagram of one possible implementation of an amorphous material based accelerometer.

Figure 7 shows the principle of the connection of the accelerometer and the processing of the signals from it.

FIG. 8 shows the impulse response of an accelerometer, where the signal on the Y-axis is the output signal (in mV), and the X-axis is the time axis.

FIG. 9 shows the results of accelerometer measurements at 1.7 Hz.

FIG. 10 shows the results of measurements made at 3.0 Hz.

Fig. 11 shows the results of measurements made at 4.4 Hz.

Fig. 12 shows the results of measurements made at 10.94 Hz.

FIG. 13 shows the relative frequency response of a reference accelerometer and the type of accelerometer produced.

Fig. 14 is a schematic illustration of one possible implementation of an amorphous material based accelerometer or AE sensor (AE ═ acoustic emission).

Fig. 15 shows an output signal of the AE sensor in a transient state.

Detailed Description

Application as glass breakage sensor

Principle of function

The transducer or indicator is composed of an amorphous ferromagnetic material having the following properties: it may have a very high permeability, 5000 < mu < 200000, while it has a relatively high magnetoelasticity, 5 < lambda, for certain alloy compositions_satLess than 40 ppm. This gives the material a very high magnetic-elastic relationship as a whole and is therefore very suitable for use as a sensor material.

Tension in a material can be detected by using a strip of about 3 x 10mm which is cut from a sheet of amorphous material 22 μm thick and then bonded to either material. By cutting in different directions relative to the direction of rotation, different properties can be imparted to the amorphous material, in this case using the longitudinal and transverse directions of the direction of rotation.

The parameters of the material may also be modified by heat treating the material in a magnetic field at a temperature close to but below the crystallization temperature. In case of breaking glass and general acoustic emission, the magnetic flow variation is detected due to the winding of a multi-turn coil around the ribbon, see fig. 1 and 2.

Theory of the invention

For detecting high frequency signals, it is an advantageous and simple way to detect only the flow variation and assume that it is proportional to the magnitude of the deformation of the strip. This means that a magnetically well-defined initial state must be achieved, since the unmagnetized strip does not produce a change in flow when the tension changes.

In principle a geomagnetic condition of 30-60 μ T (20-40A/m) is sufficient in order to achieve the basic state of magnetization, but on the other hand it is not practical to monitor the direction and magnitude of the geomagnetic field when an indicator is to be mounted and calibrated.

There are two methods to obtain a satisfactory initial state:

a slight amount of magnetism surrounds and a direct current passes through the pick-up coil.

A trace of magnetism surrounds and is biased with a permanent magnet.

The field size should be such that the magnetization is 0,2-0,7T, which means that the magnitude of the magnetization in the strip should be of the order of 2-56A/m. The field size can generally be calculated according to the following formula

Where H is the magnetization field, B is the magnetic flux density, and the permeability μ of free space₀＝4π·10^-7Vs/Am, and in this case the relative permeability μ of the amorphous band.

The measurement signal is obtained by detecting the flow change in the strip due to tension/compression. For the linear case, the following connection equation should describe the function:

ΔB＝d·Δσ+μ₀·μ·ΔH

where σ describes the mechanical stress and d is the coefficient of the magnetic-elastic relationship. The prefix delta represents a change from the initial value. The material parameter d is approximated by dividing the maximum magnetoelasticity under constant mechanical stress (Δ σ ═ 0) by the magnetization field in the magnetically saturated state, i.e. the material parameter d is approximated

Due to the fact that

At λ_max＝35·10^-6And H_maxIn the case of 200A/m, the equation gives the relationship factor d as 1.75 × 10^-7m/a, which is a very high value for all types of magneto-elastic relations.

It is expected that the output signal is proportional to the flow variation and mechanical stress

Where N is the number of turns of the pick-up coil and a is the cross-sectional area of the amorphous strip. By assuming Δ H to be 0, the following equation applies:

wherein E^HIs the modulus of elasticity in a constant magnetization field. Transform to frequency plane and given using the equation above:

where ω is the angular frequency in lines/second. The circumflex notation represents the amplitude value. Assuming an elastic modulus of the order of 100GPa, the tensile force in the sensor at 100000kHz should be of the order of 0,0025ppm for the case of P1_2, see fig. 4 and the middle of fig. 5.

Measurement results

In the case of bonding the sensor to a piece of glass, initial experiments showed that vibrations in the frequency range of 40kHz-1MHz could be detected.

The following comparative tests were performed:

TABLE 1 description of the indicators

Sensor with a sensor element	Direction of belt	Number of turns	Remarks for note	Static stateNo-load magnetic permeability [ mH]
					P1_1	Transverse direction	280	Thick adhesive joint	158
P1_2	Transverse direction	280		60
					P1_3	Longitudinal direction	280	Thick plastic package	32

The test was conducted such that the corners of the glass sheet were broken and the output signal was recorded after amplification by a factor of about 100.

FIG. 3 shows the inductance change of the sensors P1_1, P1_2 and P1_3 under different pulling forces. It is apparent here that P1_1 and P1_2 with transversely cut tapes have the highest magnetic-elastic relationship. These two samples also show a rather high permeability. This is also shown in the glass breakage experiments, where the signal levels of P1_1 and P1_2 would be higher under the same excitation. Compared with P1_2 and P1_3, the bandwidth of the signal spectrum of P1_2 is much wider. This or the permission is explained by the larger amount of binding, see table 1.

Application in an expanded first prototype of a generic accelerometer with real-time static measurements

Principle of function

The transducer or indicator is composed of an amorphous ferromagnetic material having the following properties: it may have a very high permeability, 5000 < mu < 200000, while it has a relatively high magnetoelasticity, 5 < lambda, for specific alloy compositions_satLess than 40 ppm. This gives the material a very high magnetic-elastic relationship as a whole and is therefore very suitable for use as a sensor material. The transducer or indicator consists of two amorphous strips of 3 x 16 x 0.022mm in size. Two strips are glued to a fixed block, see fig. 1. At the fixing block, one coil is wound around each tape. The coils are connected in a half bridge, see fig. 2. By connecting the coils in this way, similar changes in the two strips do not give a signal, and a high insensitivity to temperature and other symmetry disorders can be achieved. By bending a "bundle" of two amorphous ribbons and one intermediate plastic ribbon, tension in one ribbon will be obtained simultaneously with compression in the other ribbon. The output signal from the coil will thus be opposite, i.e. the inductance (permeability) increases in tension and decreases in compression.

The reaction mass at the end of the bent beam (see fig. 14) gives a bending moment that is proportional to acceleration, beam length and mass. This entails that the accelerometer can be adapted to almost any maximum acceleration. The frequency performance is generally determined by the beam stiffness and mass of the reaction mass.

Theory of the invention

Since this transducer or indicator is to have a real-time static measurement, the measurement principle cannot be based on strain induced due to flow variations. In this case it is necessary to measure the relative permeability of the band with a carrier wave whose frequency should be about 10 times higher than the desired bandwidth of the accelerometer.

For the linear case, the following connection equation should describe the function:

ΔB＝d·Δσ+μ₀·μ·ΔH

where H is the magnetization field, B is the magnetic flux density, magnetic permeability μ of free space₀＝4π·10^-7Vs/Am, and in this case the relative permeability μ of the amorphous band.

In addition, σ represents a mechanical tension and d is a magnetic-elastic relation coefficient. The prefix delta represents a change from the initial value. The material parameter d is approximated by dividing the maximum magnetoelasticity under constant mechanical stress (Δ σ ═ 0) by the magnetization field in the magnetically saturated state, i.e. the material parameter d is approximated

Due to the fact that

At λ_max＝35·10^-6And H_maxIn the case of 200A/m, the equation gives the relationship factor d as 1.75 × 10^-7m/a, which is a very high value for all types of magneto-elastic relations. The amplitude of the measurement of interest here is thus the permeability as a function of the elongation. Assuming that a well-defined magnetic state, i.e. a field of constant and known magnetization, can be achieved, the change in magnetic flux density can be expressed as:

ΔB＝d·E^H··Δλ

whereby the change in magnetic flux density is proportional to the elongation of the ribbon with a proportionality constant d.E^HWhen E is^HWhen the ratio is 100GPa, the proportionality coefficient is about 1.75 multiplied by 10⁴T。

Assume that the coils are connected in one half bridge and there is 10ppm stretch in one band and 10ppm compression in the other band. Since the H-field can be assumed to be constant and the change in the B-field is proportional to the change in permeability and, of course, inductance in the coil, it means that the output signal from the balanced bridge should be

ΔU＝1.75·10⁴·2·10·10^-6·＝0,35V

This is a very strong output signal so that it does not require amplification.

Measurement results

Each coil has 800 turns which gives an inductance of 8,2 mH. Sinusoidal voltages with amplitudes of 4,4V and 19,3kHz are supplied to the half bridge. Since the coils are connected in series, this means that the impedance of the bridge can be kept in the order of 10k omega, which is well suited for the case of driving by an operational amplifier.

For the calibration of the transducer, the earth's gravity of 9.81G is utilized. This gives a sensitivity of 35 mV/G. The transducer is saturated at about 1V, which means that the linear region is about ± 0.5C, equivalent to ± 14G. By studying the impulse response, it was measured that the resonance frequency reached about 80Hz, which, see fig. 3, can be calculated by the following formula:

measurements in accelerometer test equipment

To check linearity, and to some extent frequency performance, measurements were made in an accelerometer test equipment.

A common feature of figures 4, 5, 6 and 7 is that a curve with a relatively large change in output signal shows the output signal from the reference accelerometer, another curve with the same large change in output signal shows the signal from the prototype accelerometer, and an almost solid continuous curve shows the acceleration of the analytical simulation, which should be perfectly accurate. The scale on the axis is acceleration in G for the y-axis and time in seconds for the x-axis. Showing about 1,5 cycles throughout.

By comparing the output signals of the accelerometers and linking them to the simulated acceleration, the frequency response can be deduced, see fig. 8.

The unfolded accelerometer showed good linearity up to the desired linearity limit 14G. There is no reason to assume any form of frequency dependence unless the frequency begins to approach the resonant frequency at 80 Hz. The drop at 11Hz in fig. 8 can be explained by the saturation having been reached.

Use in a first prototype of an acoustic emission sensor

Principle of function

The transducer or indicator is composed of an amorphous ferromagnetic material having the following properties: it may have a very high permeability, 5000 < mu < 200000, while it has a relatively high magnetoelasticity, 5 < lambda, for specific alloy compositions_satLess than 40 ppm. This gives the material a very high magnetic-elastic relationship as a whole and is therefore very suitable for use as a sensor material. The transducer or indicator consists of a strip of amorphous ribbon of size 3 x 18 x 0.022 mm. The tape is wound two turns with an insulating plastic tape in between. It is of utmost importance that the different layers of the strip are not in electrical contact with each other, because the strip becomes a short-circuited second coil if there is electrical contact. The resulting active cylinder is glued to the measurement object with a thin glued joint and on the other side to the bottom of a bowl-shaped plastic bobbin. A reaction block is fixed to the bottom of the plastic bobbin and 1000 turns of coil are wound around its side surface. This transducer principle is best suited for detecting dynamic periods, since there is only one coil. By using two coupled in a half-bridgeIndividual coils (assuming that the coils operate differently, i.e. one coil gives a positive output signal and the other gives a corresponding negative signal for positive accelerations) can provide the following advantages: the influence of all currents (electromagnetic waves in the air, etc.) and variations caused by external, global phenomena (heat, magnetic fields, etc.) occurring symmetrically with respect to the coil is reduced/eliminated.

The reaction mass fixed to the bottom of the plastic bobbin (see fig. 14) induces a reaction force on the movable cylinder that is proportional to the acceleration and mass. This undoubtedly provides the possibility of adapting the accelerometer to almost any maximum acceleration and resonant frequency. The frequency performance is generally determined by the cylinder stiffness and the mass of the reaction mass.

Theory of the invention

For detecting high frequency signals, it is an advantageous and simple way to detect only the flow variation and assume that it is proportional to the magnitude of the deformation of the strip. This means that a magnetically well-defined initial state must be achieved, since the unmagnetized strip does not produce a change in flow when the tension changes. In principle a geomagnetic condition of 30-60 μ T (20-40A/m) is sufficient in order to achieve the basic state of magnetization, but on the other hand it is not practical to monitor the direction and magnitude of the geomagnetic field when a transducer or indicator is to be mounted and calibrated. There are two methods to obtain a satisfactory initial state:

1. a slight amount of magnetism surrounds and a direct current passes through the pick-up coil.

2. A trace of magnetism surrounds and is biased with a permanent magnet.

The field size should be such that the magnetization is 0,2-0,7T, which means that the magnetization field in the strip should be of the order of 2-56A/m. The field size can generally be calculated according to the following formula

Where H is the magnetization field, B is the magnetic flux density, and the permeability μ of free space₀＝4π·10^-7Vs/Am, and in this case the relative permeability μ of the amorphous band. By detecting the flow changes in the strip due to tension/compression, a measurement signal will be obtained. For the linear case, the following connection equation should describe the function:

ΔB＝d·Δσ+μ₀μ·ΔＨ

where σ describes the mechanical stress and d is the coefficient of the magnetic-elastic relationship. The prefix delta represents a change from the initial value. The material parameter d is approximated by dividing the maximum magnetoelasticity under constant mechanical stress (Δ σ ═ 0) by the magnetization field in the magnetically saturated state, i.e. the material parameter d is approximated

Due to the fact that

At λ_max＝35·10^-6And H_maxIn the case of 200A/m, the equation gives the relationship factor d as 1.75 × 10^-7m/a, which is a very high value for all types of magneto-elastic relations.

It is expected that the output signal is proportional to the flow variation and mechanical stress

Where N is the number of turns of the pick-up coil and a is the cross-sectional area of the amorphous strip. By assuming Δ H to be 0, the following equation applies:

wherein E^HIs the modulus of elasticity in a constant magnetization field. Transform to frequency plane and given using the equation above:

where ω is the angular frequency in lines/second. The circumflex notation represents the amplitude value.

Measurement results

The coil measured had 650 turns, giving an inductance of 3.2 mH. The resonant frequency can be calculated as:

assuming that the modulus of elasticity is 100GPa, the height of the movable cylinder is 3mm, and the cross-sectional area is 2X 3X π X0,022 mm²And the resonant frequency is about 10kHz given by the above equation for a 4 gram reaction mass. Fig. 2 shows the output signal from the transducer after 50 times amplification, with the transducer mounted on a large iron billet and excited with a hammer blow.

Frequency analysis in the time series of figure 15 shows that the signal appears broadband up to about 5kHz, after which there is a distinct peak at 8kHz and one at 60 kHz. It appears that a signal of approximately 8kHz is the transducer resonance, while a 60kHz signal is a so-called acoustic emission signal, i.e. for example a transient release of energy when a material deforms. The broadband signal content below 5kHz is composed of vibrations in the detection body.

Claims (8)

1. A method of sensing and displaying permanent state deviations by detecting temporary internal material oscillations in real time in vital parts for hardware design and construction within existing production equipment, e.g. machinery, and/or monitoring of previously established infrastructure, characterized in that one or more at least approximately 20 μm thick amorphous or nanocrystalline band elements with high permeability and relatively high magnetoelasticity are added to an associated part, said one or more band elements are each at least partially surrounded by a multi-turn coil, whereby state deviations of any occurring particle movements (oscillations) are transmitted to said band element/elements, said deviations or causing a clearly measurable and detectable magnetic flow variation (dB/dt) in said coil proportional to said particle movements, or cause a similar measurable and detectable change in inductance in the coil/coils.

2. A method as claimed in claim 1, characterized in that a carrier (voltage) with a small amplitude (for example 20kHz) is applied to the coil/coils for only causing the current through the coil/coils to be measured to vary, or for measurement through a plurality of bridged coils, the voltage difference between the pairs of bridged coils being measured, these amplitudes being substantially proportional to the mechanical stress in the bands.

3. A device for sensing and displaying permanent state deviations by detecting temporary internal material oscillations in real time in vital parts for hardware design and construction within existing product equipment (e.g. machinery) and/or monitoring previously established infrastructure, characterized in that it comprises one or more amorphous or nanocrystalline band elements of at least about 20 μm thickness having high permeability and relatively high magnetoelasticity, said element/elements being treated by magnetic field heat treatment, said band element/elements being surrounded by a multi-turn coil in order to achieve the desired material structure, whereby any occurring state deviations of particle motion (oscillations) due to their merging in said band element/elements, thereby either inducing a clearly measurable and detectable change in magnetic flux (dB) in said coil in proportion to said particle motion dt) or cause a similar measurable and detectable change in inductance in the coil/coils.

4. A device as claimed in claim 3, characterised in that the strap member/members associated with the coil/coils are encapsulated in an elastically deformable epoxy polymer.

5. A device as claimed in claim 3 or 4, characterized in that the band element/elements and the coil/coils are glued to an object, the permanent state deviation of which is to be displayed.

6. A device as claimed in any one of claims 3 to 5, characterized in that the sensitivity of the device differs depending on the orientation of the detection direction relative to the direction of rotation of the belt element/elements, due to direction-dependent properties in the material.

7. The device according to any of claims 3 to 6, characterized in that the plurality of strip elements connected to the coil are respectively bridged and connected to an amplifier for increasing the sensitivity and detectability.

8. The device according to any one of claims 3 to 7, characterized in that it is realized as a glass breakage indicator, accelerometer, acoustic emission transducer or load indicator.