JPH08226944A - Multi-functional device for measuring ground resistance - Google Patents

Abstract

PURPOSE: To attain the transmission to outside devices of a measured result and to receive the instruction from a host such as measuring operation procedure by providing a multifunctional device for measuring ground resistance with a power source means for applying voltage, a switch means for switching and applying voltage, a current measuring means and an alarm means. CONSTITUTION: A ground resistance measuring part A comprises a potential detection circuit 10, a current detection circuit 20 and a current generation circuit 30. The measuring part A is provided with an E pole terminal for connecting a ground electrode to be measured, a P pole terminal for connecting a potential auxiliary pole and a C terminal for connecting a current auxiliary pole. The circuit 30 is provided with a built-in battery 31 and a rectangular wave oscillator 33 receives the supply of electric power from the battery 31. The circuit 20 selects only the signal component of the applied current owing to BPF by LPF 22 and HPF 24. The circuit 10 measures voltage between the P pole terminal obtained owing to the applied current and the E pole terminal. An attenuator 11 prevents the damage of a ground resistance measuring device owing to overvoltage and measures the voltage in the case where ground resistance is large.

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 having multiple functions, and more particularly to a multi-function ground resistance measuring device not only capable of measuring ground resistance but also having a communication function capable of transmitting a measurement result.

[0002]

2. Description of the Related Art Some distribution facilities are obliged to provide grounding facilities to ensure safety. Currently, the ground resistance is measured by the voltage drop method, which adheres to the ground resistance measurement principle most faithfully, and is also used for measuring the ground resistance of large-scale grounding bodies such as substations.

On the other hand, in a power transmission and distribution business, a grounding resistance measuring system has been developed which is capable of performing from grounding resistance measuring work, which is one of the important works in the power distribution department, to grounding management. Have been implemented. In this system, the branch organization, which is a subordinate organization of the business entity, is requested in writing to provide various items such as the date and place of grounding resistance measurement of the grounding equipment, and the measurement data obtained by the branch organization is written in the business entity. The collected measurement data will be input to the host computer and organized by the business entity, and these data will be used for the next measurement plan formulation and grounding facility management plan.

[0004]

In the measurement of the ground resistance using the voltage drop method, an error due to the resistance of the voltage auxiliary pole,
Failure due to the floating potential of the ground, the potential of the ground electrode is affected by the potential distribution of the current auxiliary electrode, the potential auxiliary electrode is affected by the potential distribution of the ground electrode, due to the coupling between the potential auxiliary lead wire and the potential auxiliary lead wire A large error is included in the measurement result due to the error caused by the induced voltage. In consideration of the above, various measurement error ranges are legally set in the measurement of the ground resistance, but it is preferable to minimize the error in the measurement.

Further, in the above ground resistance measuring system, the destination engine reports the data collected by the ground resistance measurement to the business entity in writing, and the instruction to the destination engine is also issued in writing. If the efficiency is poor and the accuracy of the collected measurement data is poor, it is impossible to operate a high quality system.

The present invention aims to improve the above-mentioned conventional drawbacks, and an object thereof is to improve the measurement accuracy of a ground resistance measuring device used as a terminal on the host side and to measure measured data. Is to obtain a ground resistance measuring device capable of communicating with the host side by transmission and receiving various command data from the host side through communication.

[0007]

In order to solve the above-mentioned problems, according to the present invention, a ground electrode E, a current auxiliary electrode C and a potential auxiliary electrode P are provided, and the ground electrode E and the current auxiliary electrode C are connected. In a ground resistance measuring device for measuring the resistance value of the ground electrode from the current and the potential between the potential auxiliary electrode P and the ground electrode E when a current is applied between the current auxiliary electrode C and the ground electrode E, and the potential auxiliary electrode. Power supply means for applying a voltage between P and the ground electrode E; switching means for switching and applying a voltage from the voltage means between the current auxiliary electrode C and the ground electrode E and between the potential auxiliary electrode P and the ground electrode E; The potentials of the potential auxiliary electrode P and the ground electrode E are measured when a voltage is applied between the auxiliary electrode C and the ground electrode E, and the input resistance is larger than the resistance value between the potential auxiliary electrode P and the ground electrode E. Voltage measuring means, potential auxiliary electrode P and ground And a current measuring means having an input resistance larger than the resistance value between the potential auxiliary electrode P and the ground electrode E for detecting a current flowing between these two electrodes when a voltage is applied between the electrodes E. , When a voltage is applied between the potential auxiliary electrode P and the ground electrode E to detect a current flowing between these two electrodes, an alarm is issued when the current measuring means measures a current value smaller than a predetermined current value. There is provided a multi-function earth resistance measuring device characterized by comprising an alarm means for emitting.

Further, the ground electrode E, the current auxiliary electrode C, and the potential auxiliary electrode P are provided, and when the current is passed between the ground electrode E and the current auxiliary electrode C, the current, the potential auxiliary electrode P, and the ground electrode. In a ground resistance measuring device for measuring a resistance value of a ground electrode from a potential between E, a power supply means for applying a voltage between the current auxiliary electrode C and the ground electrode E and a potential auxiliary electrode P and the ground electrode E, and the voltage means. Switching means for switching and applying a voltage between the current auxiliary electrode C and the ground electrode E and between the potential auxiliary electrode P and the ground electrode E, and a potential assist when the voltage is applied between the current auxiliary electrode C and the ground electrode E. A voltage measuring unit that measures the potentials of the electrode P and the ground electrode E and that has an input resistance larger than the resistance value between the potential auxiliary electrode P and the ground electrode E, and a voltage between the potential auxiliary electrode P and the ground electrode E. Between these two electrodes when applying Detecting the current, potential auxiliary electrode P
A current measuring means having an input resistance greater than the resistance value between the ground electrode E and the ground electrode E; operation command means for instructing the measurement operation sequence; and an interface circuit capable of sending the measurement result to an external device. Auxiliary electrode P and ground electrode E
And an alarm means for issuing an alarm when the current measuring means measures a current value smaller than a predetermined current value while applying a voltage between them and detecting a current flowing between these two electrodes. A featured multifunction ground resistance measuring device is also provided.

[0009]

Operation: With the voltage applied between the C-pole terminal and the E-pole terminal, the current flowing between them and the voltage between the E-pole and the P-pole are measured by the measuring means having a high input resistance, and the measured values are calculated from these measured values. Calculate the ground resistance. In this measurement, a voltage is applied between the E pole and the P pole to confirm that the P pole is in an ungrounded state when no current flows. An attenuator is provided on the input side of the voltage measuring means so that it can be inserted and removed freely, and the measurement range is expanded without manual switching. The measurement result can be transmitted to an external device such as a host computer, and a command such as a measurement operation procedure can be accepted from the host.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described in detail with reference to the drawings. FIG. 1 is a block diagram of a multifunctional earth resistance measuring device according to the present invention. As shown in FIG. 1, the multifunctional ground resistance measuring device includes a ground resistance measuring unit A and a data processing unit B. The ground resistance measuring unit A is a potential detection circuit 1
0, a current detection circuit 20, and a current generation circuit 30. The ground resistance measuring unit A includes an E pole terminal for connecting a ground electrode to be measured, a P pole terminal for connecting a potential auxiliary pole, and a C pole terminal for connecting a current auxiliary pole. In addition, in FIG.
, RP and RC respectively represent the resistance to be measured, the resistance of the voltage auxiliary pole and the resistance of the current auxiliary pole.

The current generating circuit 30 has a built-in battery 3
1, the square wave oscillator 33 is supplied with electric power from the battery 31 and has a maximum value of 60 at about 470 to 480 Hz.
Generates a square wave with V and maximum current of 80 mA. This square wave is converted into a constant current by the constant current control circuit 35 and applied between the E pole terminal and the C pole terminal. The energizing current due to this voltage application is detected as a voltage across the current detection resistor RD (10Ω).

The current detection circuit 20 includes a low pass filter 2
2 and the high-pass filter 24 to select only the signal component of the energizing current by the band-pass filter, and amplified by the amplifier 26 to the input voltage of the A / D converter provided at the entrance of the data processing unit B described later. After that, the RMS value calculator 28 further converts the AC voltage into a DC voltage, which is then input to the A / D converter.

The voltage detection circuit 10 measures the voltage between the P-pole terminal and the E-pole terminal obtained by the energizing current. Attenuator 1
1 is installed to prevent damage to the ground resistance measuring device due to excessive voltage and to measure the voltage when the ground resistance is large. In the measurement, the voltage that first passed through the attenuator 11 is measured, If measurement is possible without overscaling even if the voltage is multiplied by 10, the measurement is performed again without the attenuator 11.

In the voltage obtained between the P-pole terminal and the E-pole terminal, the low-pass filter 12 removes a signal having a frequency higher than the signal component generated by the energization current, and the ground voltage elimination filter 13 and the high-pass filter 14 eliminate the signal component. Signals of lower frequency and ground voltage are removed. The ground voltage removal filter removes the noise of the hum component that leaks from the commercial power supply in particular. When the hum component is removed from the input signal, the S / N ratio dramatically improves and the accuracy of voltage measurement improves. To do.

The measurement procedure will be described later, but in the ground voltage measurement performed in the pre-measurement step of this measurement procedure, the ground voltage removal filter 13 and the high-pass filter 14 are used.
Not used. This selection is made by the changeover switch 15. For the voltage passed through the low-pass filter 12, only the energizing signal component is selected. If necessary, this signal is amplified up to 10 times by the amplifier 16, and the effective value calculator 17 is further added.
After being converted from an AC voltage to a DC voltage by, the input voltage is input to the A / D converter.

The data processing unit B has a computer structure, and an A / D converter 51 for converting an analog signal output from the current measuring unit A into a digital signal which can be taken in by the data processing unit B is a bus. Line B
It is connected to L. On the bus line BL, a CPU, a RAM memory 52 for storing data such as calculation results and an effective program, a keyboard 53 for inputting numerical values and characters used for commands and the like, an OS and ground resistance measurement are executed on the bus line BL. ROM memory 54 for storing programs and the like, floppy disk driver 55 for storing data obtained by data processing on a floppy disk, and reading programs and data stored on the floppy disk, kanji data RS-232C interface 5 used for sending and receiving data to and from the host side computer in the ground resistance measuring system, a Kanji ROM 56 storing data used for conversion of
7. Calendar clock 58 as an accessory mechanism, printer interface 60 for connecting an external printer, LCD
The display devices 61 are organically connected to each other. Reference numeral 62 denotes an interface circuit for sending the operation of each part of the ground resistance measuring section A from the data processing section B. The operation of each part of the ground resistance measuring section A is performed by a command from the data processing section B.

To explain this in more detail, the operation command of not only the ground resistance measuring unit A but also the data processing unit B is RO
It is performed by the CPU according to the programs stored in the M memory 54 and the RAM memory 52. The RAM memory 5
The measurement program on the disk 2 can be read from the floppy disk through the floppy disk driver 55. The operation of the multifunction ground resistance measuring apparatus according to the present invention is performed by pressing a key on the keyboard 53, and the measurement result and other data are displayed on the LCD display 61.
The RAM memory 52 retains the stored contents in the memory by the backup battery for the memory even when the power is turned off, and the calendar clock 58 operates even when the power is turned off by the backup battery. The date and time of the execution can be recorded in the RAM memory 52. RS-23
The 2C interface 57 can transfer data to an external computer and output data by connecting to an external printer.

Next, the measurement of the ground resistance will be outlined. First, if the grounding current I ampere flows into the grounding body and the potential of the grounding body rises by E volts compared to before the inflow, the grounding resistance of the grounding body means that the E / I ohm is grounded to the grounding body. Called resistance. That is, measuring the ground resistance means measuring the potential rise of the grounding body, and accurately measuring the grounding resistance of the grounding body means accurately measuring the potential of the grounding body.

Various methods for measuring the resistance of the grounded body have been devised conventionally, but the most frequently used measuring method today is the voltage drop method. The apparatus according to the present invention shown in FIG. 1 uses this voltage drop method, and a current is applied to the E pole terminal to measure the voltage rise at this electrode terminal. In this type of ground resistance measurement, an error occurs in the ground resistance, that is, the measured potential of the E pole terminal, depending on the position of the P pole that is the auxiliary electrode.

FIG. 2 shows a potential distribution when a voltage is applied to a pair of electrodes of the E pole and the C pole placed on the ground surface. That is, there is a portion that shows a sudden change near both electrodes, and the potential does not change abruptly in the middle portion, and a flat portion occurs. Therefore, a P pole, which is an auxiliary electrode, is provided in a portion where the potential gradient is flat and changes little, and the potential difference between the P pole terminal and the E pole terminal and the potential difference between the P pole terminal and the C pole terminal are measured, and VE is measured. , VC, the ground resistances RE and RC of the electrodes E and C are calculated by the following equations. RE = VE / I (1) RC = VC / I (2) Of these, RE is the ground resistance of the E electrode to be measured.

In the measurement of the ground resistance as described above, the amount of current flowing through the ground resistance measuring circuit is inversely proportional to the value obtained by adding the resistance value RC of the current auxiliary pole to the ground resistance value RE. The ground resistance RC of the auxiliary pole becomes abnormally high on asphalt pavement, dry sandy ground, and frozen ground, and only a small amount of current can flow to the current auxiliary pole. May be possible. Therefore, in the accurate measurement of the ground resistance, it is necessary to make the ground resistance ground of the C electrode, which is the current auxiliary pole, small, and it is substantially 5 KΩ.
The following is desirable. In addition, P which is a potential auxiliary pole
When the ground resistance value of the electrode is large (for example, 10 kΩ or more), if the input impedance of the potential detection circuit 10 is low, the ground potential cannot be accurately measured. Therefore, in the present invention, the input impedance of the potential detecting circuit 10 is set to a value 100 times or more the ground resistance value of the P electrode, for example.

Next, the operation of measuring the ground resistance according to the embodiment of the present invention will be described with reference to FIG. When the resistance value measurement execution key provided on the keyboard 53 of the data processing unit B is pressed (S1), the changeover switch T1 provided at the head of the ground resistance measuring unit A is switched to the side a, and the state shown in FIG. Simultaneously with the connection circuit shown, the changeover switch T3 switches to the b side, and the changeover switches T2 and T4 switch to the b side.
In this state, the voltage between the P pole terminal and the E pole terminal is measured using the attenuator 11 without applying the voltage between the C pole terminal and the E pole terminal (S4). In this pre-measurement operation, the ground voltage removal filter 13 is not used (S2, S3). As a result of this measurement, if the measured ground voltage is 11 V or higher, the process proceeds to step S5, and an error message is displayed on the LCD display 6
1 is displayed. If the cancel key is pressed, the measurement operation is stopped (S1 '). If the ground voltage is less than 11V, the process proceeds to step S6.

Next, in step S6, a maximum voltage of 60 V is applied between the C-pole terminal and the E-pole terminal, and the energizing current between the C-pole terminal and the E-pole terminal is measured (S7). The current value obtained by this measurement is taken into the data processing unit B by switching the changeover switch T2 to the a side and temporarily stored in the memory 52. At this time, if the energizing current is 8 mA or less, the error message "Extreme C pole auxiliary resistance" is displayed on the LCD.
It is displayed on the display 61 (S8). Along with this measurement operation, the voltage between the P-pole terminal and the E-pole terminal is measured, the changeover switch T2 is changed over to the b side, and the data is taken into the data processing section B and temporarily stored in the memory 52 (S9).

In this energization potential measurement operation (S1
0), the changeover switch T3 is switched to the b side, and the attenuator 1
The value obtained through 1 is obtained, and if the value is 9.8 volts or less, the changeover switch T3 is switched to the a side and the conduction potential is measured again without the attenuator (S11, S12, S13), and this value is The voltage value stored in the memory 52 as a new value is rewritten to a new value. In this measurement, when the voltage value is 0.98V or less, the changeover switch T4 is switched to the side a, the voltage is amplified by the amplifier 16 and the voltage is further measured (S14, S15, S16), and the measurement is performed. Voltage is 4
If it is less than millivolts, the data processing unit B detects this and displays the error message “Excessive resistance of P pole auxiliary resistance” on the LCD.
It is displayed on the display 61. Returning to step S10 above,
If the measured voltage is 102.3 volts or higher, an error message "Excessive input voltage" is displayed on the LCD display 61 (S18).

When the above-mentioned measurement operation of the first stage is completed and no error message is displayed for both the potential and the current measurement, the measurement operation of the second stage described below is started. In the measurement operation of the second stage, the changeover switch T1 is changed over to the b side,
After configuring the connection circuit shown in FIG. 5, a voltage of 60 V is applied between the P-pole terminal and the E-pole terminal (S19), and the conduction on the potential circuit side is confirmed (S20). In this measurement operation, when the energizing current is 5 mA or less and almost no conduction is observed, the error message “Excessive resistance of P pole auxiliary resistance” is displayed.
It is displayed on the CD display 61 (S21).

The reason why it is necessary to check the continuity of the potential circuit is that the voltage is measured even when the P pole is not grounded when the input impedance is large in the potential measurement. However, this value does not mean that the voltage between the P pole and the E pole is accurately measured, and therefore the grounding state of the P pole needs to be confirmed. In addition, the reason why the measurement circuit of the second stage is provided after the first stage (ground measurement) is that the earth has a lot of soil with high chargeability. This is because I was concerned that

When no error message is issued in either of the first and second measurement steps, the CPU moves to the memory 52.
The passing current I and the potential difference VE between the P-pole terminal and the E-pole terminal stored in the memory are read out, the ground resistance RE of the electrode E is obtained using the above formula (1), and these calculated values are stored in the memory. At the same time, these values are displayed on the LCD display 61 (S22).

Although the present invention has been described with reference to the above-described embodiments, various modifications are possible within the scope of the gist of the present invention, such as the measurement of the ground resistance by exchanging the first measurement step and the second measurement step. And applications are possible, and these modifications and applications are not excluded from the scope of the present invention.

[0029]

As described in detail above, the present invention provides
The input resistance has a current and voltage measuring means having an input resistance value significantly larger than the measured resistance value, and PE
Since it is provided with a means for confirming conduction between the electrodes, it is possible to find the ungrounded state of the potential auxiliary electrode. Therefore, the ground resistance can be accurately measured. Further, since the attenuator is provided on the input side of the voltage measuring means in a freely switchable manner, it is possible to obtain a ground resistance measuring device with a wide measurement range without using a manual switching means, and the voltage measuring means has a Since a ground voltage removal filter is provided,
The ham component contained in the obtained measured value is removed, and an accurate measured value is obtained. Furthermore, since it is provided with an operation command means for commanding the measurement operation sequence and an interface circuit capable of sending the measurement result to an external device, the measurement operation sequence can be freely set from the outside, and the degree of freedom of measurement is widened. Since the measurement operation can be freely commanded from the host side and the data such as the measurement result can be sent to the host side, the ground resistance measuring system can be operated smoothly and quickly.

[Brief description of drawings]

FIG. 1 is a block diagram showing one embodiment of the present invention.

FIG. 2 is a potential distribution when a voltage is applied between the E pole and the C pole placed on the ground surface.

FIG. 3 is a flowchart for explaining the operation of the present invention.

FIG. 4 is a circuit diagram when a voltage is applied between a C pole and an E pole.

FIG. 5 is a circuit diagram when a voltage is applied between the E pole and the P pole.

[Explanation of symbols]

 A ... ・ Grounding resistance measuring unit B ・ ・ ・ ・ Data processing unit T1 ・ ・ ・ ・ Switching switch T2 ・ ・ ・ ・ Switching switch T3 ・ ・ ・ ・ ・ ・ Switching switch T4 ··· Changeover switch RD ··· Current detection resistor BL ··· Bus line 10 ··· Potential detection circuit 11 ··· Attenuator 12 ···・ ・ ・ ・ Low-pass filter 13 ・ ・ Earth voltage removal filter 14 ・ ・ ・ High-pass filter 15 ・ ・ ・ Switch 16 ・ ・ ・ Amplifier 17 ・ ・RMS calculator 18 ...- Switch 20-Current detection circuit 22-Low-pass filter 24-High-pass filter 26-Amplifier 28 --- RMS calculator 30 --- Current generator circuit 3・ ・ ・ ・ Battery 33 ・ ・ Square wave oscillator 35 ・ ・ Constant current control circuit 51 ・ ・ A / D converter 52 ・ ・ ・ ・ RAM memory 53 ・・ ・ ・ ・ ・ Keyboard 54 ・ ・ ・ ・ ・ ROM memory 55 ・ ・ ・ ・ ・ Floppy disk driver 56 ・ ・ ・ ・ ・ ・ Kanji ROM 57 ・ ・ ・ ・ ・ RS-232C interface 58 ・ ・ ・・ ・ Calendar clock 59 ・ ・ ・ ・ ・ ・ Earth tester input interface 60 ・ ・ Printer interface 61 ・ ・ LCD display 62 ・ ・ ・ ・ ・ ・ Interface circuit

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hitoshi Toda 3-7-1, Ichibancho, Aoba-ku, Sendai-shi, Miyagi Tohoku Electric Power Co., Inc. (72) Ichihiro Yahagi, Ibaraki, Aoba-ku, Sendai-shi, Miyagi 3-7-1, Machi Tohoku Electric Power Co., Inc. (72) Tatsuo Oda, Inventor Tatsuo Oda 4-1-1, Enooka, Miyagino-ku, Sendai City, Miyagi Prefecture (72) Inventor, Gen Gen Satoshi Edobukuro, Kawaguchi City, Saitama Prefecture 2-1-2 Nihon Jiko Co., Ltd. (72) Inventor Kazuo Nakamura 2-1-2 Edobukuro, Kawaguchi City, Saitama Nihon Jiko Co., Ltd.

Claims (4)

[Claims] 1. A ground electrode E having a ground electrode E and a current auxiliary electrode C which are connected to the ground and are spaced apart from each other, and a potential auxiliary electrode P provided in a ground current path between these electrodes. In the ground resistance measuring device for measuring the resistance value of the ground electrode from the current and the potential between the potential auxiliary electrode P and the ground electrode E when a current is applied between the current auxiliary electrode C and the ground Power supply means for applying a voltage between the electrodes E and between the potential auxiliary electrode P and the ground electrode E, and switching the voltage from the voltage means between the current auxiliary electrode C and the ground electrode E and between the potential auxiliary electrode P and the ground electrode E. Switching means for applying, measuring the potentials of the potential auxiliary electrode P and the ground electrode E while applying a voltage between the current auxiliary electrode C and the ground electrode E, and measuring the resistance value between the potential auxiliary electrode P and the ground electrode E. Voltage measuring means with a larger input resistance , A current flowing between these two electrodes is detected when a voltage is applied between the potential auxiliary electrode P and the ground electrode E, and an input resistance larger than the resistance value between the potential auxiliary electrode P and the ground electrode E is provided. Current measuring means, and when a voltage is applied between the potential auxiliary electrode P and the ground electrode E to detect a current flowing between these two electrodes, the current measuring means is higher than a predetermined current value. A multi-function earth resistance measuring device comprising alarm means for issuing an alarm when a small current value is measured. 2. A ground electrode E having a ground electrode E and a current auxiliary electrode C which are connected to the ground and are spaced apart from each other, and a potential auxiliary electrode P provided in a ground current path between these electrodes. In the ground resistance measuring device for measuring the resistance value of the ground electrode from the current and the potential between the potential auxiliary electrode P and the ground electrode E when a current is applied between the current auxiliary electrode C and the ground Power supply means for applying a voltage between the electrodes E and between the potential auxiliary electrode P and the ground electrode E, and switching the voltage from the voltage means between the current auxiliary electrode C and the ground electrode E and between the potential auxiliary electrode P and the ground electrode E. Switching means for applying, measuring the potentials of the potential auxiliary electrode P and the ground electrode E while applying a voltage between the current auxiliary electrode C and the ground electrode E, and measuring the resistance value between the potential auxiliary electrode P and the ground electrode E. Voltage measuring means with a larger input resistance , The current flowing between these two electrodes is detected when a voltage is applied between the potential auxiliary electrode P and the ground electrode E, and the input resistance is larger than the resistance value between the potential auxiliary electrode P and the ground electrode E. It comprises current measuring means, operation commanding means for instructing the measurement operation sequence, and an interface circuit capable of sending the measurement results to an external device, and applying a voltage between the potential auxiliary electrode P and the ground electrode E to provide these 2 Multi-function ground resistance, comprising alarm means for issuing an alarm when the current measuring means measures a current value smaller than a predetermined current value while detecting a current flowing between two electrodes. measuring device. 3. The voltage measuring means comprises means for measuring the ground voltage of the potential auxiliary electrode P and the ground electrode E when no voltage is applied to any of the electrodes. Alternatively, the multi-function earth resistance measuring device according to claim 2. 4. The multi-function earth resistance measuring device according to claim 3, further comprising alarm means for issuing an alarm when the voltage measuring means measures a ground voltage larger than a predetermined value.