Transmission Line Effects - National Instruments NI Vision CVS-1454 User Manual

Transmission Line Effects

© National Instruments Corporation
Transmission line effects can degrade the signals on the I/O cables and
cause instability. To minimize transmission line effects, use twisted-pair
wires with a characteristic impedance of 118 Ω to connect external signals
to the 44-pin I/O DSUB connector. Use a 75 Ω coaxial cable, such as
RG-179, to connect to the SMB connectors.
Figure 3-8 shows connections to the 44-pin DSUB connector and the
TRIG 0 SMB connector that minimize transmission line effects.
TRIG 0
TTL OUT(0)
TTL IN(0)
NI CVS-1450 device
When connecting to TTL inputs on the NI CVS-1450 device, match the
output impedance of the transmitting device to the characteristic impedance
of the cable. For example, if the cable characteristic impedance is 118 Ω,
make R equal to 118 Ω, as shown in Figure 3-8.
s
TRIG 0
SMB
75 Ω
44-Pin
DSUB
118 Ω
3
2
+5 V
62 kΩ
16
17
Figure 3-8. Example Connections
3-15
Chapter 3 Digital I/O Functionality
RG-179
Coaxial Cable
Receiving
Equipment
Receiving
Equipment
R
S
Transmitting
Equipment
NI CVS-1450 Series User Manual