Quadrature voltage transformer - a name proposed by W.E. Sumpner for a circuit ensuring that the current flowing through a moving coil is in quadrature with the applied voltage. ¹⁾

Quadrature voltage transformer can be used for a construction of a voltmeter^{2) United States Patent and Trademark Office, Public Domain}

A capacitor of a suitable value connected in series with a moving coil will ensure that the current flowing through the coil is a derivative of the applied voltage (for sinusoidal signals it will be in quadrature). The circuit could be used for a construction of a voltmeter as described in the original patent.³⁾

• Quadrature current transformer