The TRM-20 is Vanguard Instruments’ third generation transformer winding resistance meter. The TRM-20 is designed specifically to measure DC resistance values of transformer windings, rotating machine windings, or any dc resistance of an inductive device.

The TRM-20 features dual resistance-reading input channels that can measure two winding resistances simultaneously (primary and secondary windings of a transformer). It can provide a fast and stable reading of very large transformers by utilizing a 60Vdc power supply. The TRM-20 is capable of outputting a selectable test current from 1A to 20A.

Since the TRM-20 can accurately measure resistance values from 1 micro-ohm to 2,000 Ohms, it can be used as micro-ohm meters to measure EHV circuit breaker contact resistance, or for any low resistance measuring application. The TRM-20 can automatically demagnetize the inductive device under test, eliminating the manual task of demagnetizing the transformer core after a resistance test.