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MRU-30 

– USER MANUAL 

22 

4.6  Earth resistance measurement with two-clamp method (2C) 

The two-clamp measurement is employed when there is no possibility of using auxiliary electrodes. 

 

 

NOTE! 

The  two-clamp  method  is  used  specifically  only  in  the  case  of  multiple  earth 
ground systems. 

 

 

 

 

Use the 

<<

 or 

>>

 buttons to select the 

measurement mode: 

. The LED 

 

is 

illuminated. The meter is now in the state of 
measuring interfering noise voltage be-
tween the measurement terminals, and also 
measuring current sensed by the receiving 
current clamp. 

 

 

 

 

 

 

 

 

Connect the transmission clamp to terminals 

H

 and 

E

The measurement current clamp should be connected to the clamp terminal  . 
Attach the transmission clamp and the measurement clamp around the 
tested earth electrode object of test at least 30 cm / 12 in from each other. 

 

 

 

 
 
The meter  is  ready  for 
measurement. 
 

 

 

 

Press 

START 

to begin measurement. 

Connect the test leads according to this diagram: 

 

Summary of Contents for MRU-30

Page 1: ......

Page 2: ...MRU 30 USER MANUAL 2 ...

Page 3: ...USER MANUAL EARTH GROUND RESISTANCE METER MRU 30 SONEL S A Świdnica Poland SONEL TEST MEASUREMENT Santa Clara CA 95054 Version 1 05 26 07 2021 ...

Page 4: ... the following two conditions 1 This device may not cause harmful interference and 2 this device must accept any interference received including interference that may cause undesired operation This equipment has been tested and found to comply with the limits for a Class B digital device pursuant to part 15 of the FCC Rules These limits are designed to provide reasonable protection against harmful...

Page 5: ...resistivity measurement ρ 29 5 Memory of measurement results 33 5 1 Storing the measurement results in the memory 33 5 2 Viewing memory data 35 5 3 Deleting memory data 36 5 3 1 Deleting cell data 36 5 3 2 Deleting bank data 37 5 3 3 Deleting the whole memory 39 6 Data transmission 40 6 1 Computer connection accessories 40 6 2 Data transmission through USB port 40 7 Firmware update 41 8 Power supp...

Page 6: ...arth resistance measurement for two clamp method 2C 48 12 2 5 Influence of the relation of the resistance measured with clamp for the multiple earthing branch to the resultant resistance RE3P C 48 12 2 6 Additional uncertainties in accordance with IEC 61557 5 RE3P RE4P 48 13 Accessories 49 13 1 Standard accessories 49 13 2 Optional accessories 49 14 Manufacturer 50 15 Laboratory services 51 ...

Page 7: ...nvironments consult with the individual responsible for health and safety Do not operate the meter in the following situations A meter that is damaged or completely or partially malfunctioning A meter with damaged test leads or insulation A meter stored for long periods in unfavorable conditions e g excessive humidity or tempera ture extremes If the meter is transferred from a cold to a warm envir...

Page 8: ...off Switch off the meter by pressing and and holding the button for approx 2 sec Emer gency si tuations Pressing the button for approx 7 seconds will turn off the meter in case of emergency 3 Meter configuration Turn on the meter by pressing the button and the SET SEL button simulta neously When the Fn screen is displayed use the and buttons to set the local mains frequency 50 Hz or 60 Hz 50 Hz is...

Page 9: ...Use the and buttons to turn the au dio sound ON or OFF Press the and buttons to show the oFF screen to allow the setting of the auto power off time Auto OFF Use the and buttons to set the time to turn the meter off automatically Auto OFF The choices are 300 s 600 s 900 s or none dashes Auto OFF is disa bled ...

Page 10: ...fault Use and buttons to show the UPdt screen to install new firmware updates Press ENTER to enter firmware update mode The update process is described in section 7 After changing the parameters to exit the SETUP menu either Press the ENTER button to memorize set tings not applicable for the Update screen Or press the ESC button to go to the meas urement screen without confirming changes ...

Page 11: ... other sockets and displays the value of the interfering voltage on the screen Additional information displayed by the meter VN 100V 100V and a continuous tone NOISE and The voltage on the measurement terminals is 100 V The measurement cannot proceed VN xxV 40V and a continuous tone NOISE and Where xx is the value of the interfering voltage The volt age on the measurement terminals is 40 V The mea...

Page 12: ...measuring interfering noise volt age between the measurement terminals Press the SET SEL button to select the measurement voltage Use the and buttons to set the measurement voltage value to 25 V or 50 V or Press ENTER to save the setting or press ESC to exit without saving The meter is ready for measurement Press START to begin measurement Connect the test leads according to the drawing ...

Page 13: ...he value of the interfering voltage The volt age on the measurement terminals is 40 V The meas urement cannot proceed VN xxV 24V NOISE and Where xx is the value of the interfering voltage The volt age on the measurement terminals is 24 V but 40 V The measurement cannot proceed NOISE The value of the interfering voltage is 24 V but has a high value Results may be affected by additional uncer tainty...

Page 14: ...urement voltage value to 25 V or 50 V or Press ENTER to save the setting or press ESC to exit without saving Drive the current electrode into the ground and connect it to the H terminal of the meter Drive the voltage electrode into the ground and connect it to the S terminal of the meter Connect the earth electrode object of test to the E terminal of the meter All 3 electrodes should be aligned in...

Page 15: ...and repeat the measurements Note Earth resistance measurements are usually good if the interference voltage is 24 V The meter can measure in the presence of interference voltage up to 100 V Over 40 V it is indicated as hazardous Do not connect the meter to a volt age exceeding 100 V Pay attention to the quality of the connection to the electrode object of test with the test leads the contact area ...

Page 16: ...n displayed by the meter RE 9999Ω Measurement range exceeded VN 100V 100V and a continuous tone NOISE and The voltage on the measurement terminals is 100 V The measurement cannot proceed VN xxV 40V and a continuous tone NOISE and Where xx is the value of the interfering voltage The volt age on the measurement terminals is 40 V The meas urement cannot proceed VN xxV 24V NOISE and Where xx is the va...

Page 17: ...f measuring interfering noise voltage be tween the measurement terminals Press the SET SEL button to select the measurement voltage Use the and buttons to select the measurement voltage of 25 V or 50 V or Press ENTER to save the setting or press ESC to exit without saving Drive the current electrode into the ground and connect it to the H terminal of the meter Drive the voltage electrode into the ...

Page 18: ...e re sistance of the electrodes VN interfering noise voltage The result is displayed for 20 seconds Press ENTER to display again S Repeat the test two or more times by moving the voltage electrode a couple of meters or yards alter nately towards and away from the earth electrode object of test E and repeat steps 7 8 and 9 If the RE test results differ by more than 3 it is necessary to significantl...

Page 19: ...round for example by means of moistening of the place when the electrode is driven its driving into the ground in another place or using a 80 cm electrode Check also the test leads and make sure the insulation is not damaged and the contacts test lead banana plug electrode are not corroded or loosened In most cases the achieved resolution of the measurement is sufficient but it is necessary to be ...

Page 20: ...t the measurement voltage value to 25 V or 50 V or Press ENTER to save the setting or press ESC to exit without saving Drive the current electrode into the ground and connect it to the H terminal of the meter Drive the voltage electrode into the ground and connect it to the S terminal of the meter Connect the earth electrode object of test to the E terminal of the meter Attach the receiving clamp ...

Page 21: ... begin measurement After the measurement completes view the results on the screen Use the and buttons to toggle between the measurement results RH resistance of current electrode RS resistance of voltage electrode ER additional uncertainty caused by the re sistance of the electrodes VN interfering noise voltage IL leakage current The result is displayed for 20 seconds Press ENTER to display again ...

Page 22: ... distorted by additional uncertainty A particularly high measurement uncertainty is generated if we measure a low value of the earth resistance with electrodes of a loose contact with the soil such a situation occurs often if the earth electrode is properly made and the upper layer of the ground is dry and characterized by a low conductivity Then the relation between the electrode resistance and t...

Page 23: ...0 V The measurement cannot proceed NOISE The value of the interfering voltage is 24 V but has a high value Results may be affected by additional uncer tainty and ER along with value The uncertainty caused by resistance of the electrodes is 30 Uncertainties calculated on the basis of the meas ured values and RH or RS along with Ω value The resistance of H and S electrodes or one of them ex ceeds 19...

Page 24: ...he meter is now in the state of measuring interfering noise voltage be tween the measurement terminals and also measuring current sensed by the receiving current clamp Connect the transmission clamp to terminals H and E The measurement current clamp should be connected to the clamp terminal Attach the transmission clamp and the measurement clamp around the tested earth electrode object of test at ...

Page 25: ...ent clamps must be purchased separately The current clamps must be calibrated before they are used for the first time It is recommended to periodically re calibrate current clamps The clamp calibration option is described in section 4 7 Additional information displayed by the meter RE 99 9Ω Measurement range exceeded Flashing clamp symbols Transmitting clamp disconnected Flashing clamp symbol Rece...

Page 26: ... enter the screen where test voltage can be selected then use and buttons to enter the screen where the measuring clamp calibration can be performed Flashing CAL message indicates meter is ready for the clamp cali bration procedure Connect the E and the H termi nals together with a test lead and put the clamp around the lead Press START button The meter has determined the correction factor for con...

Page 27: ...urement can be started Press ESC or ENTER to skip and re turn to the standby screen immediately Note Make sure the test lead passes centrally through the clamp Additional information displayed by the meter Flashing symbols and oPEn Flashing symbols E H indicate a test lead is disconnected from the measurement terminals Flashing clamp sym bol Measurement clamp is disconnected ...

Page 28: ... specified in the standard EN 61557 4 V 24V I 200mA and R 10Ω Use or buttons to select the measurement mode RCONT 200mA The LED is illuminated The meter is now in the state of measuring interfering noise voltage between the measurement terminals The meter is ready for measurement Press START to begin measurement Connect the test leads according to this diagram ...

Page 29: ...oltage on the measurement terminals is 100 V The measurement cannot proceed VN xxV 40V and a continuous tone NOISE and Where xx is the value of the interfering voltage The volt age on the measurement terminals is 40 V The meas urement cannot proceed VN xxV 3V NOISE and Where xx is the value of the interfering voltage The volt age on the measurement terminals is 3 V but 40V The measurement cannot p...

Page 30: ...lashing AUTO ZERO mes sage indicates the test leads cali bration procedure is ready to begin Press the START button When a steady AUTO ZERO message is displayed on the screen the test leads calibration procedure is complete The results now include the cor rection value for RCONT and is indi cated by AUTO ZERO displayed on screen This value is saved in memory and will be overwritten whenever the Au...

Page 31: ...th ground resistance measurement but includes the distance between the electrodes The result is the resistance value calculated in accordance with the following formula ρ 2 LRE Wenner s measurement method The method assumes equal distances between elec trodes Use or buttons to select the earth resistivity measurement mode The LED is illuminated The meter is now in the state of measuring interferin...

Page 32: ...ect the current electrode to the H socket of the meter Connect the voltage electrode to the S socket of the meter Connect the voltage electrode to the ES socket of the meter Connect the current electrode to the E socket of the meter The meter is ready for measurement Press START to begin measurement After the measurement completes view the results on the screen ...

Page 33: ...ement of the RE earth electrode will be distorted by additional uncertainty A particularly high measurement uncertainty is generated if we measure a low value of the earth resistance with electrodes of a loose contact with the soil such a situation occurs often if the earth electrode is properly made and the upper layer of the ground is dry and characterized by a low conductivity Then the relation...

Page 34: ...ceed VN xxV 24V NOISE and Where xx is the value of the interfering voltage The volt age on the measurement terminals is 24 V but 40 V The measurement cannot proceed NOISE The value of the interfering voltage is 24 V but has a high value Results may be affected by additional uncer tainty and ER along with value The uncertainty caused by resistance of the electrodes is 30 Uncertainties calculated on...

Page 35: ...repeat them without losing other data Results stored in the memory can be recalled or downloaded to a computer Results of single measurement can be stored in one memory cell After entering the measurement result the number of the cell its ID number is automatically increased It is a good practice before performing a new series of measurements to delete the memory contents of cells that are going t...

Page 36: ...e flashing Use the and buttons to select the de sired number of the bank After selecting the desired bank and cell press the ENTER button to save the result in the memory A tri ple beep sound indicates data is being reorded To return to the measurement screen without saving Press ESC If you try to store data in an occupied memory cell the OVEr warning message will appear or Press ENTER to overwrit...

Page 37: ...ory the last result may be recalled by pressing ENTER All results for a given measuring function and preset measurement settings are stored in the memory 5 2 Viewing memory data Use the or buttons to select the memory function MEM the LED is Illuminated Use the and buttons to preview any test results stored in a selected cell To change the cell number or bank number When the cell number is flashin...

Page 38: ...y or individual cells or banks 5 3 1 Deleting cell data Use the or buttons to select the memory function MEM The LED is illuminated Set the cell number to be deleted by using the and buttons Press ENTER The message is displayed Press ENTER The symbol and dEL ConF mes sages appear ...

Page 39: ...rowsing The contents of the cell have been deleted 5 3 2 Deleting bank data Use the or buttons to select the memory function MEM The LED is illuminated Set the bank number to be deleted by pressing the SET SEL button until the bank number flashes Press the SET SEL button again The cell number will flash Set the cell number to before 01 by pressing the button Then the message is displayed ...

Page 40: ...ER The symbol and dEL ConF mes sages appear or Press ENTER to delete the selected bank After deleting the bank the meter beeps three times Press ESC to can cel and return to memory browsing The contents of the bank have been deleted ...

Page 41: ... memory function MEM The LED but ton is illuminated Press the SET SEL button until the bank number flashes Set the bank number to before 0 by pressing the but ton The bank number will change to Then the message is displayed Press ENTER The symbol and dEL ConF mes sages appear ...

Page 42: ...rchased along with the meter they are available from the Sonel or an authorized Sonel distributor These accessories may also be used with SONEL instruments equipped with a USB interface Detailed information regarding software is available from Sonel or an authorized Sonel distributor 6 2 Data transmission through USB port Use the or buttons to select the memory function MEM The LED is illuminated ...

Page 43: ...truc tions 8 Power supply of the meter 8 1 Monitoring the power supply voltage The charge level of the rechargeable batteries is indicated by the battery symbol in the right upper corner of the display Batteries are charged Batteries are nearly discharged No battery symbol on screen with charger connected indicates the battery is either disconnected or has malfunctioned The bAtt message indicates ...

Page 44: ...attery pack is charged in background charging mode Full charge is indicated by the FULL message and beep If the charging time exceeds 10 hours the meter will automatically switch off for safety To fully turn the device off unplug the power charger and turn the meter off CAUTION Do not power the meter from sources other than those described in this manual Note Battery charging may finish prematurel...

Page 45: ... a high temperature reduces battery lifetime and causes a further increase of the battery temperature which will not allow charging to full capacity With quick charging batteries are charged to approximately 80 of their capacity Better results may be obtained if charging is continued Charging will continue but with a low current After a couple of hours the batteries are charged to their full capac...

Page 46: ... VN RMS Range Resolution Accuracy 0 to 100 V 1 V 5 m v 2 digits measurement for fN 45 to 65 Hz frequency of measurements minimum two measurements s Measurement of earth resistance 2 pole method RE2P Range Resolution Accuracy 0 01 Ω to 19 99 Ω 0 01 Ω 3 m v 3 digits 20 0 Ω to 199 9 Ω 0 1 Ω 200 Ω to 1999 Ω 1 Ω 5 m v 2000 Ω to 9999 Ω 1 Ω 8 m v Measurement of earth resistance 3 pole method RE3P 4 wire ...

Page 47: ... 1 00 to 5 00 A 0 01 A 5 m v 5 digits measurement for fN 45 Hz to 65 Hz Measurement of resistance of protective conductors and equipotential bonding RCONT The measurement method technical in accordance with IEC 61557 4 Range of measurement in accordance with IEC 61557 4 0 13 to 1999 Range Resolution Accuracy 0 00 to 19 99 Ω 0 01 Ω 2 m v 3 digits 20 0 to 199 9 Ω 0 1 Ω 200 to 1999 Ω 1 Ω Ground resis...

Page 48: ...umber of measurements for RE 2000 RE 10 RH RS 100 25 V 50 Hz 2 measurements min q RCONT resistance measurement duration 4 s r duration of a resistance and resistivity measurement by means of other methods 8 s s dimensions 200 x 150 x 73 mm 7 9 x 5 9 x 2 9 in without test leads t weight with batteries 1140 g 2 5 lbs u working temperature 10 C to 50 C 14 F to 122 F v temperature range for battery ch...

Page 49: ... electrodes on earth resistance measure ments for methods RE3P RE4P RE3P C ρ RH RS Additional uncertainty RH 5 kΩ and RS 5 kΩ 𝑅𝑆 𝑅𝑆 100000 150 𝑅𝐻 0 004 𝑅𝐸 1 5 10 8 𝑅𝐻 2 RH 5 kΩ or RS 5 kΩ or RH and RS 5 kΩ 7 5 𝑅𝐻 0 004 𝑅𝐸 1 5 10 8 𝑅𝐻 2 RE Ω RS Ω and RH Ω are values which are displayed by the device 12 2 3 Influence of the interference current IZ on the result of the earth re sistance for method RE...

Page 50: ...ured with clamp for the multiple earthing branch to the resultant resistance RE3P C RC Additional uncertainty Ω 50 Ω 0 003 𝑅𝐶 𝑅𝑊 2 50 Ω 0 5 𝑅𝐶 𝑅𝑊 RC Ω is the value of the resistance measured with clamps for the branch displayed by the device and RW Ω is the value of the resultant multiple earth resistance 12 2 6 Additional uncertainties in accordance with IEC 61557 5 RE3P RE4P Influencing factor S...

Page 51: ...ds WAPRZ050YEBBSZ Black crocodile clip WAKROBL20K01 Pin probe with banana connector red WASONREOGB1 Cramp with banana socket WAZACIMA1 Soft carrying case for the meter and accessories WAFUTM9 Carrying case for the meter and accessories WAFUTL10 USB cable WAPRZUSB Power supply adaptor Z7 WAZASZ7 Calibration certificate issued by an accredited laboratory User manual 13 2 Optional accessories Optiona...

Page 52: ...land tel 48 74 858 38 60 fax 48 74 858 38 09 E mail export sonel pl Web page www sonel pl SONEL Test Measurement Santa Clara Ca 95054 USA tel 1 408 898 2215 fax 1 408 988 4869 E mail testsupport soneltest com Web www soneltest com Attention Service and repairs must be carried out only by Sonel or an authorized Sonel service center ...

Page 53: ...rs o luxmeters The Calibration Certificate is a document that presents a relation between the calibration standard of known accuracy and meter indications with associated measurement uncertainties The calibration standards are normally traceable to the national standard held by the National Metrological Institute According to ILAC G24 Guidelines for determination of calibration intervals of measur...

Page 54: ...MRU 30 USER MANUAL 52 NOTES ...

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Page 56: ...MRU 30 USER MANUAL 54 ...

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