National Instruments NI 9478 - Manual (Page 10)

NI 9478 Operating Instructions and Specifications 10 ni.com
Using Long Cables
The inductance of the cabling that connects the NI 9478, the loads,
and the external supply stores up energy when a channel is on and
passing current through the cables. Each time a channel is turned
off, the energy stored in the cables is released as flyback voltage
and dissipates as heat in the NI 9478. The total power dissipated in
the module increases with higher switching frequencies, higher
currents, and longer cable lengths. The cable length is the total
distance from the digital output pin of the NI 9478 channel,
through the load, through the external power supply, and back
to the COM pin, as shown in Figure 4.
Figure 4. Cable Length of the NI 9478
NI 9478 COM
V
sup
DO
+
–
External
Power
Supply
Cable
Length
Load
Cable
Clamp