zero position or E.Z. When the rotor shaft is displaced from E.Z., the resulting output signals have a magnitude and phase relationship proportional to the direction of rotation. Because RVDTs perform essentially like a transformer, excitation voltages changes will cause directly proportional changes to the output (transformation ratio). However, the voltage out to excitation voltage ratio will remain constant. Since most RVDT signal conditioning systems measure signal as a function of the transformation ratio (TR), excitation voltage drift beyond 7.5% typically has no effect on sensor accuracy and strict voltage regulation is not typically necessary. Excitation frequency should be controlled within ±1% to maintain accuracy. Although the RVDT can theoretically operate between ±45°, accuracy decreases quickly after ±35°. Thus, its operational limits lie mostly within ±30°, but some up to ±40°. Certain types can operate up to ±60°. Varieties An RVDT can also be designed with two laminations, one containing the primary and the other, the secondaries. These types can operate on larger rotations. A similar transformer is called the Rotary Variable Transformer and contains only one secondary winding giving only one voltage: See also LVDT, Linear-movement counterpart to the RVDT Rotary encoder Resolver, an angle sensor which operates over a full 360° Synchro, a three-phase variant of the resolver High Accuracy References Electric transformers Position sensors