Chapter 3
Connecting the UMI-7774/7772 to Drives and Other Devices
©
National Instruments Corporation
3-19
National Instruments UMI-7774/7772 User Manual
Figure 3-14.
Encoder Signal Phasing, CW (Forward) Direction
Closed-loop servo applications require consistent directional polarity
between the motor and encoder for correct operation. The National
Instruments motion control standard directional polarity is as follows:
•
Positive = forward = clockwise (CW) facing motor shaft
•
Negative = reverse = counter-clockwise (CCW) facing motor shaft
Caution
Using an unshielded cable allows noise to corrupt the encoder signals, which
could result in lost counts, reduced accuracy, and other erroneous encoder and controller
operations.
When connecting the encoder wiring to the UMI-7774/7772, use shielded
wire of at least 24 AWG. National Instruments recommends you use cables
with twisted pairs and an overall shield for improved noise immunity and
signal integrity. Figure 3-15 shows twisted pairs in a shielded cable.
Figure 3-15.
Shielded Twisted Pairs
Phase A
Phase B
Index
Encoder A
Encoder A
Encoder B
Encoder B
Encoder Index
Encoder Index
+5 V
Digital Ground
Shield
Drain
