The accurate measurement of AC Voltage is complicated by the necessity to minimize the burden the measuring instrument places on the primary circuit. The incorporation of a 1:1 current style voltage transformer in the AC voltage measuring circuit offers several advantages.
A minimal burden on the primary voltage circuit, with essentially zero primary circuit load,
Isolation of the primary AC circuit and the secondary output signal, and
Exceptional accuracy with a minimal phase shift.
The AC current style voltage transformer is designed with either a 1mA to 1mA or 2mA to 2mA ratio. An example of the implementation using an operational amplifier I/V (current to voltage) circuit or a resistor sampling circuit;
The input resistor R limits the current to the 1mA or 2mA input. An application note document provide additional information – Application Note 1:1 Voltage Transformer (pdf 510kb).
The TV31 with UL Recognition Certification is an example of a current style AC Voltage Transformer.