Chapter 4
Accessory and Cable Connections
©
National Instruments Corporation
4-9
NI 951x User Manual
•
Cables with twisted pairs and an overall shield are recommended for
optimized noise immunity. Figure 4-7 shows twisted pairs in a
shielded cable. Unshielded cables can cause noise to corrupt the
encoder signals, resulting in lost or additional counts and reduced
motion system accuracy.
Figure 4-7.
Shielded Twisted Pairs
•
Tie the encoder cable shield to COM at the encoder side only.
Connecting Optional Signals
This section contains information about wiring optional NI 951x signals.
Connecting a Brake Signal
The NI 951x digital outputs do not provide enough current to drive typical
motor brakes. For this reason, the NI 951x digital outputs must
not
be used
to directly control motor brakes. However, you can use the NI 951x digital
outputs to control external circuitry that does meet the higher current
requirements of motor brakes. Refer to the specifications for the motor
brake to determine the maximum current requirements. Use the following
recommendations when using an NI 951x digital output to control external
circuitry driving the motor brake:
•
Do not exceed the maximum current specifications of the NI 951x
digital outputs.
•
If the same power supply is used for the NI 951x module and the brake
circuit, ensure that the power supply meets the maximum requirements
of both the NI 951x and the brake circuit.
Encoder A+
Encoder A–
Encoder B+
Encoder B–
Encoder Index+
Encoder Index–
+5 V OUT
COM
Shield
Drain