Integrated fluxgate magnetic gradient sensor

An integrated fluxgate magnetic gradient sensor includes a common mode sensitive fluxgate magnetometer and a differential mode sensitive fluxgate magnetometer. The common mode sensitive fluxgate magnetometer includes a first core adjacent to a second core. The first and second cores are wrapped by a first excitation wire coil configured to receive an excitation current that affects a differential mode magnetic field. The differential mode sensitive fluxgate magnetometer includes a third core adjacent to the first core and a fourth core adjacent to the second core. The third and fourth cores are wrapped by a second excitation wire coil configured to receive an excitation current that affects a common mode magnetic field.

BACKGROUND

Magnetic field measurement may be utilized in a variety of systems. For example, as current flows through a metallic material, a magnetic field is generated. Thus, the measurement of the magnetic field created indicates the amount of current through the metallic material. However, in addition to the magnetic field generated by the current, background magnetic fields (e.g., the magnetic field created by Earth) may also be present. In order to account for background magnetic fields, the measurement of a magnetic field gradient (i.e., the difference in magnetic field density at one location and another location) is utilized in many applications. For example, a magnetic field gradient may be utilized to measure industrial currents (e.g., currents through bus bars). Conventional systems use two magnetic sensors, such as fluxgate sensors, to measure the magnetic field gradient of a magnetic field.

SUMMARY

The problems noted above are solved in large part by systems and methods for measuring a magnetic field gradient. In some embodiments, an integrated fluxgate magnetic gradient sensor includes a common mode sensitive fluxgate magnetometer and a differential mode sensitive fluxgate magnetometer. The common mode sensitive fluxgate magnetometer includes a first core adjacent to a second core. The first and second cores are wrapped by a first excitation wire coil configured to receive an excitation current that affects a differential mode magnetic field. The differential mode sensitive fluxgate magnetometer includes a third core adjacent to the first core and a fourth core adjacent to the second core. The third and fourth cores are wrapped by a second excitation wire coil configured to receive an excitation current that affects a common mode magnetic field.

Another illustrative embodiment is a driver circuit that includes a differential voltage driver and a single-ended voltage driver. The differential voltage driver is configured to drive a differential voltage through a common mode sensitive fluxgate magnetometer and a differential mode sensitive fluxgate magnetometer. The single-ended voltage driver is configured to drive a single-ended voltage through the differential mode sensitive fluxgate magnetometer. An input to the differential voltage driver is a voltage across a common mode sense wire coil which is included in the common mode sensitive fluxgate magnetometer. An input to the single-ended voltage driver is a voltage across a differential mode sense wire coil which is included in the differential mode sensitive fluxgate magnetometer.

Yet another illustrative embodiment is a method for measuring a magnetic field gradient. The method includes driving, by a differential voltage driver, a differential voltage through a common mode compensation wire coil wrapped around a first core and a second core. The method also includes driving the differential voltage through a differential mode compensation wire coil wrapped around a third core and a fourth core. The method also includes driving, by a single-ended voltage driver, a single-ended voltage through the differential mode compensation wire coil. The method also includes sensing a magnetic field gradient voltage across a shunt resistor that is coupled to the single-ended voltage driver and the differential mode compensation wire coil.

NOTATION AND NOMENCLATURE

DETAILED DESCRIPTION

In many systems, a magnetic field gradient is measured. For example, a magnetic field gradient may be utilized to determine the amount of current flowing through a bus bar. In conventional systems, two separate magnetic sensors (e.g., fluxgate sensors) are utilized to measure the magnetic field gradient. For example, one sensor may be placed at one location within the magnetic field while the second sensor may be placed at a second location within the magnetic field. The output of the second sensor then may be subtracted from the output of the first sensor. This requires a precision subtraction of the sensor output signals. Thus, separate logic and/or additional analog components outside of the sensors is required to compute the subtraction and a relatively large offset is created. Additionally, as the magnetic field gets larger, more current is required to compensate the fluxgate sensors. Thus, more power is required in the system.

In some conventional systems, driver circuits are utilized to compensate the fluxgate sensors. This compensation current, due to a feedback loop with the fluxgate sensor, corresponds with the magnetic field at the location of the sensor and is typically sensed utilizing a shunt resistor. Because the conventional system requires two fluxgate sensors, two driver circuits are required to provide the compensation current to the two fluxgate sensors, and two matched shunt resistors are required to sense the compensation current. Therefore, a conventional system requires matched shunt resistors as well as matched instrumentation amplifiers to read the voltage across the shunt resistors. This is difficult to implement and requires excessive chip area and power use. Therefore, it is desirable to design a system that utilizes a single integrated magnetic gradient sensor and a driver circuit that does not require matched shunt resistors and matched amplifiers to drive the sensor.

In accordance with the disclosed principles, a single integrated fluxgate magnetic gradient sensor is disclosed. To compensate for common mode magnetic fields, the integrated fluxgate magnetic gradient sensor may include a common mode sensitive fluxgate magnetometer surrounded by a differential mode sensitive fluxgate magnetometer. In the magnetic domain, common mode fields are magnetic fields in the same direction while differential mode fields are magnetic fields in opposite directions. The common mode sensitive fluxgate magnetometer may include two cores adjacent to one another, each wrapped by three wires, a compensation wire, an excitation wire, and a sense wire. The differential mode sensitive fluxgate magnetometer may also include two cores, one adjacent to one of the cores of the common mode sensitive fluxgate magnetometer and the second core adjacent to the second core of the common mode sensitive fluxgate magnetometer. Similar to the cores of the common mode sensitive fluxgate magnetometer, each of the cores of the differential mode sensitive fluxgate magnetometer is wrapped by three wires, a compensation wire, an excitation wire, and a sense wire. However, the differential mode sensitive fluxgate magnetometer cores are wrapped by the wires such that the differential mode sensitive fluxgate magnetometer is sensitive to the difference in the density of the magnetic field at the location of the two cores (i.e., sensitive to magnetic fields in opposite directions in the two cores) while the common mode sensitive fluxgate magnetometer cores are wrapped by the wires such that it is sensitive to common mode fields at the location of the two cores (i.e., sensitive to magnetic fields in the same direction in the two cores).

The driver circuit is configured to compensate the cores of both magnetometers with a differential voltage and/or a differential mode drive current generated by a differential voltage driver. The sensed voltage of the common mode sensitive fluxgate magnetometer is then fed back to the driver circuit to drive the differential mode drive current. Thus, the differential mode sensitive fluxgate magnetometer is compensated for common mode magnetic fields. Additionally, the driver circuit is configured to compensate the cores of the differential mode sensitive magnetometer with a single-ended voltage and/or drive current generated by a single-ended voltage driver. The sensed voltage of the differential mode sensitive fluxgate magnetometer is then fed back to the driver circuit to drive the single-ended drive current. Once the sensed voltage of the differential mode sensitive fluxgate magnetometer is zero, the compensation current of the differential mode sensitive magnetometer, as driven by the driver circuit, corresponds to the gradient of the magnetic field and may be measured as a voltage across a single shunt resistor.

FIG. 1shows an illustrative block diagram of a current measurement system100utilizing an integrated fluxgate magnetic gradient sensor104in accordance with various embodiments. The current measurement system100may include a bus bar102and the integrated fluxgate magnetic sensor104. Bus bar102may be a metallic bar or strip (e.g., aluminum, brass, and/or copper), that may have a cross-sectional area that is greater than a wire, and is configured to conduct current. In some embodiments, bus bar102may be utilized within a battery bank, a distribution board, a substation, a switchboard, and/or any other electrical apparatus and/or system.

In some examples, bus bar102includes a hole of any shape (e.g., circular), through the bus bar102. Thus, as current122flows through bus bar102, which may be hundreds of Amperes in magnitude, a magnetic field124is generated around the hole. More particularly, magnetic field124may be generated as two field components, one around one half of the bus bar102(one half of the bus bar102separated by the hole) and the other around the other half of the bus bar102. Additionally, one or more background magnetic fields126(e.g., magnetic field generated by Earth) may surround the bus bar102. The integrated fluxgate magnetic sensor104may be positioned within the hole in the bus bar102as a single integrated circuit. The integrated fluxgate magnetic sensor104may be configured to measure the gradient of the magnetic field124. In other words, integrated fluxgate magnetic sensor104may be configured to determine the difference in magnitude of the density of magnetic field124in two separate locations. For example, integrated fluxgate magnetic sensor104may be configured to determine the magnitude of the magnetic field124in one location within the hole and a separate location within the hole in bus bar102. More particularly, integrated fluxgate magnetic sensor104may be configured to determine the total magnetic field (i.e., magnetic fields124and126) in the two locations. Because the background fields126are equal in both locations in the hole, the integrated fluxgate magnetic sensor104may measure the gradient of the magnetic field124by determining the difference in the total magnetic field in the two locations.

The magnitude of the gradient of the magnetic field124then may be utilized to calculate and/or measure the magnitude of current122. In some embodiments, a processing device within the integrated fluxgate magnetic sensor104may utilize the gradient of the magnetic field124to calculate the current122, while in other embodiments, integrated fluxgate magnetic sensor104may sense the gradient of the magnetic field124and transmit the gradient information to other devices for processing.

While the current measurement system100shown inFIG. 1is configured to measure current122through bus bar102utilizing integrated fluxgate magnetic sensor104, in alternative embodiments, current through any other device may be determined by utilizing the gradient in a magnetic field measured by integrated fluxgate magnetic sensor104. Furthermore, as discussed above, a current need not be determined by integrated fluxgate magnetic sensor104. Instead, the integrated fluxgate magnetic sensor104may be configured to sense the gradient in any magnetic field, including magnetic fields that are not located around bus bars, but in any location.

FIG. 2shows an illustrative block diagram of integrated fluxgate magnetic gradient sensor104in accordance with various embodiments. The integrated fluxgate magnetic sensor104may include a driver circuit202, a common mode sensitive magnetometer204, a differential mode sensitive magnetometer206, and a processing device208. In some embodiments, the components of the integrated fluxgate magnetic gradient sensor104(i.e., driver circuit202, a common mode sensitive magnetometer204, a differential mode sensitive magnetometer206, and a processing device208) may be integrated on the same integrated circuit substrate and/or disposed in a common package. Driver circuit202may be configured to drive voltage and/or current to common mode sensitive magnetometer204(i.e., drive a differential mode drive current generated by a differential voltage driver to common mode sensitive magnetometer204) and differential mode sensitive magnetometer206(i.e., drive a single-ended drive current generated by a single-ended voltage driver to differential mode sensitive magnetometer204). In some embodiments driver circuit202drives the common mode sensitive magnetometer204through wire222and the differential mode sensitive magnetometer through the wire224. Additionally, the driver circuit202may be coupled to common mode sensitive magnetometer204in a closed loop system, such that a sense voltage226from the common mode sensitive magnetometer204may be utilized as an input into the driver circuit202. Similarly, the driver circuit202may be coupled to differential mode sensitive magnetometer206in a closed loop system, such that a sense voltage228from the differential mode sensitive magnetometer206may be utilized as an input into the driver circuit202.

Common mode sensitive magnetometer204may be a fluxgate magnetometer that is configured such that it receives an excitation current that generates a differential magnetic field and thus, is capable of sensing common mode magnetic fields as common mode sense voltage226. Differential mode sensitive magnetometer206may be a fluxgate magnetometer that is configured such that it receives an excitation current that generates a common mode magnetic field and thus, is capable of sensing differential mode magnetic fields as differential mode sense voltage228.

In some embodiments, integrated fluxgate magnetic sensor104includes processing device208. In alternative embodiments, integrated fluxgate magnetic sensor104does not include processing device208. Processing device208may be any type of electrical processing device, such as a microprocessor and/or a microcontroller or other electrical processing device, and may include a processor core, memory, and programmable input/output peripherals. The memory may be in the form of flash, read-only memory, random access memory, or any other type of memory or combination of types of memory. The components of the processing device208may be implemented as a system on a chip (SoC) on a single integrated circuit with the other components of integrated fluxgate magnetic sensor104. In alternative embodiments, the processing device208may be implemented across multiple integrated circuits.

FIG. 3shows an illustrative block diagram of common mode sensitive magnetometer204and differential mode sensitive magnetometer206included in an integrated fluxgate magnetic gradient sensor104in accordance with various embodiments. Common mode sensitive magnetometer204may include two magnetic cores (sometimes called bars)302and304adjacent to one another. In some embodiments, cores302-304are comprised of a ferromagnetic material (e.g., a nickel-iron soft magnetic alloy with high permeability). An excitation wire coil310(sometimes called a primary coil) may be wound around cores302-304. An excitation current352then may be driven through excitation wire coil310by an excitation circuit (not shown). The excitation current may be an alternating current that causes the cores302-304to enter into a cycle of magnetic saturation and unsaturation. When in an unsaturated state, cores302-304are highly permeable (i.e., there is a strong linkage between the coils of excitation wire coil310). However, when in a saturated state, cores302-304are weakly permeable (i.e., there is no or a weak linkage between the coils of excitation wire coil310). The point at which the cores302-304saturate depends on the combined magnetic field124-126at the location of the common mode sensitive magnetometer204.

The excitation coil wire310is configured and/or wound around cores302-304such that the excitation current352generates opposite excitation magnetic fields332-334in the in the cores302-304. In the presence of an external magnetic field (e.g., magnetic field124and/or126), one of cores302-304may saturate sooner than the other of cores302-304. This may induce a signal in a sense wire coil314that has a relationship to the combined magnetic field124-126. The sense wire coil314may be configured and/or wound around cores302-304such that the voltage induced in the sense wire coil314is proportional to the sum of the field change in cores302-304. In other words, the excitation magnetic fields332-334are differential mode such that they cancel each other out in a common mode sense. Thus, the common mode sense voltage226is the voltage across the sense coil wire314.

The common mode sense voltage226may be provided as an input to the driver circuit202to drive a current through common mode compensation wire coil222. Common mode compensation wire coil222is configured and/or wrapped around cores302-304, in some embodiments in the same direction as the sense coil wire314is wrapped around cores302-304, creating compensation magnetic fields336-338in cores302-304. Compensation magnetic fields336-338are common mode fields (i.e., in the same direction in both cores302-304) and, in some embodiments, equal in magnitude. This provides compensation (i.e., corrects) for any external magnetic fields (e.g., fields124-126). Through the feedback loop, the driver circuit202is configured to drive current through compensation wire coil222until the common mode sense voltage226is zero. The amount of current required to drive the common mode sense voltage226to zero corresponds to the magnitude of the combined magnetic fields124-126.

Differential mode sensitive magnetometer206may include two magnetic cores306-308. In some embodiments, core306is adjacent to core302and core308is adjacent to core304. Thus, in some embodiments, the cores306-308are separated by the common mode sensitive magnetometer206. In some embodiments, cores306-308are comprised of a ferromagnetic material (e.g., a nickel-iron soft magnetic alloy with high permeability). Furthermore, the cores302-308may all be approximately the same thickness. An excitation wire coil312may be wound around cores306-308. An excitation current354then may be driven through excitation wire coil312by an excitation circuit (not shown). The excitation current354may be an alternating current that causes the cores306-308to enter into a cycle of magnetic saturation and unsaturation. When in an unsaturated state, cores306-308are highly permeable (i.e., there is a strong linkage between the coils of excitation wire coil312). However, when in a saturated state, cores306-308are weakly permeable (i.e., there is no or a weak linkage between the coils of excitation wire coil312). The point at which the cores306-308saturate depends on the combined magnetic field124-126at the respective locations of the cores306-308.

The excitation coil wire312is configured and/or wound around cores306-308such that the excitation current354generates excitation magnetic fields342-344in the cores306-308in the same direction (i.e., common mode). In the presence of an external magnetic field (e.g., magnetic field124and/or126), one of cores306-308may saturate sooner than the other of cores306-308. This may induce a signal in a sense wire coil316that has a relationship to the difference in the combined magnetic field124-126at the location of core306and the combined magnetic field124-126at the location of core308. The sense wire coil316may be configured and/or wound around cores306-308such that the voltage induced in the sense wire coil314is proportional to the difference of the field change in cores306-308. In other words, the excitation magnetic fields342-344are common mode such that the sense coil wire316is sensitive to a differential field. Thus, the differential mode sense voltage228is the voltage across the sense coil wire316and it corresponds with the gradient of the magnetic field124.

The differential mode sense voltage228may be provided as an input to the driver circuit202to drive a current through differential mode compensation wire coil224. In some embodiments, differential mode compensation wire coil224is configured to have the same resistance as common mode compensation wire coil222. Differential mode compensation wire coil224is configured and/or wrapped around cores306-308, in some embodiments in the same direction as the sense coil wire316is wrapped around cores306-308, creating compensation magnetic fields346-348in cores306-308. Differential magnetic fields346-348are differential mode fields (i.e., the magnetic field in core306is opposite in direction as the magnetic field in core308) and, in some embodiments, equal in magnitude. Through the feedback loop, the driver circuit202is configured to drive current through compensation wire coil224until the differential mode sense voltage228is zero. The amount of current required to drive the differential mode sense voltage228to zero corresponds to the magnitude of the gradient of the combined magnetic fields124-126, and thus corresponds with the magnitude of the gradient of magnetic field124.

FIG. 4shows an illustrative block diagram of driver circuit202included in integrated fluxgate magnetic gradient sensor104in accordance with various embodiments. The driver circuit202may include a differential voltage driver402, a single-ended voltage driver404, and a shunt resistor406. Differential voltage driver402may be an amplifier configured to drive a differential voltage and/or a differential mode compensation current, via common mode compensation wire coil222, through common mode sensitive fluxgate magnetometer204. Additionally, to compensate for the common mode magnetic field, differential voltage driver402may be configured to drive the differential voltage and/or differential mode compensation current, via differential mode compensation wire coil224, through the differential mode sensitive fluxgate magnetometer206. Thus, the differential voltage driver402may be coupled to the common mode sensitive fluxgate magnetometer204and the differential mode sensitive fluxgate magnetometer206in parallel at terminals422-424. The difference in current at from terminal422to424may be the differential mode compensation current. Furthermore, as discussed previously, the common mode sense voltage226may be utilized as an input to the differential voltage driver402. Thus, differential voltage driver402may be configured to compensate for the common mode magnetic field by generating a differential voltage (in the electrical domain).

The single-ended voltage driver404may be coupled, through its output, to shunt resistor406and the differential mode sensitive fluxgate magnetometer206. The single-ended voltage driver404may be an amplifier configured to drive a single-ended voltage and/or a compensation current, via differential mode compensation wire coil224, through differential mode sensitive fluxgate magnetometer206. Furthermore, as discussed previously, the differential mode sense voltage228may be utilized as an input to the differential mode driver404. As discussed previously, the single-ended voltage (i.e., the output of single-ended voltage driver404) corresponds with the gradient of the magnetic field124due to the nature of the integrated fluxgate magnetic gradient sensor104and the feedback loop with the driver circuit202, and more particularly differential mode driver404. In other words, single-ended voltage driver404may be configured to compensate for the differential magnetic field by generating a single-ended voltage which creates a current in coil wire224that is common mode (i.e., the same direction in cores306-308) and equal in magnitude.

Thus, the voltage across shunt resistor406, labelled as magnetic field gradient voltage408, and/or the current through shunt resistor406corresponds with the magnetic field124. Therefore, the magnetic field gradient voltage408may be sensed and provided to a processing device, such as processing device208for further processing. In this manner, a single sensor (i.e., integrated fluxgate magnetic gradient sensor104) may determine the gradient of a magnetic field compensating for the presence of a common mode field.

FIG. 5shows an illustrative flow diagram of a method500for measuring a magnetic field gradient in accordance with various embodiments. Though depicted sequentially as a matter of convenience, at least some of the actions shown can be performed in a different order and/or performed in parallel. Additionally, some embodiments may perform only some of the actions shown. In some embodiments, at least some of the operations of the method500, as well as other operations described herein, can be performed by integrated fluxgate magnetic gradient sensor104including driver circuit202, common mode sensitive magnetometer204, and/or differential mode sensitive magnetometer206and implemented by a processor executing instructions stored in a non-transitory computer readable storage medium.

The method500begins in block502with driving a differential voltage and/or a differential mode compensation current through a common mode compensation wire coil. For example, a differential voltage and/or differential mode compensation current may be driven by differential voltage driver402through common mode compensation wire coil222which may be wrapped around cores302-304. The method500continues in block504and508. In block504, the method500continues with sensing a common mode voltage across a common mode sense wire coil. For example, common mode sense voltage226may be sensed across the common mode sense wire coil314. The differential voltage through common mode compensation wire coil222affects the magnetic fields336-338and the common mode sense voltage226. The method500continues in block506with inputting the common mode sense voltage into the differential voltage driver. For example, the common mode sense voltage226may be input into an amplifier that comprises the differential voltage driver402. This type of feedback loop enables the differential voltage driver402, with a sufficient drive voltage and/or current, to drive the common mode sense voltage226to zero.

In block508, the method500continues with driving the differential voltage through a differential mode compensation wire coil. For example, the differential voltage may be driven by differential voltage driver402through differential mode compensation wire coil224which may be wrapped around cores306-308. The method500continues in block510with driving a single-ended voltage and/or compensation current through the differential mode compensation wire coil. For example, a single-ended voltage may be driven by single-ended voltage driver404through the differential mode compensation wire coil224. In block512, the method500continues with sensing a differential mode voltage across a differential mode sense wire coil. For example, differential mode sense voltage228may be sensed across the differential mode sense wire coil316. The single-ended voltage and/or compensation current through differential mode compensation wire coil224affects the magnetic fields346-348and the differential mode sense voltage228. The method500continues in block514with inputting the differential mode sense voltage into the single-ended voltage driver. For example, the differential mode sense voltage228may be input into an amplifier that comprises the single-ended voltage driver404. The method500continues in blocks510and block516. In block510, the method500continues with again driving a single-ended voltage and/or compensation current through the differential mode compensation wire coil. This type of feedback loop enables the single-ended voltage driver404, with a sufficient drive current, to drive the differential mode sense voltage228to zero. In block516, the method continues with sensing the magnetic field gradient voltage across a shunt resistor. For example, the voltage across shunt resistor406may be sensed. Once the differential mode sense voltage is driven to zero, the single-ended voltage and/or the compensation current corresponds with the magnetic field gradient voltage408.