A dual-core low-temperature drift Hall current sensor

Abstract

A dual-core low-temperature drift Hall current sensor, two magnetic rings with the same geometric size and different open air gap thicknesses are used as the magnetic core of the sensor, two Hall chips with completely consistent characteristics are respectively placed in the open air gaps of the two magnetic rings, and the outputs of the two Hall chips are respectively connected to the positive and negative input terminals of a low-temperature drift differential amplifier to form a dual-core low-temperature drift Hall current sensor. A subtractor is used to subtract the output voltages of the two Hall chips to obtain the difference between the voltages of the two, and an amplifier is used to amplify the voltage difference to obtain a voltage output proportional to the current to be measured. The dual-core low-temperature drift Hall current sensor of the present invention can significantly improve the temperature drift of the open-loop Hall current sensor without the need for a temperature compensation circuit, and improve the sensitivity and accuracy.

Description

Technical Field

[0001] The invention relates to a Hall current sensor, in particular to a double-core low-temperature drift Hall current sensor. Background Art

[0002] Open-loop Hall current sensors are widely used in industrial-grade large current measurement (above 200A) due to their simple structure, low cost, low power consumption, good accuracy, ability to measure AC and DC, no need to contact the original circuit, and ability to achieve online monitoring of the mA to kA range.

[0003] The performance of the open-loop Hall current sensor depends on the Hall device and the magnetic ring that provides the magnetic focusing effect. As a semiconductor device, the zero point and sensitivity of the Hall device will drift with the change of temperature. In addition, since the magnetic ring is a soft magnetic material, its magnetic permeability will also decrease significantly with the increase of temperature, resulting in a decrease in the magnetic focusing effect. The above two reasons affect the temperature stability and current measurement accuracy of the open-loop Hall current sensor. Some existing high-precision Hall devices have integrated temperature compensation circuits to meet industrial-grade temperature requirements. For example, DS-CC6501 has a normal operating temperature of -40℃~120℃. After using it in the design of Hall current sensors, it will not affect the current measurement. Therefore, the temperature drift of the open-loop Hall current sensor is mainly caused by the magnetic ring. There are two main types of existing solutions: one is to eliminate the temperature drift problem through temperature compensation; the other is to form a closed-loop Hall current sensor by adding a feedback coil. There are two main temperature compensation schemes. One is the hardware compensation method, which requires knowing the relationship between the core material, the Hall device, and the temperature in advance. However, the relationship between the three is complex, and simple linear or nonlinear circuits are difficult to achieve temperature compensation requirements within the full range. In addition, the hardware structure of the compensation circuit is complex, which increases the cost of the sensor. The other is software compensation, but it needs to be completed with the help of a processor, which increases the complexity of the system. The closed-loop Hall current sensor has certain advantages in accuracy and temperature drift compared to the open-loop Hall current sensor because of its closed-loop structure. However, when measuring large currents above 200A, the closed-loop Hall current sensor is restricted by the volume, process complexity, cost, power consumption, etc. of the current sensor, which is not conducive to online monitoring of industrial-grade large currents. Summary of the invention

[0004] In order to reduce the temperature drift of the open-loop Hall current sensor and overcome the shortcomings of the prior art, the present invention provides a dual-core low-temperature drift Hall current sensor, which can significantly improve the temperature drift of the open-loop Hall current sensor and improve sensitivity and accuracy without the need for a temperature compensation circuit.

[0005] The technical solution adopted by the present invention is:

[0006] A dual-core low-temperature drift Hall current sensor comprises two magnetic rings with the same geometric size and different open air gap thicknesses as the magnetic cores of the sensor, two Hall chips with completely identical characteristics are respectively placed in the open air gaps of the two magnetic rings, and the outputs of the two Hall chips are respectively connected to the positive and negative input terminals of a low-temperature drift differential amplifier to form a dual-core low-temperature drift Hall current sensor.

[0007] The output voltages of the two Hall chips are subtracted by a subtractor to obtain the voltage difference between the two, and the voltage difference is amplified by an amplifier to obtain a voltage output proportional to the current to be measured.

[0008] The principle of the Hall current sensor of the present invention is Figure 1 As shown, when the measured current I P When passing through the sensor core, the magnetic field generated around the wire is concentrated by the magnetic cores C1 and C2, so that a magnetic field H is generated above the Hall chip DS-CC6501. Here, because the air gap widths of the magnetic cores are different, the magnetic induction intensities B corresponding to the two Hall chips are different, so the output voltages of the two Hall chips are different. After a subtractor, the output voltage U o It is the voltage difference generated by the two Hall chips after passing through the in-phase proportional amplifier.

[0009]

[0010] The dual-core Hall current sensor is specifically implemented through three parts, namely, a dual-core magnetic circuit for providing different magnetic induction intensities required by two Hall devices, a subtractor circuit for subtracting the voltages generated by the two Hall devices, and a common-phase proportional amplifier circuit for achieving the target gain of the sensor.

[0011] The dual-core magnetic circuit for providing two Hall devices with different magnetic induction intensities is specifically a dual-core formed by two identical magnetic rings with different air gaps.

[0012] For a current-carrying wire, its length is long enough and the current passing through it is I P , the magnetic induction intensity B generated at a distance r from the center can be expressed by the following formula:

[0013]

[0014] When the current-carrying wire passes through the ring, the magnetic induction intensity B in the magnetic ring core It can be expressed as follows:

[0015]

[0016] Where μ0 is the relative magnetic permeability of vacuum, which is 1; μ r is the relative magnetic permeability of the magnetic ring; D is the outer diameter of the ring; d is the inner diameter of the ring.

[0017] When the core is opened, due to the air gap l air It is much smaller than the size of the magnetic ring, so the magnetic field at the opening can be considered to be continuous and uniform. According to Ampere's circuit law, we can get:

[0018]

[0019] When the temperature rises, the soft magnetic material μ r decrease, resulting in B air This is the main reason for the temperature drift of the magnetic circuit part of the Hall current sensor.

[0020] Because the selected magnetic core is made of soft magnetic material, its magnetic permeability is extremely high. So the magnetic induction intensity B at the air gap air Simplified to:

[0021]

[0022] From the above formula, it can be seen that the magnetic induction intensity at the air gap of the magnetic core changes linearly with the size of the air gap. Furthermore, due to the different opening sizes of C1 and C2, the magnetic induction intensity at the air gap is different. Suppose the magnetic induction intensity at the air gap of the magnetic core C1 is B air1 , the magnetic induction intensity at the C2 air gap is B air2 ,so:

[0023]

[0024] The voltages generated by two identical Hall devices across the two air gaps are:

[0025]

[0026] Wherein U1 is the voltage generated by the Hall device at the air gap of the magnetic core C1, and U2 is the voltage generated by the Hall device at the air gap of the magnetic core C2.

[0027] Furthermore, the subtractor circuit for subtracting the voltages generated by the two Hall devices is composed of an operational amplifier OP07, a resistor R1, a resistor R2, a resistor R3 and a resistor R4. One end of the resistor R1 is connected to the Hall chip H1, and the other end of the resistor R1 is respectively connected to one end of the resistor R3 and the non-inverting input end of the first operational amplifier; one end of the resistor R2 is connected to the Hall chip H2, and the other end of the resistor R2 is respectively connected to one end of the resistor R4 and the inverting input end of the first operational amplifier; the other end of the resistor R3 is connected to the GND end, and the other end of the resistor R4 is connected to the output end of the first operational amplifier.

[0028] Subtracting the voltages generated by the two Hall devices gives:

[0029]

[0030] Among them, U3 is the voltage difference generated by the two Hall devices.

[0031] Furthermore, the in-phase proportional amplifier circuit for achieving the target gain of the sensor is composed of an operational amplifier OP07, a resistor R5, a resistor R6, a resistor R7, and a capacitor C1. One end of the resistor R5 is connected to the GND terminal, and the other end of the resistor R5 is connected to the in-phase input terminal of the second operational amplifier; one end of the resistor R6 is connected to the output terminal of the first operational amplifier, and the other end of the resistor R6 is respectively connected to one end of the resistor R7, one end of the capacitor C1, and the inverting input terminal of the second operational amplifier; the other end of the resistor R7 and the other end of the capacitor C1 are connected to the output terminal of the second operational amplifier OP07.

[0032] To achieve the target gain, the resistors R6 and R7 need to be adjusted, which can be expressed as:

[0033]

[0034] The present invention provides a dual-core low-temperature drift Hall current sensor, which has the following beneficial effects:

[0035] 1: From the above formula, we can see that K H I is a constant value, and the output voltage of the dual-core Hall current sensor changes with the external magnetic field, that is, the measured current I P Linear change. The sensitivity can be improved by selecting a high-sensitivity Hall chip and its corresponding signal processing circuit. It can be seen from the formula that when the temperature rises, B air2 and B air1 At the same time, B air2 -B air1 Basically unchanged, so the sensor can reduce temperature drift compared with the existing open-loop Hall current sensor.

[0036] 2: Compared with the prior art, without the need to introduce a temperature compensation circuit, the temperature drift on the magnetic circuit of the Hall current sensor can be reduced, thereby improving the measurement accuracy of the Hall current sensor in a larger temperature range and the temperature stability of the Hall current sensor.

[0037] 3: No need to eliminate temperature drift through temperature compensation, the dual core subtractor circuit is used to reduce the temperature drift of the open-loop Hall current sensor, meeting the performance requirements of the open-loop Hall current sensor used for industrial-grade large current measurement. Compared with the temperature compensation circuit, this solution has the following advantages: simple structure, strong versatility and can significantly reduce the temperature drift of the open-loop Hall current sensor. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0039] Figure 1It is a schematic diagram of the present invention.

[0040] Figure 2 This is the circuit diagram of the Hall device.

[0041] Figure 3 This is the circuit diagram of the subtractor.

[0042] Figure 4 This is a schematic diagram of gain amplification.

[0043] Figure 5 It is the hardware circuit diagram of the present invention. DETAILED DESCRIPTION

[0044] A dual-core low-temperature drift Hall current sensor comprises two magnetic rings with the same geometric size and different open air gap thicknesses as the magnetic cores of the sensor, two Hall chips with completely identical characteristics are respectively placed in the open air gaps of the two magnetic rings, and the outputs of the two Hall chips are respectively connected to the positive and negative input terminals of a low-temperature drift differential amplifier to form a dual-core low-temperature drift Hall current sensor.

[0045] The output voltages of the two Hall chips are subtracted by a subtractor to obtain the voltage difference between the two, and the voltage difference is amplified by an amplifier to obtain a voltage output proportional to the current to be measured.

[0046] A dual-core low-temperature drift Hall current sensor is invented, which is divided into two parts: a magnetic circuit part and a circuit part.

[0047] (I) Design of magnetic circuit:

[0048] (1) Magnetic ring structure: The magnetic ring has two shapes: square and round. The square structure is used for square busbars or busbars with large currents, and the round structure is used for general round conductors. Therefore, a round structure is used, with one opening, an inner diameter of 16 mm, and an outer diameter of 28 mm.

[0049] (2) Opening size design: according to It can be seen that the size of the opening directly determines the magnitude of the magnetic induction intensity at the magnetic ring. Considering the continuity and uniformity of the magnetic field, the smaller the opening size, the better the continuity and uniformity of the magnetic field. However, too small an opening size can easily lead to saturation of the magnetic ring, resulting in output distortion. Therefore, the magnetic ring C1 of the present invention is 2 cm, and C2 is 1.5 cm.

[0050] (3) Magnetic ring material selection: The selection of dual soft magnetic materials should mainly consider three points: high magnetic permeability for rapid magnetic concentration; low coercivity, the lower the hysteresis loss; low temperature coefficient, reducing sensor temperature drift. The soft magnetic material used in the present invention is Permalloy, which has the characteristics of high magnetic permeability and low coercivity.

[0051] (II) Design of the circuit part:

[0052] (1) Figure 2 As shown in the figure, the selected chips are two identical Hall devices CC6501. When the measured current I P When passing through, the voltages U1 and U2 generated under different air gaps in the same core are:

[0053] The function of the capacitor is to short-circuit high-frequency interference signals to the ground, thereby reducing sensor noise.

[0054] (2) According to the design scheme, the operational amplifier needs to be a rail-to-rail dual operational amplifier with low temperature drift precision. The operational amplifier used in the present invention is OP07.

[0055] (3) The voltage obtained after U1 and U2 pass through the subtractor composed of operational amplifier OP07, resistor R1, resistor R2, and resistor R3 is U3, U3 = U1-U2 = K H I(B air2 -B air1 ).like Figure 3 Shown is the specific circuit diagram of the subtractor.

[0056] (4) To obtain the target gain, U3 needs to be amplified proportionally, such as Figure 4 As shown, resistors R5, R6, R7 and capacitor C1 constitute the proportional amplification circuit of the present invention.

[0057] The sensor target gain can be changed by adjusting the values ​​of resistors R6 and R7. Capacitor C1 is used to reduce the operational amplifier's own noise.

[0058] (5) U4 is the final output voltage of the sensor of the present invention. The entire hardware circuit diagram is as follows Figure 5 shown.

Claims

1. A dual-core low-temperature drift Hall current sensor, characterized in that: Two magnetic rings with the same geometric size and different opening air gap thickness are used as the magnetic core of the sensor. Two Hall chips with completely identical characteristics are placed in the opening air gaps of the two magnetic rings respectively. The outputs of the two Hall chips are respectively connected to the positive and negative input terminals of the low-temperature drift differential amplifier to form a dual-core low-temperature drift Hall current sensor. The output voltages of the two Hall chips are subtracted by a subtractor to obtain the voltage difference between the two, and the voltage difference is amplified by an amplifier to obtain a voltage output proportional to the current to be measured.

2. According to claim 1, a dual-core low-temperature drift Hall current sensor is characterized in that include: A dual-core magnetic circuit used to provide two Hall devices with different magnetic induction intensities. Subtractor circuit for subtracting voltages generated by two Hall devices and A common-mode proportional amplifier circuit used to achieve the target gain of the sensor.

3. According to claim 2, a dual-core low-temperature drift Hall current sensor is characterized in that: The subtractor circuit includes a first operational amplifier, a resistor R1, a resistor R2, a resistor R3, and a resistor R4; One end of the resistor R1 is connected to the Hall chip H1, and the other end of the resistor R1 is respectively connected to one end of the resistor R3 and the non-inverting input end of the first operational amplifier; one end of the resistor R2 is connected to the Hall chip H2, and the other end of the resistor R2 is respectively connected to one end of the resistor R4 and the inverting input end of the first operational amplifier; the other end of the resistor R3 is connected to the GND end, and the other end of the resistor R4 is connected to the output end of the first operational amplifier.

4. According to claim 2, a dual-core low-temperature drift Hall current sensor is characterized in that: The in-phase proportional amplification circuit includes a second operational amplifier, a resistor R5, a resistor R6, a resistor R7, and a capacitor C1; One end of the resistor R5 is connected to the GND end, and the other end of the resistor R5 is connected to the non-inverting input end of the second operational amplifier; one end of the resistor R6 is connected to the output end of the first operational amplifier, and the other end of the resistor R6 is respectively connected to one end of the resistor R7, one end of the capacitor C1, and the inverting input end of the second operational amplifier; the other end of the resistor R7 and the other end of the capacitor C1 are connected to the output end of the second operational amplifier OP07.

5. According to claim 1, a dual-core low-temperature drift Hall current sensor is characterized in that: Magnetic ring structure: The shape of the magnetic ring is square or round. The square structure is used for square busbars or busbars with large currents, and the round structure is used for general round conductors.

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