CN116106610A - TMR current sensor and design method - Google Patents
TMR current sensor and design method Download PDFInfo
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- CN116106610A CN116106610A CN202210897178.5A CN202210897178A CN116106610A CN 116106610 A CN116106610 A CN 116106610A CN 202210897178 A CN202210897178 A CN 202210897178A CN 116106610 A CN116106610 A CN 116106610A
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R15/00—Details of measuring arrangements of the types provided for in groups G01R17/00 - G01R29/00, G01R33/00 - G01R33/26 or G01R35/00
- G01R15/14—Adaptations providing voltage or current isolation, e.g. for high-voltage or high-current networks
- G01R15/20—Adaptations providing voltage or current isolation, e.g. for high-voltage or high-current networks using galvano-magnetic devices, e.g. Hall-effect devices, i.e. measuring a magnetic field via the interaction between a current and a magnetic field, e.g. magneto resistive or Hall effect devices
- G01R15/205—Adaptations providing voltage or current isolation, e.g. for high-voltage or high-current networks using galvano-magnetic devices, e.g. Hall-effect devices, i.e. measuring a magnetic field via the interaction between a current and a magnetic field, e.g. magneto resistive or Hall effect devices using magneto-resistance devices, e.g. field plates
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R19/00—Arrangements for measuring currents or voltages or for indicating presence or sign thereof
- G01R19/0092—Arrangements for measuring currents or voltages or for indicating presence or sign thereof measuring current only
Abstract
The invention provides a TMR current sensor and a design method thereof, comprising the following steps: the magnetic circuit comprises a magnetic gathering ring, a feedback coil, a TMR chip, a signal amplifying loop, a temperature compensation circuit, a bias zero-setting circuit and a power supply unit; the input end of the bias zero setting circuit is connected with the output end of the TMR chip, and the output end of the bias zero setting circuit is connected with the input end of the signal amplifying circuit; the output end of the signal amplifying loop is connected with the feedback coil; the feedback coil is wound on the magnetic focusing ring, and the feedback coil, the TMR chip and the signal amplifying circuit form a closed loop feedback circuit, when the current conductor to be tested passes through the magnetic focusing ring, the feedback coil generates a magnetic field, and the magnetic field direction of the magnetic field is opposite to the magnetic field direction generated by the current conductor to be tested, so that the TMR chip works in a zero magnetic field range. The TMR chip is arranged on one side of the air gap far away from the magnetic focusing ring, so that good output sensitivity of the TMR chip can be ensured, and the current measuring range of the sensor can be increased.
Description
Technical Field
The invention relates to the technical field of power equipment, in particular to a TMR current sensor and a design method.
Background
Along with the development of smart power grids and novel power systems, higher requirements are put forward on current sensing technology, waveforms appearing in the power grids are complicated transient current waveforms except single direct current, power frequency and impulse current, the complicated transient current waveforms comprise the impulse waveforms which are overlapped on the direct current waveforms, or the impulse current waveforms are overlapped with power frequency current, and the technical requirements of current measurement of the power systems are difficult to meet by using the existing single current sensor.
The current sensor used in the past mainly comprises a current transformer, a Rogowski coil, a shunt, a Hall coil and various magnetic resistance sensors, wherein the current transformer is mainly used for measuring power frequency current, the highest frequency of a frequency band is 10kHz, the Rogowski coil is used for measuring changed current, the upper limit frequency of the current can reach 100MHz, but the low-frequency cut-off frequency is higher, and direct current cannot be measured; when the shunt is used for measuring, an original measuring loop needs to be disconnected, heating can occur under high current, and a coaddition effect can occur under high-frequency current; the magnetic sensor commonly used at present comprises a Hall current coil, a giant magneto-resistance sensor and a tunnel magneto-resistance sensor, wherein the Hall current coil is generally used for measuring direct current, the upper limit frequency is 100kHz, the measurement of impulse current cannot be realized, the giant magneto-resistance sensor has the advantages of wide measurement frequency band and small volume, but the magnetic field measurement range is narrow, the requirement of large current measurement cannot be met, the tunnel magneto-resistance sensor has wider application in recent years, and compared with the giant magneto-resistance sensor, the magnetic field measurement range is wider, but the giant magneto-resistance sensor or the tunnel magneto-resistance sensor is used for measuring direct current and alternating current, no mature magneto-resistance sensor product capable of measuring transient current exists at present, and the tunnel magneto-resistance sensor capable of measuring transient current needs to be developed, so that the measurement from DC current to transient current of a single current sensor can be realized.
The traditional Tunnel Magnetic Resistance (TMR) current sensor adopts a plurality of TMR chips to be annularly arranged, when a magnetic core structure is not adopted, if the TMR current sensor adopts a closed loop feedback structure, a good negative feedback effect can be realized only by adopting a plurality of turns of feedback coils, but the more the feedback coils are, the larger the inductance and capacitance values of a signal processing loop are, the measurement bandwidth of the signal processing loop is seriously affected, the distortion of a measurement waveform is caused, and the measurement accuracy of a transient current waveform is seriously affected; when the TMR current sensor adopts a structure with a magnetic core, a TMR chip is usually placed at an air gap of an opening of the magnetic core, but a magnetic field at the air gap of a magnetic ring is generally strong, the TMR chip is extremely easy to saturate, and the measuring current range is very narrow, so that the development of the TMR current sensor which has wide current amplitude measuring range and can cover DC to transient current in measuring bandwidth is needed.
Disclosure of Invention
In view of the above, the invention provides a TMR current sensor and a design method thereof, which aim to solve the problem that the measurement result is inaccurate when the traditional TMR current sensor is used for measuring transient current.
In one aspect, the present invention provides a TMR current sensor comprising: the magnetic circuit comprises a magnetic gathering ring, a feedback coil, a TMR chip, a signal amplifying loop, a temperature compensation circuit, a bias zero-setting circuit and a power supply unit; wherein, the liquid crystal display device comprises a liquid crystal display device,
an air gap is formed in the magnetic focusing ring, and the TMR chip is arranged on one side, far away from the magnetic focusing ring, of the air gap;
the first branch of the power supply unit is connected with the power supply end of the temperature compensation circuit, and the output end of the temperature compensation circuit is connected with the power supply end of the TMR chip;
the second branch of the power supply unit is connected with the power supply end of the signal amplification circuit, the input end of the bias zero setting circuit is connected with the output end of the TMR chip, and the output end of the bias zero setting circuit is connected with the input end of the signal amplification circuit; the output end of the signal amplification loop is connected with the feedback coil;
the feedback coil is wound on the magnetic focusing ring, the feedback coil, the TMR chip and the signal amplifying circuit form a closed loop feedback circuit, when a current conductor to be tested passes through the magnetic focusing ring, the feedback coil generates a magnetic field, and the magnetic field direction of the magnetic field is opposite to the magnetic field direction generated by the current conductor to be tested, so that the TMR chip works in a linear magnetic field range.
Further, in the TMR current sensor, the first end of the feedback coil is connected to the output end of the second-stage amplifying circuit in the signal amplifying circuit, and the second end of the feedback coil is connected to the current limiting resistor in series and then to the ground.
Further, in the TMR current sensor described above, the signal amplifying circuit includes: the first-stage amplifying circuit, the filter circuit and the second-stage amplifying circuit are sequentially connected; wherein, the liquid crystal display device comprises a liquid crystal display device,
the output voltage of the TMR chip is connected with the input end of the first-stage amplifying circuit after being subjected to bias zeroing of the bias zeroing circuit, and the output end of the first-stage amplifying circuit is connected with the input end of the second-stage signal amplifying circuit through the filter circuit.
Further, in the TMR current sensor, the width of the air gap notch on the magnetic flux collecting ring is 5 mm-10 mm.
Further, in the TMR current sensor, the distance between the TMR chip and the notch in the radial direction of the magnetic focusing ring is 1-8mm.
Further, in the TMR current sensor, the relative permeability of the magnetic flux collecting ring is less than or equal to 10000.
Further, in the TMR current sensor, the number of turns of the feedback coil is 5 turns or less.
Further, the TMR current sensor further includes: a shielding housing; wherein, the liquid crystal display device comprises a liquid crystal display device,
the shielding shell is provided with a cavity for accommodating the magnetic focusing ring, the feedback coil, the TMR chip, the signal amplifying circuit, the temperature compensation circuit, the closed-loop feedback circuit and the power supply unit, and is used for achieving a magnetic field shielding effect and an electric field shielding effect.
Further, the TMR current sensor further includes: a conductor insulation fixing member; wherein, the liquid crystal display device comprises a liquid crystal display device,
the conductor insulation fixing piece is sleeved in the magnetic focusing ring and is used for enabling the current conductor to be tested to vertically penetrate through the center of the magnetic focusing ring.
Further, in the TMR current sensor described above, the conductor insulation mount includes: insulation column, buckle and clasp; wherein, the liquid crystal display device comprises a liquid crystal display device,
the insulating column penetrates through the inside of the magnetic focusing ring, and a penetrating hole is formed in the middle of the insulating column and used for penetrating a current conductor to be tested;
an annular groove is formed in the upper side of the insulating column, and the clamping ring is sleeved in the annular groove and used for clamping with the top of the magnetic focusing ring;
the buckle is located at the bottom of the insulating column, and an annular flange is arranged on the buckle and used for clamping with the bottom of the magnetic gathering ring.
On the other hand, the invention also provides a design method of the TMR current sensor, which comprises the following steps:
and 5, determining a closed loop feedback loop according to the saturated magnetic field value of the TMR chip, the parameters of the feedback coil and the signal amplification loop, so that the feedback coil generates a magnetic field with the opposite direction to the magnetic field generated by the current conductor to be tested, and the TMR chip is ensured to work in a linear magnetic field range.
Further, in the above method for designing a TMR current sensor, the step 2 includes the following steps:
determining the material type of the magnetic focusing ring according to the saturated magnetic field value of the TMR chip;
determining the minimum distance between the current conductor to be tested and the magnetic gathering ring according to the rated current value of the current conductor to be tested and the voltage value of the conductor, and determining the minimum distance between the current conductor to be tested and the magnetic gathering ring as the minimum inner diameter value r of the magnetic gathering ring according to the requirement of the insulation distance;
determining a minimum outer diameter value R of the magnetic flux collecting ring and the width X of the gap according to the minimum inner diameter value R and the material type of the magnetic flux collecting ring;
and determining the placement position of the TMR chip according to the magnetic field uniformity requirement in a preset range outside the gap at the gap of the magnetic focusing ring.
Further, in the above method for designing a TMR current sensor, the step 3 includes the following steps:
according to the maximum operating magnetic field value of the TMR chip at the position without feedback coil and the output voltage value of the TMR chipU 1 ；
Determining the maximum current capacity of the feedback coil wire according to the wire diameter of the feedback coilI 1， According to the output voltage value U of the TMR chip 1 Maximum current capacity with the feedback coil wireI 1 Determining the series resistance value of the feedback coilR 1 ；
Based on the series resistance value of the feedback coilR 1 The number of turns of the winding coil is gradually increased, the difference of time parameters between the output waveform of the TMR sensor and the measurement waveform of the standard sensor is compared, and when the error between the output waveform of the TMR sensor and the measurement waveform of the standard sensor is close to 0, the corresponding number of turns N of the winding is the optimal parameter value.
According to the TMR current sensor, the TMR chip is arranged on one side, far away from the magnetic focusing ring, of the air gap, so that good output sensitivity of the TMR chip can be ensured, magnetic field saturation of the TMR chip can be avoided, and the current measurement range of the sensor is improved; by adopting a closed loop feedback loop, the TMR chip is ensured to work in the range near the 0 magnetic field, the magnetic saturation of the TMR chip is avoided, the good frequency response characteristic of the TMR current sensor is ensured, and the accurate measurement of the transient current can be realized.
Drawings
Various other advantages and benefits will become apparent to those of ordinary skill in the art upon reading the following detailed description of the preferred embodiments. The drawings are only for purposes of illustrating the preferred embodiments and are not to be construed as limiting the invention. Also, like reference numerals are used to designate like parts throughout the figures. In the drawings:
fig. 1 is a schematic structural diagram of a TMR current sensor according to an embodiment of the present invention;
FIG. 2 is a schematic diagram showing a positional relationship between a TMR chip and a magnetic flux collecting ring core in a TMR current sensor according to an embodiment of the invention
Fig. 3 is a schematic structural diagram of a closed loop feedback loop in a TMR current sensor according to an embodiment of the present invention;
fig. 4 is a schematic diagram of a system of a power supply unit in a TMR current sensor according to an embodiment of the present invention;
fig. 5 is a cross-sectional view of an insulating fixture in a TMR current sensor provided by an embodiment of the present invention;
fig. 6 is a schematic structural diagram of a snap ring in an insulation fixing member according to an embodiment of the present invention;
fig. 7 is a flow chart of a design method of a TMR current sensor according to an embodiment of the present invention.
Detailed Description
Exemplary embodiments of the present disclosure will be described in more detail below with reference to the accompanying drawings. While exemplary embodiments of the present disclosure are shown in the drawings, it should be understood that the present disclosure may be embodied in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art. It should be noted that, without conflict, the embodiments of the present invention and features of the embodiments may be combined with each other. The invention will be described in detail below with reference to the drawings in connection with embodiments.
Device embodiment
Referring to fig. 1 and 2, a TMR current sensor according to an embodiment of the present invention includes: the magnetic focusing ring 1, the feedback coil 2, the TMR chip 3, the signal amplifying circuit, the temperature compensating circuit, the bias zero setting circuit and the power supply unit; wherein, the liquid crystal display device comprises a liquid crystal display device,
an air gap 11 is formed in the magnetic focusing ring 1, and the TMR chip 3 is arranged on one side of the air gap far away from the magnetic focusing ring 1; the first branch of the power supply unit is connected with the power supply end of the temperature compensation circuit; the output end of the temperature compensation circuit is connected with the power supply end of the TMR chip; the second branch of the power supply unit is connected with the power supply end of the signal amplification circuit, the input end of the bias zero setting circuit is connected with the output end of the TMR chip, and the output end of the bias zero setting circuit is connected with the input end of the signal amplification circuit; the output end of the signal amplification loop is connected with the feedback coil; the feedback coil is wound on the magnetic focusing ring, the feedback coil, the TMR chip and the signal amplifying circuit form a closed loop feedback circuit, when a current conductor to be tested passes through the magnetic focusing ring, the feedback coil generates a magnetic field, and the magnetic field direction of the magnetic field is opposite to the magnetic field direction generated by the current conductor to be tested, so that the TMR chip works in a linear magnetic field range.
Specifically, the air gap notch 11 penetrates through the magnetic focusing ring body to form a channel penetrating through the hollow part of the magnetic focusing ring and the outside of the magnetic focusing ring, and the air gap notch is formed on the magnetic focusing ring, so that the TMR chip can measure the magnetic field generated by the current conductor to be measured, and the shielding effect of the TMR current sensor and the sensitivity of an output signal can be ensured.
The width X of the air gap 11 may be 5-10mm, preferably 8mm. This distance ensures that the operating magnetic field range of the TMR chip located outside the air gap is within its linear operating magnetic field range.
In this embodiment, the relative permeability of the magnetic flux collecting ring is less than or equal to 10000, so that the magnetic field at the air gap of the magnetic flux collecting ring is not greater than the saturation magnetic field of the TMR chip, thereby being beneficial to improving the measurement current range of the TMR current sensor.
In order to ensure that the output signal of the tunnel magneto-resistance sensor has higher sensitivity, a two-stage signal amplifying circuit is adopted in the signal processing loop, and more specifically, the signal amplifying circuit comprises: the first-stage amplifying circuit, the filter circuit and the second-stage amplifying circuit are sequentially connected; the TMR chip is connected with the input end of the first-stage amplifying circuit after the measurement signal of the TMR chip is subjected to bias zeroing through the bias zeroing circuit; the output end of the first-stage amplifying circuit is connected with the input end of the second-stage amplifying circuit through the filter circuit.
In this embodiment, the power supply ends of the first-stage signal amplifying circuit and the second-stage signal amplifying circuit are both connected to the second branch of the power supply unit, so as to operate by using the electric energy provided by the power supply unit. The input end of the second-stage amplifying circuit is connected with the output end of the filter circuit, so that the power of the output signal of the first-stage signal amplifying circuit can be amplified.
After the output signal of TMR chip is amplified by two stages, one path is connected with waveform measuring device, and another path is connected with feedback coil.
Preferably, the second-stage amplifying circuit adopts push-pull circuit output to avoid the signal amplifying circuit from reducing the bandwidth of the sensor.
In connection with fig. 1 and 3, the tmr chip, the signal amplifying loop and the feedback coil form a closed loop feedback circuit, the voltage between the input of which and the current limiting resistor is proportional to the current carrying of the current conductor to be measured.
In this embodiment, a feedback magnetic field is generated by the feedback coil to offset the external magnetic field, so as to reduce the actual working magnetic field of the sensor, and make the sensor work near the zero magnetic field, so as to improve the linearity and measurement range of the sensor, where the magnitude of the feedback magnetic field is equal to that of the measured magnetic field, and the actual magnitude of the feedback magnetic field can be determined by measuring the magnitude of the feedback current.
As can be seen from fig. 3: when the current i of the current conductor to be measured 1 When the magnetic field intensity in the magnetic focusing ring changes, a corresponding variable delta H is generated, the TMR chip senses the variable delta H, corresponding to the corresponding differential change delta V generated between the pin 2 and the pin 4 of the output end of the TMR chip, and the delta V input A1 generates an output voltage V1 (corresponding to ground potential) corresponding to the delta H.
V1 is phase-shifted by A1 and amplified to output A2, and the amplified power is output to a feedback coil w to form a secondary ampere turn w i ，w i The generated feedback magnetic field is equal to i 1 And (2) the measured magnetic field delta H balance, and regulating the current-limiting resistor R B Resistance value of (d) for outputting voltage V out Reaching the required value to generate a feedback current i 2 A corresponding magnetic field.
More specifically, a first end of the feedback coil is connected with an output end of a second-stage amplifying circuit in the signal amplifying loop, and a second end of the feedback coil is connected with a current limiting resistor in series.
In this embodiment, preferably, the number of turns of the feedback coil 2 is less than or equal to 5 turns, when the TMR chip is placed at a position 5mm away from the outer side of the magnetic ring air gap 11, the effect of closed loop feedback can be achieved by only a few turns of the feedback coil, the inductance and capacitance value in the TMR current sensor loop can be increased by introducing the feedback coil 2, the influence of stray capacitance and stray inductance on the TMR current sensor can be reduced by reducing the number of turns of the feedback coil as much as possible, and the working bandwidth range of the signal processing loop is ensured.
With continued reference to fig. 1, since the TMR chip is relatively sensitive to temperature, the access of the temperature compensation circuit can ensure that the TMR chip works in a wider temperature variation range.
Referring to fig. 4, in order to avoid the interference of the power supply system to the signal processing circuit, the power supply unit is powered by a 12V lithium battery, in this embodiment, after the power supply unit is powered by the 12V lithium battery, the power supply unit is filtered and conditioned, and then is converted into multiple voltage signal outputs to supply power to the temperature compensation circuit, the TMR chip, the first-stage signal amplifying circuit and the second-stage signal amplifying circuit respectively.
The foregoing clearly indicates that, in the TMR current sensor provided in this embodiment, the TMR chip is disposed on the side of the air gap far from the magnetic focusing ring, so that good output sensitivity of the TMR chip can be ensured, magnetic field saturation of the TMR chip can be avoided, and current measurement range of the sensor is improved; by adopting a closed loop feedback loop, the TMR chip is ensured to work in the range near the 0 magnetic field, the magnetic saturation of the TMR chip is avoided, the good frequency response characteristic of the TMR current sensor is ensured, and the accurate measurement of the transient current can be realized.
In order to further reduce the working magnetic field value of the TMR chip, the distance d between the TMR chip and the notch in the radial direction of the magnetic focusing ring is 1-8mm; preferably 5mm.
In the above embodiment, the current limiting resistor and the number of turns of the feedback coil connected in series need to be matched with the position of the current conductor to be measured away from the TMR chip, the current limiting resistor is reduced, the number of turns of the coil is increased, the magnitude of the feedback reverse magnetic field can be increased, and vice versa, the final effect needs to enable the TMR chip to be in the 0 magnetic field working range, and the current sensor has good measurement bandwidth.
In order to prevent the eccentricity of the current conductor to be measured and influence the measurement accuracy of the TMR current sensor, the above embodiments further include: a conductor insulation fixing member 4; the conductor fixing piece is sleeved in the magnetic focusing ring and is used for enabling the current conductor to be tested to vertically penetrate through the center of the magnetic focusing ring.
Further, referring to fig. 5 and 6, the conductor insulation mount 4 includes: an insulating column 41, a clasp 42 and a clasp 43; wherein, the insulation column 41 is penetrated in the magnetic flux collecting ring 1, and a penetrating hole is formed in the middle of the insulation column 41 for penetrating the current conductor to be tested; an annular groove 411 is formed in the upper side of the insulating column 41, and the clamping ring 43 is sleeved in the annular groove and used for clamping with the top of the magnetic focusing ring; the buckle 42 is located at the bottom of the insulation column 41, and an annular flange 421 is provided on the buckle 42, so as to clamp with the bottom of the magnetic flux collecting ring.
Specifically, the snap ring 43 may have an annular structure provided with a notch in the radial direction.
Diameter D of insulating column 1 Slightly smaller than the inner diameter of the magnetic ring and the diameter D of the buckle 2 Slightly larger than the inner diameter of the magnetic ring and the diameter D of the penetrating hole 3 Slightly larger than the diameter of the current conductor to be measured, the inner diameter of the clamping ring is D 1 -2×H 1 (depth of annular groove), the outer diameter of the snap ring is slightly larger than D 1 。
In each of the above embodiments, further includes: a shield case (not shown in the drawings); the shielding shell is provided with a cavity for accommodating the magnetic focusing ring, the feedback coil, the TMR chip, the signal amplifying circuit, the temperature compensating circuit, the closed-loop feedback circuit and the power supply unit.
Specifically, the magnetic focusing ring, the feedback coil, the TMR chip, the signal amplifying circuit, the temperature compensation circuit, the closed-loop feedback circuit and the power supply unit are all arranged inside the shielding shell so as to ensure the shielding effect of an electric field and a magnetic field through the shielding shell.
Specifically, the shield case may be made of a material formed by compounding a metallic material and a ferromagnetic material, and preferably, the shield case includes: a permalloy layer and an aluminum alloy layer; wherein, the permalloy layer is located the inlayer, and the aluminum alloy layer is located the skin. The shape of the shield case may be determined according to practical situations, and is not limited in any way in this embodiment. The shield case in this embodiment has both an electric shielding effect and a magnetic shielding effect.
In summary, the sensor adopts a magnetic gathering ring structure, the magnetic gathering ring is provided with an air gap notch, and in order to avoid the saturation of the TMR chip, the TMR chip is arranged at a preset position away from the outer diameter of the magnetic ring, so that the good output sensitivity of the TMR chip can be ensured, the magnetic field saturation of the TMR chip can be avoided, and the current measurement range of the sensor is improved; temperature compensation control is carried out in a power supply link, so that the TMR sensor can work in a wide temperature change range; the loop integrally adopts a closed loop feedback structure to ensure that the TMR chip works in the range near 0 magnetic field, and the magnetic saturation of the TMR chip is avoided; the TMR chip is arranged at a certain position outside the gap of the opening of the magnetic ring, the number of the feedback coils is regulated, smaller stray capacitance and stray inductance of a loop can be ensured, and good frequency response characteristic of the TMR current sensor is ensured; the shielding shell compounded by metal and magnetic materials is designed, so that the TMR chip can be prevented from being interfered by an external magnetic field and the signal processing loop can be prevented from being interfered by an external electric field.
Method embodiment:
referring to fig. 7, in another aspect, the present invention further provides a method for designing a TMR current sensor, including the steps of:
and S1, determining a saturated magnetic field value of the TMR chip according to the frequency range of the transient current generated by the current conductor to be tested and the amplitude of the current to be tested.
Specifically, according to the transient current amplitude to be measured, the waveform frequency range and the model of the TMR chip in the TMR current sensor, when the upper limit frequency of the current waveform to be measured is higher, the resistance value of the corresponding TMR chip is smaller, and under the condition that the frequency range meets the requirement, the chip with large saturated magnetic field value and high output sensitivity coefficient is selected as much as possible. In this embodiment, the saturation magnetic field value is the maximum of the linear magnetic field range.
And S2, determining parameters of a magnetic focusing ring according to the saturated magnetic field value of the TMR chip and the working characteristics of the current conductor to be tested, setting an air gap notch on the magnetic focusing ring, and determining the placement position of the TMR chip relative to the magnetic focusing ring.
Specifically, the magnetic focusing ring can increase the magnetic field working range of the TMR chip and increase the output voltage signal of the chip; the TMR chip is far away from the magnetic focusing ring, and the smaller the magnetic field is, the larger the relative magnetic permeability of the magnetic focusing ring can be; if the TMR chip is close to the magnetic flux collecting ring, the magnetic flux collecting ring can only select the magnetic flux collecting ring with smaller relative magnetic permeability for the same saturation magnetic field range. In practice, when the current value to be measured is fixed, the magnetic field at the air magnetic field at a certain distance from the current conductor to be measured can be calculated, and after the magnetic flux collecting ring is added, the magnetic permeability of the magnetic flux collecting ring is high, so that the field intensity at the position can be increased, but the magnetic field value cannot be larger than the saturated magnetic field value of the TMR chip, otherwise, the measurement accuracy of the chip can be influenced, the relative magnetic permeability of the magnetic flux collecting ring can be determined according to the magnetic field value, and the material type of the magnetic flux collecting ring can be determined.
In specific implementation, determining the relative permeability of the magnetic focusing ring according to the saturated magnetic field value of the TMR chip;
in order to reduce measurement errors, the material of the magnetic gathering ring is a soft magnetic material with high initial magnetic permeability and easy demagnetization, and the relative magnetic permeability is not more than 10000, so that the proper magnetic gathering ring material is determined according to the material; determining the minimum distance between the conductor and the magnetic gathering ring according to the rated current value of the current conductor to be measured, the voltage value of the conductor and the requirement of the insulation distance, wherein the minimum distance corresponds to the minimum inner diameter value r of the magnetic gathering ring; according to the determined inner diameter value R and the material type of the magnetic gathering ring, calculating and analyzing a minimum outer diameter value R and a maximum opening size distance X required by the magnetic field uniformity at the gap of the opening air gap in simulation software; the determination method specifically comprises the following steps:
1) The larger the outer diameter R of the magnetic gathering ring is, the more uniform the magnetic field at the gap of the magnetic gathering ring should be, but in consideration of the size limitation of the TMR current sensor, R should be reduced as much as possible, in the electromagnetic simulation calculation software, the outer diameter value of the magnetic gathering ring is set as an initial value R 0 The corresponding opening size distance is set to be an initial value X 0 The outer diameter value is gradually increased by the same step length, the uniformity of the magnetic field at the position of the magnetic ring opening air gap and the position of the magnetic ring opening air gap, which is far away from the center of the conductor, is recorded under each corresponding size, the uniformity of the magnetic field is the deviation between the maximum magnetic field value and the minimum magnetic field value in the range of the concerned space area, when the deviation between the maximum magnetic field value and the minimum magnetic field value is smaller, the magnetic field is more uniform, when the outer diameter size of the magnetic ring is gradually increased, when the difference between the minimum magnetic field and the maximum magnetic field in the space area is smaller than 10%, the outer diameter of the corresponding magnetic ring is taken as the minimum outer diameter;
2) The larger the width of the gap of the magnetic gathering ring, the more uneven the magnetic field at the gap is, but the larger the width of the gap is, the larger the magnetic field outside the gap is, so the maximum gap width value when the magnetic field is uniform should be determined, the size of the opening gap is firstly set to be 1mm, the step length of 1mm is gradually increased, and once the difference between the minimum magnetic field and the maximum magnetic field of the calculated area is more than or equal to 10%, the opening gap at the moment is determined to be the final opening width X.
3) And determining the placement position of the TMR chip according to the magnetic field uniformity requirement in a preset range outside the gap at the gap of the magnetic focusing ring.
Specifically, in order to ensure the uniformity of the magnetic field at the gap of the magnetic flux collecting ring and within a preset range outside the gap, the height of the magnetic flux collecting ring can be set to be 10mm, so that the size of the sensor is not too large. The preset range refers to the area of the outer side of the notch of the magnetic focusing ring along the radial direction of the magnetic focusing ring, and preferably, the TMR chip is placed at a position with a distance d= (1-8 mm) from the notch in the radial direction of the magnetic focusing ring, in this embodiment, when d=5 mm, the current conductor to be measured is the largest, the magnetic field at the position where the TMR chip is located is just the saturated magnetic field value, and at this moment, the optimal position of the TMR chip, that is, the position with a distance of 5mm between the TMR chip and the air gap notch in the radial direction of the magnetic focusing ring is corresponding.
And S3, determining parameters of a feedback coil according to the maximum working magnetic field value of the position of the TMR chip and the output voltage value of the TMR chip at the moment.
Specifically, the parameters of the feedback coil include: the wire diameter, turns and series resistance of the feedback coil.
In order to avoid that the stray inductance and capacitance parameters of the feedback coil reduce the measurement bandwidth of the TMR current sensor, the number of turns of the feedback coil is reduced as much as possible, the number of turns of the feedback coil is directly related to the relative magnetic permeability of the magnetic core and the positions of the current conductor to be measured and the TMR chip, and when the relative magnetic permeability of the magnetic core is higher, the required feedback number of turns is smaller; the more feedback turns are needed as the TMR chip is positioned closer to the opening slit; the method for determining the number of turns of the feedback coil and the current-limiting resistance comprises the following specific implementation processes:
a) First, determining the maximum working magnetic field value of the TMR chip at the position without feedback coil and the output voltage value of the TMR chipU 1 ；
b) Determining series resistance of feedback coilR 1 : determining maximum current capacity of feedback coil wire according to wire diameter of feedback coilI 1， According to the output voltage value U of the TMR chip 1 Maximum current capacity with the feedback coil wireI 1 Determining the series resistance value of the feedback coilR 1 。
Specifically, in order to minimize the longitudinal height of the TMR current sensor, the diameter of the feedback coil should not be selected to be excessively large, and the wire diameter of the feedback coil should be selected to be within 0.5 mm; when the wire diameter of the feedback coil is 0.5mm, correspondingly determining the maximum current capacity of the wire of the feedback coilI 1 According to the output voltage of the TMR chip determined in the step a)U 1 Divided by I 1 Can preliminarily determine the inverseSeries resistance value of feed coilR 1 At this time, the minimum series resistance corresponds to the greater feedback coil loop current, and the fewer turns needed, as the series resistance is smaller.
c) Based on the series resistance value of the feedback coilR 1 And gradually increasing the number of windings of the windings by adopting a test verification mode, comparing the difference of time parameters between the output waveform of the TMR sensor and the measurement waveform of the standard sensor, and when the error between the output waveform of the TMR sensor and the measurement waveform of the standard sensor is close to 0, obtaining the corresponding number of windings N as the optimal parameter value. The standard sensor herein refers to a transient current shunt with accurate and reliable measurement.
And S4, designing a bias zero setting circuit, a signal amplifying circuit and a temperature compensating circuit according to the characteristics of the TMR chip, and determining the type of a power supply unit according to the signal amplifying circuit and the temperature compensating circuit.
Specifically, a suitable power supply, such as a 12V lithium battery, can be selected according to the actual application scenario.
And S5, determining a closed loop feedback loop according to the saturated magnetic field value of the TMR chip, the parameters of the feedback coil and the signal amplification loop, so that the feedback coil generates a magnetic field with the opposite direction to the magnetic field generated by the current conductor to be tested, and the TMR chip is ensured to work in a linear magnetic field range. Reference is made to the system embodiments described above for specific design.
It will be apparent to those skilled in the art that various modifications and variations can be made to the present invention without departing from the spirit or scope of the invention. Thus, it is intended that the present invention also include such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof.
Claims (13)
1. A TMR current sensor, comprising: the magnetic circuit comprises a magnetic gathering ring, a feedback coil, a TMR chip, a signal amplifying loop, a temperature compensation circuit, a bias zero-setting circuit and a power supply unit; wherein, the liquid crystal display device comprises a liquid crystal display device,
an air gap is formed in the magnetic focusing ring, and the TMR chip is arranged on one side, far away from the magnetic focusing ring, of the air gap;
the first branch of the power supply unit is connected with the power supply end of the temperature compensation circuit, and the output end of the temperature compensation circuit is connected with the power supply end of the TMR chip;
the second branch of the power supply unit is connected with the power supply end of the signal amplification circuit, the input end of the bias zero setting circuit is connected with the output end of the TMR chip, and the output end of the bias zero setting circuit is connected with the input end of the signal amplification circuit; the output end of the signal amplification loop is connected with the feedback coil;
the feedback coil is wound on the magnetic focusing ring, the feedback coil, the TMR chip and the signal amplifying circuit form a closed loop feedback circuit, when a current conductor to be tested passes through the magnetic focusing ring, the feedback coil generates a magnetic field, and the magnetic field direction of the magnetic field is opposite to the magnetic field direction generated by the current conductor to be tested, so that the TMR chip works in a linear magnetic field range.
2. The TMR current sensor according to claim 1, wherein a first end of the feedback coil is connected to an output end of a second stage amplifying circuit in the signal amplifying circuit, and a second end of the feedback coil is connected to the current limiting resistor in series and then to the ground.
3. The TMR current sensor according to claim 1, wherein the signal amplification circuit includes: the first-stage amplifying circuit, the filter circuit and the second-stage amplifying circuit are sequentially connected; wherein, the liquid crystal display device comprises a liquid crystal display device,
the output voltage of the TMR chip is connected with the input end of the first-stage amplifying circuit after being subjected to bias zeroing of the bias zeroing circuit, and the output end of the first-stage amplifying circuit is connected with the input end of the second-stage signal amplifying circuit through the filter circuit.
4. The TMR current sensor of claim 1, wherein the width of the air gap on the poly ring is 5 mm-10 mm.
5. The TMR current sensor according to claim 1, characterized in that a distance between the TMR chip and the notch in a radial direction of the magnetism collecting ring is 1-8mm.
6. The TMR current sensor according to claim 1, wherein the relative permeability of the magnetism collecting ring is 10000 or less.
7. The TMR current sensor according to claim 1, wherein the number of turns of the feedback coil is 5 turns or less.
8. The TMR current sensor of claim 1, further comprising: a shielding housing; wherein, the liquid crystal display device comprises a liquid crystal display device,
the shielding shell is provided with a cavity for accommodating the magnetic focusing ring, the feedback coil, the TMR chip, the signal amplifying circuit, the temperature compensation circuit, the closed-loop feedback circuit and the power supply unit, and is used for achieving a magnetic field shielding effect and an electric field shielding effect.
9. The TMR current sensor of claim 1, further comprising: a conductor insulation fixing member; wherein, the liquid crystal display device comprises a liquid crystal display device,
the conductor insulation fixing piece is sleeved in the magnetic focusing ring and is used for enabling the current conductor to be tested to vertically penetrate through the center of the magnetic focusing ring.
10. The TMR current sensor of claim 9, wherein said conductor insulation mount comprises: insulation column, buckle and clasp; wherein, the liquid crystal display device comprises a liquid crystal display device,
the insulating column penetrates through the inside of the magnetic focusing ring, and a penetrating hole is formed in the middle of the insulating column and used for penetrating a current conductor to be tested;
an annular groove is formed in the upper side of the insulating column, and the clamping ring is sleeved in the annular groove and used for clamping with the top of the magnetic focusing ring;
the buckle is located at the bottom of the insulating column, and an annular flange is arranged on the buckle and used for clamping with the bottom of the magnetic gathering ring.
11. A method of designing a TMR current sensor as claimed in any one of claims 1 to 10, characterized by comprising the steps of:
step 1, determining a saturated magnetic field value of a TMR chip according to a frequency range of transient current generated by a current conductor to be tested and a current amplitude to be tested;
step 2, determining parameters of a magnetic focusing ring according to a saturated magnetic field value of the TMR chip and the working characteristics of the current conductor to be tested, setting an air gap notch on the magnetic focusing ring, and determining the placement position of the TMR chip relative to the magnetic focusing ring;
step 3, determining parameters of a feedback coil according to the maximum working magnetic field value of the position of the TMR chip and the output voltage value of the TMR chip at the moment;
step 4, designing a bias zeroing circuit, a signal amplifying circuit and a temperature compensating circuit according to the characteristics of the TMR chip, and determining the type of a power supply unit according to the signal amplifying circuit and the temperature compensating circuit;
and 5, determining a closed loop feedback loop according to the saturated magnetic field value of the TMR chip, the parameters of the feedback coil and the signal amplification loop, so that the feedback coil generates a magnetic field with the opposite direction to the magnetic field generated by the current conductor to be tested, and the TMR chip is ensured to work in a linear magnetic field range.
12. The method for designing a TMR current sensor according to claim 11, wherein said step 2 comprises the steps of:
determining the minimum distance between the current conductor to be tested and the magnetic gathering ring according to the rated current value of the current conductor to be tested, the voltage value of the current conductor and the insulation distance requirement, wherein the minimum distance corresponds to the minimum inner diameter value r of the magnetic gathering ring;
determining a minimum outer diameter value R of the magnetic flux collecting ring and the width X of the gap according to the minimum inner diameter value R and the material type of the magnetic flux collecting ring;
and determining the placement position of the TMR chip according to the magnetic field uniformity requirement in a preset range outside the gap at the gap of the magnetic focusing ring.
13. The TMR current sensor design method according to claim 11, wherein said step 3 comprises the steps of:
when no feedback coil is arranged on the magnetic focusing ring, determining the maximum working magnetic field value of the position of the TMR chip and the output voltage value of the TMR chip at the momentU 1 ；
Determining the maximum current capacity of the feedback coil wire according to the wire diameter of the feedback coilI 1 According to the output voltage value U of the TMR chip 1 Maximum current capacity with the feedback coil wireI 1 Determining the series resistance value of the feedback coilR 1 ；
Based on the series resistance value of the feedback coilR 1 The number of turns of the winding coil is gradually increased, the difference of time parameters between the output waveform of the TMR sensor and the measurement waveform of the standard sensor is compared, and when the error between the output waveform of the TMR sensor and the measurement waveform of the standard sensor is close to 0, the corresponding number of turns N of the winding is the optimal parameter value.
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