JP5985420B2 - Ground resistance meter and method for measuring ground resistance - Google Patents

Description

  The present invention relates to a ground resistance meter, and relates to an AC potentiometer type ground resistance meter. The present invention also relates to a ground resistance measurement method executed in this ground resistance meter.

  As this type of ground resistance meter, a ground resistance meter disclosed in Non-Patent Document 1 below is known. This ground resistance meter is driven by grounding two auxiliary grounding rods, each serving as an auxiliary grounding electrode (current electrode for supplying measurement current and potential electrode for measuring voltage), into the ground. Precise measurement (measurement by the three-electrode method), and existing grounding with low grounding resistance, such as metal buried objects such as metal water pipes, joint grounds of commercial power supplies and Class A grounding poles (lightning rods) of buildings Any of the simple measurements in which the ground resistance of the ground electrode to be measured is measured by the two-electrode method using the poles can be executed.

  The ground resistance meter has a ground voltage measurement function. When measuring the ground resistance, first, the ground voltage is measured, and the ground voltage is measured in advance by a predetermined voltage (for example, 3 V. Hereinafter, “threshold voltage”). In the following cases, ground resistance measurement is performed, and when the ground voltage exceeds the threshold voltage, the error of the measured ground resistance may increase. , It is configured to display the fact (the fact that the earth voltage is high).

  This ground resistance meter has three measurement ranges (2000Ω, 200Ω, and 20Ω), and the current value is fixedly defined in advance for each measurement range (for example, 0.2 mA, 200Ω in the 2000Ω range). AC constant current (specified at 2 mA for the range and 20 mA for the 20Ω range (both effective values)) is supplied as a measurement current Ic from the built-in constant current source between the measured ground electrode and the auxiliary ground electrode (current electrode). At this time, the voltage value generated between the ground electrode to be measured and the auxiliary ground electrode (potential electrode) is measured with a built-in voltmeter, and the built-in processing unit converts the measured voltage value into the current value of the measured current Ic. Divide by to measure the ground resistance of the ground electrode under test.

  In this case, since the ground resistance Re of the measured ground electrode and the ground resistance Rc of the auxiliary ground electrode (current electrode) are connected in series with the voltage source that generates the ground voltage Ve, the ground resistance Re The peak value of the voltage between the measured grounding electrode and the auxiliary grounding electrode (current electrode) at the time of measurement is expressed as a voltage value obtained by adding (Re + Rc) × Ic × √2 to the peak value of Ve (Ve1). The maximum value of the peak value is the peak value of the voltage when the measured current Ic is the maximum (in the above example, 20 mA).

Further, since the constant current source must be able to supply (output) the maximum measurement current Ic in the presence of the ground voltage Ve, when the maximum output voltage value is Vmax, the following formula (1) Need to be met. When the maximum output voltage value Vmax of the constant current source does not satisfy this formula (1), it becomes impossible to supply a specified constant current as the measurement current Ic, and it is difficult to accurately measure the ground resistance Re.
Vmax> Ve1 + (Re + Rc) × Ic × √2 (1)

  However, since the resistance values of the ground resistors Re and Rc are known only after actual measurement, if the threshold voltage with respect to the ground voltage Ve for determining that measurement is possible is increased under such circumstances, the maximum value of the constant current source is increased. Since the margin to the output voltage value Vmax is reduced, a situation in which the above equation (1) is not satisfied frequently occurs due to the resistance values of the ground resistors Re and Rc. For this reason, in order to avoid frequent occurrence of a situation that does not satisfy the above formula (1), the threshold voltage with respect to the ground voltage Ve is generally regulated to a low voltage value with a margin. .

Battery type digital ground resistance meter MODEL 4105A Instruction Manual, Kyoritsu Electric Instruments Co., Ltd. homepage, [Search February 25, 2013], Internet <http://www.kew-ltd.co.jp/en/download/ pdf / manual / 4105A_IM_92-1499D_E.pdf>

  However, the above ground resistance meter has the following problems to be improved. That is, in this ground resistance meter, as described above, the threshold voltage with respect to the ground voltage is regulated to a low voltage value with a margin, so inaccurate ground resistance measurement can be sufficiently avoided, There is a problem to be improved that ground voltage often exceeds the threshold voltage at the ground voltage measurement stage before measuring resistance, and there is a possibility that ground resistance measurement may not be performed frequently. ing.

  The present invention has been made to improve such a problem, and a ground resistance meter and a ground that can enable measurement of ground resistance at a place where a higher ground voltage is generated while avoiding inaccurate measurement of ground resistance. The main purpose is to provide a resistance measurement method.

  In order to achieve the above object, a ground resistance meter according to claim 1, wherein a constant current source supplying an AC constant current between a measured ground electrode and an auxiliary ground electrode, and between the measured ground electrode and the auxiliary ground electrode Based on a current value of the AC constant current and a voltage value of the AC voltage measured by the voltmeter in the supply state of the AC constant current by the constant current source. A ground resistance meter including a processing unit for performing a resistance calculation process for calculating a ground resistance of the ground electrode to be measured, wherein the constant current source can supply the AC constant current with a plurality of different current values. And the processing unit uses the voltage value of the AC voltage measured by the voltmeter in a state where the supply of the AC constant current to the constant current source is stopped as the voltage value of the first voltage. First voltage measurement to measure And by defining the current value of the AC constant current as a current value on the lower side of the plurality of current values and executing the resistance calculation process, the measured ground electrode and the auxiliary ground electrode Based on the first ground resistance calculation process for calculating the resistance value of each ground resistance as a temporary ground resistance value, the temporary ground resistance value, the voltage value of the first voltage, and the maximum output voltage value of the constant current source. , A current value of one of the plurality of current values, and an added voltage value obtained by adding the voltage value of the first voltage to the voltage generated at each ground resistor is less than the maximum output voltage value, and A current value determining process for determining a current value closest to the maximum output voltage value as a measured current value, and executing the resistance calculating process by defining the current value of the AC constant current as the determined measured current value , The grounding resistance of the measured grounding electrode Performing a second ground resistor calculation processing of calculating a resistance value.

  According to a second aspect of the present invention, there is provided a ground resistance measuring method between the measured ground electrode and the auxiliary ground electrode in a state where an AC constant current is supplied from a constant current source between the measured ground electrode and the auxiliary ground electrode. A resistance calculation process for measuring the AC voltage generated in the voltmeter and calculating the ground resistance of the ground electrode to be measured based on the current value of the AC constant current and the voltage value of the AC voltage measured by the voltmeter Using the constant current source configured to be able to supply the AC constant current with a plurality of different current values as the constant current source, and to measure the AC constant current from the constant current source. A first voltage measurement process for measuring a voltage value of the alternating voltage measured by the voltmeter as a voltage value of the first voltage in a state where supply of current is stopped; and a lower side of the plurality of current values The current value of A first ground resistance calculation process for calculating a resistance value of each ground resistance of the ground electrode to be measured and the auxiliary ground electrode as a temporary ground resistance value by defining the current value of a constant current and executing the resistance calculation process A current value of one of the plurality of current values based on the temporary ground resistance value, the voltage value of the first voltage, and the maximum output voltage value of the constant current source, and each ground resistance Current value determination processing for determining a current value closest to the maximum output voltage value, which is less than the maximum output voltage value, as an added voltage value obtained by adding the voltage value of the first voltage to the voltage generated at And a second ground resistance calculation process for calculating a resistance value of the ground resistance of the ground electrode to be measured by defining the current value of the AC constant current as the determined measurement current value and executing the resistance calculation process. And execute.

  In the ground resistance meter according to claim 1 and the ground resistance measurement method according to claim 2, a constant current source configured to be able to supply an alternating constant current with a plurality of different current values is used. The sum voltage value obtained by adding the voltage value of the first voltage to the voltage generated at each ground resistance is less than the maximum output voltage value of the constant current source and is closest to the maximum output voltage value. The resistance calculation process is executed by defining the optimum current value as the measured current value. Therefore, according to the ground resistance meter and the ground resistance measuring method, a conventional ground resistance meter or ground that compares the measured first voltage with a predetermined threshold voltage to determine whether or not the ground resistance can be measured is determined. Unlike the resistance measurement method, if the ground resistance value of the auxiliary grounding electrode is small even if the first voltage is somewhat large (even at the place where the higher first voltage is generated), the range is less than the maximum output voltage value of the constant current source The constant current source can supply an AC constant current at a specified measurement current value, and the ground resistance value of the ground electrode to be measured can be accurately measured.

1 is a configuration diagram showing a configuration of a ground resistance meter 1. FIG. 5 is a flowchart for explaining a ground resistance measuring method together with the operation of the ground resistance meter 1.

  Hereinafter, embodiments of a ground resistance meter and a ground resistance measurement method will be described with reference to the accompanying drawings.

  First, the configuration of the ground resistance meter 1 will be described with reference to the drawings.

  As shown in FIG. 1, the ground resistance meter 1 includes a constant current source 2, a voltmeter 3, a switch unit 4, connection terminals 5, 6, 7, a processing unit 8, and an output unit 9, and includes a first auxiliary grounding electrode P And the second auxiliary grounding pole C (both auxiliary grounding poles P and C are each an example of an auxiliary grounding pole), and the ground resistance Re of the measured grounding pole (in this example, the grounding pole E) is measured by the three-electrode method. To do.

  The constant current source 2 is controlled by the processing unit 8, generates an alternating current having a constant frequency (for example, a sine wave current), and outputs the alternating current as a measured current I from the pair of output terminals 2 a and 2 b. The constant current source 2 is configured to be able to generate the measurement current I with a plurality of different current values (effective values) I1, and is controlled by the processing unit 8, whereby the processing unit among the plurality of current values I1. The measurement current I is generated with the current value I1 instructed from 8, and is output as an AC constant current.

  In addition, since the frequency of the ground voltage Ve as a first voltage to be described later is usually 50 Hz or 60 Hz, the measurement current I is regulated to a frequency that avoids this frequency (as an example, about 80 Hz to 1 kHz). The output terminals 2 a and 2 b of the constant current source 2 are connected to the switch unit 4.

  The voltmeter 3 has one input terminal 3 a of the pair of input terminals 3 a and 3 b connected to the switch unit 4 and the other input terminal 3 b connected to the other output terminal 2 b of the constant current source 2. Yes. The voltmeter 3 generates AC voltage waveform data Dv by sampling the AC voltage input between the pair of input terminals 3 a and 3 b, and outputs the waveform data Dv to the processing unit 8.

  The switch unit 4 is disposed between the constant current source 2 and the voltmeter 3 and the three connection terminals 5, 6, and 7. The switch unit 4 includes a plurality of changeover switches (three changeover switches 11, 12, 13 as an example in this example) controlled by the processing unit 8, and includes output terminals 2a, 2b of the constant current source 2 and The input terminals 3 a and 3 b of the voltmeter 3 are connected to a connection terminal selected from the connection terminals 5, 6 and 7. In this case, the connection terminal 5 is connected to the ground electrode E, the connection terminal 6 is connected to the first auxiliary ground electrode P, and the connection terminal 7 is connected to the second auxiliary ground electrode C.

  Specifically, in this example, the switch unit 4 is configured such that each change-over switch 11, 12, 13 is a single-pole double-throw (one-circuit, two-contact type) change-over switch. Further, the changeover switch 11 has a common contact com connected to one contact of the changeover switch 13 and connected to the output terminal 2a of the constant current source 2, one contact connected to the connection terminal 7, and the other contact. Are connected to one contact of the changeover switch 12 and the other contact of the changeover switch 13 and to the connection terminal 6.

  The changeover switch 12 has a common contact com connected to the output terminal 2b of the constant current source 2 and the input terminal 3b of the voltmeter 3, and one contact is connected to the other contact and the connection terminal 6 of the changeover switch 11 as described above. The other contact is connected to the connection terminal 5. The changeover switch 13 has its common contact com connected to the input terminal 3a of the voltmeter 3, one contact connected to the common contact com of the changeover switch 11 as described above, and the other contact as described above. 11 and the other contact of the changeover switch 12 and the connection terminal 6.

  The processing unit 8 includes a CPU and an internal memory (both not shown), and includes a resistance measurement process 20 (ground voltage measurement process (first voltage measurement process), first ground resistance calculation process shown in FIG. , Current value determination processing, second ground resistance calculation processing, and output processing). In this case, the internal memory stores a plurality of current values I1 (4 mA, 2 mA, 1 mA, 0.5 mA, 0.25 mA (all of which are examples) in the current source determination process. (Effective value) four current values I1) and a maximum output voltage value Vmax that the constant current source 2 can output from between the pair of output terminals 2a and 2b are stored in advance.

  For example, the output unit 9 includes a display device such as an LCD (Liquid Crystal Display), and displays the result of the resistance measurement process executed by the processing unit 8 on the screen. Instead of the display device, the output unit 9 may be configured by a communication device that performs data communication with an external device, and the result of the resistance measurement process may be output to the external device.

  Next, together with the operation of the ground resistance meter 1, a ground resistance measurement method will be described with reference to FIGS. As shown in FIG. 1, the first auxiliary grounding pole P and the second auxiliary grounding pole C are preliminarily defined with reference to the grounding pole E grounded to the ground G (for example, disclosed in Non-Patent Document 1). It shall be grounded at the precise measurement position). The resistor Re indicates the ground resistance of the ground electrode E, the resistor Rp indicates the ground resistance of the first auxiliary ground electrode P, and the resistor Rc indicates the ground resistance of the second auxiliary ground electrode C.

  In order to facilitate understanding of the invention, the resistance value of the ground resistance Re is represented by a resistance value (also referred to as a ground resistance value) Re, and the resistance value of the ground resistance Rp is represented by a resistance value (also referred to as a ground resistance value) Rp. The resistance value of the ground resistance Rc is represented by a resistance value (also referred to as a ground resistance value) Rc. Further, it is assumed that the connection terminal 5 is connected to the ground electrode E, the connection terminal 6 is connected to the first auxiliary ground electrode P, and the connection terminal 7 is connected to the second auxiliary ground electrode C in advance.

  In the ground resistance meter 1, the processing unit 8 executes a resistance measurement process 20 shown in FIG. In the resistance measurement process 20, the processing unit 8 first executes a ground voltage measurement process (step 21). In this earth voltage measurement process, the processing unit 8 executes control on the constant current source 2 to stop the output (supply) of the measurement current I. Further, the processing unit 8 controls the switch unit 4 to shift the changeover switch 12 to a connection state indicated by a solid line (a state in which the common contact com is connected to the other contact), and to change the changeover switch 13. A transition is made to a connection state indicated by a solid line (a state where the common contact com is connected to the other contact). Thereby, the ground resistance meter 1 shifts to a connection state in which the voltmeter 3 is connected between the connection terminal 5 and the connection terminal 6, that is, between the ground electrode E and the first auxiliary ground electrode P via the switch unit 4. .

  Moreover, the process part 8 performs control with respect to the voltmeter 3 in this state, and measures the alternating voltage input into a pair of input terminals 3a and 3b. In this state, the voltmeter 3 is connected between the ground electrode E and the first auxiliary ground electrode P via the switch unit 4, the connection terminal 5 and the connection terminal 6, so that the ground electrode E and the first auxiliary ground electrode are used. Waveform data Dv for the AC voltage Vep generated between P is measured and output to the processing unit 8. In this case, since the supply of the measurement current I from the constant current source 2 to the ground G is stopped, the voltmeter 3 generates the ground voltage Ve generated between the ground electrode E and the first auxiliary ground electrode P. Measurement is performed as an AC voltage Vep, and the waveform data Dv of the ground voltage Ve is output to the processing unit 8.

  The processing unit 8 acquires waveform data Dv for at least one period of the ground voltage Ve from the voltmeter 3 and stores it in the internal memory. Further, the processing unit 8 measures the peak value Ve1 of the absolute value of the ground voltage Ve as the voltage value of the ground voltage Ve based on the waveform data Dv stored in the internal memory, and stores it in the internal memory. Thereby, the ground voltage measurement process is completed.

  Next, the processing unit 8 executes a first ground resistance calculation process (step 22). In the first ground resistance calculation process, the processing unit 8 firstly selects the lower side of a plurality of current values for the measurement current I of the constant current source 2 (for example, the center current when arranged in ascending or descending order). Current value lower than the value, since the current value at the center in this example is 1 mA, 0.5 mA and 0.25 mA are the current values on the lower side) (in this example, a more preferable minimum value) The current value of the measurement current I is defined as a current value of 0.25 mA).

  Next, in this first ground resistance calculation process, the processing unit 8 calculates the resistance for calculating the ground resistance Re of the ground pole E, the ground resistance Rp of the first auxiliary ground pole P, and the ground resistance Rc of the second auxiliary ground pole C. Execute the process. In this resistance calculation process, the processing unit 8 firstly combines the ground resistance E between the ground electrode E and the first auxiliary ground electrode P (= Re + Rp) and the composite ground resistance Rec between the ground electrode E and the second auxiliary ground electrode C. (= Re + Rc) and each resistance value of the combined ground resistance Rpc (= Rp + Rc) between the first auxiliary grounding pole P and the second auxiliary grounding pole C are calculated in this order as an example.

  In the following, in order to facilitate understanding of the invention, the resistance value of the composite ground resistor Rep is a resistance value (also referred to as a composite ground resistance value) Rep, and the resistance value of the composite ground resistor Rec is a resistance value (combined ground resistance value). (Also referred to as “Rec”), the resistance value of the combined ground resistance Rpc is expressed as a resistance value (also referred to as a combined ground resistance value) Rpc.

  Specifically, when calculating the combined grounding resistance value Rep of the combined grounding resistor Rep, the processing unit 8 first performs control on the switch unit 4 to connect the changeover switch 13 to a connection state (common contact com) indicated by a broken line. Is switched to a connection state indicated by a solid line, and the changeover switch 12 is shifted to a connection state indicated by a solid line. Thereby, in the ground resistance meter 1, the constant current source 2 and the voltmeter 3 are connected in parallel, and this parallel circuit is connected between the connection terminal 5 and the connection terminal 6 via the switch unit 4, that is, the ground electrode E and the first electrode. A transition is made to a connection state connected between the one auxiliary grounding poles P.

  Next, the processing unit 8 controls the constant current source 2 to output the measurement current I at the current value defined as described above (0.25 mA in this example). This measurement current I is supplied from the output terminal 2 a of the constant current source 2 to the changeover switch 11 of the switch unit 4, the connection terminal 6, the first auxiliary grounding electrode P, the ground G, the grounding electrode E, the connection terminal 5, and the switch unit 4. The current flows through the change-over switch 12 and returns to the output terminal 2b of the constant current source 2.

  In this example, the current value I1 of the measurement current I is defined as a minimum current value of 0.25 mA, which is one of the above-described lower-side current values among a plurality of current values. As a result, even if the ground voltage Ve is generated between the ground electrode E and the first auxiliary ground electrode P, the measurement current I flows through the ground resistance Re of the ground electrode E and the ground resistance Rp of the first auxiliary ground electrode P. In this case, the total voltage value ((Re + Rp) × I1) of the voltages generated in the ground resistors Re and Rp can be suppressed to a low voltage value.

  Therefore, the peak voltage value ((Re + Rp)) of the alternating voltage Vep obtained by adding the peak value Ve1 of the absolute value of the ground voltage Ve to the voltage (peak voltage value) obtained by multiplying the total voltage value ((Re + Rp) × I1) by √2 The occurrence of a situation where (× I1 × √2 + Ve1) exceeds the maximum output voltage value Vmax of the constant current source 2 is greatly reduced. That is, it is possible to execute the resistance calculation process in a state where the measurement current I is output from the constant current source 2 at a specified current value (here, 0.25 mA).

  The voltmeter 3 measures the voltage value ((Re + Rp) × I1 + Ve) of the AC voltage Vep and outputs the waveform data Dv to the processing unit 8. In addition, the processing unit 8 acquires the waveform data Dv for at least one cycle of the AC voltage Vep from the voltmeter 3, and the frequency component of the measurement current I among the frequency components included in the acquired waveform data Dv. The signal extraction process to extract (that is, the process of removing the frequency component of the ground voltage Ve) is executed to extract the waveform data Dv having the voltage value ((Re + Rp) × I1). Note that the frequency component of the measurement current I may be extracted in advance from the AC voltage Vep using a filter circuit, a synchronous detection circuit, or the like.

  Subsequently, the processing unit 8 does not include the AC voltage Vep (the ground voltage Ve) generated between the ground electrode E and the first auxiliary ground electrode P based on the waveform data Dv of this voltage value ((Re + Rp) × I1). The voltage value (effective value) of the voltage in the state is calculated. Next, the processing unit 8 divides the calculated voltage value of the AC voltage Vep by the current value I1 of the measurement current I, thereby obtaining a combined ground resistance value Rep (= Re + Rp) between the ground electrode E and the first auxiliary ground electrode P. ) Is calculated and stored in the internal memory. Finally, the processing unit 8 causes the constant current source 2 to stop outputting the measurement current I. This completes the calculation of the combined ground resistance value Rep of the combined ground resistance Rep.

  Further, when calculating the combined grounding resistance value Rec of the combined grounding resistance Rec, the processing unit 8 first performs control on the switch unit 4 and leaves the changeover switches 12 and 13 in the above-mentioned connection state, and the changeover switch. 11 is shifted to a connection state indicated by a broken line (a state where the common contact com is connected to one contact). Thereby, the ground resistance meter 1 includes a parallel circuit of the constant current source 2 and the voltmeter 3 between the connection terminal 5 and the connection terminal 7 via the switch unit 4, that is, between the ground electrode E and the second auxiliary ground electrode C. Transition to connected state.

  Next, the processing unit 8 controls the constant current source 2 in the same way as when calculating the composite ground resistance Rep, and measures at the current value defined as described above (0.25 mA in this example). While outputting the current I, the waveform data Dv for the voltage value ((Re + Rc) × I1 + Ve) of the AC voltage Vec output from the voltmeter 3 at this time is acquired. Further, the processing unit 8 performs signal extraction processing on the acquired waveform data Dv, extracts waveform data Dv having a voltage value ((Re + Rc) × I1), and grounding is performed based on the waveform data Dv. A voltage value (effective value) of the AC voltage Vec generated between the pole E and the second auxiliary grounding pole C is calculated.

  Subsequently, the processing unit 8 divides the calculated voltage value of the AC voltage Vec by the current value I1 of the measurement current I, thereby combining the ground resistance Ec between the ground electrode E and the second auxiliary ground electrode C (= Re + Rc) is calculated and stored in the internal memory. Finally, the processing unit 8 causes the constant current source 2 to stop outputting the measurement current I. This completes the calculation of the combined ground resistance value Rec of the combined ground resistance Rec.

  Further, when calculating the combined grounding resistance value Rpc of the combined grounding resistance Rpc, the processing unit 8 first controls the switch unit 4 so that the changeover switches 11 and 13 remain in the above connected state, and the changeover switch is set. 12 is shifted to a connection state indicated by a broken line (a state where the common contact com is connected to one contact). As a result, the ground resistance meter 1 is configured such that the parallel circuit of the constant current source 2 and the voltmeter 3 is connected between the connection terminal 6 and the connection terminal 7 via the switch unit 4, that is, the first auxiliary ground pole P and the second auxiliary A transition is made to a connection state connected between the ground poles C.

  Next, the processing unit 8 controls the constant current source 2 in the same way as when calculating the composite ground resistance Rep, and measures at the current value defined as described above (0.25 mA in this example). While outputting the current I, the waveform data Dv for the voltage value ((Rp + Rc) × I1) of the AC voltage Vpc output from the voltmeter 3 at this time is acquired. Further, the processing unit 8 calculates a voltage value (effective value) of the AC voltage Vpc generated between the first auxiliary grounding pole P and the second auxiliary grounding pole C based on the acquired waveform data Dv.

  Subsequently, the processing unit 8 divides the calculated voltage value of the AC voltage Vpc by the current value I1 of the measurement current I, thereby combining the ground resistance value between the first auxiliary grounding pole P and the second auxiliary grounding pole C. Rpc (= Rp + Rc) is calculated and stored in the internal memory. Finally, the processing unit 8 causes the constant current source 2 to stop outputting the measurement current I. Thereby, the calculation of the combined ground resistance value Rpc of the combined ground resistance Rpc is completed.

Next, the processing unit 8 solves the following ternary simultaneous linear equations (Equations (2) to (4)) based on the calculated combined ground resistance values Rep, Rec, and Rpc, whereby the ground electrode E The grounding resistance value Re, the grounding resistance value Rp of the first auxiliary grounding pole P, and the grounding resistance value Rc of the second auxiliary grounding pole C are calculated.
Rep = Re + Rp (2)
Rec = Re + Rc (3)
Rpc = Rp + Rc (4)

  The ground resistance values Re, Rp, and Rc calculated in this way are measured by defining the current value I1 of the measurement current I as the current value on the lower side of the current values that can be supplied by the constant current source 2. The current value I1 of the measured current I is determined in consideration of the current value (ground voltage Ve, the maximum output voltage value Vmax, and each ground resistance value Re, Rp, Rc) determined in a current value determination process described later. There is a possibility that the accuracy is lower than the current value to be determined and measured by defining the ground resistance value Re as a preferable current value that may be measured with higher accuracy. Therefore, the processing unit 8 stores the calculated ground resistance values Re, Rp, Rc in the internal memory as the temporary ground resistance value Re, the temporary ground resistance value Rp, and the temporary ground resistance value Rc. Thereby, the first ground resistance calculation process is completed.

Next, the processing unit 8 executes current value determination processing (step 23). In this current value determination process, the processing unit 8 uses the following formula (based on the temporary ground resistance values Re and Rp, the voltage value of the ground voltage Ve (peak value Ve1), and the maximum output voltage value Vmax of the constant current source 2): The largest current value I1 among the current values I1 satisfying 5) is determined as a new current value I1 of the measurement current I.
Vmax> (Re + Rp) × I1 × √2 + Ve1 (5)

  That is, the voltage generated at each of the ground resistors Re and Rp, which is one of the plurality of current values I1 of the constant current source 2 and whose resistance value is defined as the temporary ground resistance values Re and Rp. The current value I1 that is the sum of the peak value of the ground voltage Ve and the voltage value of the ground voltage Ve (peak value Ve1) is less than the maximum output voltage value Vmax and is closest to the maximum output voltage value Vmax is the current of the measured current I The value (measured current value) is determined as I1.

  For example, the peak value Ve1 of the measured ground voltage Ve is 20V, the temporary grounding resistance value Re is 100Ω, the temporary grounding resistance value Rp is 1.5kΩ, and the maximum output voltage value Vmax of the constant current source 2 is When the voltage is 25 V, the current value I1 is calculated to be less than about 2.2 mA. For this reason, the processing unit 8 sets 2 mA of the four current values 4 mA, 2 mA, 1 mA, 0.5 mA, and 0.25 mA for the constant current source 2 as a new current value I1 (measured current) of the measured current I. Value). Thereby, the current value determination process is completed. In this current value determination process, the processing unit 8 uses the temporary grounding resistance value Rc instead of the temporary grounding resistance value Rp, and a new current value I1 (measured current value) for the measurement current I described above. Can also be determined.

  Next, the processing unit 8 executes a second ground resistance calculation process (step 24). In the second ground resistance calculation process, the processing unit 8 first defines the current value I1 of the measurement current I of the constant current source 2 to the current value I1 determined in the current value determination process. In this case, when the current value I1 determined in the current value determination process is larger than the current value I1 defined in the first ground resistance calculation process, the measurement current I is output with the current value I1 determined in the current value determination process. In the state, the AC voltages Vep, Vpc, Vec measured by the voltmeter 3 are measured as higher voltage values Vep, Vpc, Vec. For this reason, the measurement accuracy of the ground resistance values Re, Rp, Rc calculated based on the AC voltages Vep, Vpc, Vec is improved.

  Next, the processing unit 8 executes a resistance calculation process for calculating the ground resistance value Re of the ground electrode E in the second ground resistance calculation process. In this resistance calculation process, the processing unit 8 first executes control on the switch unit 4 to shift the changeover switch 11 to a connection state indicated by a broken line and connect the changeover switches 12 and 13 to a connection state indicated by a solid line. To migrate. As a result, the ground resistance meter 1 includes a constant current source 2 connected between the connection terminal 5 and the connection terminal 7 via the switch unit 4, that is, between the ground electrode E and the second auxiliary ground electrode C, and the voltmeter 3 The connection state is established between the connection terminal 5 and the connection terminal 6 via the switch unit 4, that is, between the ground electrode E and the first auxiliary ground electrode P.

  Next, the processing unit 8 controls the constant current source 2 to output the measurement current I at the new current value I1 (2 mA in this example) determined as described above. This measurement current I is supplied from the output terminal 2 a of the constant current source 2 to the changeover switch 11 of the switch unit 4, the connection terminal 7, the second auxiliary grounding electrode C, the ground G, the grounding electrode E, the connection terminal 5, and the switch unit 4. The current flows through the change-over switch 12 and returns to the output terminal 2b of the constant current source 2.

  The voltmeter 3 measures the voltage value (Re × I1 + Ve) of the AC voltage Vep through the connection terminal 5 and the connection terminal 6 and outputs the waveform data Dv to the processing unit 8. Further, the processing unit 8 acquires waveform data Dv for at least one cycle of the AC voltage Vep from the voltmeter 3 and performs signal extraction processing on the acquired waveform data Dv to obtain a voltage value (Re Extract the waveform data Dv of × I1).

  Subsequently, the processing unit 8 is based on the waveform data Dv of the voltage value (Re × I1) and generates an AC voltage Vep (not including the ground voltage Ve) generated between the ground electrode E and the first auxiliary ground electrode P. Voltage value (effective value). Next, the processing unit 8 calculates the ground resistance value Re of the ground electrode E by dividing the calculated voltage value of the AC voltage Vep by the current value I1 of the measurement current I, and stores it in the internal memory. Finally, the processing unit 8 causes the constant current source 2 to stop outputting the measurement current I. Thereby, the calculation of the final ground resistance value Re is completed, and the second ground resistance calculation process is completed.

  When the current value I1 of the measured current I determined in the current value determination process in step 23 is the same as the current value I1 in the first ground resistance calculation process in step 22, the ground calculated in the second ground resistance calculation process The ground resistance value Re of the resistor Re is calculated with the same accuracy as the ground resistance value Re of the ground resistor Re calculated in the first ground resistance calculation process. Therefore, the second ground resistance calculation process is not executed, and the ground resistance value Re of the ground resistance Re calculated in the first ground resistance calculation process is set as the final ground resistance value Re.

  Finally, the processing unit 8 executes the output process, and finally calculates the ground resistance value Re of the ground resistance Re calculated in the second ground resistance calculation process (as described above, in the first ground resistance calculation process as the case may be). The calculated final ground resistance value Re) is displayed on the screen of the output unit 9 (step 25). Thereby, the resistance measurement process 20 is completed.

  As described above, in the ground resistance meter 1 and the ground resistance measurement method, the constant current source 2 configured to be able to supply the measurement current I with a plurality of different current values I1 is used, and the peak value Ve1 of the ground voltage Ve (ground A ground voltage measurement process for measuring the voltage Ve) and a resistance calculation process by defining the current value I1 of the measurement current I as one current value I1 on the lower side of the plurality of current values I1. The first ground resistance calculation process for calculating the ground resistance value Re of the ground electrode E, which is the ground electrode to be measured, and the ground resistance values Rp and Rc of the auxiliary ground electrodes P and C as temporary ground resistance values, Based on the ground resistance values Re and Rp, the peak value Ve1 of the ground voltage Ve, and the maximum output voltage value Vmax of the constant current source 2, one current value I1 of the plurality of current values I1 and each ground resistance Re , Rp generated voltage (peak voltage : The added voltage value ((Re + Rp) × I1 × √2 + Ve1) obtained by adding the peak value Ve1 of the ground voltage Ve to (Re + Rp) × I1 × √2) is less than the maximum output voltage value Vmax and becomes the maximum output voltage value Vmax By executing the resistance calculation process by defining the current value I1 of the measurement current I of the constant current source 2 as the determined measurement current value and determining the current value I1 that is closest to the measurement current value. Then, a second ground resistance calculation process for calculating the ground resistance value Re of the ground electrode E is executed.

  Therefore, according to the ground resistance meter 1 and the ground resistance measuring method, the peak value Ve1 of the ground voltage Ve where the ground electrode E is grounded, the ground resistance values Re and Rp, and the maximum output voltage of the constant current source 2 The optimum current value I1 corresponding to the value Vmax can be selected from a plurality of current values I1 and defined as the current value of the measurement current I, and the ground resistance value Re of the ground electrode E can be measured. Therefore, according to the ground resistance meter 1 and the ground resistance measurement method, the conventional ground resistance meter that compares the measured ground voltage Ve with a predetermined threshold voltage and determines whether or not the ground resistance can be measured. Unlike the ground resistance measuring method, even if the ground voltage Ve is large to some extent (even at a place where a higher ground voltage Ve is generated), when the ground resistance values Re and Rp are small, the ground voltage Ve is within the range below the maximum output voltage value Vmax. The constant current source 2 supplies a specified measurement current I, and the ground resistance value Re of the ground electrode E can be accurately measured.

  In the ground resistance meter 1 and the ground resistance measuring method described above, the ground resistance value Re of the ground electrode E is measured using the first auxiliary ground electrode P and the second auxiliary ground electrode C. However, for example, the changeover switches 11 and 13 of the switch unit 4 are shifted to the connection state indicated by the broken lines, and the changeover switch 12 is shifted to the connection state indicated by the solid lines, and the connection terminal 6 is not used. Using the terminal 5 and the connection terminal 7, the connection terminal 5 is connected to the ground electrode E, and the connection terminal 7 is connected to an existing ground electrode having a small ground resistance such as a metal buried object described in the background art. Therefore, the ground resistance meter 1 and the ground resistance measuring method can be applied to simple measurement by the two-electrode method.

  Also in this case, the peak value Ve1 of the ground voltage Ve where the ground electrode E is grounded, the ground resistance value Re of the ground electrode E and the ground resistance value of the ground electrode of the small ground resistance, and the constant current source 2 Since the optimum current value I1 corresponding to the maximum output voltage value Vmax can be selected from a plurality of current values I1 and defined as the current value of the measurement current I, the ground resistance E of the ground electrode E can be measured. Even if the voltage Ve is large to some extent (even at a place where a higher ground voltage Ve is generated), when the ground resistance value Re of the ground electrode E and the ground resistance value of the ground electrode of the small ground resistance are small, the maximum output voltage value Vmax Within the range, the constant current source 2 supplies the prescribed measurement current I, and the ground resistance value Re of the ground electrode E can be accurately measured.

  In the above example, since the constant current source 2 generates and outputs a sine wave current as the measurement current I, a value obtained by multiplying the current value (effective value) I1 of the measurement current I by √2 is used. The voltage generated at each ground resistance Re, Rp (peak voltage value: (Re + Rp) × I1 × √2) is calculated, but the constant current source 2 generates a square wave current or a triangular wave current as the measurement current I. It is also possible to adopt a configuration that outputs the output. In this configuration, when a square wave current is output as the measurement current I, a value obtained by multiplying the current value (effective value) I1 of the measurement current I by 1 is used in calculating the peak voltage value. When the peak voltage value ((Re + Rp) × I1 × 1) is calculated and a triangular wave current is output as the measurement current I, the current value of the measurement current I ( The peak voltage value ((Re + Rp) × I1 × √3) is calculated using a value obtained by multiplying the effective value I1 by √3.

DESCRIPTION OF SYMBOLS 1 Grounding resistance meter 2 Constant current source 3 Voltmeter 8 Processing part C 2nd auxiliary earthing electrode E Earthing electrode I Measurement current P 1st auxiliary earthing electrode Rc, Re, Rp Earthing resistance Vec, Vep, Vpc AC voltage

Claims (2)

A constant current source for supplying an alternating constant current between the measured grounding electrode and the auxiliary grounding electrode;
A voltmeter for measuring an alternating voltage generated between the ground electrode to be measured and the auxiliary ground electrode;
A resistor that calculates a ground resistance of the ground electrode to be measured based on a current value of the AC constant current and a voltage value of the AC voltage measured by the voltmeter in a supply state of the AC constant current by the constant current source A ground resistance meter including a processing unit that executes a calculation process,
The constant current source is configured to be able to supply the AC constant current with a plurality of different current values,
The processing unit measures a voltage value of the AC voltage measured by the voltmeter as a voltage value of a first voltage in a state where supply of the AC constant current to the constant current source is stopped. And performing the resistance calculation process by defining the current value of the AC constant current to one current value on the lower side of the plurality of current values, and performing the resistance calculation process, thereby the ground electrode to be measured and the auxiliary A first ground resistance calculation process for calculating a resistance value of each ground resistance of the ground electrode as a temporary ground resistance value, the temporary ground resistance value, the voltage value of the first voltage, and the maximum output voltage value of the constant current source. On the basis of this, a current value of one of the plurality of current values, which is obtained by adding the voltage value of the first voltage to the voltage generated at each ground resistor, is less than the maximum output voltage value. Closest to the maximum output voltage Current value determination processing for determining the current value to be measured current value, and the resistance calculation processing by defining the current value of the AC constant current as the determined measurement current value, A ground resistance meter for executing a second ground resistance calculation process for calculating a resistance value of the ground resistance. In a state where an AC constant current is supplied from a constant current source between the measured grounding electrode and the auxiliary grounding electrode, the AC voltage generated between the measured grounding electrode and the auxiliary grounding electrode is measured with a voltmeter. A ground resistance measurement method for executing a resistance calculation process for calculating a ground resistance of the ground electrode to be measured based on a current value of an AC constant current and a voltage value of the AC voltage measured by the voltmeter,
Using a constant current source configured to be able to supply the AC constant current with a plurality of different current values as the constant current source,
A first voltage measurement process for measuring a voltage value of the AC voltage measured by the voltmeter as a voltage value of the first voltage in a state where the supply of the AC constant current from the constant current source is stopped;
By defining the current value of the AC constant current to one current value on the lower side of the plurality of current values and executing the resistance calculation process, each ground of the measured ground electrode and the auxiliary ground electrode A first ground resistance calculation process for calculating a resistance value of the resistor as a temporary ground resistance value;
Based on the temporary ground resistance value, the voltage value of the first voltage, and the maximum output voltage value of the constant current source, one current value of the plurality of current values, which is generated at each ground resistance A current value determination process for determining a measured current value as a measured current value that is an added voltage value obtained by adding the voltage value of the first voltage to the voltage to be measured is less than the maximum output voltage value and closest to the maximum output voltage value;
A second ground resistance calculation process for calculating a resistance value of a ground resistance of the ground electrode to be measured by executing the resistance calculation process by defining the current value of the AC constant current as the determined measurement current value. The ground resistance measurement method to be performed.

Images