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Appendix B
B 4
The second waveform represents the new position throughput time of the
module. The third waveform represents an output programmed to turn on
an actuator device (waveform high) when the encoder position is 000 and
to turn it off (waveform low) when the encoder position is 001.
The new position throughput time of the module is based on the following
sequence of events:
a.
The encoder shaft increases one position.
b.
All 16 presets are compared to the encoder position.
c.
The module updates the outputs.
d.
The outputs are in the correct state for the given position, and
the scan period is complete.
e.
The module scan begins with the next increase in the encoder
shaft position and the process then repeats.
Let's look at the first example, where the encoder is operating near
maximum speed and control is maintained over a one-count resolution.
Comparing the input and output waveforms, the output bit comes on when
the encoder position is almost 001 and turns off when the position is
almost 002. This is due to the time needed for the software comparison.
The second example shows waveforms for a speed of one revolution per
second. Control is easily maintained over a one-count resolution, and the
output appears to follow the input more closely.
In both examples, the module throughput time is the same, depending
only on the number of outputs to be controlled (see table below). But
with increasingly lower input frequencies (slower shaft speed), the delay
from change in input to output control is smaller compared to the input
period of an encoder increment.
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