Polyphase digitizer

Abstract

A two dimensional digitizing system comprises two systems at right angles to each other, comprising two conducting grid structures each having three terminals A, B, and C, with the grid conductors running parallel to the X axis in one system and the Y axis in the other, and a cursor coil. When the cursor coil is excited with an alternating current, voltages e.sub.ab, e.sub.bc and e.sub.ca are induced between the terminal pairs AB, BC and CA respectively, whose amplitudes are functions of the position of the cursor coil relative to a cartesian co-ordinate system defined by said X and Y axes. The voltages e.sub.ab, e.sub.bc and e.sub.ca from each system are phase shifted and summed to provide two single signals e.sub.x and e.sub.y whose phase shift from a reference signal derived from the cursor coil excitation is a linear function of cursor coil displacement along the X and Y axis respectively. The phase shifting is accomplished by a passive network connected to the three grid winding terminals. In the case of a three terminal grid winding, the system can be likened to a three phase system with the phase shifted voltages e.sub.ab, e.sub.bc and e.sub.ca corresponding to the phase voltages of a three phase system. The system disclosed is not limited to a three phase system. It is generally applicable to polyphase systems using a multi-terminal grid winding in which the number of phases is equal to the number of grid winding terminals, and is an odd integer greater than one.