Transmission Line Effects - National Instruments NI 6602 User Manual

Chapter 3 Signal Connections

Transmission Line Effects

Before using a voltage follower or series termination, use digital filtering to
Note
eliminate measurement errors.
NI 660x User Manual
Table 3-9. Signals and D GND Pin Number on 68-Pin Connector Block (Continued)
PFI Number
PFI 36
PFI 37
PFI 38
PFI 39
Transmission line effects can degrade the signal and cause measurement
errors. Use twisted-pair wires to connect external signals to the device to
improve impedance matching and signal integrity. The NI 660x provide
onboard series termination to reduce signal reflections when it drives an
output.
For reflection problems that occur when the device drives the signal,
use parallel AC termination at the destination. When using a National
Instruments SH68-68-D1 cable, the recommended values for R
68 Ω and 150 pF, respectively.
For reflection problems that occur when the NI 660x receives the signal, use
series termination at the device driving the signal. The sum of R
output impedance of the source is approximately 80 Ω. Typically, this
condition results in a value of approximately 50 Ω for R
termination when the source impedance is larger than 80 Ω, use a voltage
follower with low output impedance, and connect R
voltage follower.
Pin Number for D GND
3-22
39
41
36
36
and C are
P P
and the
S
. To use serial
S
at the output of the
S
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