14 a typical rotor position transducer rpt for the 3 phase 4 rotor pole drive of fig1 is shown schematically in fig6 the three sensors are shown with 120 u00b0 mechanical offset but can have any offset that equals 120 u00b0 electrical the schematic shown has teeth with a mark space ratio of unity in practice this may be varied slightly to accommodate any non ideal characteristics of the sensors e g beam width in an optical sensor or fringing in a hall effect sensor so that the final signal from the rpt is at or acceptably near unity mark space the output from the rpt of fig6 is shown in fig7 where it will be seen that each rpt signal has a period equal to one electrical cycle of the machine typically the vane and the sensors are aligned with respect to the stator such that the transitions in a phase signal correspond to the positions of minimum and maximum inductance in that phase it is then possible at low speeds to base the commutation of the machine directly on these transitions e g the phase can be energized when the rpt output is 1 and de energized when it is 0 giving the a ab b bc excitation pattern described earlier for a 3 phase machine this pattern is described variously in the art as 50 conduction and 1 u00bd phase conduction this excitation pattern produces the maximum torque for a given phase current since it excites the phase over the half cycle in which it produces torque of the desired polarity in doing so however it energizes the phase at the parts of its torque curve where the developed torque is small so while it produces the maximum possible torque the.