Chapter 4
Signal Connections
©
National Instruments Corporation
4-13
Refer to Table 4-2 for the R
EXT
resistance values for the most common
voltages.
Wiring Concerns
Caution
The encoder input circuit is designed to tolerate 5 V signals. For voltages higher
than 5 V, you
must
connect an external resistor to avoid damage to the encoder.
The encoder inputs are connected to quadrature decoder/counter circuits.
It is very important to minimize noise at this interface. Excessive noise on
the 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.
Trigger (Position Capture) Inputs
The PCI-7390 offers additional high-performance encoder features. The
encoder channels have position capture trigger inputs. These signals are
useful for high-speed synchronization of motion with actuators, sensors,
and other parts of the complete motion system:
•
Axis <1..4> Trigger Input
—When enabled, an active high-speed
position capture input causes instantaneous position capture (<250 ns
latency) of the corresponding encoder count value. You can use this
high-speed position capture functionality for applications ranging
from simple position tagging of sensor data to complex camming
systems with advance/retard positioning and registration. An available
PCI-7390 position mode is to move an axis relative to a captured
position.
Table 4-2.
Resistance Values for Encoder Connections
Voltage
(V)
Typical
Resistance (k
Ω
)
Minimum
Resistance (k
Ω
)
Maximum
Resistance (k
Ω
)
+5
0
—
—
+24
2
1.5
2.5
+12
0.72
0.65
1.2
