CN100412520C - Amorphous Alloy Strain Gauge - Google Patents

Abstract

The middle of amorphous alloy thin strip heaves to one side and forms arch bridge type magnetic pole of a kind of amorphous alloy strain gauge. The bridge of magnetic pole parallel winds along the body of amorphous alloy thin strip and the height of heave is h, 0<h<0.5mm.There are excitation loop and measure loop enlace on the pole side by side and the magnetic field intensity is 0.01-0.05A/mm of the excitation loop. The amorphous alloy strain gauge adheres strongly on surface to measuring material so it takes distortion with measuring work piece along the portrait at the same time. It arouses the change of iron core magnetism conductance and inductance value to finish the test of piece. It utilizes well soft magnetism characteristic and steady temperature capability of amorphous alloy, so it is fit for testing tiny force and displacement with high testing sensitivity. Its temperature error is small and testing circuit is easy to be used in abominable condition with long using life.

Description

Amorphous Alloy Strain Gauge

technical field

The invention relates to a device for measuring mechanical stress, in particular to an amorphous alloy strain gauge.

Background technique

There are many techniques and methods for measuring stress. Similar to amorphous alloy strain gauges are resistance strain gauges, also known as resistance strain gauges. The working principle of resistance strain gauges is based on its strain effect. When using strain gauges to measure component stress or strain, the resistance strain gauge is pasted on the surface of the measured component, and the strain gauge and the part deform together. Since the size and resistivity of the metal wire in the sheet change, the resistance value of the metal wire also changes. The strain or stress can be obtained by measuring the change of the resistance value through the measuring circuit (resistance strain gauge). Resistance strain gauge is a common technology for measuring physical quantities such as strain, load, tension, and pressure at present, but there are also some disadvantages: the relationship between the resistance change rate and strain of conventional strain gauges is relatively nonlinear in the state of large strain, and the semiconductor strain gauge piece is more pronounced. The output signal of conventional strain gauges is small, and the signal connecting wires should be carefully shielded. Strain gauges have a certain size. Therefore, what is actually measured is the average strain on a certain area, which cannot fully display the stress gradient in the stress field. It is greatly affected by temperature. Not suitable for long-term work in harsh environments.

Contents of the invention

The technical problem to be solved by the invention is to propose an amorphous alloy strain gauge with high measurement sensitivity and small temperature error in view of the deficiencies of the prior art.

The technical problem to be solved in the present invention is achieved through the following technical scheme, an amorphous alloy strain gauge, which is characterized in that: the middle part of the amorphous alloy thin strip protrudes to one side to form an arch bridge-shaped magnetic pole, and the bridge of the magnetic pole The surface is set parallel to the main body of the amorphous alloy thin strip, the height of the magnetic pole protrusion is h, 0<h<0.5mm, the excitation coil and the measurement coil are wound side by side on the magnetic pole, and the magnetic field strength of the excitation coil is 0.01～0.05A/mm .

The technical problem to be solved by the present invention can be further realized through the following technical solutions, the number of turns of the exciting coil is 5-8 turns, and the number of turns of the measuring coil is 8-10 turns.

When using an amorphous alloy strain gauge to measure stress, the amorphous alloy strain gauge is firmly attached to the surface of the measured material, so that the entire body deforms along the longitudinal direction at the same time as the workpiece under test, thereby causing a change in the magnetic permeability in the iron core. The change causes the inductance value to change, and realizes the detection of workpiece strain. Its working principle is based on the piezomagnetic effect. The so-called piezomagnetic effect means that when the magnetized material to be tested is subjected to stress, due to the anisotropy of magnetostriction, the tensile stress will make the magnetization direction of the material whose λs is positive turn to the tensile stress. The parallel direction, that is, the magnetic permeability in the direction parallel to the tensile stress increases (reluctance decreases), and it is difficult to magnetize in the direction perpendicular to the tensile stress, that is, the magnetic permeability in the direction perpendicular to the tensile stress decreases (reluctance increase); the opposite is true for compressive stress. Amorphous alloys are a new class of materials that are increasingly being used in sensor technology due to their unique properties. The invention utilizes the good soft magnetic characteristics and stable temperature performance of the amorphous alloy, and compared with the traditional resistance strain gauge, it has the following main advantages: (1) It has higher measurement sensitivity, especially suitable for micro force or micro displacement (2) The temperature error is small; (3) The measurement circuit is simple; (4) It can work in harsh environments and has a long service life. (5) The structure is simple and easy to manufacture.

Description of drawings

Accompanying drawing is the structural diagram of the present invention.

Detailed ways

An amorphous alloy strain gauge, the middle part of the amorphous alloy thin strip 1 protrudes to one side to form an arch bridge-shaped magnetic pole 2, the bridge surface of the magnetic pole 2 is arranged parallel to the main body of the amorphous alloy thin strip 1, and the magnetic pole 2 protrudes The height is h, 0<h<0.5mm, the smaller the value, the better to reduce the additional bending moment. An exciting coil 4 and a measuring coil 3 are wound side by side on the magnetic pole 2 . At this time, the raised portion corresponds to the coil core. The specific size of the strain gauge is mainly determined by the allowable stress of the selected amorphous alloy material. At present, the specifications of the amorphous alloy thin strips provided by Antai Technology Co., Ltd. in China are: width 5-100mm, thickness 0.03mm, the length can be cut according to needs, and users can also customize special specifications according to needs. When the tensile stress is mainly measured, a relatively thin amorphous alloy strip can be used; when the compressive stress is mainly measured, a relatively thick amorphous alloy strip can be used. Users can increase the thickness of amorphous alloy thin strips by special order or by stacking.

Strain Gauge Material Selection

According to the theory of magnetoelasticity, the relationship between the relative permeability change of ferromagnetic materials and the stress σ is

$\frac{\mathrm{<span\; class="notranslate">\; \&Delta;\&mu;</span>}}{\mathrm{<span\; class="notranslate">\; \&mu;</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 2</span>}{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}}}{{\mathrm{<span\; class="notranslate">\; B</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}\mathrm{<span\; class="notranslate">\; \&sigma;\&mu;</span>}$

In the formula, μ is the magnetic permeability of the ferromagnetic material; B _m is the saturation magnetic induction. It can be seen from the above formula that in order to ensure a high measurement sensitivity of the strain gauge, the selected amorphous alloy material should have a large magnetostriction coefficient and permeability, and a small saturation magnetic induction. Among the three types of amorphous alloys that are widely used in the current technology, the material with the above characteristics is undoubtedly the TM-M type Fe-based amorphous alloy. This material has high electromechanical conversion efficiency, and its electromechanical conversion efficiency can be further improved after proper annealing treatment. In addition, the TM-M type amorphous alloy has good temperature stability and aging stability, good machinability and low price, and is very suitable for making strain gauges. At present, the main physical properties of the Fe-based amorphous alloy ribbon produced by Antai Technology Co., Ltd. in China are: saturation magnetic induction intensity Bs = 1.56T; Curie temperature Tc = 410°C; saturation magnetostriction coefficient λs = 27×10 ^{- 6} ; resistivity ρ=130Ωμ-cm; maximum magnetic permeability μ>25×10 ⁴ .

Determination of the main parameters of the strain gauge

The main parameters of the amorphous alloy strain gauge are the turns N ₁ and N ₂ of the exciting coil and the measuring coil, the exciting current I, and the magnetic field H, among which the magnetic field H has the greatest influence on the measurement sensitivity of the strain gauge. Determine the magnetic field strength H to make the amorphous alloy strain gauge work in the linear segment of the maximum permeability and magnetization curve (BH). The magnetic field strength H value usually applied when the magnetic core material is used, and the excitation magnetic field strength of the amorphous alloy strain gauge is 0.01-0.05A/mm. When the magnetic field strength H is determined, other parameters can be calculated by the following formula:

${\mathrm{<span\; class="notranslate">\; N</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; Hl</span>}}{\mathrm{<span\; class="notranslate">\; I</span>}}$

In the formula, N _l is the number of turns of the excitation coil; l is the protrusion length of the amorphous alloy strain gauge; I is the excitation current intensity. The number of turns of the exciting coil is about 5 to 8 turns, and the number of turns of the measuring coil is about 8 to 10 turns. The measurable force range is (1～100)×10 ⁴ N. When the number of turns N _l of the excitation coil is determined, the intensity of the excitation current I can be determined.

The magnetic circuit analysis of the amorphous alloy strain gauge is as follows. When the amorphous alloy strain gauge is firmly attached to the surface of the material under test, the two form a closed magnetic circuit. When the excitation coil is fed with alternating current with a certain frequency, an alternating magnetic flux φ is generated in the excitation coil. According to the law of magnetic circuit, the instantaneous magnetic flux in the magnetic circuit is:

and $R_{\mathrm{AB}}=\frac{l_{\mathrm{AB}}}{{\mathrm{\&mu;}}_{\mathrm{AB}}\mathrm{hb}}$ $R_{\mathrm{cd}}=\frac{l_{\mathrm{cd}}}{{\mathrm{\&mu;}}_{\mathrm{cd}}\mathrm{ab}}$ $r_0=\frac{{\mathrm{\&delta;}}_0}{{\mathrm{\&mu;}}_{0}b{\mathrm{the\; s}}_0}$

In the formula, I——excitation current intensity; N _l ——number of turns of excitation coil;

R _AB ——Reluctance of convex part of amorphous alloy strain gauge;

R _CD ——CD segment magnetoresistance on the surface of the tested material;

r ₀ ——air gap reluctance between the strain gauge and the material to be tested. If the two are tightly attached, the air gap reluctance can be ignored.

l _AB - the length of the raised part of the strain gauge; μ _AB - the absolute magnetic permeability of the amorphous alloy;

h—thickness of amorphous alloy strain gauge;

b——the width of the convex part of the amorphous alloy strain gauge;

l _CD - the length between CDs on the surface of the material to be tested;

μ _CD ——absolute magnetic permeability of the tested material;

α——The penetration depth of the magnetic field line on the surface of the material to be tested;

δ ₀ ——The thickness of the air gap between the amorphous alloy strain gauge and the surface of the tested material;

μ ₀ ——air magnetic permeability;

s ₀ ——the attachment length between the amorphous alloy strain gauge and the surface of the tested material.

According to Faraday's law of electromagnetic induction, the induced voltage in the measuring coil is

$\mathrm{<span\; class="notranslate">\; u</span>}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 4</span>}\mathrm{<span\; class="notranslate">\; \&pi;f</span>}{\mathrm{<span\; class="notranslate">\; IN</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; N</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}}{<span\; class="notranslate">\; (</span>\frac{{\mathrm{<span\; class="notranslate">\; l</span>}}_{\mathrm{<span\; class="notranslate">\; AB</span>}}}{{\mathrm{<span\; class="notranslate">\; \&mu;</span>}}_{\mathrm{<span\; class="notranslate">\; AB</span>}}\mathrm{<span\; class="notranslate">\; hb</span>}}<span\; class="notranslate">\; +</span>\frac{{\mathrm{<span\; class="notranslate">\; l</span>}}_{\mathrm{<span\; class="notranslate">\; cd</span>}}}{{\mathrm{<span\; class="notranslate">\; \&mu;</span>}}_{\mathrm{<span\; class="notranslate">\; cd</span>}}\mathrm{<span\; class="notranslate">\; ab</span>}}<span\; class="notranslate">\; +</span>\frac{{\mathrm{<span\; class="notranslate">\; \&delta;</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}}{{\mathrm{<span\; class="notranslate">\; \&mu;</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}\mathrm{<span\; class="notranslate">\; b</span>}{\mathrm{<span\; class="notranslate">\; the\; s</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}}<span\; class="notranslate">\; )</span>}$

In the formula, f——exciting current frequency; M ₂ ——number of turns of measuring coil.

According to the piezomagnetic effect, when there is stress on the surface of the material to be tested, for ferromagnetic materials with λ _s > 0, when the stress is tensile stress, the magnetic permeability μ increases, that is, μ _AB becomes μ _AB + Δμ _AB , μ _CD When the stress becomes μ _CD +Δμ _CD , the magnetoresistance decreases; when the stress is compressive stress, that is, μ _AB becomes μ _AB -Δμ _AB , and μ _CD becomes μ _CD -Δμ _CD , the magnetoresistance increases. The change of reluctance causes the magnetic flux to change, and the induced voltage U in the measuring coil also changes.

Since the magnetic permeability of amorphous alloys is much larger than that measured by ordinary ferromagnetic, in addition, if the air gap thickness δ ₀ can be strictly guaranteed to be zero, the above formula becomes

$\mathrm{<span\; class="notranslate">\; u</span>}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 4</span>}{\mathrm{<span\; class="notranslate">\; \&mu;</span>}}_{\mathrm{<span\; class="notranslate">\; AB</span>}}\mathrm{<span\; class="notranslate">\; hb\&pi;fI</span>}{\mathrm{<span\; class="notranslate">\; N</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; N</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}}{{\mathrm{<span\; class="notranslate">\; l</span>}}_{\mathrm{<span\; class="notranslate">\; AB</span>}}}$

That is, the output induced voltage in the measuring coil has nothing to do with the surface magnetic properties of the measured material.

The quality of bonding between the amorphous alloy strain gauge and the measured material has a great influence on the accuracy of stress measurement. Attaching the amorphous alloy strain gauge to the surface of the measured component by pasting is simple, convenient, and convenient for on-site operation, but it is necessary to choose a reasonable adhesive and treat the joint surface with high quality. The selected binder should not only have a high viscosity, but also should not produce a large volume shrinkage during curing. In addition, the thermal expansion between the amorphous alloy strain gauge material and the measured component material must be consistent. Otherwise, uneven stress will be generated inside the strain gauge, which will affect the measurement stability. Referring to the metal bonding process commonly used at present, the sticking part of the strain gauge should be polished with a grinding wheel, then cleaned and soaked with a certain concentration of sodium silicate solution for several minutes, and then pasted.

Before measuring the stress, the sensitivity coefficient of the amorphous alloy strain gauge should be calibrated, that is, only one of the strain gauges made of the same type of material should be selected for calibration.

Claims (2)

1. An amorphous alloy strain gauge is characterized in that: the middle part of the amorphous alloy strip (1) bulges to one side to form an arch bridge-shaped magnetic pole (2), and the bridge surface of the magnetic pole (2) is in contact with the amorphous state Alloy thin strip (1) body is arranged in parallel, the height of the pole (2) protrusion is h, 0<h<0.5mm, the excitation coil (4) and the measurement coil (3) are wound side by side on the pole (2), the excitation The magnetic field strength of the coil (4) is 0.01-2.05A/mm. 2. The amorphous alloy strain gauge according to claim 1, characterized in that: the number of turns of the exciting coil (4) is 5 to 8 turns, and the number of turns of the measuring coil (3) is 8 to 10 turns.

Images