Transmission Line Effects - National Instruments NI Vision CVS-1456 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,
equal to 118 Ω, as shown in Figure 3-8.
make R
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