Transformer Ohmmeter



  •   Direct 2-channel digital reading (1 µΩ to 2000 Ω)
  •   DC test current up to 10 A maximum
  •   0.25% measurement accuracy
  •   Integrated demagnetization feature
  •   Tests operation of on-load tap-changers
  •   Very fast auto safety discharge circuit

The MTO210 transformer ohmmeter is a line-operated, field-portable instrument designed specifically to measure the dc resistance of all types of magnetic windings safely and accurately. It can test transformers and rotating machine windings and perform low-current resistance measurements on connections, contacts and control circuits.

The Transformer Ohmmeter is extremely useful when testing the windings and contact resistance of tap-changers with “make-before-break” contacts and voltage regulators. This action will check for pitted or misaligned contacts as the instrument will give an indication if either condition occurs.


The MTO210 Transformer Ohmmeter is used:

  •   To verify factory test readings.
  •   As part of a regular maintenance program.
  •   To help locate the presence of defects in transformers, such as loose connections.
  •   To check the “make-before-break” operation of on-load tap-changers.
  •   A regular maintenance program that includes winding resistance measurements is the most effective way to use this instrument. Once a benchmark is established, subsequent test results can be compared to determine if changes are occurring in the transformers and associated control wiring, voltage regulators, motors, generators, breaker contacts, and all types of connections (bolted, soldered, crimped, etc.). Tap-changers are mechanical devices and the most vulnerable part of a transformer. Tap-changers result in more failures and outages than any other component and so require frequent testing and attention to ensure reliable and safe operation.