Chapter 5 Signal Connections
© National Instruments Corporation 5-9 NI 7350 User Manual
measure—inch, centimeter, millimeter, and so on. For example, a 500 line encoder has
2,000 quadrature counts per revolution.
Axis <1..8> Encoder IndexThe Index input is primarily used to establish a reference position. This
function uses the number of counts per revolution or the linear distance to
initiate a search move that locates the index position. When a valid index
signal transition occurs during a find reference routine, the position of the
index signal is captured accurately. Use this captured position to establish
a reference zero position for absolute position control or any other motion
system position reference required.
The default MAX settings guarantee that the find index routine completes
successfully if the encoder generates a high index pulse when phasesA
and B are low and the encoder is connected through an NI UMI or drive
accessory. Figure5-3 shows the default encoder phasing diagram at the
inputs to an NI UMI or drive accessory.
Figure 5-3. Quadrature Encoder Phasing Diagram
You can set the index reference criteria in MAX to change the pattern of
phases A and B for the index search. You also can set the encoder polarity
for phases A, B, and I in MAX.
Wiring Concerns
The encoder inputs are connected to quadrature decoder/counter circuits.
Itis very important to minimize noise at this interface. Excessive noise on
these encoder input signals may result in loss of counts or extra counts and
erroneous closed-loop motion operation. Verify the encoder connections
before powering up the system.
Phase A
Phase B
Index