Calculate the percentage of total allowable power each channel
uses then add the percentages for all the channels. For ambient
temperatures from 55 °C to 70 °C, the total power for all
channels must remain under 100%. For temperatures below
55 °C, the total power of all channels can run up to 150%.
Example One
The NI 9478 passes 1.25 A current through 2.0 meters of cable.
The channel cycles on for 40 μs and off for 10 μs for a total
output period of 50 μs. This yields an output frequency of
20 kHz, using 14.8% of the total power budget.
Figure 6.
Example Equation One
4 % 1.25
2
+ 0.12 % 2.0
−
0.2 1.25
2
+ 0.04 % 1.25 + 1 20 = 14.8 %
Example Two
The NI 9478 is on and passing 3 A of current through 2.0 meters
of cable for 0.25 seconds. The channel passes 1.25 A of current at
20 kHz for 1.25 seconds. The channel then drives the load off for
4 seconds.
18
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NI 9478 Getting Started Guide
