4
Denitions
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 (ΔQ): The normalized angular dierence be-
tween the actual shaft position and the position indicated
by the encoder cycle count
Cycle Error (ΔC): An indication of cycle uniformity. The dif-
ference between an observed shaft angle which gives rise
to one electrical cycle, and the nominal angular increment
of l/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 between
a transition in the output of channel A and the neighbor-
ing transition in the output of channel B. There are 4 states
per cycle, each nominally 90°e.
Output Waveforms
Figure 4.
P
C
CH. A
CH. B
ROTATION *
* SPIN DIRECTION FOLLOWS ARROW MARKING ON ENCODER
AMPLITUDE
φ
S1
S2
S4
CH. I
P
0
t
1
t
2
3
2
4
1
5
S3
State Width Error (ΔS): The deviation, in electrical degrees,
of each state width from its ideal value of 90°e.
Phase (φ): 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
direction of the arrow on top of the module, channel A will
lead channel B. If the codewheel rotates in the opposite
direction, channel B will lead channel A.
Optical Radius (R
OP
): The distance from the codewheel’s
center of rotation to the optical center (O.C.) of the en-
coder module.
Index Pulse Width (P
o
): 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.
