National Instruments Corporation SC-207 Series, Руководство пользователя

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SC-2071 Board Chapter 3
SC-207X Series User Manual 3-10 © National Instruments Corporation
+ Channel
To
Input
Multiplexer
+
AIGND AIGND
D
C
1
µ
F
Input Schematic
Channel 1
AIGND
R5
R7
Component Positions
R8 (a 1
µ
F cap)
1
µ
F Capacitor
R6 (39 k
Ω
)
39 k
Ω
Resistor
39 k
Ω
Figure 3-9. Lowpass Filter on Channel 1
Building Highpass Filters
You can easily install simple, RC highpass filters in the SC-2071 board on any input channel.
The filters are useful for accurate high-frequency measurement and low-frequency noise
rejection. By substituting resistance and capacitance values into the following formula, you can
calculate a simple, one-pole RC filter to have a -3 dB point (cutoff frequency):
fc =
1
(2
π
RC)
(Formula 3-2)
The response rolls off at a rate of -20 dB per decade drop in frequency thereafter. A Bode plot of
the amplitude versus normalized frequency is shown in Figure 3-10.