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I/O Protection
Each DIO and PFI signal has limited protection against overvoltage, undervoltage, and
overcurrent conditions as well as ESD events. Avoid these fault conditions by following these
guidelines:
•
If you configure a PFI or DIO line as an output, do not connect it to any external signal
source, ground, or power supply.
•
If you configure a PFI or DIO line as an output, understand the current requirements of the
load connected to these signals. Do not exceed the specified current output limits of the
DAQ device. NI has several signal conditioning solutions for digital applications requiring
high current drive.
•
If you configure a PFI or DIO line as an input, do not drive the line with voltages outside
of its normal operating range.
•
Treat the DAQ device as you would treat any static sensitive device. Always properly
ground yourself and the equipment when handling the DAQ device or connecting to it.
Signal Integrity Considerations
Signal integrity can be optimized by maintaining a common and matched impedance across your
entire system. The NI 6612 output impedance is 75 Ω. The SH68-68-D1 cable is also
approximately 75 Ω. When connecting signals to the NI 6612, this impedance needs to be
matched as closely as possible. When driving signals into the NI 6612, use a driver with 75 Ω
output impedance as shown in Figure 4-4.
When connecting signals to an accessory with screw terminals, use twisted-pair wires to connect
external signals to the device to improve impedance matching and signal integrity. When using
twisted-pair wires, connect your signal to one of the wires, and your ground to the other wire as
shown in Figure 4-5.
Figure 4-4. Parallel and Series Termination
6612 Driving Signal
Transmission
Line
75 Ω
75 Ω
6612 Receiving Signal
Transmission
Line
75 Ω
Receiving
SH68-68-D1
Cable
75 Ω
Driving Signal
SH68-68-D1
Cable
75 Ω
R
s
75 Ω
NI 6612 User Manual
Signal
Other
Device
Other
Device
© National Instruments | 4-5
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