JP2002228695A - Resistance measuring apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a resistance measuring capable of shortening the measurement time and attaining high accuracy in the case of measuring a low resistance value containing inductance like a current conductor of switches for electric power and reducing the size of the apparatus and the power consumption. SOLUTION: In the resistance measuring apparatus provided with a power source circuit for sending current to an object to be measured 100 including an inductance L2 part from between two terminals, a voltage measuring circuit for measuring the voltage between the two terminals of the object to be measured, a current measuring circuit for measuring current flowing in the object to be measured and a resistance calculation circuit for calculating the resistance value by dividing the voltage value measured with the voltage measuring circuit by the current value measured with the current measuring circuit, the power source circuit makes a current (i) of a waveform including a point where the current variation with time becomes 0, flow to the object to be measured 100, and the resistance calculation circuit calculates a resistance value R2 of the object to be measured 100, from the voltage and the current at the timing when the current variation becomes 0.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a resistance measuring device for measuring a low resistance value at a current conductor of a power switchgear or the like, and at a contact portion of the current conductor.

[0002]

2. Description of the Related Art In a power switchgear, if the resistance of an energizing path increases due to an abnormality in a contact portion of a current conductor or an abnormality in a current conductor itself, the contact portion or the current may be reduced when a large current is applied. There is a risk that the conductor itself will overheat and cause an accident. For this reason, the resistance value of the current conductor including the contact portion has been measured and monitored during maintenance and inspection of power switchgears and the like.

[0003] Since the resistance values of the current conductor and the contact portion are extremely low, a resistance measurement method using a four-terminal method (also referred to as a four-wire method) has conventionally been used. . FIG. 4 is a diagram for explaining the principle of a generally used conventional four-terminal resistance measuring apparatus. In FIG. 4, reference numeral 1 denotes an object to be measured such as a conductor and a conductor contact portion, 2 denotes a DC power supply, 3 denotes a constant current controller, 4 denotes a switch, and 5 denotes a voltmeter for measuring a potential difference generated between both ends of the object to be measured 1. is there.

[0004] A resistance measuring method of the resistance measuring apparatus configured as described above will be described. First, in this circuit, the switch 4 is closed, and a constant current is applied to the device under test 1.
Next, the voltmeter 5 measures a potential difference generated at both ends of the DUT 1. When the potential difference of the current flowing through the DUT 1 I, the DUT 1 and V _R, the resistance value R of the object 2 from Ohm's law becomes R = V R / _I.

[0005] If here in the current I is constant, the potential difference _{V R}
Is proportional to the resistance value R of the device under test 1. Therefore, by setting the current I to a predetermined value, by measuring the potential difference V _R,
The resistance value R of the device under test 1 can be determined. However, in the above-described conventional example, it is necessary to set the measuring current to a predetermined value according to the DUT 1 and then measure the resistance value. There is a need. Depending on the state of the conductor or the conductor contact portion as the DUT 1, the resistance value changes when energized, so it is necessary to read the value while adjusting the current I and confirming that it is stable. was there.

As described above, in the above-described conventional example, it is necessary to read the measured current and to adjust the measured current. Even with the same DUT 1, the resistance measured by the habit of the measurer or the like is required. There was a risk that the values would fluctuate or measurement errors would occur.

As another conventional example, FIG.
1 shows a resistance measuring device disclosed in Japanese Patent No. 4634. This is to automate the measurement work of the above technical example, eliminate the dispersion of measured values due to individual differences, and the problem of measurement errors, so that the resistance value of the conductor contact part can be measured with high reliability. It is.

In FIG. 5, reference numeral 6 denotes a resistance measuring device.
Both ends of the DUT 1 are connected via current cables 11a and 11b and voltage leads 12a and 12b. 7
Is a constant current power supply, includes a variable constant current circuit, and includes an energizing relay 9, a current cable 11a, a device under test 1, and a current cable 1.
A constant measurement current is supplied to the device under test 1 via 1b. Reference numeral 8 denotes an A / D converter, which receives an analog voltage generated at both ends of the DUT 1, converts the analog voltage into a digital signal, and outputs the digital signal to the controller 10.

Although not shown, the controller 10 includes an RO
M, a memory such as a RAM, an I / O port for data input / output, an operation switch section, a data display section, and the like. Execute the process.

Next, a description will be given of a method of measuring the resistance of the conventional resistance measuring apparatus configured as described above. First, the controller 10 sets a voltage generated across the DUT 1 to A / A after a predetermined time has elapsed since the start of energization of the DUT 1.
Measurement is performed a plurality of times by the D converter 8 at a fixed time, and the average voltage value is obtained, thereby stabilizing the measurement data. Further, in order to appropriately reject an abnormal voltage value from the voltage values measured a plurality of times, the controller 10 calculates an average voltage value after removing a singular value from the voltage value. Then, the resistance of the DUT 1 is obtained from the current I that has been applied to the DUT 1. In this way, along with automation of measurement work,
It prevented variations in readings and reading errors due to individual differences.

[0011]

The conventional resistance measuring apparatus is constructed as described above. In the former case of measuring the low resistance using the four-terminal method, it is necessary to read a measured current and adjust the same. Also, even with the same DUT 1, there is a risk that the measured resistance value may fluctuate or a measurement error may occur due to the habit of the measurer.

In the latter conventional measuring method, after a certain period of time has elapsed from the start of energization, measurement is further performed a plurality of times during a certain period of time, and the average voltage value is obtained. there were. Further, in the case of a current conductor such as a power switchgear as a measurement target, there is a problem that a large current is inevitably increased due to the necessity of flowing a large current, and a measurement circuit and a device are also increased in scale.

However, in the case of a large current conductor, the resistance value is very small, so the voltage generated at both ends of the DUT is small. If no power supply is used, the measurement accuracy will deteriorate. Further, unless the measurement current is gradually increased, there is a problem that a measurement error occurs due to an inductance voltage generated on a large-scale measurement circuit, and a measurement time becomes longer.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and not only simplifies the measurement work by automating the measurement, but also shortens the measurement time and improves the accuracy. It is an object of the present invention to provide a resistance measuring device capable of reducing the size and power consumption of the device.

[0015]

Means for Solving the Problems Claim 1 according to the present invention.
A resistance measuring device, a power supply circuit for flowing current from both terminals of the device under test including an inductance component,
A voltage measuring circuit for measuring a voltage between both terminals of the device under test,
A current measurement circuit for measuring a current flowing into the device under test; and a resistance calculation circuit for calculating a resistance value by dividing a voltage value measured by the voltage measurement circuit by a current value measured by the current measurement circuit. In the resistance measuring device, the power supply circuit supplies a current having a waveform including a point at which the current change becomes zero with respect to time to the device under test. The resistance value of the device under test is calculated from the voltage value and the current value.

According to a second aspect of the present invention, in the first aspect, the power supply circuit includes a capacitor, a charging circuit for charging the capacitor, and a switch for flowing a current to the device under test. The power supply circuit closes a switch and discharges an electric charge of a capacitor to a device under test, thereby supplying a current having a waveform including a point where a current change becomes zero with respect to time.

According to a third aspect of the present invention, there is provided a resistance measuring apparatus according to the first or second aspect, wherein the current measuring circuit differentiates the measured current value so that a current change with respect to time becomes zero. A certain point is obtained, and a measurement command signal for instructing detection of the current value and the voltage value at this timing is created.

According to a fourth aspect of the present invention, there is provided a resistance measuring apparatus according to any one of the first to third aspects.
The voltage measurement circuit and the current measurement circuit each include an analog / digital converter, and measure while continuously converting the voltage signal and the current signal at the same timing, respectively.
The resistance calculation circuit calculates a resistance value from a current value converted into a digital signal and a voltage value converted into a digital signal at a timing when a current change with respect to time becomes zero.

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment 1 FIG. 1 is a block diagram showing a configuration of a resistance measuring device according to Embodiment 1 of the present invention. FIG. 2 is a diagram showing an equivalent circuit as a measuring principle in the resistance measuring device shown in FIG. FIG. 4 is a schematic waveform diagram showing a current waveform and a voltage waveform during resistance measurement.

[0020] In Figure, 100 is the object to be measured comprising ₂ minutes inductance L of such conductors and the conductor contact portion, the capacitor 19 constituting the power supply circuit for resistance measurements, the 18 charging circuit of the capacitor 19, the 23 the A DC power supply connected to the charging circuit 18 charges the capacitor 19 via the charging circuit 18. Reference numeral 20 denotes a current waveform control circuit, which includes the switch 16 shown in FIG. 2 and a current sensor as a part of a current measurement circuit for detecting a flowing current i. The switch 16 uses a semiconductor switch element in order to prevent surge noise at the time of on / off.

A measuring circuit 21 has a voltage measuring circuit for measuring a voltage value of the device under test 100. Further, it is composed of two sets of A / D converters and a memory circuit, and converts an analog current signal detected by the current waveform control circuit 20 into a digital signal by the A / D converter. Then, the analog voltage signal obtained from the device under test 100 is converted to the other A / D signal.
The signal is converted into a digital signal by a converter. Then, the peak value of the current signal detected by the current waveform control circuit 20 is obtained,
The current digital signal and the voltage digital signal before and after the peak value are stored in the memory circuit.

Reference numeral 22 denotes a controller (not shown), which has various sequence control functions for measurement, and calculates the peak value of the current and the timing of the peak value. Further, a resistance calculation circuit is provided for calculating the resistance value by dividing the voltage value at the timing by the current value. Further, it comprises a measurement instructing unit for giving a measurement instruction and a display unit for displaying a measurement result. The device under test 100 is connected to the current waveform control circuit 20 by a current cable line.
And the measuring circuit 21 via a voltage lead.

Next, a method of measuring the resistance of the resistance measuring apparatus according to the first embodiment configured as described above will be described.
First, a measurement start command is given by operating the measurement instruction section of the controller 22. Next, the DC power supply 2
Control the charging circuit 18 connected to the
To a voltage at which a predetermined current flows.

Next, when the charging of the capacitor 19 is completed, the controller 22 turns on the switch 16 provided in the current waveform control circuit 20. Next, switch 1
When the switch 6 is turned on, the charge stored in the capacitor 19 is discharged to the device under test 100 connected by the current cable.

Next, the waveform of the discharged current is as shown in FIG. 3, and the current sensor i provided in the current waveform control circuit 20 detects the supplied current i and sends it to the measurement circuit 21 at the next stage. In addition, the current waveform control circuit 20 detects the energizing current i by the current sensor, and when the energizing current i reaches a predetermined current value, sends the data as a data acquisition timing signal to the next-stage measurement circuit 21.

Next, the analog current signal of the measured conduction current i and the analog voltage signal between the terminals of the device under test 100 are converted into current waveforms by two sets of A / D converters installed in the measurement circuit 21. In synchronization with the arrival of the timing signal from the control circuit 20, the digital signal is converted into a digital data signal at the same timing. Then, a predetermined number of samples is fetched into the memory circuit in the measuring circuit 21, and when the fetching of the predetermined number of samples is completed, the measurement data in the memory circuit is sent from the measuring circuit 21 to the controller 22.

Next, the controller 22 calculates the peak value (ie, the current i) from the measured data of the current value (FIG. 3A).
From continuous differentiation on the data obtained, that the current change is zero with respect to time, where the point t ₀₎ determined. Next, with respect to time of the peak values from the measured data (FIG. 3 (b)) of the voltage value, the same timing (i.e., t ₀ point) determined the voltage value taken in the calculation of the resistance value = voltage / current from seeking the resistance _{R 2} of the object to be measured 100. Then, the resistance value R ₂ is displayed as a measurement result on the display unit of the controller 22.

Next, the measurement principle of the resistance measuring apparatus described above will be described with reference to FIGS. 2 and 3. 2, the object to be measured 100 are expressed as DC resistance _{R 2} which includes an inductance _{L 2.} C is the capacitance of the capacitor 19, and i is the current flowing when the switch 16 is closed and the capacitor 19 is discharged.

The inductance L ₁ and the resistance R ₁ is, L to be distributed on the measurement circuit, L for the current waveform adjustment of the current waveform control circuit 20 for obtaining the easy peak value measured at resistance measurement and R components, R And components. In principle, as described above, the capacitor 19 is charged by the charging circuit 18 in advance. Then, by closing the switch 16, electric current i is the measured object 100, flows through the inductance _{L 1,} and a resistor _{R 1.}

Next, a current having a peak value flows in the inductance L ₂ and the resistance R ₂ of the DUT 100 on the closed circuit as the conduction current i. Then, the peak value of the conduction current i is detected, and the current value and the inductance L ₂ of the device under test 100 and the voltage drop v of the resistor R ₂ are measured.
Next, the DC resistance R of the device under test 100 is calculated from the supplied current i.
The value of ₂ is obtained by R ₂ = v / i (calculation formula described later).

From FIG. 2, the following formula is established. Assuming that L = L ₁ + L ₂ and R = R ₁ + R ₂ , Ri + Ldi / dt + vc = 0 (1) i−C (dvc / dt) = 0 (2) L ₂ di / dt + R ₂ i = v capacitance C of (3) the capacitor 19 is charged to vc = _{E 0} at t = 0. Obtaining resistance is R _2, determined by measuring the electric current i and the voltage drop v. At this time, d
When i / dt = 0 and becomes time is _{t 0, R 2 = v /} i , and the error becomes zero.

More specifically, when the switch 16 is closed and the charge of the capacitance C of the capacitor 15 that has been charged is discharged to the device under test 1, C and C on the measurement circuit are changed as shown in FIG.
A current waveform having a discharge time constant according to the constants of L and R is obtained. On this current waveform, when the change in the current flowing through the device under test 100 with respect to time is zero (that is, when the current has a peak value), this is a point where the inductance L does not affect the induced voltage.

[0033] Therefore, by generating the current waveform (adjusted to the optimum value in the inductance _{L 1} and a resistance _{R 1)} having a di / dt = 0, and the peak value of the current flowing through the object to be measured 100, at that time If the voltage value is obtained, the resistance value can be measured without error, and the measurement of low resistance can be performed in a very short time. In addition, since a capacitor is used as a power supply for the measurement, and the current supply time of the measurement current is short, it contributes to miniaturization of the apparatus including the current cable.

As described above, according to the resistance measuring apparatus of the first embodiment of the present invention, even if the object to be measured has a low resistance including inductance, such as a current conductor of a power switchgear, etc. As a power supply circuit for measurement, a capacitor and a charging circuit for the capacitor are provided. Further, a switch for flowing a current to an object to be measured is formed, and when the capacitor is discharged, di / d
Current waveform having t = 0 (inductance L ₁ and resistance R ₁
By adjusting the peak value of the current flowing through the device under test and the voltage value at that time, the measurement of the resistance value of the device under test can be performed with high accuracy. Measurement can be performed in a short time.

As described above, since the capacitor is used as the power supply for measurement, and the current supply time of the measurement current is short, a large-capacity power supply is not required, and the apparatus including the current cable can be reduced in size and power consumption can be reduced. Can contribute. Needless to say, the measurement of the resistance value is automated, and the measurement is simplified.

[0036]

As described above, according to the first aspect of the present invention, a power supply circuit for flowing a current to a device under test including an inductance from both terminals of the device under test, and both ends of the device under test Divide the voltage value measured by the voltage measurement circuit by the voltage measurement circuit that measures the voltage between the terminals, the current measurement circuit that measures the current flowing into the device under test, and the current value measured by the current measurement circuit. In a resistance measurement device including a resistance calculation circuit that calculates a resistance value, the power supply circuit passes a current having a waveform including a point where a current change with respect to time becomes zero to the device under test,
The resistance calculation circuit calculates the resistance value of the device under test from the voltage value and the current value at the time when the current change with respect to time becomes zero, so that the measurement time is reduced, the device is reduced in size, and power consumption is reduced. In addition, it is possible to provide a resistance measuring device that can measure the resistance of the device under test with high accuracy.

According to a second aspect of the present invention, in the first aspect, the power supply circuit comprises a capacitor, a charging circuit for charging the capacitor, and a switch for flowing a current to the device under test. The circuit closes the switch and discharges the charge of the capacitor to the device under test, so that a current having a waveform including a point where the current change becomes zero with respect to time is supplied. It is possible to provide a resistance measuring device capable of easily supplying a current having a waveform including a point to the device under test.

According to a third aspect of the present invention, in the first or second aspect, the current measuring circuit differentiates the measured current value to determine a point where the current change with respect to time becomes zero. Since a measurement command signal that instructs to detect the current value and the voltage value at this timing is created, a resistance measurement that can reliably determine and measure a point where the current change becomes zero with respect to time is obtained. A device can be provided.

According to a fourth aspect of the present invention, in any one of the first to third aspects, the voltage measurement circuit and the current measurement circuit each include an analog / digital converter, and include a voltage signal and a voltage signal. The current signal is measured while being continuously converted at the same timing, and the resistance calculation circuit converts the current value into a digital signal and the digital signal at the timing when the current change becomes zero with respect to time. Since the resistance value is calculated from the measured voltage value, it is possible to provide a resistance measuring device capable of measuring the resistance with high accuracy.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of a low-resistance measuring device according to a first embodiment.

FIG. 2 is a diagram showing an equivalent circuit as a measurement principle of FIG.

FIG. 3 is a schematic diagram showing a current waveform and a voltage waveform at the time of resistance measurement in FIG. 2;

FIG. 4 is a principle diagram of resistance measurement according to a conventional example using a four-terminal method.

FIG. 5 is a block diagram showing a resistance measuring apparatus according to a conventional example.

[Explanation of symbols]

16 switches, 18 charging circuits, 19 capacitors,
Reference Signs List 20 current waveform control circuit, 21 measurement circuit, 22 controller, 23 DC power supply, 100 DUT.

Claims (4)

[Claims] A power supply circuit for flowing a current to an object to be measured including an inductance from both terminals of the object to be measured;
A voltage measurement circuit that measures a voltage between both terminals of the device under test, a current measurement circuit that measures a current flowing into the device under test, and a voltage value measured by the voltage measurement circuit to the current measurement circuit. And a resistance calculating circuit for calculating a resistance value by dividing the current value by the measured current value, wherein the power supply circuit receives the current having a waveform including a point at which the current change becomes zero with respect to time. A resistance measuring apparatus, wherein a current is supplied to a measured object, and the resistance calculating circuit calculates a resistance value of the measured object from a voltage value and a current value at a timing when a current change becomes zero with respect to the time. 2. The power supply circuit includes a capacitor, a charging circuit for charging the capacitor, and a switch for flowing a current to the device under test. The power supply circuit closes the switch to connect to the device under test. 2. A current having a waveform including a point at which a change in current with respect to time becomes zero is discharged by discharging the electric charge of the capacitor.
3. The resistance measuring device according to 1. 3. The current measurement circuit differentiates the measured current value to find a point where the current change becomes zero with respect to time, and instructs to detect the current value and the voltage value at this timing. 2. A measurement command signal is generated.
Or the resistance measuring device according to claim 2. 4. The voltage measuring circuit and the current measuring circuit each include an analog / digital converter, and measure while continuously converting the voltage signal and the current signal at the same timing, respectively. 4. A resistance value is calculated from a current value converted into a digital signal and a voltage value converted into a digital signal at a timing when a current change with respect to time becomes zero. The resistance measuring device according to any one of the above.