Test and measurement device and current measurement method

Abstract

To calibrate a magnetic field probe which measures current of a device to be tested without surrounding the device to be tested.SOLUTION: A test and measurement device for measuring current in a device under test (DUT) 112, comprises a port 12 for receiving signals from a magnetic field probe 104, and a processor 106. First, while a power source of the DUT 112 is turned off, known current for calibration is supplied to a current transmission conductor in the DUT 112. The processor 106 is configured to measure a magnetic field based on the known current generated in the current transmission conductor from a signal from the magnetic field probe 104 to determine a calibration factor based on the known current and a measured value of the magnetic field. Next, when the power source of the DUT 112 is turned on, the processor 106 is configured to measure a magnetic field based on unknown current generated in the current transmission conductor from the signal from the magnetic field probe 104 to calculate a calibrated measured value of the unknown current by using a measured value of the magnetic field and the calibration factor.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a test and measurement apparatus and method for measuring current in a device under test using a magnetic field probe, and more particularly to a test and measurement apparatus and method that can obtain calibrated measurements of current. [Background technology]

[0002] Because electric current generates a magnetic field around the current in a circuit, magnetic field (H-field) sensors can be used in the form of current probes. H-field probes have been recommended for current measurements, but they suffer from at least two major drawbacks. First, the magnetic field observed by an H-field probe is sensitive to the current flow itself as well as the placement of the probe, both in terms of distance from the current flow and orientation relative to the current flow. Second, H-field probes are sensitive to the magnetic fields generated by other objects in the vicinity of the current-carrying conductor. These nearby current-carrying conductors can cause significant interference, or crosstalk, from other current waveforms when observing the desired current waveform.

[0003] In conventional systems, both drawbacks have been addressed by integrating the magnetic field around a path surrounding a conductor carrying the current of interest, for example, using a Rogowski coil or a fiber optic current probe based on the Faraday effect (see non-patent document 1), or by concentrating the magnetic field by surrounding the conductor with a magnetic core. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-215251 [Non-patent literature]

[0005] [Non-Patent Document 1] "All-Optical Fiber CT," Toshiba Review, Vol. 59, No. 6 (June 2004), pp. 50-51, published June 2004, Toshiba Corporation, [online], [Retrieved April 19, 2021], Internet <https: / / www.global.toshiba / content / dam / toshiba / migration / corp / techReviewAssets / tech / review / 2004 / 06 / 59_06pdf / rd2.pdf> [Non-patent document 2] "EMC Near-Field Probe for Oscilloscopes," Rohde & Schwarz Japan, [online], [Retrieved April 30, 2021], Internet <https: / / www.rohde-schwarz.com / jp / product / emc_near-field_probes-productstartpage_63493-73798.html> Summary of the Invention [Problem to be solved by the invention]

[0006] However, both of these approaches require wrapping the current probe around the current-carrying conductor, which may not be practical in many cases, such as on a printed circuit board. For this reason, it is desirable to address the calibration and crosstalk issues without having to completely surround the current of interest with the probe.

[0007] Embodiments of the present invention address these and other deficiencies of the prior art. [Means for solving the problem]

[0008] This application discloses a test and measurement apparatus and current measurement method for measuring current in a device under test using a magnetic field probe (i.e., an H-field probe) to obtain calibrated measurements without the need to encase or surround the device under test.

[0009] As described in more detail below, example embodiments of the present invention allow for the calibration of an H-field probe placed near a single conductor carrying a current to be measured by, for example, injecting a known calibration current into the conductor without carrying the unknown current to be measured, measuring the resulting magnetic field with the H-field probe, and dividing the measured magnetic field (and the corresponding signal or value indicated by the H-field probe) by the value of the known current to obtain a calibration factor. The current to be measured is then passed through the conductor, the resulting magnetic field is measured with the H-field probe, and the calibration factor is used to obtain a calibrated measurement of the current to be measured.

[0010] Aspects, features and advantages of embodiments of the present invention will become apparent from the following description of the embodiments, taken in conjunction with the accompanying drawings. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a block diagram of a test and measurement instrument in accordance with an example embodiment of the present invention. [Figure 2] FIG. 2 is a flow chart of an example process for calibrating a magnetic probe in the test and measurement instrument of FIG. [Figure 3] FIG. 3 is a flow chart of another example process for calibrating a magnetic probe in the test and measurement instrument of FIG. [Figure 4] FIG. 4 is a flow chart of another example process for calibrating a magnetic probe in the test and measurement instrument of FIG. [Figure 5] FIG. 5 is a schematic diagram showing an arrangement of magnetic field sensors used in the test and measurement device of FIG. DETAILED DESCRIPTION OF THE INVENTION

[0012] FIG. 1 is a block diagram of an exemplary test and measurement instrument 100, such as an oscilloscope, for implementing example embodiments disclosed herein. The test and measurement instrument 100 includes one or more ports 102, which may be any electrical signal transmission medium. The ports 102 may include receivers, transmitters, and transceivers. Each port 102 may be within a channel of the test and measurement instrument 100. For example, in some example embodiments of the present invention, one port 102 may output a known current to a device under test 112, while another port may be connected to an H-field probe 104 and receive a magnetic field value (an electrical signal corresponding to the magnetic field value) from the H-field probe 104. The ports 102 are coupled to one or more processors 106 for processing signals or waveforms received at the ports 102 from the H-field probe 104. For simplicity, only one processor 106 is shown in FIG. 1; however, one skilled in the art will recognize that multiple processors 106 of various types may be used in combination rather than a single processor 106.

[0013] Port 102 may also be connected to a measurement unit of test and measurement instrument 100, although the measurement unit is not depicted for simplicity. Such a measurement unit may include any component capable of measuring characteristics (e.g., voltage, amperage, amplitude, etc.) of signals received through port 102. Test and measurement instrument 100 may include additional hardware and processors, such as conditioning circuits (e.g., variable gain amplifiers), analog-to-digital converters, and other circuitry, to convert the received signals into waveforms for further analysis. The resulting waveforms are displayed on display 110 in addition to being stored in memory 108.

[0014] The one or more processors 106 are configured to execute instructions from the memory 108 and may perform any method or associated steps indicated by such instructions, such as calibrating the H-field probe 104 to measure current through the device under test 112. The memory 108 may be implemented as processor cache, random access memory (RAM), read-only memory (ROM), solid-state memory, a hard disk drive, or other form of memory. The memory 108 serves as a medium for storing data, computer program products, and other instructions.

[0015] A user input 114 is coupled to the one or more processors 106. The user input 114 may include a keyboard, mouse, trackball, touchscreen, or any other control device that allows a user to interact with the GUI on the display 110. The display 110 may be a digital screen, cathode ray tube-based display, or any other monitor that displays waveforms, measurements, or other data to a user. While FIG. 1 depicts the components of the test and measurement instrument 100 as integrated within the test and measurement instrument 100, one skilled in the art will appreciate that any of these components may be external to the test and measurement instrument 100 and coupled to the test and measurement instrument 100 in any conventional manner (e.g., wired or wireless communication media or mechanisms). For example, in some embodiments, the display 110 may be remote from the test and measurement instrument 100.

[0016] FIG. 2 is a flowchart illustrating the steps performed by the test and measurement instrument 100 to calibrate the H-field probe 104. While not shown in the flowchart, this process can begin with a user placing the H-field probe 104 near a target conductor (hereinafter referred to as a current-carrying conductor) on or within the DUT 112 through which the current to be measured will flow. In the example of FIG. 2, the device under test 112 is initially not powered on, and no unknown current to be measured is flowing through the current-carrying conductor. Once the H-field probe 104 is placed, in some example embodiments, the test and measurement instrument 100 may inject a known calibration current into the current-carrying conductor 202 on the device under test via one or more ports 102. In other example embodiments, the known calibration current may be injected by a separate device. The amount of current to be injected may be entered into the test and measurement instrument 100 via the user input (user interface) 114.

[0017] In step 204, the H-field probe 104 may measure the magnetic field generated by the current in the current-carrying conductor while a known calibration current is flowing through the current-carrying conductor. In step 206, one or more processors 106 may receive signals corresponding to the measured magnetic field from the H-field probe 104 and obtain a calibration factor by dividing the measured magnetic field (e.g., the value of an electrical signal from the H-field probe indicating the measured magnetic field) by the value of the known current. The calibration factor is a function of the placement and orientation of the H-field probe 104 but is not a function of the signal frequency under test or the calibration signal frequency, as long as the distance from the H-field probe 104 to the monitored current under test is small compared to the wavelength of the signal frequency or the calibration signal frequency. That is, the H-field probe 104 senses near-field radiation.

[0018] Next, in step 208, the device under test 112 may be operated under normal operating conditions (i.e., without the calibration current flowing), and the H-field probe 104 may measure the magnetic field produced by the unknown current being measured. In step 210, one or more processors 106 receive the magnetic field measurements measured for the unknown current (specifically, the values ​​of the electrical signals from the H-field probes indicating the measured magnetic field) and determine a calibrated measurement of the unknown current being measured based on the magnetic field measurements and the calibration factor. This may be done, for example, by the one or more processors 106 multiplying the measured magnetic field measurements (the values ​​of the electrical signals from the H-field probes) by the inverse of the calibration factor to determine the calibrated measurement of the unknown current.

[0019] Figure 2 shows a flow chart in which calibration is performed before turning on the device under test 112 and generating an unknown current. In the example embodiment of Figure 2, a recalibration step involving power cycling the device under test may be utilized whenever the H-field probe 104 is physically moved, whether intentionally or unintentionally.

[0020] 3 shows a flowchart of another example of the present invention that allows for simultaneous measurement of an unknown current and calibration. In this example, in step 300, a known continuous sine wave current (e.g., a pilot tone) is injected into a current-carrying conductor of a device under test 112. The current-carrying conductor also carries an unknown current to be measured from an operating device under test 112. The continuous sine wave is generated such that its frequency is outside the measurement bandwidth. The measurement bandwidth may be entered by a user via user input 114, and in response, the test and measurement instrument 100 may adjust the frequency of the continuous sine wave to be outside the measurement bandwidth.

[0021] In step 302, the H-field probe 104 can measure the magnetic field generated by the known calibration continuous sine wave current as well as the magnetic field generated by the unknown current in the device under test 112. In step 304, the test and measurement instrument 100 separates the measured magnetic field generated by the known calibration current (specifically, the components of the electrical signal from the H-field probe representing that magnetic field) from the measured magnetic field generated by the unknown current being measured (specifically, the components of the electrical signal from the H-field probe representing that magnetic field). Taking advantage of the fact that the frequency of the continuous sine wave is outside the measurement bandwidth, the test and measurement instrument 100 may use a filter to separate the components of the magnetic field generated by the continuous sine wave (the components of the electrical signal from the H-field probe representing that magnetic field) in the frequency domain. As described above with respect to step 206, in step 306, the test and measurement instrument 100 can calculate the calibration coefficients using the separated components of the magnetic field generated by the known continuous sine wave (the components of the electrical signal from the H-field probe representing that magnetic field). In step 308, the test and measurement instrument 100 may use the calibration coefficients to determine a calibrated measurement of the unknown current.

[0022] 4 illustrates another example of calibrating current measurements using H-field probe 104. Similar to the example shown in FIG. 3, a calibration signal may be continuously transmitted onto the current-carrying conductor during measurement of the unknown current, step 400. However, the calibration signal in this example may be a continuous random signal, such as a continuous pseudorandom binary sequence (PRBS) signal, a spread-spectrum positive wave signal, or other random, wideband, amplitude-limited source signal.

[0023] In step 402, the H-field probe 104 can measure the magnetic field generated by the continuous random signal as well as the magnetic field generated by the unknown current in the device under test 112. In step 404, the test and measurement instrument 100 can calculate or determine a calibration factor. In this example, the calibration factor is the continuous cross-correlation between the calibration current and the measured magnetic field measurements (represented by the electrical signal from the H-field probe) divided by the autocorrelation of the calibration current with itself. The value of the remaining unknown current under test can then be determined in step 406 by subtracting the known calibration current from the product of the measured magnetic field measurements and the inverse of the calibration factor.

[0024] The time period over which these correlations are calculated represents a trade-off: a short time period allows for fast tracking of the physical movement of the H-field probe 104, while a long time period provides better accuracy as any random correlations between the calibration current and the magnetic field of the unknown current being measured are averaged out over a longer time period.

[0025] It should be noted that example embodiments of the present invention are not limited to a single H-field probe 104. In some examples, multiple H-field probes 104 may be provided and connected to the test and measurement instrument 100 via the ports 102.

[0026] A calibration technique using multiple H-field probes 104 and multiple calibrated current sources can also be useful in solving crosstalk problems. If there are N adjacent current conductors and M adjacent H-field probes 104 to these same current conductors, where M is greater than or equal to N, then an N×M sensitivity matrix A can be defined. The N×M sensitivity matrix A has components A i,j It can be defined as, where represents the magnetic field induced in probe j by a current flowing in conductor i.

[0027] If the number of H-field probes 104, M, is equal to the number of current conductors, N, i.e., M=N, the unknown currents in the conductors can be found by multiplying the inverse matrix of A by the column vector of measurements, Y, of the H-field probes 104. If the number of H-field probes 104, M, is greater than the number of current conductors, N, i.e., M>N, a least squares linear regression technique, shown in Equation 1, can be applied to estimate the unknown currents with minimal noise: where C is the column vector of unknown currents and Y is the column vector of magnetic field measurements.

[0028] C=[A·A T ] -1 A Y (1) The example embodiments described above in connection with Figures 2, 3 and 4 for separating measurements of the magnetic field resulting from the calibration current and measurements of the magnetic field resulting from the unknown current for a single current-carrying conductor and a single probe are equally applicable to situations where there are multiple current-carrying conductors.

[0029] For example, with the test equipment 112 powered off, calibration currents may be introduced into one current-carrying conductor at a time, thereby measuring one column of matrix A at a time. In another example, by selecting a different frequency for the pilot tone signal for each current-carrying conductor, multiple different calibration currents may be sequentially sent through the current-carrying conductors simultaneously with the unknown current, and the resulting H-field (magnetic field) measurements may be separated in the frequency domain. In yet another example, orthogonal, uncorrelated pseudorandom sequences (PRBS) may be selected for each of the calibration currents. When the device under test 112 is powered on and known currents are also flowing, it is necessary to separate the magnetic field measurement components generated by each of the known currents from the measured magnetic field, which also includes the magnetic field measurement components generated by the unknown currents, as in the example described above with reference to Figures 3 and 4.

[0030] Inverse of A (if M is equal to N) or A·A TTo potentially avoid significant noise increase (when M is greater than N), at least one H-field probe 104 may be positioned in the correct orientation near the magnetic field emanating from each of the N current-carrying conductors. The more H-field probes 104 used, the greater the likelihood of reducing noise increase, but at the expense of requiring more channels or ports 102 in the test and measurement instrument 110 and a digitizer (not shown) in the test and measurement instrument 100 to capture the waveforms of the multiple magnetic field sensors.

[0031] In some example embodiments, multiple H-field probes 104 may be disposed in or on a flexible material or fabric. For example, as shown in Figure 5, an array 500 of H-field probes 104 may be flexible. The entire array 500 of H-field probes 104 may be attached or placed on a device under test to measure multiple different current-carrying conductors.

[0032] As described above, the known current may be injected into each of the current-carrying conductors either (1) while the device under test is powered off and no unknown current to be measured is flowing, or (2) while the unknown current to be measured is simultaneously flowing, but the known current has a frequency outside the measurement bandwidth of the unknown current to be measured (e.g., a higher frequency) or is in a random sequence, allowing for isolation of measurements of the magnetic field caused by the known current. The array 500 of H-field probes 104 allows for multiple measurement points, which allows for averaging and more accurate measurements of each unknown current using Equation 1 above. Advantageously, array 500 eliminates the need for a user to individually place H-field probes 104 near multiple current-carrying conductors; instead, the user can place the entire array 500 over a larger area of ​​the device under test 12.

[0033] In some situations, there may be large magnetic field sources external to the device under test 112, such as those caused by the Earth's magnetic field, currents flowing in utility power lines, electrical appliances, etc. As long as these external magnetic field sources are far away compared to the spacing of the H-field probes 104, and therefore these fields are essentially constant with respect to position within the H-field probe 104 sensor array, these fields can be treated as arising from independent current loops surrounding the H-field probe 104 sensor array in each of the three spatial dimensions. Thus, if the number M of H-field probes 104 is greater than or equal to the number N of current-carrying conductors plus three, i.e., M≧N+3, then one or more processors 106 can solve for the unknown currents in the N current-carrying conductors and the three vector components of the external magnetic field.

[0034] If each of the M H-field probes 104 is independently movable, i.e., independent of the others, determining the calibration matrix A may practically require placing three independent current loops around the device under test 112 and providing three additional calibration currents. However, if the M H-field probes 104 are held in a relatively constant position and orientation, the responses of these sensors to the external magnetic field, i.e., the three rows of matrix A, may be measured during probe manufacture and stored in the memory of the H-field probe 104 or in the memory 108 of the test and measurement equipment for later use in calibration.

[0035] Aspects of the disclosed technology may operate on specially created hardware, firmware, digital signal processors, or specially programmed general-purpose computers, including processors that operate according to programmed instructions. The terms "controller" or "processor" herein contemplate microprocessors, microcomputers, ASICs, and dedicated hardware controllers, among others. Aspects of the disclosed technology may be implemented as computer-usable data and computer-executable instructions, such as one or more program modules, executed by one or more computers (including a monitoring module) or other devices. Generally, program modules include routines, programs, objects, components, data structures, etc., which, when executed by a processor in a computer or other device, perform particular tasks or implement particular abstract data formats. Computer-executable instructions may be stored in computer-readable storage media, such as hard disks, optical disks, removable storage media, solid-state memory, RAM, etc. Those skilled in the art will appreciate that the functionality of the program modules may be combined or distributed as desired in various embodiments. Furthermore, such functionality may be embodied in whole or in part in firmware or hardware equivalents, such as integrated circuits, field programmable gate arrays (FPGAs), etc. Certain data structures may be used to more effectively implement one or more aspects of the disclosed technology, and such data structures are considered within the scope of the computer-executable instructions and computer-usable data described herein.

[0036] The disclosed aspects may, in some cases, be implemented in hardware, firmware, software, or any combination thereof. The disclosed aspects may also be implemented as instructions carried by or stored on one or more computer-readable media, which may be read and executed by one or more processors. Such instructions may be referred to as a computer program product. As used herein, computer-readable media refers to any medium that can be accessed by a computing device. By way of example, and not limitation, computer-readable media may include computer storage media and communication media.

[0037] "Computer storage media" means any medium that can be used to store computer-readable information. By way of example and not limitation, computer storage media may include random access memory (RAM), read-only memory (ROM), electrically erasable programmable read-only memory (EEPROM), flash memory and other memory technologies, compact disc read-only memory (CD-ROM), digital versatile disc (DVD) and other optical disk storage, magnetic cassettes, magnetic tape, magnetic disk storage and other magnetic storage devices, and any other volatile or nonvolatile, removable or non-removable medium implemented in any technology. "Computer storage media" excludes signals themselves and transitory forms of signal transmission.

[0038] A communication medium means any medium usable for communicating computer-readable information. By way of example, and not limitation, communication media may include coaxial cable, fiber optic cable, air, or any other medium suitable for communicating electrical, optical, radio frequency (RF), infrared, acoustic, or other types of signals. Example

[0039] The following examples are provided to aid in understanding the technology disclosed in this application. Embodiments of the technology may include one or more of the examples described below, and any combination thereof.

[0040] Example 1 is a test and measurement apparatus for measuring a current in a device under test, comprising an input section configured to receive a signal from a magnetic field probe; and one or more processors configured to measure a magnetic field based on a known current (calibration current) generated by a current-carrying conductor of the device under test from the signal of the magnetic field probe, determine a calibration factor based on the known current and the measurement of the magnetic field based on the known current, and generate a calibrated measurement of an unknown current (current to be measured) in the current-carrying conductor using the measurement of the magnetic field based on the unknown current generated by the current-carrying conductor and the calibration factor.

[0041] Example 2 is the test and measurement device of Example 1, in which the magnetic field generated by the current-carrying conductor is generated based on a known current and an unknown current.

[0042] Example 3 is the test and measurement instrument of example 2, wherein the known current is a continuous sine wave whose frequency is outside the bandwidth of the unknown current, and the test and measurement instrument further comprises a filter configured to separate from the magnetic field probe signal a component based on the magnetic field generated by the known current and a component based on the magnetic field generated by the unknown current.

[0043] Example 4 is the test and measurement instrument of example 2, wherein the known current is a continuous random signal, and the calibration factor is determined by dividing the cross-correlation between the known current and the measured magnetic field by the autocorrelation of the known current with itself.

[0044] Example 5 is the test and measurement instrument of example 4, wherein the calibrated measurement of the unknown current is generated by subtracting the value of the known current from the product of the value of the known current and the reciprocal of a calibration factor.

[0045] Example 6 is the test and measurement device of any of Examples 1 to 5, further comprising a plurality of inputs, each configured to receive a signal from a corresponding magnetic field probe, and the one or more processors are further configured to measure a magnetic field based on a known current generated by the current-carrying conductor from the signal of each magnetic field probe, determine a calibration factor for the magnetic field probe based on the known current and magnetic field, and generate a calibrated measurement of an unknown current in the current-carrying conductor using the magnetic field based on the unknown current generated by the current-carrying conductor and the calibration factor.

[0046] A seventh embodiment is the test and measurement apparatus of the sixth embodiment, wherein the number of magnetic fields measured by each of the magnetic field probes is equal to or greater than the number of current-carrying conductors measured in the device under test.

[0047] An eighth embodiment is the test and measurement apparatus of the seventh embodiment, wherein the number of magnetic fields measured from each of the magnetic field probes is greater than the number of current-carrying conductors measured in the device under test.

[0048] Example 9 is the test and measurement device of example 6, wherein each of the known currents is a continuous sine wave having a different frequency outside the bandwidth of the unknown current, and the test and measurement device further comprises a filter configured to separate components based on the magnetic fields generated by the known currents and components based on the magnetic fields generated by the unknown currents from the magnetic field probe signal.

[0049] Example 10 is the test and measurement instrument of example 6, wherein each of the known currents is a continuous random signal, and the calibration factor is determined by dividing the cross-correlation between the known current and the measured magnetic field by the autocorrelation between the known current and itself.

[0050] Example 11 is the test and measurement device of example 10, wherein the calibrated measurement of the unknown current is generated by subtracting the known current value from the product of the known current value and the reciprocal of a calibration factor.

[0051] Example 12 is the test and measurement apparatus of Examples 6 to 11, further comprising an array of flexible magnetic field probes configured to be positioned over a large area on the device under test.

[0052] Example 13 is a method for measuring a current in a device under test, comprising: measuring with a magnetic field probe a magnetic field based on a known current generated by a current-carrying conductor in the device under test; determining a calibration factor based on the measurements of the known current and the magnetic field; and generating a calibrated measurement of the unknown current in the current-carrying conductor using the measurement of the magnetic field based on an unknown current generated by the current-carrying conductor and the calibration factor.

[0053] Example 14 is the method of example 13, wherein the magnetic field comprises a magnetic field generated by a current-carrying conductor based on a known current and an unknown current.

[0054] Example 15 is the method of example 14, wherein the known current is a continuous sine wave outside the bandwidth of the unknown current, and the method further comprises separating components based on the magnetic field generated by the known current and components based on the magnetic field generated by the unknown current from the magnetic field probe signal.

[0055] Example 16 is the method of example 14, wherein the known current is a continuous random signal, and determining the calibration factor comprises dividing the cross-correlation between the known current and the measured magnetic field by the autocorrelation between the known current and itself.

[0056] Example 17 is the method of example 16, wherein the calibrated measurement of the unknown current is generated by subtracting the value of the known current from the product of the value of the known current and the reciprocal of the calibration factor.

[0057] Example 18 is the method of any of Examples 13 to 17, further comprising: measuring a plurality of magnetic fields based on known currents generated by a plurality of current-carrying conductors from signals of a plurality of magnetic field probes; determining calibration factors for the plurality of magnetic field probes based on the known currents and the measured magnetic fields; and generating a calibrated measurement of an unknown current in the current-carrying conductor using the measurement of the magnetic field based on the unknown currents generated by the current-carrying conductors and the calibration factor.

[0058] Example 19 is the method of example 18, wherein the number of magnetic fields measured from each of the magnetic field probes is equal to or greater than the number of current-carrying conductors measured in the device under test.

[0059] Example 20 is the method of example 19, wherein the number of magnetic fields measured from each of the magnetic field probes is greater than the number of current-carrying conductors measured in the device under test.

[0060] Example 21 is a computer program including instructions that, when executed by one or more processors of a test and measurement instrument, cause the test and measurement instrument to measure a magnetic field based on a known current generated by a current-carrying conductor in a device under test, determine a calibration factor based on the known current and magnetic field, and generate a calibrated measurement of an unknown current in the current-carrying conductor using the magnetic field based on the unknown current generated by the current-carrying conductor and the calibration factor.

[0061] Example 22 is the computer program of example 21, wherein the known current is a continuous sine wave outside the bandwidth of the unknown current, and the computer program further includes instructions for separating from the magnetic field probe signal a component based on the magnetic field generated by the known current and a component based on the magnetic field generated by the unknown current.

[0062] Example 23 is the computer program of Example 21, wherein the known current is a continuous random signal, and the process for determining the calibration coefficient includes a process for dividing the cross-correlation between the known current and the measured magnetic field by the autocorrelation between the known current and its own value.

[0063] Example 24 is the computer program of example 23, wherein the calibrated measurement of the unknown current is generated by subtracting the known current from the product of the value of the known current and the reciprocal of the calibration factor.

[0064] Although the above-described exemplary embodiments of the disclosed subject matter have many advantages that have been described or that will be apparent to those skilled in the art, not all of these advantages or features are required in every embodiment of the disclosed devices, systems, or methods.

[0065] Additionally, the description of this application refers to specific features. It should be understood that the disclosure herein includes all possible combinations of these specific features. When a specific feature is disclosed in the context of a particular aspect or embodiment, that feature can also be used in the context of other aspects and embodiments, to the extent possible.

[0066] Furthermore, when this application refers to a method having two or more defined steps or processes, these defined steps or processes may be performed in any order or simultaneously, unless the circumstances do not preclude this possibility.

[0067] Although specific embodiments of the invention have been illustrated and described for purposes of illustration, it will be appreciated that various modifications can be made therein without departing from the spirit and scope of the invention. Accordingly, the invention should not be limited except as by the appended claims. [Explanation of symbols]

[0068] 100 Test and measurement equipment Port 102 104 H-field probe 106 processors 108 memory 110 Display section 112 Device Under Test 114 User Input Section 500 probe sequences

Claims

1. 1. A test and measurement apparatus for measuring current in a device under test, comprising: an input configured to receive a signal from the magnetic field probe; measuring a magnetic field based on a known current generated by a current-carrying conductor of the device under test from the magnetic field probe signal; determining a calibration factor based on the ratio of the measured magnetic field to the known current value; generating a calibrated measurement of the unknown current in the current-carrying conductor using the measurement of the magnetic field based on the unknown current generated by the current-carrying conductor and the calibration coefficient; one or more processors configured to Equipped with the known current is a continuous sine wave outside the bandwidth of the unknown current; The test and measurement instrument further comprises a filter configured to separate components of the magnetic field probe signal that are based on the magnetic field generated by the known current and components that are based on the magnetic field generated by the unknown current.

2. further comprising a plurality of input units; Each of the plurality of input units is configured to receive a signal from a corresponding magnetic field probe, and the one or more processors: measuring a magnetic field based on the known current generated by the current-carrying conductor from a signal of each of the magnetic field probes; determining a calibration factor for the magnetic field probe based on a ratio of the measured magnetic field to the known current value; 2. The test and measurement instrument of claim 1, further configured to generate a calibrated measurement of the unknown current in the current-carrying conductor using the calibration factor and a measurement of a magnetic field based on the unknown current generated by the current-carrying conductor.

3. measuring a magnetic field based on a known current generated by a current-carrying conductor in the device under test from a signal of the magnetic field probe; determining a calibration factor based on a ratio of the measured magnetic field to the known value of the current; generating a calibrated measurement of the unknown current in the current-carrying conductor using a measurement of a magnetic field based on an unknown current generated by the current-carrying conductor and the calibration coefficients; and Equipped with The method for measuring the current of a device under test, wherein the known current is a continuous sine wave outside the bandwidth of the unknown current, and further comprising processing for separating components based on the magnetic field generated by the known current and components based on the magnetic field generated by the unknown current from the signal of the magnetic field probe.

4. measuring a plurality of magnetic fields based on known currents generated by a plurality of current-carrying conductors from signals of a plurality of magnetic field probes; determining calibration factors for the plurality of magnetic field probes based on ratios of the known current values ​​to the measured magnetic field values; generating a calibrated measurement of the unknown current in the current-carrying conductor using the measurement of the magnetic field based on the unknown current generated by the current-carrying conductor and the calibration factor; 4. The method of measuring current in a device under test of claim 3, further comprising:

5. 5. A computer program comprising instructions which, when executed by one or more processors of a test and measurement instrument, cause the test and measurement instrument to perform the method of claim 3 or 4.

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