Measurement-computing CIO-CTRxxHD Bedienungsanleitung PDF herunterladen (Seite 16)

The cut-off frequency is that frequency above which no variation of voltage with

respect to time may enter the circuit. For example, if a low-pass filter had a cut-off

frequency of 30 Hz, interference associated with line voltage (60 Hz) would be mostly

filtered out but a signal of 25 Hz would pass with less attenuation.

Also, in a digital circuit, a low-pass filter is often used to remove contact bounce noise

signals from a switch or a relay contacts. Also, in a digital circuit, a low pass filter

might be used to “de-bounce” (filter) an input from a switch or external relay. (Unless

switch/relay contacts are mercury-whetted, they tend to bounce briefly on closure,

generating a pulsating noise signal. This can easily lead to erroneous counts unless

filtered out.)

A simple low-pass filter can be constructed from one resistor (R) and one capacitor

(C). The cut-off frequency is determined according to the formula:

Fc =

1 Where π= 3.14...

2 π R C R = ohms

C = farads

Fc = cut-off frequency in cycles/second

R = 1

. 2π C Fc

1 2 ... 11 12 13 14 15 16 17 18 19 20

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Measurement-computing CIO-CTRxxHD Bedienungsanleitung Seite 16