CN102384715A - Piezoelectric current sensor - Google Patents

Abstract

The invention discloses a piezoelectric current sensor, which is characterized in that the current sensor is composed of an energized conductor (1), piezoelectric material (2), an electrode (3), an insulated shell (4), a connecting piece (5), a signal lead (6) and a signal processing and displaying system (7), wherein pressure generated by the deformation of the energized conductor (1) is transferred to the piezoelectric material (2) by the connecting piece (5) via the insulated shell (4); pre-pressure is formed on the piezoelectric material (2); and a voltage signal generated by the piezoelectric material is led out by the electrode (3) and the signal lead (6) and is transferred to the signal processing and displaying system (7). The novel piezoelectric current sensor disclosed by the invention can measure high-frequency alternating current and transient pulse current within a large dynamic range. The piezoelectric current sensor has the characteristics of simple structure, small volume, high insulation isolation, small electromagnetic interference and good temperature characteristics.

Description

A kind of piezoelectric type current sensor

Technical field

The present invention relates to a kind of based on the deformation of electrical conductor pressurized and adopt piezoelectric device to measure the current sensor of conductor deformation; Has specific use aspect power supply and the current measurement of converting equipment and the control; Also can be widely used in current measurement, control, calibration and overcurrent protection and the monitoring of industrial products and equipment, comprise measurement, control and the protection of a railway car momentary current detection and the big electric currents of industry such as metal smelt and chemical industry.

Background technology

Current sense is a research topic that relates generally in engineering and the scientific research with measuring, like the current measurement and the control of power supply and converting equipment, the current measurement of industrial products and equipment, control, calibration and overcurrent protection and monitoring.At present traditional current sensor ammeter is arranged, based on the current sensor of Hall effect with based on the fibre optic current sensor of Faraday effect.The tradition ammeter uses simple but the use of need connecting with electrical conductor, and it is little to measure electric current; Based on the simple in structure of the current sensor of Hall effect but temperature characterisitic is not good, receive big, the big electric current of influence of temperature drift to cause the iron core magnetic saturation; Receive electromagnetic interference (EMI) little but receive the influence of temperature drift big based on the fibre optic current sensor of Faraday effect, and complex structure, cost is higher, the also rare ripe fibre optic current sensor of existing market.Above-mentioned three kinds of current sensors are active sensor, need power supply during work.

The present invention provides a kind of piezoelectric type current sensor based on the deformation of electrical conductor pressurized, adopts piezoelectric device to measure conductor deformation and conductor current.The piezoelectric type current sensor of electrical conductor distortion measurement is a kind of passive electrical flow sensor.That current sensor provided by the invention has is simple in structure, high insulation isolates, receives that electromagnetic interference (EMI) is little, the characteristics of good temp characteristic.The measurement range of this New type of current sensor is wide, the response time is short, can detect the non-detectable big current value of conventional current sensor, for high power is supplied power and the current measurement and the control of converting equipment provide a kind of robust techniques means.

Summary of the invention

Principle of the present invention is following:

Principle of the present invention is based on the deformation of electrical conductor pressurized and adopts piezoelectric device to measure the current sensor of conductor deformation.If electric current I is the endless cylindrical conductor of a through radius.Current density, J in the cylindricality lead is I/ (π a ²).The magnetic field H that electric current produces is parallel to the cross section and perpendicular to cylinder r radially, and is as shown in Figure 1.According to Amp, the magnetic field H that conduction current produces is:

$H=\frac{\mathrm{<figure-callout\; id="2"\; label="I"\; filenames="HSA00000434205800022.png"\; state="\{\{state\}\}">I</figure-callout>}}{2\mathrm{\&pi;a}}(r=a),$

$H=\frac{\mathrm{<figure-callout\; id="2"\; label="rI"\; filenames="HSA00000434205800022.png"\; state="\{\{state\}\}">rI</figure-callout>}}{2\mathrm{\&pi;}{a}^2}(r<a).$

Getting a little angle is the sector crosssection of δ θ, and the suffered Lorentz pressure F of unit length sector crosssection is:

$F=\&Integral;j\&times;\mathrm{BdV}=\frac{{\mathrm{\&mu;}}_0{\mathrm{<figure-callout\; id="2"\; label="I"\; filenames="HSA00000434205800022.png"\; state="\{\{state\}\}">I</figure-callout>}}^2}{6{\mathrm{\&pi;}}^{2}a}\mathrm{\&delta;\&theta;},$

B is magnetic induction density (B=μ in the formula ₀H, μ ₀Be permeability of vacuum).The direction of Lorentz force F be parallel to the cylindricality lead radially and point to the axle center.The pressure f of damaged surface is:

$f=\frac{{\mathrm{\&mu;}}_0{\mathrm{<figure-callout\; id="2"\; label="I"\; filenames="HSA00000434205800022.png"\; state="\{\{state\}\}">I</figure-callout>}}^2}{6{\left(\mathrm{\&pi;a}\right)}^2},$

The size of pressure is proportional to square I of electric current ², be inversely proportional to the sectional area π a of cylinder ²The Lorentz pressure P that acts on the unit length cartridge outer surface is:

$P=\frac{{\mathrm{\&mu;}}_0{\mathrm{<figure-callout\; id="2"\; label="I"\; filenames="HSA00000434205800022.png"\; state="\{\{state\}\}">I</figure-callout>}}^2}{3\mathrm{\&pi;a}}.$

If cylindrical conductor is ferromagnetic material (Fe, Co, Ni and an alloy thereof), then magnetic permeability μ is μ=μ ₀μ _r, μ in the formula _rBe relative permeability.The relative permeability of common metal conductor is μ _r≈ 1.Since the relative permeability of ferromagnetic material very high (for pure iron, μ _r≈ 5000), so electric current is very big through the deformation that ferromagnetic material causes.Electric current through the Lorentz pressure that unit length ferromagnetic material cartridge outer surface is produced is:

$P=\frac{{\mathrm{\&mu;}}_0{\mathrm{\&mu;}}_{\mathrm{<figure-callout\; id="2"\; label="r\; I"\; filenames="HSA00000434205800022.png"\; state="\{\{state\}\}">r</figure-callout>}}{I}^{}{}^2}{3\mathrm{\&pi;a}}.$

Under the function of current, the radial variations δ r that cylinder produces is:

$\mathrm{\&delta;r}=-\frac{\mathrm{\&beta;}{\mathrm{\&mu;}}_0{\mathrm{\&mu;}}_r{I}^2}{6\mathrm{\&pi;}},$

β is the compressibility coefficient of conductor in the formula.For pure iron, β=6.135 * 10 ^-12(m ²/ N).Numerical value by the radial variations of following formula estimation is: δ r=-2 * 10 ^-15I ²(m).If electrical current is 1000A, then the radial variations value is 2nm.Conductor through big electric current all can receive very big pressure.Lorentz force makes the cylindricality lead produce deformation.The size of pressure and deformation is proportional to square I of electric current ²If the frequency of exchange current is f, then the frequency of lead deformation is 2f.The frequency of exchange current is generally 50Hz or 60Hz, so the frequency of lead deformation is 100Hz or 120Hz, is in the audio range.Pressure or deformation through surveying damaged surface can be measured the electric current through cylindrical conductor.The present invention adopts piezoelectric device to survey the deformation of damaged surface.Through extracting frequency that piezoelectric device produces is that the voltage signal of 2f is detectable electric current through cylindrical conductor.Because the frequency of exchange current is f, so the New type of current sensor receives the electromagnetic interference (EMI) of conduction current little.At 2f frequency place, voltage signal amplitude V that piezoelectric device produces and the relation between exchange current and the ringing pulse electric current I are:

I＝kV，

K is a proportionality constant in the formula.When a known exchange current is measured voltage signal that piezoelectric device produces during through conductor, confirmed that proportionality constant is k, and accomplish demarcation to system.The response time of piezoelectric device is short, dynamic range is wide, so the New type of current sensor can be measured the pulse current of high frequency exchange current and transition in big dynamic range.

Description of drawings

Below in conjunction with accompanying drawing the present invention is done further explain:

Fig. 1 is cylindrical electrical conductor force analysis synoptic diagram;

Fig. 2 is the structural representation that is connected in the electrical conductor current sensor;

Fig. 3 is connected in the structural representation that electrical conductor is the current sensor of ferromagnetic material.

Specific embodiment

Embodiment 1: the current sensor of electrical conductor distortion measurement is made up of electrical conductor 1, piezoelectric 2, electrode 3, insulation crust 4, web member 5, signal lead 6 and signal Processing and display system 7, and is as shown in Figure 2.By web member 5 pressure that electrical conductor 1 deformation produces is passed to piezoelectric 2 and on piezoelectric 2, forms precompression through insulation crust 4, signal Processing and display system 7 are drawn and be transferred to the voltage signal that piezoelectric produces by electrode 3 and signal lead 6.Piezoelectric can be crystalline material (α-SiO ₂, ZnO, LiNbO ₃, LiTaO ₃, AlPO ₄, BaTiO ₃Deng), stupalith (BaTiO ₃-pottery, PZT etc.), high polymer piezoelectric material (PVDF etc.).The sandwich construction that the piezoelectric device of being made up of piezoelectric 2 and electrode 3 can be single layer structure or is composed in series.But the Al of insulation crust 4 selector tools and good insulation preformance ₂O ₃Insulating material such as-pottery or phenolics.At 2f frequency place, exchange current that voltage signal amplitude V that piezoelectric device produces and frequency are f and the relation between the ringing pulse electric current I are I=kV, and k is a proportionality constant in the formula.When a known exchange current Ir passed through conductor 1, the measured value of establishing the voltage signal of piezoelectric device generation was Vr, and then proportionality constant is: k=Ir/Vr.After the system calibrating, the relation between the voltage signal V that exchange current and ringing pulse electric current I and piezoelectric device produce is: I=IrV/Vr.

Embodiment 2: the current sensor of electrical conductor distortion measurement is made up of the ferroelectric conductor of energising 1, piezoelectric 2, electrode 3, insulation crust 4, signal lead 5 and signal Processing and display system 6, and is as shown in Figure 3.The pressure that the ferroelectric conductor deformation of switching on produces is passed to piezoelectric 2 through insulation crust 4; Signal Processing and display system 6 are drawn and be transferred to the voltage signal that piezoelectric produces by electrode 3 and signal lead 5.Piezoelectric can be crystalline material (α-SiO ₂, ZnO, LiNbO ₃, AlPO ₄, BaTiO ₃Deng), stupalith (BaTiO ₃-pottery, PZT etc.), high polymer piezoelectric material (PVDF etc.).The sandwich construction that the ring-type piezoelectric device of being made up of piezoelectric 2 and electrode 3 can be single layer structure or is composed in series.But the Al of insulation crust 4 selector tools and good insulation preformance ₂O ₃Insulating material such as-pottery or phenolics.The ferroelectric conductor 1 of column type is with the ring-type piezoelectric device that wringing fit is connected and on piezoelectric device 2, form precompression.Since the relative permeability of ferromagnetic material very high (for pure iron, μ _r≈ 5000), so electric current is very big through the deformation that ferromagnetic material causes.Electric current through the Lorentz pressure that unit length ferromagnetic material cartridge outer surface is produced is:

$P=\frac{{\mathrm{\&mu;}}_0{\mathrm{\&mu;}}_{\mathrm{<figure-callout\; id="2"\; label="r\; I"\; filenames="HSA00000434205800022.png"\; state="\{\{state\}\}">r</figure-callout>}}{I}^{}{}^2}{3\mathrm{\&pi;a}}.$

Under the function of current, the radial variations δ r that cylinder produces is:

$\mathrm{\&delta;r}=-\frac{\mathrm{\&beta;}{\mathrm{\&mu;}}_0{\mathrm{\&mu;}}_r{I}^2}{6\mathrm{\&pi;}},$

β is the compressibility coefficient of conductor in the formula.For pure iron, β=6.135 * 10 ^-12(m ²/ N).Numerical value by the radial variations of following formula estimation is: δ r=-2 * 10 ^-15I ²(m).If electrical current is 1000A, then the radial variations value is 2nm.Conductor through big electric current all can receive very big pressure.Voltage signal amplitude V that piezoelectric device produces and the relation between exchange current and the ringing pulse electric current I are I=kV; K is a proportionality constant in the formula; The measured value of establishing the voltage signal that piezoelectric device produces as a current known Ir during through conductor 1 is Vr, and then proportionality constant is: k=Ir/Vr.After the system calibrating, the relation between the voltage signal V that exchange current and ringing pulse electric current I and piezoelectric device produce is: I=IrV/Vr.

Because piezoelectric is a highly-resistant material, can realize that therefore the height insulation of electrical conductor and current sensor is isolated in the present invention.If adopt the AT section of quartz piezoelectric crystal to process piezoelectric device, it is little that then the influence of temperature drift is stablized, received to the temperature performance of piezoelectric device and current sensor.The New type of current sensor is to be that the voltage signal of 2f is surveyed the electric current through lead through extracting frequency that piezoelectric device produces.Because the frequency of exchange current is f, so the New type of current sensor receives the electromagnetic interference (EMI) of conduction current little.The response time of piezoelectric device is short, dynamic range is wide, so the New type of current sensor can be measured the pulse current of high frequency exchange current and transition in big dynamic range.That current sensor provided by the invention has is simple in structure, volume is little, high insulation isolates, receives that electromagnetic interference (EMI) is little, the characteristics of good temp characteristic.

Claims (4)

1. piezoelectric type current sensor; It is characterized in that: current sensor is made up of electrical conductor (1), piezoelectric (2), electrode (3), insulation crust (4), web member (5), signal lead (6) and signal Processing and display system (7); By web member (5) pressure that electrical conductor (1) deformation produces is passed to piezoelectric (2) and upward forms precompression at piezoelectric (2) through insulation crust (4), signal Processing and display system (7) are drawn and be transferred to the voltage signal that piezoelectric produces by electrode (3) and signal lead (6).

2. a kind of piezoelectric type current sensor as claimed in claim 1 is characterized in that: electrical conductor (1) is made up of the ferromagnetic conductor material.

3. a kind of piezoelectric type current sensor as claimed in claim 1 is characterized in that: the sandwich construction that the piezoelectric device of being made up of piezoelectric (2) and electrode (3) can be single layer structure or is composed in series.

4. a kind of piezoelectric type current sensor as claimed in claim 1; It is characterized in that: the multilayer ring texture that the piezoelectric device of being made up of piezoelectric (2) and electrode (3) can be the individual layer ring texture or is composed in series, the pressure that column type electrical conductor (1) deformation produces is passed to single or multiple lift ring-type piezoelectric device through insulation crust (4).

Images