DV Power RMO40T Winding Resistance OhmMeter


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The DV Power RMO40T Winding Resistance OhmMeter is designed for resistance measurement of inductive test objects.  DV Power RMO40T generates true, filtered DC current. Both injection of current and discharge of energy from the inductance is automatically regulated.

DV Power RMO40T injects current with a voltage as high as 60V. This ensures that the duration of test is as short as possible, and that the desired test current is reached as soon as possible. Two independent channels enable testing of two series windings, or primary and secondary windings.  There is enough memory within the DV Power RMO40T instrument to store 100 measurements. All measurements are time and date stamped.

The set is equipped with thermal and overcurrent protection. The DV Power RMO40T has very high ability to cancel electrostatic and electromagnetic interference in high HV electric fields. It is achieved byvery efficient filtration. The filtration is made utilizing appropriate hardware and software.

On Load Tap Changers

DV Power RMO40T can measure the winding resistance of the individual taps of a power transformer’s tap changer, and can check whether the on-load tap changer (OLTC) switches without an interruption.

In the moment the tap is changed from tap to tap, the device detects the sudden, very short drop of the current flow. A properly working of tap changer differs from a malfunctioning one, e.g., an interruption during the change, by the magnitude of the ripple and slope values. An interruption will result in much higher ripple and slope values than a properly functioning of tap changer.


Using RMOWin-T software a test can be operated from PC, and the results can be obtained directly in PC. Using RWOWin-T the result can be printed like an Excel table which later can be shown as a diagram and used for a report. Also, the diagram of the current during the on-load tap changer test can be obtained using RMOWin-T software.

Typical application of DV Power RMO40T is measuring the resistance of:
  • Power transformers
  • On-Load Tap Changers
  • Generators and electrical motors
  • High-current busbar joints
  • Cable splices
The Good:

The Bad:

The Bottom Line:

Full Review

  • Lightweight – 13 kg (Plastic Case) 8.5 kg (Metal Case)
  • Test current 5 mA – 40 A DC
  • Measuring range 0,1 μΩ - 2 kΩ
  • Two voltage sense channels
  • Extremely quick measurement
  • Automatic discharge circuit
  • Built-in Tap Changer Control Unit
Technical data
1 - Mains Power Supply
  • Connection according to IEC/EN60320-1; UL498, CSA 22.2
  • Voltage single phase 110 V – 240 V AC, + 10 % - –15 %
  • Frequency 50 / 60 Hz

2 - Output data
  • Test current 5 mA DC – 40 A DC
  • Measuring range / Resolution:
0,1 μΩ - 999,9 μΩ 0,1 μΩ
1,000 mΩ - 9,999 mΩ 1 μΩ
10,00 mΩ - 99,99 mΩ 10 μΩ
100,0 mΩ - 999,9 mΩ 0,1 mΩ
1,000 Ω - 99,99 Ω 10 mΩ
100,0 Ω - 999,9 Ω 0,1 Ω
1000 Ω - 2000 Ω 1 Ω
  • Typical accuracy ±(0,2% rdg + 0,2% FS)

3 – Environmental conditions
  • Operating temperature -10oC - +50oC / 14oF - +122oF
  • Storage and transportation -25 oC - +70oC / -13 oF - +158 oF
  • Humidity 5 % - 95 % relative humidity, non condensing

4 - Dimensions and Weight

Plastic Case:
  • Dimensions 502 mm x 190 mm x 395 mm (19.75 in x 7.48 in x 15.53 in) (W x H x D)
  • Weight 13 kg/28.6 lb

Metal Case:
  • Dimensions 198 mm x 255 mm x 380 mm (7.8 in x 10 in x 15 in) (W x H x D) without handle
  • Weight 8.5 kg/18.7 lb

5 – Safety Standards
  • European standards EN 61010-1
  • International standards IEC 61010-1

6 – Electromagnetic Compatibility (EMC)
  • CE conformity EMC standard 89/336/EEC
  • Emission EN 50081-2, EN 61000-3-2/3
  • Interference Immunity EN 50082-2

*Specifications are subject to change without notice.
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