4
Defi nitions
Note: Refer to Figure 2
Count (N): The number of bar and window pairs or counts
per revolution (CPR) of the codewheel.
One Cycle (C): 360 electrical degrees (°e), 1 bar and win-
dow pair.
One Shaft Rotation: 360 mechanical degrees, N cycles.
Position Error (ΔΘ): The normalized angular diff erence
between the actual shaft position and the position indi-
cated by the encoder cycle count.
Cycle Error (ΔC): An indication of cycle uniformity. The
diff erence between an observed shaft angle which gives
rise to one electrical cycle, and the nominal angular incre-
ment of 1/N of a revolution.
Pulse Width (P): The number of electrical degrees that
an output is high during 1 cycle. This value is nominally
180°e or 1/2 cycle.
Pulse Width Error (ΔP): The deviation, in electrical degrees,
of the pulse width from its ideal value of 180°e.
State Width (S): The number of electrical degrees be-
tween a transition in the output of channel A and the
neighboring transition in the output of channel B. There
are 4 states per cycle, each nominally 90°e.
State Width Error (ΔS): The deviation, in electrical degrees,
of each state width from its ideal value of 90°e.
Phase (f): The number of electrical degrees between the
center of the high state of channel A and the center of
the high state of channel B.
This value is nominally 90°e for quadrature output.
Phase Error (Δφ): The deviation of the phase from its ideal
value of 90°e.
Direction of Rotation: When the codewheel rotates in
the clockwise direction viewing from top of the module
(direction from V to G), channel A will lead channel B. If
the codewheel rotates in the opposite direction, channel
B will lead channel A.
Optical Radius (Rop): The distance from the codewheel’s
center of rotation to the optical center (O.C) of the en-
coder module.
Index Pulse Width (Po): The number of electrical degrees
that an index is high during one full shaft rotation. This
value is nominally 90°e or 1/4 cycle.
