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Measurement Computing CIO-DI48 User Manual

Page 22

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interference associated with line voltage (60 Hz) would be filtered out but a signal of
25 Hz would be allowed to pass.

In digital input circuits, low-pass filters are sometimes used to “de-bounce” inputs
from relay or switch contacts.

A simple low-pass filter may be constructed from one resistor (R) and one capacitor
(C). The cut-off frequency is determined by the formula:

Fc = 1
2 *

π

* R * C

R = 1
2*

π

* C * Fc

Where

π

= 3.14...

Fc = frequency in cycles per second
R = resistance in Ohms
C = capacitance in Farads

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