Chapter 3
Signal Connections
NI 951x User Manual
3-14
ni.com
Position Capture Input and Position Compare Output
The NI 951x drive interface modules have a high-speed Position Capture
input and Position Compare output. These signals are useful for high-speed
synchronization of motion with actuators, sensors, vision and data
acquisition devices, and other components in the complete motion system.
Tip
Refer to the
Signal Connection Recommendations
section of Chapter 4,
Accessory
and Cable Connections
, for wiring and cabling recommendations.
•
Position Capture
—When enabled, an active transition on a
high-speed Position Capture input causes instantaneous position
capture of the corresponding encoder count value. You can use this
high-speed position capture functionality for applications ranging
from simple logging of feedback sensor data to complex camming
systems with advance/retard positioning and registration.
Caution
If you use an open collector driver for the Position Capture input, provide the
voltage equivalent of a logical high during the off state of the open collector driver. A
common method to achieve this is by adding a pull-up resistor to the output. Refer to the
Motion I/O
section of Appendix A,
Specifications
, for information about the Position
Capture input voltage levels.
The active edge on the Position Capture input can be set to rising edge
or falling edge. In addition, the Position Capture input signal is
digitally filtered. Refer to the
NI SoftMotion Module
book of the
LabVIEW Help
for more information about Position Capture input
configuration options.
•
Position Compare
—You can program a Position Compare output to
transition when the associated encoder value equals the position
compare position. You can use a Position Compare output to directly
control actuators or as a trigger to synchronize data acquisition or other
functions in the motion control system.
You can program the Position Compare output for a
single
or for
periodic
positions. The active state of the Position Compare output is
configurable in software to high or low, and the action taken at the
compare position can be set in software to
pulse
,
set
, or
toggle
. Refer
to the
NI SoftMotion Module
book of the
LabVIEW Help
for more
information about Position Compare output functionality and
configuration.