© National Instruments
|
3-11
A typical encoder with a specification of
N
(
N
= number) lines per unit of measure in revolutions
or linear distance, produces 4
×
N
counts per unit of measure.
The count is the basic increment
of position in closed-loop motion systems.
Note
To determine your encoder counts per revolution, multiply the specified
encoder counts per revolution by four. For example, a 500 line encoder has
2,000 counts per revolution.
If an encoder resource is not needed for axis control, it is available for other functions including
position monitoring, as a digital potentiometer encoder input, or as a master encoder input for
electronic gearing or electronic camming applications.
Encoder Index
The Index input is primarily used to establish a reference position. The Index signal produces a
single pulse per revolution. You can use software to capture the Index pulse position and
establish a reference zero position for absolute position control. Figure 3-10 shows the
single-ended representation of the encoder pulses.
Figure 3-10.
Incremental Encoder Phasing Diagram
You can set the index reference criteria in software to change the line state of Phase A and Phase
B used in the Index search. Refer to the
NI SoftMotion Module
book of the
LabVIEW Help
for
more information about encoder settings.
Encoder Input Circuit
The NI 951x drive interface modules support RS-422 differential and single-ended inputs for
Phase A, Phase B, and Index signals, and provide a +5 V output for encoder power.
You also can set the encoder active state for Phases A, Phase B, and Index to high or low using
software. Refer to the
NI SoftMotion Module
book of the
LabVIEW Help
for more information.
Tip
Signal Connection Recommendations
section of Chapter 4,
Accessory and Cable Connections
, for additional wiring and cabling
recommendations.
Ph
as
e A
Ph
as
e B
Index
