JP2002139530A - Earth resistance measuring device - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To measure ground resistance with high accuracy. SOLUTION: In a grounding resistance measuring device 1 for measuring the grounding resistance of a grounding rod, a signal generating unit 6 for generating an AC signal so that a frequency can be varied is connected between a lead wire 14 and the signal generating unit 6. An output resistor 8 and an output end of the output resistor 8;
A signal switching means for outputting a voltage of a part selected from the input terminal and the zero potential part; a synchronous detection part for synchronously detecting an output voltage from the signal switching means with an AC signal; The arithmetic control unit 12 changes the AC signal frequency of the signal generation unit 6 when the output terminal is selected by the signal switching unit 9 and calculates the lowest DC voltage component Vmr generated by the synchronous detection unit 10 and its output. DC voltage component Vmr∞ generated when the input terminal is selected while maintaining the frequency.
The ground resistance is measured based on the DC voltage component Vmr0 generated when the zero potential portion is selected while maintaining the frequency.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ground resistance measuring device for measuring a ground resistance using a signal voltage ratio.

[0002]

2. Description of the Related Art FIG.
Has been conventionally known.
The ground resistance measuring device 51 is configured to be able to measure the ground resistance without using an auxiliary electrode. The first terminal 2, the second terminal 3 connected to the device ground, the operation unit 54, the signal generation unit 6, 1st amplifier 7, output resistance (resistance value Ro: known)
8, a synchronous detection unit 10, a second amplifier 11, a calculation unit 52, a third amplifier 53, and a display unit 55. Further, a lead wire 14 is connected to the first terminal 2, and a return wire 15 is connected to the second terminal 3. Further, a grounding rod 16 to be measured, which is made of a metal rod or the like and is embedded in the ground 17, is connected to the tip of the lead wire 14. in this case,
The return wire 15 is formed of a conductive wire with an insulating coating having a certain length (usually 10 m or more), and is freely arranged on the ground 17 in an insulated state. Instead of the return line 15, a metal plate that can be disposed on the ground 17 in a state insulated from the ground 17 can be used.

The operating section 54 includes frequency setting means (specifically, a variable resistor) for outputting a frequency setting signal, and this frequency setting means is operated by an operator. The signal generator 6 generates a high-frequency sine wave (hereinafter, also referred to as a high-frequency signal vc) having a frequency specified by the frequency setting signal as a measurement signal. Therefore, when the frequency setting unit in the operation unit 54 is operated, the signal generation unit 6 generates a high-frequency signal vc having a frequency corresponding to the operation. First
The amplifier 7 functions as a buffer, and outputs the input high-frequency signal vc as an injection signal Vo with low impedance. The output resistor 8 is connected between the first amplifier 7 and the first terminal 2. Therefore, the injection signal Vo output from the first amplifier 7 is connected to the lead 14 via the output resistor 8.
Supplied to Further, the injection signal Vo supplied to the lead wire 14 is injected into the ground rod 16 to be measured, and the return signal 1
The signal is returned to the ground resistance measuring device 51 via a path including the return line 15 and the second terminal 3 via a coupling capacitance between the ground 5 and the ground 17. The synchronous detection unit 10 receives the voltage Vm generated between the second terminal 3 and the first terminal 2 and performs synchronous detection with the injection signal Vo to thereby obtain the real component (only DC Voltage component). For example, as shown in FIG. 6, the synchronous detection unit 10 includes a multiplier 10a that multiplies the injection signal Vo and the voltage Vm, and a low-pass filter 10b that passes a DC voltage component of the output voltage of the multiplier 10a. It consists of. The second amplifier 11 adjusts the voltage level of the DC voltage component generated by the synchronous detection unit 10, and outputs the result as the final DC voltage component Vmr. The arithmetic unit 52 is configured using, for example, a multiplier, performs a predetermined analog arithmetic process using a DC voltage component Vmr, and performs a predetermined process on the ground resistance Rg.
Generates a voltage that is proportional to the magnitude of the resistance value. The third amplifier 53 performs scaling adjustment on the voltage generated by the calculation unit 52. The display unit 55 is configured by an analog meter, and displays the ground resistance Rg by swinging the meter needle according to the voltage after the scaling adjustment.

Next, the principle of a ground resistance measuring method using the ground resistance measuring device 51 will be described. First, the ground resistance measuring device 51, the lead wire 14, the return wire 15,
FIG. 7 shows an equivalent circuit of a measurement system including the ground 17 and the ground rod 16 to be measured. In this case, in the figure, Rg is the ground resistance of the ground rod 16 to be measured, L is the inductance component of the lead wire 14, C is the ground-to-ground coupling capacitance of the return wire 15,
R means the insulation resistance of the film of the return line 15.
The impedance Zm between the first terminal 2 and the second terminal 3 (that is, the impedance of the loop including the lead wire 14, the ground bar 16 to be measured, the ground 17, and the return wire 15) is expressed by the following equation (1). Is done. Zm = Rm + Im (1) where Rm represents a real number component and Im represents an imaginary number component, and are represented by the following equations (2) and (3), respectively. Rm = Rg + R / (1+ (ωCR) ² ) Formula (2) Im = jωL−jωCR ² / (1+ (ωCR) ² ) Formula (3)

On the other hand, since Im = 0 at the resonance frequency of the loop forming the impedance Zm,
From the expression (3), the following expression (4) is established. R / (1+ (ωCR) ² ) = L / CR (4) In this case, since equation (4) is equal to the second term on the right side of equation (2), CR 、 Under the condition of L, the value of the second term on the right side of the equation (2) becomes zero. As a result, the following equation is established. Rm ≒
Rg Therefore, the ground resistance Rg of the measured ground rod 16 is
It can be calculated based on the voltage Vm obtained by dividing the voltage Vo of the injection signal vo by the output resistance 8 (resistance value Ro) and the ground resistance Rg. For this reason, in the grounding resistance measuring device 51, first, the synchronous detection unit 10 sets the frequency of the injection signal vo equal to the resonance frequency of the loop, and
The voltage Vm at the terminal 2 is synchronously detected with the voltage Vo of the injection signal, and the second amplifier 11 generates a DC voltage component Vmr by adjusting the voltage level. Next, the operation unit 5
2 is (x / (1-
x)) is subjected to an analog operation to generate a DC voltage, and the third amplifier 53 amplifies the DC voltage generated by the operation unit 52 with a predetermined gain, so that the ground resistance R
A DC voltage corresponding to the resistance value of g is generated and output to the display unit 55. As a result, the display unit 55 displays the resistance value of the ground resistance Rg. Rg = Ro × Vmr / (Vo−Vmr) = Ro × x / (1-x) (5) where x = Vmr / Vo

Accordingly, the operator monitors the value of the grounding resistance Rg displayed on the display unit 55 while operating the operation unit 54.
By gradually changing the frequency of the high-frequency signal vc generated by the signal generator 6 by operating the frequency setting means, and searching for a point where the displayed ground resistance Rg becomes the smallest, the smallest value is used as the ground resistance Rg. Can be measured.

[0007]

However, the conventional ground resistance measuring device 51 has the following problems. That is, the value of the DC voltage component Vmr in the above equation (5) is determined by the first amplifier 7, the synchronous detection unit 10, and the second amplifier 1
When the gain or offset voltage at 1 fluctuates, it changes according to the fluctuation. Further, the resistance value of the ground resistance Rg also changes according to the change in the DC voltage component Vmr. On the other hand, it is extremely difficult to keep the above-mentioned gain and offset voltage constant with respect to temperature changes and temporal factors. Therefore, the conventional ground resistance measuring device 51 includes:
There is a problem that it is difficult to measure the ground resistance Rg with high accuracy due to the fluctuation of the gain of the synchronous detection unit 10 and the first amplifier 7 and the like.

The present invention has been made in view of such a problem, and has as its main object to provide a grounding resistance measuring device capable of measuring grounding resistance with high accuracy.

[0009]

According to a first aspect of the present invention, there is provided a ground resistance measuring apparatus, comprising: a lead wire connected to a ground rod to be measured; and a return conductor disposed on the ground in an insulated state. In a ground resistance measuring device configured to be connectable and to measure a ground resistance of the ground rod to be measured, a signal generator configured to generate an AC signal and variably control the frequency thereof, and the lead wire or the An output resistor connected between the return conductor and the signal generation unit, an output end of the output resistor on the lead wire or the return conductor side, an input end of the output resistance on the signal generation unit side, and Signal switching means for selecting one of the zero potential parts and outputting the voltage of the selected part; and synchronously detecting the voltage output from the signal switching means with the AC signal. A synchronous detection unit that generates a flowing voltage component, and an arithmetic control unit, wherein the arithmetic control unit changes the frequency of the AC signal in the signal generation unit when the output terminal is selected by the signal switching unit. The calculated minimum DC voltage component Vmr generated by the synchronous detection unit
And a DC voltage component Vmr # generated by the synchronous detection unit when the input terminal is selected by the signal switching unit while maintaining the frequency, and the zero by the signal switching unit while maintaining the frequency. Based on the DC voltage component Vmr0 generated by the synchronous detection unit at the time of selecting a potential portion, a first subtraction value obtained by subtracting the DC voltage component Vmr0 from the DC voltage component Vmr is calculated equivalently, DC voltage component Vm
A second subtraction value obtained by subtracting the DC voltage component Vmr from r∞ is calculated, and an arithmetic process of multiplying a value obtained by dividing the first subtraction value by the second subtraction value by a resistance value of the output resistor is performed. And measuring the ground resistance.

According to a second aspect of the present invention, in the grounding resistance measuring apparatus according to the first aspect, the DC voltage component Vmr, the DC voltage component Vmr∞, and the DC voltage component Vmr0 are each calculated a plurality of times. The arithmetic control unit may measure the ground resistance by averaging the DC voltage components calculated a plurality of times and performing the arithmetic processing based on the averaged values. .

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of a ground resistance measuring apparatus according to the present invention will be described below with reference to the accompanying drawings. Note that the same components as those of the conventional ground resistance measuring device 51 are denoted by the same reference numerals, and redundant description will be omitted.

As shown in FIG. 1, a ground resistance measuring device 1 comprises a first terminal 2, a second terminal 3, an operation unit 4, a display unit 5 for digitally displaying the measured ground resistance Rg by numerical values,
A signal generator 6 for generating a high-frequency signal vc as a measurement signal;
A synchronous detection unit 10 that generates a DC voltage component by synchronously detecting the voltage output from the amplifier 7, the output resistor 8 having the resistance value Ro, the switch 9, and the switch 9 with the injection signal Vo;
A second amplifier 11 that outputs a DC voltage generated by the synchronous detection unit 10 as a DC voltage component Vmr with low impedance and an operation control unit 12 are provided. Further, a lead wire 14 is connected to the first terminal 2, and a return wire 15 is connected to the second terminal 3. In this case, the lead wire 14 is connected to the measured ground rod 16 buried in the ground 17. On the other hand, the return line 15 is freely arranged on the ground 17 while being insulated from the ground 17.

The signal generator 6 is provided with a DDS (Dire
ct Digital Synthesizer), and generates a high-frequency signal vc having a frequency corresponding to the digital data output by the arithmetic control unit 12.

The operating section 4 includes a frequency setting circuit 41 for outputting a frequency setting signal of an analog signal for setting the frequency of the high frequency signal vc generated by the signal generating section 6.
And an operation start switch 42 that outputs a start signal to the operation control unit 12 to start the operation of calculating the ground resistance Rg. Specifically, the frequency setting circuit 4
1 is provided with a variable resistor as frequency setting means, and a voltage corresponding to the resistance value of the variable resistor is output to the arithmetic and control unit 12 as a frequency setting signal. Switch 9
The first terminal 2 of the output resistor 8 is constituted by, for example, a relay or an analog switch.
One is selected from the output terminal on the side of the first side, the input terminal on the first amplifier 7 side of the output resistor 8, and the zero potential region, and the voltage generated at the selected region is output to the synchronous detection unit 10.
The synchronous detector 10 converts the voltage of the output terminal of the output resistor 8 output from the switch 9, the voltage of the input terminal of the output resistor 8 (the voltage of the injection signal Vo), or the ground potential (0 V) into the injection signal Vo. By performing synchronous detection, corresponding DC voltage components Vmr, Vmr∞, and Vmr0 are generated.

The arithmetic control unit 12 includes two A / D converters, a CPU (or DSP) that operates according to predetermined software, and a memory that stores software and data (both are shown). Zu).
In this case, one A / D converter corresponds to the second amplifier 11
Voltage component (Vmr,
Vmr∞, Vmr0) to digital data.
On the other hand, another A / D converter converts the frequency setting signal output by the frequency setting means of the operation unit 4 into digital data and outputs the digital data to the signal generating unit 6. Also, CPU
Before the operation start switch 42 is operated, the ground resistance Rg is calculated according to the above equation (5) and is displayed on the display unit 5. On the other hand, when the operation start switch 42 is operated by the operator, the CPU switches the switch 9 to control the three types of DC voltage components Vmr, Vmr.
Ｖ, Vmr0 are calculated, and the values of the DC voltage components Vmr, Vmr∞, Vmr0 converted into digital data are stored in the internal memory. In this case, the CPU
Are the three types of DC voltage components Vmr, Vmr∞,
Using Vmr0 and the resistance value Ro of the output resistor 8, a first subtraction value obtained by subtracting the DC voltage component Vmr0 from the DC voltage component Vmr is calculated equivalently, and the DC voltage component is obtained from the DC voltage component Vmr #. A true ground resistance Rg is calculated by calculating a second subtraction value obtained by subtracting Vmr, and multiplying the resistance value of the output resistance by a value obtained by dividing the first subtraction value by the second subtraction value. I do. Specifically, the following (6)
According to the equation, a process of calculating the ground resistance Rg is performed. Also,
The CPU causes the display unit 5 to display the calculated ground resistance Rg. Rg = Ro × (Vmr−Vmr0) / (Vmr∞−Vmr) Equation (6)

Next, the ground resistance measuring process by the ground resistance measuring device 1 will be described. This process is roughly divided into a process of searching for a resonance frequency and a process of calculating the ground resistance Rg, as described later.

First, before the measurement, the return line 15 is connected to the second terminal 3, and then the return line 15 is arranged on the ground 17. Next, the measured ground rod 16 driven into the ground 17 and the first terminal 2 are connected by the lead wire 14. Thereafter, the power of the ground resistance measuring device 1 is turned on.

In the power-on state, the arithmetic and control unit 12 first executes a resonance frequency search process. In this process, the arithmetic control unit 12 controls the switch 9 to select the output terminal of the output resistor 8. In this state, the voltage Vm at that location is input to the synchronous detector 10 via the switch 9. Next, the arithmetic control unit 12 converts the frequency setting signal input from the operation unit 4 into digital data, and outputs the digital data to the signal generation unit 6. Thereby, the signal generator 6 outputs the high-frequency signal vc having a frequency corresponding to the frequency setting signal output from the operation unit 4.
As a result, the frequency of the high-frequency signal vc generated by the signal generator 6 is
Arbitrarily changes according to the operation of. Next, the high-frequency signal vc is input to the first amplifier 7 and output as an injection signal Vo. In this case, the injection signal Vo corresponds to the output resistance 8
Is supplied to the lead wire 14 through the
The ground 17, the ground-to-ground coupling capacitance between the return line 15 and the ground 17, the return to the ground resistance measuring device 1 via the return line 15 and the second terminal 3. At this time, the synchronous detection unit 10
Is the second terminal 3 (the device ground in the ground resistance measuring device 1)
A voltage Vm generated between the input terminal and the first terminal 2 is input, and a DC voltage component is generated by synchronous detection with the injection signal Vo. Next, the second amplifier 11 amplifies with a predetermined gain and outputs it as a DC voltage component Vmr. Next, the arithmetic control unit 12 performs a predetermined arithmetic process (the arithmetic process of the equation (5)) based on the DC voltage component Vmr, thereby obtaining the ground resistance Rg.
Is calculated. At this time, the arithmetic and control unit 12 causes the display unit 5 to display the calculated ground resistance Rg.

In this case, the operator operates the frequency setting circuit 41 of the operation unit 4 to gradually change the frequency of the high-frequency signal vc while monitoring the value of the ground resistance Rg displayed on the display unit 5. Search for the resonance frequency of the measured system at which the displayed value of the ground resistance Rg becomes the smallest.
Next, when detecting the resonance frequency, the operator operates the calculation start switch 42 in the operation unit 4. As a result, an operation start signal is output from the operation unit 4 to the operation control unit 12. Next, the arithmetic and control unit 12 sets the true ground resistance Rg
Is started.

At this time, the arithmetic and control unit 12 fixes the frequency setting digital data output to the signal generating unit 6 to data corresponding to the resonance frequency, so that the high frequency signal vc generated by the signal generating unit 6 is fixed. Is maintained at the resonance frequency. Next, the arithmetic control unit 12 stores the DC voltage component Vmr input from the second amplifier 11 in the internal memory. Next, the arithmetic control unit 12 controls the switch 9 to select the input terminal of the output resistor 8, input the injection signal Vo to the synchronous detection unit 10 via the switch 9, and output the output signal from the second amplifier 11. DC voltage component Vmr
∞ is stored in the internal memory. Next, the arithmetic control unit 12
Controls the switch 9 to select the zero potential portion, thereby inputting the ground potential to the synchronous detector 10 via the switch 9 and storing the DC voltage component Vmr0 output from the second amplifier 11 in the internal memory. Remember. At this time,
The arithmetic and control unit 12 controls the DC voltage components Vm and Vmr within a short time such that the gain fluctuation and the drift fluctuation can be regarded as steady.
∞, Vmr0 is measured. Also, the DC voltage component Vmr
The order of measuring ∞ and the DC voltage component Vmr0 can be reversed.

When the measurement of each DC voltage component is completed, the arithmetic control unit 12 reads out each DC voltage component Vmr, Vmr0, Vmr∞ stored in the internal memory, and
The ground resistance Rg is calculated by an arithmetic process based on the equation (6). Next, the arithmetic control unit 12 causes the display unit 5 to display the calculated ground resistance Rg. As a result, the final true ground resistance Rg is measured. Further, for the arithmetic control unit 12,
The above-described measurement of each DC voltage component Vmr, Vmr0, Vmr # is repeatedly performed plural times, and an average value is calculated for each DC voltage component Vmr, Vmr0, Vmr #, and then grounded based on each average value. It may be configured to calculate the resistance Rg. According to this configuration, the influence of noise can be eliminated, so that the ground resistance Rg can be calculated with high accuracy.

Next, the basis for calculating the true ground resistance Rg by the above equation (6) will be described with reference to FIG.

First, it is assumed that the high-frequency signal vc generated by the signal generator 6 is represented by the following equation. vc = Vc × cosωt In this case, the voltage waveform Wx1 at the input terminal X1 of the multiplier 10a in the synchronous detector 10, the voltage waveform Wy1 at the input terminal Y1 of the multiplier 10a, and the voltage waveform at the input terminals X2 and Y2 of the multiplier 10a. Wx2, Wy2, the voltage waveform Ww at the output terminal W of the multiplier 10a, and the DC voltage component VDC at the output terminal of the low-pass filter 10b are expressed by the following equations, respectively. Here, α is the gain variation rate of the first amplifier 7, ofs1 and ofs2 are the drift amounts of the first amplifier 7 and the second amplifier 11, respectively, and ofx and ofy are the inputs of the input terminals X1 and Y1 of the synchronous detection unit 10, respectively. The offset, U is the gain in the synchronous detector 10, Z is the output offset of the synchronous detector 10, and θ is the output resistance 8.
Means the phase difference of the high-frequency signal vc at both ends.

[0024]

(Equation 1)

From the equation (11), the DC voltage component Vmr output from the second amplifier 11 is expressed by the following equation (12), and from the equation (12), Rg is expressed by the equation (13). Here, A means the gain of the second amplifier 11, β means the gain variation rate of the second amplifier 11, and ofs3 means the drift of the second amplifier 11.

[0026]

(Equation 2)

Further, based on the equation (12), the DC component V
mr0 is represented by the following equation (14), and the DC component Vmr
∞ is expressed by equation (15). Therefore, the ground resistance R
g is finally expressed by Expression (6) from Expressions (13) to (15).

[0028]

(Equation 3)

As described above, according to the ground resistance measuring apparatus 1, the gain fluctuation and the drift of the first amplifier 7 and the second amplifier 11, the gain and the offset voltage of the synchronous detector 10, and the output resistance 8 Even if there is a phase difference between the high-frequency signals vc at both ends of the circuit, the switch 9 is switched within a short time in which these can be regarded as stationary, and the respective DC voltage components Vmr, Vmr0, Vmr 測定 are measured to obtain a true ground. The resistance Rg can be accurately calculated. This eliminates the need for a compensating circuit for gain fluctuations and the like, so that the number of components and the number of adjustment steps can be significantly reduced. In addition, according to the ground resistance measuring device 1, since the circuit for calculating the ground resistance Rg is digitized, compared with the circuit configuration of the conventional ground resistance measuring device 51 that calculates the ground resistance Rg by an analog circuit, The circuit configuration can be simplified.

The present invention is not limited to the configuration shown in the above-described embodiment. For example, like an earth resistance measuring device 21 shown in FIG. 3, an A / D converter 22 for converting the injection signal Vo into digital data and an A / D converter for converting the voltage output from the switch 9 into digital data.
A / D converter 23 and a CPU (or a D / D converter) operating the synchronous detector 24 in accordance with predetermined software.
SP), the entire synchronous detection circuit can be digitized. According to this configuration, since analog parts can be eliminated, the ground resistance measuring device 21 can be reduced in size and cost can be reduced. Further, the A / D converters 22 and 23, the digitized synchronous detector 24, and the arithmetic control
It can also be formed integrally with an SP or the like, and when such a configuration is adopted, the circuit configuration can be further simplified. Also, a return line 15 is connected to the first terminal 2,
Also, the lead wire 14 is connected to the second terminal 3 so that the ground resistance R
Of course, g can be measured.

Further, in addition to the configuration of the above-described embodiment, the frequency of the high-frequency signal vc generated by the signal generating unit 6 varies with the amount of operation of the frequency setting means (for example, a variable resistor) operated by the operator. It is also possible to add a frequency correction circuit that performs correction so as to change linearly. According to this configuration, the search for the resonance frequency becomes easy. In this case, the frequency correction circuit can be configured by hardware or software processing by the arithmetic control unit 12.

In the above-described embodiment, the operation unit 4
The manual method for setting the frequency of the measurement signal output from the signal generator 6 by operating the frequency setting means (variable resistor) in the frequency setting circuit 41 provided in the above is described, but the present invention is not limited to this. For example, a configuration in which the arithmetic and control unit 12 controls the frequency setting circuit 41 can be adopted as in a ground resistance measuring device 31 shown in FIG.
According to this configuration, the arithmetic control unit 12 can automatically search for the resonance frequency while changing the frequency of the high-frequency signal vc, and can also automatically calculate the ground resistance Rg.

Further, in the above-described embodiment, the arithmetic control unit 12 calculates the ground resistance Rg by the arithmetic processing of the equation (5) before the operation of the arithmetic start switch 42, and ( Although the example in which the true ground resistance Rg is calculated by the arithmetic processing of the expression 6) has been described, the present invention is not limited to this. For example, it is also possible to adopt a configuration in which the arithmetic control unit 12 automatically switches the switch 9 and always calculates the true ground resistance Rg by the arithmetic processing of the equation (6) without providing the arithmetic start switch 42. . According to this configuration, the high-frequency signal vc
Every time the frequency is changed, the high-frequency signal vc of that frequency
Are sequentially displayed on the display unit 5, the operator can measure the smallest value of the displayed ground resistances Rg as the true ground resistance Rg.

The inductance component between the first terminal 2 and the second terminal 3 generally has a small value mainly because of the inductance component of the lead wire 14. For this reason, the resonance frequency of the impedance may be a high frequency on the order of MHz. In such a case, it is necessary to consider high frequencies in the circuit design of the synchronous detection unit 10 and the like. For this reason, it is difficult to design the circuit configuration and the board, and as a result, the design time is lengthened. Therefore, this problem can be solved by forcibly increasing the inductance component between the first terminal 2 and the second terminal 3 and shifting the resonance frequency to a lower frequency. In this case, FIG.
As shown by a broken line, by connecting the resonance point shifting inductance 26 between the output resistor 8 and the first terminal 2, it is possible to increase the inductance component and lower the resonance frequency.

When the ground resistance measuring device 1 is driven by a battery, as shown by a broken line in FIG. 1, a power supply control unit 28 for controlling on / off of an output of a power supply unit 27 including a battery is provided. It is also possible to adopt a configuration in which the unit 28 controls on / off of power supply to other components. According to this configuration, even when the main power switch of the ground resistance measuring device 1 is maintained in the ON state,
The power supply control unit 28 is operated by the
When it is detected that has not been operated for a certain period of time or more, power supply to the components other than the power control unit 28 and the operation unit 4 can be stopped. When this configuration is adopted, the grounding resistance measuring device 1 at the time of non-measurement when the operation unit 4 is not operated by the operator
Can be shifted to a standby state with low power consumption. As a result, power consumption of the battery can be suppressed, and the frequency of battery replacement can be reduced.

[0036]

As described above, according to the ground resistance measuring apparatus of the first aspect, the DC voltage components Vmr, Vmr∞, V
By measuring the ground resistance based on mr0, it is possible to eliminate the influence of gain fluctuation and drift in a circuit inside the device such as the synchronous detection unit, so that the ground resistance can be measured with high accuracy.

Further, according to the ground resistance measuring apparatus of the present invention, the DC voltage components Vmr, Vmr∞, Vmr0 are calculated and averaged a plurality of times, respectively, and arithmetic processing is performed based on the averaged values. By measuring the grounding resistance, the effects of noise can be eliminated,
The ground resistance can be measured with higher accuracy.

[Brief description of the drawings]

FIG. 1 is a ground resistance measuring device 1 according to an embodiment of the present invention.
FIG. 3 is a block diagram showing the configuration of FIG.

FIG. 2 is a block diagram mainly showing a configuration of a synchronous detection unit 10;

FIG. 3 is a block diagram showing a configuration of a ground resistance measuring device 21 according to another embodiment.

FIG. 4 is a block diagram showing a configuration of a ground resistance measuring device 31 according to still another embodiment.

FIG. 5 is a block diagram showing a configuration of a conventional ground resistance measuring device 51.

FIG. 6 shows a synchronous detector 10 in the ground resistance measuring device 51.
3 is a block diagram mainly showing the configuration of FIG.

FIG. 7 is an equivalent circuit diagram of a measurement system for measuring a ground resistance Rg.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Grounding resistance measuring device 6 Signal generator 8 Output resistance 9 Switch 10 Synchronous detector 12 Operation controller 14 Lead wire 15 Return line 16 Grounding rod to be measured 17 Ground Vmr, Vmrｍ, Vmr0 DC component

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Kazuo Murakawa 3-19-2 Nishishinjuku, Shinjuku-ku, Tokyo East Japan Nippon Telegraph and Telephone Corporation (72) Inventor Eiji Ohashi 3-19 Nishishinjuku, Shinjuku-ku, Tokyo No. 2 Tohoku Nippon Telegraph and Telephone Corporation (72) Mitsuo Hattori Inventor F-term (reference) 2G028 AA01 BC06 CG05 DH05 DH11 FK01 in the Nippon Telegraph and Telephone Corporation 3-19-2 Nishishinjuku, Shinjuku-ku, Tokyo FK07 GL03 MS02

Claims (2)

[Claims] 1. A grounding resistance measurement for measuring a grounding resistance of a grounding rod to be measured, wherein a lead wire connected to the grounding rod to be measured and a return conductor arranged on the ground in an insulated state are connectable. In the apparatus, a signal generating unit configured to generate an AC signal and variably control the frequency thereof, an output resistor connected between the lead wire or the return conductor and the signal generating unit, Signal switching for selecting one of the output end of the lead wire or the return conductor side, the input end of the output resistor on the signal generating side, and a zero potential portion to output a voltage of the selected portion. Means, a synchronous detector for generating a DC voltage component by synchronously detecting the voltage output from the signal switching means with the AC signal, and an arithmetic control unit; Is the lowest DC voltage component Vmr generated by the synchronous detector obtained by changing the frequency of the AC signal in the signal generator when the output terminal is selected by the signal switching means, and the frequency In the maintained state, the DC voltage component V generated by the synchronous detection unit when the input terminal is selected by the signal switching unit.
based on the DC voltage component Vmr0 and the DC voltage component Vmr0 generated by the synchronous detector when the zero potential portion is selected by the signal switching means while the frequency is maintained at the frequency. A first subtraction value obtained by subtracting the DC voltage component Vmr0 is calculated, and the DC voltage component Vmr
The ground resistance is measured by calculating a second subtraction value obtained by subtracting the first resistance value and multiplying the resistance value of the output resistance by a value obtained by dividing the first subtraction value by the second subtraction value. A ground resistance measuring device. 2. The DC voltage component Vmr, the DC voltage component Vmr∞, and the DC voltage component Vmr0 are calculated a plurality of times, respectively, and the arithmetic control unit averages the DC voltage components calculated a plurality of times. The ground resistance measuring apparatus according to claim 1, wherein the ground resistance is measured by performing the arithmetic processing based on the averaged values.