JPH08101262A - Magnetic field waveform measurement system - Google Patents

Abstract

PURPOSE: To accurately measure the waveform on time axis of magnetic field and current with a wide range of frequency components without being restricted by the shape of an object to be measured. CONSTITUTION: The measuring system consists of a probe 2 for measuring magnetic field, a voltage waveform measuring instrument 3 for converting the waveform into numeric data and transferring the data externally, and a waveform processing device 4. The waveform processing device consists of a numeric value operation part 5 for performing operation to the numeric data of time-axis waveform transmitted from the voltage waveform measuring instrument, a probe calibration data storage part 6 for measuring magnetic field with a function for inputting amplitude and phase related to the ratio of a magnetic field strength H (f) to be measured of the probe for measuring magnetic field to an output voltage V (f) and storing the data, and a display part 7 for outputting the operated data and displaying the data as a time-axis waveform.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a measuring system for measuring a time axis waveform of a magnetic field generated by a periodic signal such as a clock signal of a computer or an aperiodic current caused by electrostatic discharge.

[0002]

2. Description of the Related Art Conventionally, as shown in FIG. 8, in measuring a magnetic field waveform, a current probe 32 and an oscilloscope 33 for measuring a magnetic field produced by a current flowing in a cable around it.
(Sony Tektronix: Current probe measurement technology), or a measurement system 41 (Haga, which combines a loop probe 42 in which an integrating circuit 43 is connected to the output stage and an oscilloscope 44 as shown in FIG. 10). et. al.] "A Measu
element of Electrical and M
Aggressive Field Radiated fr
om VDT, "Proceedings of 19"
94 International Symposium
m on Electromagnetic Comp
Ability, EMC'94 SENDAI, 1
9P302, pp. 647-650) was used.

As shown in FIG. 9, the current probe 32 is formed by winding a secondary coil 35 around a ring-shaped ferrite core 34 to form a transformer. The current probe 32 is used by passing a cable 36 to be measured through the ring-shaped core 34. Cable to be measured 36
In order to pass through, the ring-shaped core 34 has a structure in which a line can be divided and opened and closed. The high frequency current flowing through the cable to be measured 36 generates a high frequency magnetic field around it. This magnetic field is detected by the ring-shaped core 34 and the voltage induced in the load on the secondary side is measured to convert the current value from the winding ratio of the transformer and the load value to obtain the value.

An integrating circuit 43 is provided next to the loop probe 42.
In the measurement method 41 in which the output voltage of the loop probe 42 is proportional to the time derivative of the interlinkage magnetic flux according to Faraday's law of electromagnetic induction, the output voltage of the loop probe 42 can be ignored. . By passing the time-differentiated voltage waveform through the electrical time integration circuit 43, the time-axis waveform of the magnetic field can be measured.

Further, as shown in FIG. 11, a wideband antenna 45 originally used for measuring frequency characteristics is used, and an antenna coefficient showing the relationship between the input electric field strength and the output voltage of the antenna is used to calculate the time axis of the electromagnetic field. A means for measuring a waveform has also been proposed (see, for example, “Measurement and Analysis of Electromagnetic Pulses Associated with Indirect ESD” by Masugi et al., IEICE Transactions B-II, No. 9, pp 647-654).

[0006]

Since the clock signal of the computer and the electromagnetic field generated by electrostatic discharge have frequency components over a wide band, the frequency characteristic of the wide band is improved in order to improve the measurement accuracy of the time axis waveform. A probe or antenna with is required.

Since the current probe 32 according to the related art does not have the function of internally correcting the characteristics of the current probe, the frequency characteristic is limited by the core 34 of the transformer, and the measurement frequency range has a relationship between the output voltage and the output current of 1: 1. It is limited to the range that satisfies: 1. Further, since the measured cable 36 is inserted into the current probe 32 for measurement, a wide cable such as a flat cable or a cable that cannot be inserted into the current probe 32 such as a transmission line on a printed wiring board or a magnetic field near the line is detected. It had a defect that it could not be measured.

An integrating circuit 43 is provided next to the loop probe 42.
The measurement system 41 provided with is based on the fact that the output voltage of the loop probe 42 is proportional to the derivative of the time change of the magnetic field strength as described above. However, in the high frequency band where the effect of its self-inductance cannot be ignored in the loop probe, the output of the loop probe is no longer proportional to the derivative of the change over time of the magnetic field strength, and it is measured for waveforms with frequency components in the high frequency range. It had a drawback that the accuracy became poor.

FIG. 12 shows an example of frequency characteristics of the ratio (a) of the amplitude of the measured magnetic field strength H (f) to the amplitude of the output voltage V (f) and the phase difference (b) of a loop having a loop area of 10 mm in diameter. It is a figure. In each figure, the horizontal axis represents the frequency on a logarithmic scale and the amplitude is in dB. In the frequency band of 10 ⁸ Hz or less, the amplitude ratio changes linearly with respect to the frequency, and the phase is almost constant at −π / 2 radians, and an output voltage proportional to the time differential characteristic of the measured magnetic field can be obtained. On the other hand, 10 ⁸
In the frequency band above Hz, the amplitude ratio deviates from the straight line,
The phase also greatly changes from -π / 2 radians, and the output voltage is no longer proportional to the time differential characteristic of the magnetic field to be measured. FIG. 13 shows a result obtained by measuring a waveform including such a frequency region with the measuring system 41 as shown in FIG. In contrast to the actual magnetic field waveform of (a), the measured waveform is as shown in (b), and the time axis waveform of the magnetic field cannot be reproduced only by the correction by adding the integrating circuit.

In a measurement method in which a wideband antenna 45 for measuring the frequency characteristics of an electromagnetic field is used and is corrected by the electromagnetic field strength and the antenna coefficient of the output voltage, only the amplitude is calibrated in a normal antenna and the phase difference is corrected. Since there is no data on the above, there is no data on the output voltage signal of the antenna for the correction (Masugi et al. "Measurement and analysis of electromagnetic pulse accompanying indirect ESD", IEICE Transactions B-II, No. 9, pp. 647-654).

An object of the present invention is to provide a measuring system for measuring the time-axis waveforms of a magnetic field and a current having a broadband frequency component without being restricted by the shape of an object to be measured and with high accuracy.

[0012]

To achieve the above object, in the present invention, for magnetic field measurement in which a calibration coefficient, which is the relationship between the measured magnetic field strength in the frequency domain and the amplitude ratio and phase difference of the output voltage, is known. It is composed of a probe, a voltage waveform measuring device that can convert the input waveform into numerical data and transfer it to an external device, and a waveform processing device that processes the numerical data of the time axis waveform sent from the voltage waveform measuring device. The device has an arithmetic unit for arithmetically processing the input numerical data, a magnetic field measurement probe calibration coefficient data storage unit for inputting and storing amplitude and phase data related to the ratio of the measured magnetic field strength of the magnetic field measurement probe to the output voltage, and an arithmetic unit. It is characterized in that it is configured by a display unit for displaying the generated time axis waveform data.

The arithmetic unit of the waveform processing device has a function of performing Fourier transform on the inputted numerical data of the waveform, a function of performing arithmetic processing on the stored data of the calibration coefficient of the magnetic field measuring probe and the numerical data after the Fourier transform. It is characterized by having a function of performing an inverse Fourier transform on numerical data after arithmetic processing.

A magnetic field measuring probe having a known calibration coefficient, which is the relationship between the measured magnetic field strength and the output voltage amplitude ratio and phase difference in the frequency domain, and an oscilloscope for measuring the output voltage waveform of the probe are used. The oscilloscope has a function of converting the input waveform data into numerical data, a function of performing a Fourier transform on the converted numerical data, a function of inputting and storing the data of the calibration coefficient of the magnetic field measurement probe, and a function of the calibration coefficient and the Fourier transform. It is characterized by having a function of performing arithmetic processing on numerical data, a function of performing an inverse Fourier transform on the numerical data after the arithmetic processing, and a function of displaying the numerical data after the inverse Fourier transform as a waveform.

[0015]

In the measurement of the magnetic field waveform, the ratio C (f) between the measured magnetic field H (f) and the output voltage when terminated with an impedance equal to the input impedance of the waveform measuring receiver is known in the band related to the measurement. A magnetic field measuring probe is used. f is a frequency, and the terminal impedance is usually 50 ohms. C (f) consists of amplitude ratio and phase difference data. Output voltage waveform v (t) of magnetic field measurement probe
Let V (f) be the Fourier transform of H (f), and let H (f) be the frequency characteristic of the received magnetic field. H (f) = C (f) between V (f), C (f), and H (f). ) V (f) (1). Equation (1) separately calculates the amplitude and the phase difference. The amplitude term is multiplied and the phase difference term is added. The time-axis waveform h (t) of the magnetic field is obtained by inverse Fourier transforming H (f).

According to this method, the measurable frequency band of a voltage waveform measuring device such as an oscilloscope and the amplitude ratio and phase difference between the measured magnetic field strength H (f) and the output voltage V (f) of a magnetic field measuring probe such as a loop probe are measured. Waveforms can be measured within the frequency band for which data is obtained, and are not limited by the frequency characteristics of the magnetic field measurement probe.

The measurable frequency band is determined from the frequency band of the electric field waveform measuring device or the calibratable frequency band of the magnetic field measuring probe.

Measured magnetic field strength H of the magnetic field measuring probe
The amplitude ratio and the phase difference between (f) and the output voltage V (f) can be measured by using a microstrip line having a sufficiently wide ground plane and matching termination as a standard magnetic field source (for example, by Sasaki et al. , "Calibration of loop probe for magnetic field measurement", Proceedings of the 1994 IEICE Spring National Convention, B-285).

[0019]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing a measuring system 1 according to the present invention. The measurement system 1 includes a magnetic field measurement probe 2, a voltage waveform measurement device 3 that converts a waveform into numerical data and can be transferred to the outside, and a waveform processing device 4. The waveform processing device 4 calculates the magnetic field strength H (f) and the output voltage V of the magnetic field measurement probe 2 and the numerical calculation part 5 that calculates the numerical data of the time axis waveform sent from the voltage waveform measurement device 3.
It is composed of a magnetic field measurement probe calibration data storage unit 6 having a function of inputting and storing amplitude and phase data relating to the ratio (f), and a display unit 7 for outputting the calculated data and displaying it as a time axis waveform.

An information processing device such as a computer or a workstation may be used as the waveform processing device 4, and software for enabling the above-mentioned functions may be incorporated in this information processing device.

FIG. 2 shows a state of numerical processing in the waveform processing device 4. Waveform v (t) on the input time axis t
The numerical data 51 is subjected to Fourier transform 52 in the numerical processing calculation unit 5 to obtain data V (f) on the frequency axis f. V
(F) has amplitude and phase data for each frequency. Calculation 54 is performed on V (f) and the calibration coefficient C (f) 53 on the frequency axis f of the measured voltage of the magnetic field measurement probe stored in the calibration data storage unit 6 and the output voltage. C (f) is composed of amplitude and phase data, and the amplitude is multiplied at each frequency,
The phases are added together and the magnetic field data H on the frequency axis f
Obtain (f). The time-axis waveform h (t) is obtained by inverse Fourier transforming H (f) 55. The time axis data is displayed 56 on the waveform display unit 7 as waveform data.

A signal having a periodicity such as a clock signal of a computer has a discrete data on the frequency axis.
In the conversion from (f) to h (t), it can be obtained as the sum of sine waves having the amplitude and phase difference at each frequency. In the case of a non-periodic magnetic field created by the current associated with electrostatic discharge, the frequency spectrum becomes continuous, and it is necessary to execute the inverse Fourier transform. Both the Fourier transform and the inverse Fourier transform are based on the already provided calculation means or method of FFT.

Next, as an actual measurement example, an example of measuring a magnetic field waveform in the vicinity of a matching-terminated microstrip line substrate having a characteristic impedance of 50 ohms will be described with reference to the drawings. FIG. 3 shows the measurement block 11. A pulse generator 16 was used to supply a pulsed repetitive current having a frequency of 10 MHz to the microstrip line 15. The high frequency magnetic field generated in the vicinity of the microstrip line substrate 15 by this current is measured using the magnetic field measuring probe 12. A loop probe 12 having a loop surface with a diameter of 10 mm was used as a magnetic field measurement probe.

FIG. 4 shows the calibration coefficient which is the relationship between the measured magnetic field strength of the loop probe 12 used for the measurement and the amplitude ratio and phase difference of the output voltage. For the output voltage waveform of the loop probe 12, a digitizing oscilloscope 13 capable of converting the waveform into numerical data was used as the voltage waveform measuring device 13. FIG. 5 shows the output voltage waveform v of the loop probe 12 when the square wave current (a) and the triangle wave current (b) are supplied.
(T) is shown.

Voltage waveform v (t) converted into numerical data
Is transferred to the waveform processing device 14 and the time axis waveform of the magnetic field after the data processing shown in FIG. 2 is performed is shown by the solid line in FIG. The vertical axis is shown in terms of the current flowing through the microstrip line 15. The broken line in FIG. 6 is a time-axis waveform of the current obtained by measuring the voltage between the strip conductor and the ground plane of the microstrip line 15 with a receiver having an input impedance of 50 ohms and dividing the voltage by the input impedance.

The high frequency current flowing on the transmission line generates a high frequency magnetic field. Therefore, the waveform of the high frequency current can be obtained by measuring the waveform of the high frequency magnetic field near the current.

FIG. 7 is a block diagram of the measuring system 21 according to the second embodiment of the present invention. Main measurement system 2
Reference numeral 1 is composed of a loop probe 22 and an oscilloscope 23 having a known calibration coefficient, which is the relationship between the measured magnetic field strength in the frequency domain and the amplitude ratio phase difference of the output voltage. The oscilloscope 23 has a function 2 for converting waveform data into numerical data.
4, arithmetic operation of this numerical data, Fourier transform,
It has a calculation function 25 that enables calculation of the inverse Fourier transform, a function 26 that inputs and stores the calibration coefficient of the loop probe 22 that measures the magnetic field strength, and a function 27 that displays the waveform data after calculation. The processing of the output voltage of the loop probe 22 follows the same flow as in FIG.

[0029]

As described above, in the time domain waveform measuring system of the magnetic field according to the present invention, the frequency component of the measured magnetic field waveform is the relationship between the measured magnetic field strength of the magnetic field measuring probe, the amplitude ratio of the output voltage, and the phase difference. As long as it is included in the calibrated frequency band, it can be measured without being limited by the frequency characteristics of the magnetic field measurement probe, so it is possible to measure magnetic fields and currents that have wide-band frequency components due to computer clock signals and electrostatic discharge. It has an effect that the time axis waveform can be accurately measured. Further, if a loop antenna is used as the magnetic field measuring probe, it is not necessary to penetrate a cable or the like, so that there is no restriction due to the object to be measured.

[Brief description of drawings]

FIG. 1 is a block diagram of a magnetic field waveform measuring system according to a first embodiment of the present invention.

FIG. 2 is a diagram showing a processing flow of numerical data.

FIG. 3 is a block diagram showing a measurement example of a magnetic field waveform.

FIG. 4 is a frequency characteristic diagram of a calibration coefficient of a loop probe.

FIG. 5 is an output voltage waveform diagram.

FIG. 6 is a magnetic field waveform diagram.

FIG. 7 is a block diagram of a magnetic field waveform measuring system according to a second embodiment of the present invention.

FIG. 8 is a current waveform measurement block diagram according to a conventional technique.

FIG. 9 shows a current probe according to the prior art.

FIG. 10 is a block diagram of a magnetic field waveform measurement according to a conventional technique.

FIG. 11 is a block diagram of a conventional electromagnetic field waveform measurement.

FIG. 12 is a frequency characteristic diagram of the calibration coefficient of the loop probe.

FIG. 13 is a diagram showing a measurement result of a magnetic field waveform according to a conventional technique.

[Explanation of symbols]

 1 Magnetic field waveform measurement system 2 Waveform measurement probe 3 Voltage waveform measurement device 4 Waveform processing device 5 Numerical calculation unit 6 Magnetic field measurement probe calibration data storage unit 7 Waveform data display unit 11 Measurement block diagram 12 Loop probe 13 Digitizing oscilloscope 14 Waveform Processing device 15 Microstrip line 16 Pulse generator 21 Magnetic field waveform measurement system 22 Magnetic field measurement probe 23 Oscilloscope 24 Waveform data-numerical data conversion function 25 Calculation function 26 Magnetic field measurement probe calibration data storage function 27 Calculation processing data display function 31 Current Waveform measurement system 32 Current probe 33 Oscilloscope 34 Ring core 35 Secondary coil 36 Cable to be measured 41 Magnetic field waveform measurement system 42 Loop probe 43 Integration circuit 44 Oscilloscope 45 Broadband antenna 51 Numerical data v (t) 52 Fourier transform process of voltage time axis waveform 53 Calibration data C (f) 54 of magnetic field measurement probe 54 Calculation process for selling frequency characteristics of magnetic field 55 Magnetic field time axis waveform data h (T) Display of 56 data

Claims (3)

[Claims] 1. A magnetic field measuring probe having a known calibration coefficient, which is the relationship between the measured magnetic field strength in the frequency domain and the amplitude ratio and phase difference of the output voltage, and an input waveform that can be converted into numerical data and transferred to an external device. It is composed of a voltage waveform measuring device and a waveform processing device for processing the numerical data of the time axis waveform sent from the voltage waveform measuring device. The waveform processing device is an arithmetic unit for arithmetically processing the input numerical data and a magnetic field measuring probe. Of the magnetic field measurement probe calibration coefficient data storage unit for inputting and storing amplitude and phase data related to the ratio of the measured magnetic field strength to the output voltage, and a display unit for displaying the calculated time-axis waveform data. Characteristic magnetic field waveform measurement system. 2. The calculation unit of the waveform processing device has a function of performing a Fourier transform on the input numerical data of the waveform, and a function of calculating the stored data of the calibration coefficient of the magnetic field measuring probe and the numerical data after the Fourier transform. 2. The magnetic field waveform measuring system according to claim 1, further comprising a function of performing an inverse Fourier transform on the numerical data after the arithmetic processing. 3. A magnetic field measurement probe having a known calibration coefficient, which is the relationship between the measured magnetic field strength in the frequency domain and the amplitude ratio and phase difference of the output voltage, and an oscilloscope for measuring the output voltage waveform of the probe. The oscilloscope has a function of converting the input waveform data into numerical data, a function of performing a Fourier transform on the converted numerical data, a function of inputting and storing the calibration coefficient data of the magnetic field measurement probe, a calibration coefficient and a Fourier transform. A magnetic field waveform characterized by having a function of performing arithmetic processing on the subsequent numerical data, a function of performing an inverse Fourier transform on the numerical data after the arithmetic processing, and a function of displaying the numerical data after the inverse Fourier transform as a waveform. Measuring system.