Handheld Winding Ohmmeter DV Power RMO-TH

The DV Power RMO-TH instruments is a handheld winding ohmmeter. It can measure the resistance of distribution and instrument transformers, motors, generators, and any non-inductive test object.

• Handheld device, powered by internal battery
• Maximum test current for HV windings 2 A DC
• Maximum test current for LV winding 10 A DC

Intended use

The handheld winding ohmmeter, DV Power RMO-TH, is designed for measuring the resistance of distribution and instrument transformers, rotating machines, as well as any non-inductive test object. The device can also perform demagnetization of distribution and instrument transformers, and also motors and generators.

How to use RMO-TH?

Both single phase and three phase transformers can be tested using RMO-TH. RMO-TH instructs the user to properly connect instrument for each phase and each test when testing three phase transformers. Winding resistance can be measured in all tap positions. Upon winding resistance test, RMO-TH can successfully demagnetize transformer core. For ease of analysis, all findings are saved in one record.

RMO-TH winding ohmmeter design

The instrument measures the resistance of the transformer windings using two output DC sources. The first DC source, having a maximum output of 2 A DC, injects current into the transformer's high voltage winding. With a maximum output of 10 A DC, the second DC source is used to test the transformer's low voltage winding. This is very useful for evaluating the winding resistance of distribution transformers. The high voltage and low voltage windings of these transformers have very different resistances as a result of their high turns ratio. During the winding resistance test, it is also possible to demagnetize the transformer core. Demagnetization is a safe and fully automated process.
RMO-TH is powered by an inbuilt Li-Ion battery. When charged completely, the battery can power up to 100 tests.

Connecting RMO-TH to a test object

Two sets of cables are included with the RMO-TH instrument, one for attaching to the high voltage transformer winding and the other for attaching to the low voltage transformer winding.
RMO-TH cables' connection strategy is based on the Kelvin (four-point) measurement principle. This method produces accurate readings by employing discrete "Voltage Sense" terminals attached to one side of the measuring clamps and "Current Cables" attached to the other side. The resistance of the current wires and clamps has no real impact on the resistance measurement. This design helps in the providing of precise and reliable resistance data by minimizing the impact of any additional resistance in the measuring setup.