Справочник Пользователя для National Instruments NI 1450 Series

© National Instruments Corporation

When an inductive load, such as a relay or solenoid, is connected to an 
output, a large counter-electromotive force may occur at switching time 
due to energy stored in the inductive load. This flyback voltage can damage 
the outputs and the power supply.

To limit flyback voltages at the inductive load, install a flyback diode across 
the load. Mount the flyback diode as close to the load as possible. Use this 
protection method if you connect any of the isolated outputs on the NI 1450 
to an inductive load.

Figure 4-7 shows an example of using an external flyback diode to protect 
inductive loads.

Figure 4-7.  Example of Using an External Flyback Diode for Inductive Loads

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 4-8 shows connections to the 44-pin DSUB connector and the 
TRIG 0 SMB connector that minimize transmission line effects.

Digital

Output

Viso

Ciso

Vcc

NI 1450

External
Flyback 

Diode for 

Inductive Loads

Load