Chapter5 SignalConnections
7344/7334Hardware User Manual 5-8 ni.com
Encoder <1..4> Index
The Index input is primarily used with the Find Index function. This
function uses the number of counts per revolution (or linear distance) to
initiatea search move thatlocates the index position. When a valid Index
signal transition occurs during a Find Index sequence, the position of the
Index signal is captured very accurately. You then uset his captured
positionto est ablish a reference zero position for absolute position control
oran yo ther motion system position reference required. Figure 5-3 shows
the quadrature encoder phasing diagram.
Figure5-3. Quadrature Encoder Phasing Diagram
Wiring Concerns
The encoder inputs are connected to quadrature decoder/counter circuits.
Itis veryimportant to minimize noise at this interface. Excessive noise on
theseencoder input signals may re sult in loss of counts or extra counts and
erroneous closed-loop motion operation. Verify the encoder connections
before powering up the system.
Caution Wireencoder signals and their ground connections separately from all other
connections.Wiring these signals near the motor drive/amplifier or other signals can cause
positioning errors and faultyop eration.
Encodersw ith differentialline driveroutputs are strongly recommended
forall applications and must beu sedi f the encoder cable length is longer
than10 ft (3.05 m). Shielded, 24AWG wire is the minimum recommended
size for the encoder cable. Cables with twisted pairs and an overall shield
are recommended for optimized noise immunity.
AllN ational Instrumentspower drives andUMI accessoriesprovide
built-in circuitry that converts differential encoder signals to single-ended
encodersignals.
PhaseA
PhaseB
Index