©
National Instruments Corporation
31
UMI Accessory User Guide — UMI-Flex4
The UMI-Flex4 accessory allows for differential inputs for Phase A,
Phase B, and Index signals. You can easily accommodate encoders with
phase relationships different from Figure 38 by swapping the signals as
required by the specific application. The Index pulse must occur when both
Phase A and Phase B signals are logic low as shown in Figure 38. Servo and
closed-loop stepper applications require encoder feedback and consistent
directional polarity between the motor and encoder for stable operation.
The UMI-Flex4 uses the following standards for motor direction:
•
Positive = forward = Clockwise (CW) facing motor shaft
•
Negative = reverse = Counter-clockwise (CCW) facing motor shaft
Figure 38.
Encoder Signal Phasing—CW Rotation
The encoder inputs are filtered by both analog and digital noise filters. You
must use cables with twisted pairs and an overall shield for improved noise
immunity. When connecting the encoder to the UMI-Flex4, you should use
at least 24-AWG wire.
Caution
Using an unshielded cable allows noise to corrupt the encoder signals, which
results in lost counts, reduced accuracy, and other erroneous encoder and controller
operations.
Phase A
Phase B
Index
Summary of Contents for UMI-4A
Page 35: ......
