Adding Power Filters - National Instruments SCB-68 User Manual

Chapter 4 Adding Components for Special Functions

Adding Power Filters

Caution NI is not liable for any device damage resulting from improper use of the SCB-68
and the DAQ device.
XF1 (Clip)
800 mA
5x20 mm
+5 V
(I/O Pin 8)
D GND
(I/O Pin 7)
AI GND
(I/O Pin 56)
SCB-68 User Manual for Advanced Functions
Refer to the SCB-68 User Guide for information about the +5 V power lines
and SCB-68 fuse replacement.
A 470 Ω series resistor (R21) is part of the power filter for the +5 V power
on the SCB-68. Due to the nature of the filter design, as the filtered +5 V is
loaded, the voltage supplied to the SCB-68 circuitry and screw terminal 8
decreases. Pad R20, shown in Figure 3-1,
Diagram, is in parallel with R21. You can install a resistor, if needed, to
decrease the overall resistance used in the filter and reduce the loading
effect. However, completely shorting R20 bypasses the filter while
capacitively coupling D GND to AI GND and AO GND and is not
recommended.
Figure 4-44 shows the power supply circuitry on the SCB-68.
+5 V Screw Terminal
ACC Not Powered
S1
ACC Powered
D GND
Non-MIO
Screw Terminal
(NC)
S2
MIO
AI GND
Non-MIO
Screw Terminal
(NC)
S3
MIO
(Optional)
(NC)
C2 C1
(10 μF) (0.1 μF)
AI
Figure 4-44. +5 V Power Supply
4-38
SCB-68 Printed Circuit Board
R20
R21
C6
(10 μF) (0.1 μF)
AI AI
+5 V
C4
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