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Earthing resistance and soil resistivity meter
Technical Specification
  • Description

    Multifunctional earthing and soil resistivity meter

    The Sonel MRU-200-GPS earth resistance and soil resistivity meter is a versatile meter for earth resistance and soil resistivity measurements. The device allows the use of all known earth resistance measurement methods. This renders it an unrivalled measuring instrument in its category and definitely makes it stand out from other devices of its kind. Sonel MRU-200-GPS allows you to perform tests with the 3-pole and 4-wire method, using additional clamps (multiple earthing), as well as the two-clamp method and impulse method (earth impedance measurement).

    The application of the two-core measurement method allows, under certain conditions, to perform earth resistance measurements without the use of auxiliary probes which are driven into the ground. The impact method, on the other hand, is used for diagnosing lightning protection earthing, but can also be used to measure extensive, multiple and connected earthing (including underground) without interfering with the circuit. With the use of the impact method it is possible to carry out measurements in accordance with EN 62305 - the need to measure earth impedance. It is worth noting that the instrument also has a built-in GPS receiver, which allows for recording the result along with the coordinates of the location. An additional function of the meter is the possibility of carrying out measurements of soil resistivity, continuity of protective and equalising connections and, with the use of clamps, also leakage or fault currents.

    The high class of the device is confirmed by the excellent accuracy of the result it produces. The meter makes measurements in accordance with the PN-EN 61557 standard starting from 0.100 Ω.

    Measurement methods

    • Impulse method – measurement of lightning protection systems with a measuring impulse ramp of 4/10 μs, 8/20 μs, 10/350 μs
    • 3-pole and 4-wire method – measurement of earthing systems using auxiliary probes
    • 3-pole method with clamp – measurement of earthing systems with multiple earth electrodes
    • Two-clamp method – measurement of earthing system when the auxiliary probes cannot be used
    • Earth resistivity – Wenner method
    • Resistance of earth and compensatory conductors measured using current ≥200 mA with auto-zero function – meets the requirements of EN 61557-4
    • Measurement of leakage current

    Additional features

    • Built-in GPS receiver – recording results with location coordinates 
    • Measurement of resistance of auxiliary electrodes RS and RH
    • Measurement of interference voltage
    • Measurement of interference frequency
    • Measurement in the presence of interference voltage generated by power networks with frequency of 16 2/3 Hz, 50 Hz, 60 Hz, 400 Hz
    • Selection of maximum measuring voltage (25 V and 50 V)
    • Automatic calculation of soil resistivity in ohm-meters (Ωm) and ohm-feet (Ωft)
    • Memory of 990 measurement results (10 banks of 99 cells each)
    • Calibration of clamp used
    • Real time clock (RTC)
    • Data transmission to the computer and mobile devices
    • Battery indication


    MRU-200-GPS meter was created for the most difficult working conditions. It generates a measuring current exceeding 200 mA, which provides effective measurements of grounding of energy objects such as transformer stations and power stations.

    Thanks to the methods using clamps, it is not necessary to disconnect the control connectors, which is sometimes a very tedious operation. This plays a special role when performing works on objects exposed to weather conditions, where the connecting elements are sometimes corroded or tarnished.

    The graphical user interface provides clear readings and explicit messages. This translates into quick, trouble-free service.

    Impulse method

    MRU-200-GPS may be used to test earthing of lightning protection systems, as this meter is able to simulate the conditions occurring during a lightning strike – it generates current with a standardized pulse leading edge and a time to half-peak. Available impulse ramps include 4/10 μs, 8/20 μs, 10/350 μs.

    Compatible with ERP-1 adapter

    ERP-1 adapter allows user to test earthing systems using flexible clamps. This is particularly useful, e.g. in case of lattice towers – there is no need to switch off the line or disconnect control connectors. Proprietary algorithm allows user to check the current direction in the individual measurements and facilitates damage detections, e.g. corroded steel strip (hoop).


    The measuring methods available in the device allow for comprehensive control of working and protective grounding. The calibration function of the test leads eliminates the influence of their resistance on the result. However, this is just the beginning.

    • The four-lead method provides very accurate measurement of the expected small values of resistance – eliminates the resistance of the test leads connecting the meter to grounding.
    • Measurement of the continuity of protective connections and equipotential bondings with a current exceeding 200 mA meets the requirements of EN 61557-4 standard.
    • Before performing the measurement, the meter checks whether the tested object is a subject to excessive interference voltage, which may indicate additional problems.

    Memory and results

    The results can be saved to the device’s memory. It is divided into 10 banks of  99 cells, each corresponding to one measurement. These results can be easily transferred to the Sonel Reader software for archiving or subsequent analysis and research.

    Bluetooth wireless interface may be used to transfer measurement results to PC software or to a mobile phone with dedicated app – Sonel MRU Mobile. This provides not only data archiving function, but further data transfer – directly from the measurement site via an e-mail.

  • Technical Specification
    Measurement functions Measurement range Display range Resolution Accuracy
    Interference voltage 0 V…100 V 0 V…100 V 1 V ±(2% m.v. + 3 digits)
    Resistance of earth connection and equipotential bonding 0.045 Ω…19.99 kΩ acc. to EN 61557-4 0.00 Ω…19.9 kΩ from 0.001 Ω from ±(2% m.v. + 2 digits)
    Earth resistance
    3-pole and 4-wire method 0.100 Ω…19.99 kΩ acc. to EN 61557-5 0.00 Ω…19.9 kΩ from 0.001 Ω from ±(2% m.v. + 2 digits)
    3-pole + clamp method 0.120 Ω…1999 Ω acc. to EN 61557-5 0.00 Ω…1999 Ω from 0.001 Ω ±(8% m.v. + 3 digits)
    two-clamp method 0.00 Ω…149.9 Ω 0.00 Ω…149.9 Ω from 0.01 Ω from ±(10% m.v. + 3 digits)
    impulse method 4/10 μs, 8/20 μs, 10/350 μs pulse 0.0 Ω…199 Ω 0.0 Ω…199 Ω from 0.1 Ω ±(2.5% m.v. + 3 digits)
    auxiliary electrodes resistance 0 Ω…19.9 kΩ 0 Ω…19.9 kΩ from 1 Ω ±(5% (RE +RH+RS) + 8 digits)
    Earth resistivity 0.0 Ωm…999 kΩm 0.0 Ωm…999 kΩm from0.1 Ωm Depends on the accuracy of the RE 4p measurement, but not less than ±1 digit
    Leakage current 0.1 mA…300 A 0.1 mA…300 A from 0.1 mA from ±(5% m.v. + 5 digits)

    “m.v.” - measured value

  • Files

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