Checking the earth electrodes of a lightning protection system means measuring their impedance with an impulse wave that simulates the discharge, not just their low-frequency resistance, and doing so without disconnecting the circuit. The AMRU-200 measures earth impedance by the impulse method from 0 to 200 Ω with ±(2.5 % m.v. + 3 digits), using impulses of about 1500 V and 1 A, plus 3- and 4-wire resistance from 0.10 Ω to 19.9 kΩ per IEC 61557-5 with 0.001 Ω resolution, clamp and double-clamp measurements, soil resistivity and leakage current from 0.1 mA to 300 A.
AMRU-200 key data
- Impulse method: 4-wire earth impedance from 0.0 to 200 Ω with ±(2.5 % m.v. + 3 digits), 4/10 μs, 8/20 μs or 10/350 μs waveform, impulse current of approx. 1 A and peak voltage of approx. 1500 V.
- 3- and 4-wire earth: 0.10 Ω to 19.99 kΩ per IEC 61557-5; 0.001 Ω resolution up to 3.999 Ω; ±(2 % m.v. + 4 digits) up to 3.999 Ω, ±(2 % m.v. + 2 digits) up to 3999 Ω and ±(5 % m.v. + 2 digits) up to 19.99 kΩ; over 200 mA at 25 or 50 V.
- Multiple earths: 3-wire plus clamp from 0.12 to 1999 Ω per IEC 61557-5 with ±(8 % m.v. + 4 digits) up to 3.999 Ω and ±(8 % m.v. + 3 digits) above; double clamp from 0.00 to 149.9 Ω with ±(10 % m.v. + 3 digits) up to 19.99 Ω.
- Interference: automatic or manual selection of 16 2/3, 50, 60 or 400 Hz; interference voltage measured up to 100 V with ±(2 % m.v. + 3 digits) and its frequency from 15 to 450 Hz with ±(1 % m.v. + 2 digits); earth measurement possible with up to 24 V of interference.
- Resistivity and leakage: Wenner method from 0.0 Ωm to 999 kΩm with electrode spacing from 1 to 50 m; clamp leakage current from 0.1 mA to 300 A (±(8 % m.v. + 5 digits) up to 99.9 mA) between 45 and 400 Hz.
- Continuity: equipotential bonding and protective connections from 0.045 Ω to 19.99 kΩ, at 200 mA or more, ±(2 % m.v. + 4 digits) up to 3.999 Ω and auto-zero of the leads.
- Instrument: 4.8 V 4.2 Ah Ni-MH battery, 990 date- and time-stamped measurements downloadable over USB, IP54, 288 × 223 × 75 mm and about 2 kg.
Measurement methods
- Earth resistance using auxiliary electrodes, by the 2-, 3- and 4-wire method.
- Earth resistance using auxiliary electrodes and a clamp, for multiple earth electrodes.
- Earth resistance using two clamps, when auxiliary electrodes cannot be driven into the ground.
- Dynamic earth resistance (impedance) by the impulse-wave method, with a 4/10 μs or 10/350 μs test impulse.
- Soil resistivity by the Wenner method, and leakage current with a current clamp or a flexible clamp.
- Continuity of equipotential bonding and protective conductors, with auto-zero and a 200 mA test current, to IEC 60364-6-61:2000 section 6.12.2.
Applications
The impulse method checks the earthing of lightning protection systems, simulating the current wave of a strike without needing to disconnect the circuit, which is especially useful on lattice towers and lines where service should not be interrupted. The clamp and double-clamp methods verify multiple and interconnected earths, and the automatic or manual selection of the mains frequency (16 2/3 Hz, 50 Hz, 60 Hz or 400 Hz) allows work next to railway or industrial lines with particular interference.
Power, memory and software
It runs from a rechargeable 4.8 V 4.2 Ah Ni-MH battery pack, giving over 300 measurements per charge and recharged through the supplied Z7 adaptor or a car cigarette-lighter cable. It stores up to 990 measurements in 10 banks of 99 cells, each with the real-time clock's time stamp, and transfers them to a computer over the supplied USB cable. An optional PC application for creating measurement documentation completes the meter, installed on a computer to organise and print the downloaded readings.
Technical specifications
| Earth resistance (3- and 4-wire) | 0.00 Ω...19.9 kΩ; to IEC 61557-5, from 0.10 Ω |
| Resistance with clamp (3-wire + clamp) | 0.00...1999 Ω; to IEC 61557-5, from 0.12 Ω |
| Resistance with double clamp | 0.00...149.9 Ω |
| Earth impedance (impulse method) | 0.0...200 Ω, 4/10 μs or 10/350 μs impulse |
| Soil resistivity | 0.00 Ωm...999 kΩm (Wenner method) |
| Leakage current with clamp | 0.1 mA...300 A |
| Protective continuity | 0.00 Ω...19.9 kΩ; to IEC 61557-5, from 0.045 Ω |
| Measurement category | CAT III 600 V, to EN 61010-1 |
| Protection rating | IP54 |
| Memory | 990 measurements (10 banks of 99 cells) |
| Warranty | 36 months |
| Accuracy (3- and 4-wire) | ±(2 % m.v. + 4 digits) up to 3.999 Ω; ±(2 % m.v. + 2 digits) up to 3999 Ω; ±(5 % m.v. + 2 digits) up to 19.99 kΩ |
| Impulse method accuracy | ±(2.5 % m.v. + 3 digits); impulse of approx. 1 A and 1500 V |
| Interference frequency | 15...450 Hz, ±(1 % m.v. + 2 digits) |
Frequently asked questions
Which earth tester can measure a lightning protection earth by the impulse method?
One that measures impedance with an impulse wave simulating the lightning current. The AMRU-200 measures earth impedance from 0 to 200 Ω with ±(2.5 % m.v. + 3 digits), using 4/10 μs, 8/20 μs or 10/350 μs impulses of approx. 1 A and 1500 V, by the 4-wire method and without disconnecting the circuit.
What resolution and accuracy does the AMRU-200 offer on very low earth resistances?
It resolves 0.001 Ω from 0 to 3.999 Ω with ±(2 % m.v. + 4 digits); its range per IEC 61557-5 starts at 0.10 Ω with the 3- and 4-wire method and at 0.12 Ω with a clamp, with a test current above 200 mA.
What is the impulse method used for?
To measure the dynamic resistance (impedance) of lightning protection earths, with a 4/10 μs or 10/350 μs test impulse.
Can it measure leakage current?
Yes, with a current clamp or a flexible clamp, over a range from 0.1 mA to 300 A.
Which mains frequencies does it filter against interference?
It filters interference at 16 2/3 Hz, 50 Hz, 60 Hz and 400 Hz, with automatic or manual selection.
How are measurements transferred to a computer?
Through the supplied USB cable.
How many measurements does it store?
Up to 990 measurements, organised in 10 banks of 99 cells, each with the date and time from the real-time clock.
