JPH0660913B2 - High frequency current measurement method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial application] The present invention inserts a small resistor for current detection into a circuit to be measured and measures the potential difference across the small resistance to measure the high frequency current flowing in the circuit to be measured. More specifically, it relates to a method for measuring a high-frequency current that indirectly measures, when measuring a circuit current related to a high frequency of a circuit under measurement, a frequency characteristic of a small resistor for current detection is measured in advance and stored in a storage unit. Therefore, when a current detection resistor is actually inserted in the circuit under test, the stored characteristic value is corrected and calculated from the measured value obtained from the potential difference between both ends of the resistance for current detection. The present invention relates to a high-frequency current measuring method capable of correcting an actually measured value obtained from a resistor and measuring an accurate high-frequency current.

[Prior Art] Usually, when measuring the current of a circuit under test, as shown in the example in FIG. 1, a shunt having a small resistance value in the current path to be measured in the circuit under test 2. Insert a resistor Rs or a primary coil (not shown) of the current transformer in the current path to be measured to measure the voltage drop of the shunt resistor Rs or the voltage generated in the secondary coil of the current transformer. A method of observing with a voltmeter 4 or a measuring instrument such as an oscilloscope (not shown) is used.

However, when the frequency component of the current of the circuit under measurement becomes about 100 KHz or more, the stray impedance or the stray impedance such as the stray inductance or the stray capacitance existing in the shunt resistor Rs itself shown by the symbol of pure resistance in FIG. It becomes impossible to ignore the measurement error that occurs due to the non-constant frequency characteristic of the primary current-secondary current conversion characteristic of the current transformer. It is not uncommon for the measurement error to reach a value of several tens of percent or more.

Therefore, conventionally, efforts have been made to devise a structure for reducing the stray inductance or stray capacitance of the detector itself related to the shunt resistance Rs and the like.

However, the improvement of these detectors itself cannot reduce the physical size beyond a certain limit because, for example, a problem of a change in resistance due to heat generation of the shunt resistor Rs newly occurs. Therefore, the error factor that the stray impedance of the shunt resistor Rs induces a measurement error at high frequency has not been eliminated. In particular, there is a drawback that the measurement error at the time of measuring a high-frequency large current greatly exceeds a normal allowable limit of, for example, ± 5%.

[Problems to be Solved by the Invention] The present invention has been made in order to overcome the above-mentioned inconvenience, and when measuring a high frequency circuit current of a circuit under measurement, impedance of a shunt resistor which is a current detection element is previously measured. ,
Frequency characteristics such as phase are measured and stored in storage means,
Next, the current detection element is inserted into the circuit under measurement to detect the current value from the circuit under measurement, and then the characteristic of the current detection element stored in the storage means from the measured value obtained by measurement. An object of the present invention is to provide a high-frequency current measuring method capable of correcting a measured value by performing a correction calculation of a value and performing a true high-frequency current measurement.

[Means for Solving the Problems] In order to achieve the above-mentioned object, the present invention, when measuring a high frequency current of a circuit under measurement, has a frequency characteristic of impedance of a current detecting means or a current transformer of a current transformer in advance. A first step of measuring a frequency characteristic of the ratio; a second step of storing the data obtained by the first step in a first storage means; and a step of connecting the current detection means to a circuit under measurement, A third step of decomposing the signal obtained from the current detection means into a plurality of frequency component signals based on the signal waveform, and the signal related to the frequency component obtained by the third step is stored in the second storage means. A fourth step of calculating a high-frequency current flowing through the circuit to be measured by performing a correction operation on the data in the second storage means using the data in the first storage means for each frequency component; Characterized in that comprising the steps.

[Embodiment] Next, a high-frequency current measuring method according to the present invention will be described in detail below with reference to preferred embodiments in relation to an apparatus for carrying out the method, with reference to the accompanying drawings.

FIG. 2 is a schematic configuration diagram of an apparatus for carrying out the present invention, in which reference numeral 10 indicates a high frequency current detecting apparatus. The high-frequency current detection device 10 basically includes a shunt resistor 12 that detects a high-frequency current, a waveform storage unit 14 including a wave memory or a digital storage oscilloscope, and a microprocessor unit 16 (hereinafter, referred to as M
And a control unit 18 including a PU). Here, the shunt resistor 12 is inserted in a desired current path of the circuit under test, and the potential difference V across the shunt resistor 12 is stored in the waveform storage section 14.
It is introduced to the A / D converter 20 in the waveform storage section 14 via the signal introduction terminals 15a and 15b. In the A / D converter 20, the instantaneous value of the input voltage V is quantized and digitized and stored in the memory 22.
Transferred to. In this case, the waveform storage unit 14 is provided with a GPIB interface 24, and the waveform signal as a digital signal stored in the memory 22 is the GPIB interface 24, the GPIB bus line 25 and the G signal in the control unit 18.
It is stored in the RAM 28, for example, in the first storage area 28a based on the judgment processing operation of the MPU 16 via the PIB interface 26.

The control unit 18 includes the MPU 16 and GPIB interface.
26, RAM 28, ROM 30, output interface 32,
The input interface 34 is basically formed, and the respective constituent elements are connected to each other by a bus line forming a data bus, an address bus, or the like. Here, a keyboard input signal from the keyboard 36 is introduced to the input interface 34, and a display display signal is supplied from the output interface 32 to the display 38.

The device for carrying out the current detection method according to the present embodiment is basically constructed as described above, and its operation and effect will be described below.

When measuring a high frequency current by the high frequency current detecting device 10 according to the method of the present invention, first, it is necessary to measure the impedance characteristic of the shunt resistor 12. Now, let the impedance of the shunt resistor 12 be Z (nω). Here, the reference symbol ω is the angular frequency of the fundamental wave, and n is a multiple and represents a natural number. Impedance Z (nω) of shunt resistor 12
The relationship between frequency and frequency should be measured in the entire frequency range expected by an impedance measuring instrument such as a high frequency bridge prepared separately.

In this case, if the frequency characteristic of impedance is expressed by a mathematical formula, it can be expressed by the following formulas (1) to (3).

Here, the equation (1) is the impedance Z of the shunt resistor 12.
(nω) is a real part R _e [Z (nω)] and an imaginary part I _m [Z (nω)].
Equation (2) indicates the absolute value of impedance Z (nω), and Equation (3) indicates impedance Z (nω).
is an equation showing the phase characteristic of ω). In this case, if the present inventors show an actual measurement example, when an allowable power consumption of 5 W as the shunt resistance 12 and a metal film resistance of a nominal resistance value of 1 Ω are measured, the equivalent circuit shown in FIG. 3 is obtained. It was That is, the equivalent circuit is an RLC parallel series circuit composed of a resistance R ₀ , a stray inductance L ₀ , and a stray capacitance C ₀ , and the resistance R _{0 has} a value of 1Ω, the stray inductance L _{0 has} a value of 14 _n H, and the stray capacitance C _0.
The value of is 400 _P F. In this impedance characteristic, the absolute value | Z (nω) | is represented as shown by the characteristic curve in FIG. 4b, and the impedance angle φ (nω) is represented as shown by the specific curve in FIG. 4a. . As can be seen from FIG. 4b, the absolute value | Z (nω) | has an impedance of about 35Ω at the antiresonance frequency of about 67 MHz. At that frequency, the phase angle φ (nω) is delayed by approximately -80 °. In the coordinates of the characteristic curves in FIGS. 4A and 4B, the frequency on the horizontal axis and the absolute value of the impedance on the vertical axis | Z (nω) | are logarithmic expressions.
The phase angle φ (nω) on the vertical axis is a real number expression.

Therefore, these data are stored in the first data of the RAM 28 in the control unit 18.
The frequency is stored in advance in the storage area 28a with the frequency as an address.

Next, the current flowing through the load 42 when the power is supplied from the power supply 40 having the internal resistance R _i as the circuit under test to the load 42 will be described.

Since a high frequency current I (nω) including a fundamental wave and its harmonic components generally flows through the shunt resistor 12,
A voltage drop V (nω) occurs between the terminals. The high frequency voltage V (nω) is expressed as in Expression (4).

Here, φ _n is the phase angle of the nth harmonic. The voltage V (nω) including this harmonic is A / D converter 2 of the waveform storage unit 14.
After being stored in the memory 22 digitized by 0, G
The data is transferred to the control unit 18 through the PIB interfaces 24 and 26. In this case, the FFT (Fast FoF) previously written in the ROM 30 based on the determination processing of the MPU 16.
urier Transform) or DFT (Discrete Fourier T)
Fourier transform by a program of ransform), decomposed into a fundamental frequency and its nth harmonic, and stored in the second storage area 28b of the RAM 28.

When the acquisition of the waveform is completed, the MPU 16 then performs a correction calculation for each frequency from the measured high frequency current of the circuit under measurement 40 included in the second storage area 28b and the measurement value of the shunt resistor 12 measured in advance. Then, the true value of the high frequency current I (nω) flowing through the load 42 is calculated. In this case, the high frequency current I (nω) is expressed as shown in the equation (5).

The actual measurement value V (nω) of the voltage is corrected and the true value I (nω) of the high frequency current is calculated by executing the correction calculation according to the calculation formula shown in the formula (5) in the control unit 18, and the RAM 28 is calculated. Is stored in the third storage area 28c. The desired high frequency current I (nω) can be displayed on the display 38 via the output interface 32, for example, or can be displayed on a printer (not shown). It is possible.

In the above embodiments, the shunt resistor is used as the current detection element, but instead of the shunt resistor, for example,
The method of the present invention can be carried out even when a current transformer is used. In this case, the transformation ratio between the primary current and the secondary current of the current transformer is stored in advance in a predetermined storage area of the RAM 28 in the control unit 18 as a function of frequency. Of course, it is only necessary to let it be done.

[Advantages of the Invention] As described above, according to the present invention, when the high frequency current of the circuit under measurement is measured, the frequency characteristic of the current detection element is measured in advance and stored in the storage means. Therefore, it is possible to perform extremely accurate current measurement even at a high frequency by correcting and calculating the previously measured value from the value obtained by actually inserting the current detecting element into the circuit to be measured. Moreover, since a waveform memory or digital storage oscilloscope is used as the waveform storage unit and a microprocessor is used as the control unit, signal acquisition and correction calculation can be executed in an extremely short time, resulting in high-frequency current measurement. Has the effect that it can be executed accurately and in a short time.

Although the present invention has been described with reference to the preferred embodiment, the present invention is not limited to this embodiment,
It goes without saying that various improvements and design changes can be made without departing from the scope of the present invention.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of a current detection circuit for implementing a conventional high-frequency current measuring method, FIG. 2 is a block diagram including a current detecting device for implementing the method of the present invention, and FIG. 3 is a current detecting means. FIG. 4 is an actual equivalent circuit diagram of the shunt resistor, and FIG. 4 is an impedance diagram and a phase characteristic diagram of the shunt resistor. 10 …… High frequency current detector 12 …… Shunt resistance, 14 …… Waveform storage section 16 …… MPU, 18 …… Control section 20 …… A / D converter, 22 …… Memory 24 …… GPIB interface 25 …… GPIB bus line 26 ... GPIB interface 28 ... RAM, 30 ... ROM 32 ... output interface 34 ... input interface 36 ... keyboard, 38 ... display 40 ... measured circuit, 42 ... load resistance

Claims (4)

[Claims] 1. When measuring a high frequency current of a circuit to be measured, a first step of measuring a frequency characteristic of an impedance of a current detecting means or a frequency characteristic of a current transformation ratio of a current transformer in advance, and the first step A second step of storing the obtained data in the first storage means; connecting the current detection means to a circuit under test, and converting the signal obtained from the current detection means into a plurality of frequency components based on the signal waveform. A third step of decomposing into a signal, a fourth step of storing the signal related to the frequency component obtained in the third step in a second storage means, and a step of storing the data in the second storage means in the second step. 1. A high frequency current measuring method comprising: a fifth step of calculating a high frequency current flowing through the circuit to be measured by performing a correction calculation for each frequency component using the data related to one storage means. 2. The high frequency current measuring method according to claim 1, wherein the current detecting means is a shunt resistor or a current transformer. 3. The high frequency current measuring method according to claim 1, wherein the detection of the signal from the current detecting means is performed by the waveform storing means. 4. A high-frequency current measuring method according to claim 1, wherein the data storage means is controlled by a microcomputer.