Chapter 3
Signal Connections
NI 951x User Manual
3-12
ni.com
Encoder Phase A/Phase B
Encoder input channel converts pulses on Phase A and Phase B into 32-bit
up/down counter values. Pulses are generated by optical, magnetic, laser,
or electronic devices that provide two signals, Phase A and Phase B, that
are 90 degrees out of phase. The leading phase, A or B, determines the
direction of motion. The four transition states of the relative signal phases
provide distinct pulse edges that are used to determine position.
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
Phase A
Phase B
Index