For attenuation greater than 5:1, no resistor should be less than 1K.
The CIO-TERMINAL has the circuitry on board to create custom voltage dividers. The CIO-TERMINAL is a 16" by 4" screw
terminal board with two 37 pin D type connectors and 56 screw terminals (12 - 22 AWG). Designed for table top, wall or rack
mounting, the board provides prototype, divider circuit, filter circuit and pull-up resistor positions which you may complete with the
proper value components for your application.
8.2
LOW-PASS FILTERS
A low-pass filter is placed on the signal wires between a signal and an
A/D board. It attenuates frequencies greater than the cut-off frequency,
preventing them from entering the A/D board's analog or digital inputs.
The key term in a low-pass filter circuit is cut-off frequency. The cut-off
frequency is that frequency above which no variation of voltage with
respect to time can enter the board’s input circuit. For example, if a
low-pass filter had a cut off frequency of 30 Hz, the kind of interference
associated with line voltage (60 Hz) would be filtered out but a signal of
25 Hz would pass.
In a digital circuit, a low-pass filter can be used to filter an input from
pushing a momentary contact switch.
A 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 * p * R * C
R = _____1_____
2* p * C * Fc
Where: p = 3.14...
R is Ohms
C is Farads
Fc is Hz (cycles per second)
-21-
SIGNAL HIGH
SIGNAL LOW
A/D BOARD
HIGH INPUT
A/D BOARD
LOW INPUT
SIGNAL
VOLTS
LOW PASS FILTER
R
C
F
C
=
2 *P i*R *C
1
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