The Vanguard TRF-250A 3-Phase Transformer Turns Ratio Finder determines the turns-ratio of the transformer under test using the IEEE C57.12.90 measurement method. The turns-ratio range is from 0.8 to 50,000 to 1. Transformer turns ratio, excitation current, and winding polarity are displayed on the built-in 128 x 64 pixels graphic LCD screen. The TRF-250A can be used as a standalone unit or can be computer-controlled.

The TRF-250A battery offers approximately 3 hours of continuous use. The TRF-250A features a built-in charger that allows the unit to be used while charging, and provides a test voltage of 250Vac, a wireless Bluetooth PC interface, and features a 44-key “QWERTY”-style membrane keyboard. All these features greatly improve the accuracy of the turns-ratio readings, ease of operation, and reliability.