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Chapter 2 Function Reference — SCXI_Configure_Filter
NI-DAQ FRM for PC Compatibles 2-334
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National Instruments Corporation
2: Configure the filter to use an external signal. The module divides the external
signal by cutoffDivDown to determine the filter cutoff frequency. The module
also divides the external signal by outClkDivDown and sends it to the module
front connector OUTCLK pin. You can use this filter mode to configure a
tracking filter. You can use this mode only with the SCXI-1141.
3: Enable the filter (the reverse of filterMode 0).
freq is the cutoff frequency you want to select from the frequencies available on the module
if filterMode = 1.
The SCXI-1122 has two possible cutoff frequencies:
4.0: –10 dB at 4 Hz
4,000.0: –3 dB at 4 kHz
The SCXI-1126 has four possible cutoff frequencies (1 Hz, 40 Hz, 320 Hz, and 1 kHz), which
attenuate at –80 dB.
The SCXI-1141 has a range of cutoff frequencies from 10 Hz to 25 kHz.
SCXI_Configure_Filter produces the frequency you want as closely as possible by
dividing an internal 10 MHz signal on the SCXI-1141. The function returns the exact cutoff
frequency produced in the output parameter actualFreq.
If filterMode = 2, set freq to the approximate frequency of the external signal you are using.
Chapter 2 of the SCXI-1141 User Manual explains the impact of different signal frequencies
on the filters.
If filterMode = 0 or 3, NI-DAQ ignores freq.
cutoffDivDown is an integer by which the module divides the external signal to determine
the filter cutoff frequency when filterMode = 2. NI-DAQ ignores this parameter if
filterMode is not 2.
Range: 2 to 65,535
outClkDivDown is an integer by which the module divides either the internal 10 MHz signal
(if filterMode = 1) or the external signal (if filterMode = 2) to send back to the module front
connector OUTCLK pin. This parameter is only used for the SCXI-1141.
Range: 2 to 65,535
actualFreq returns the actual cutoff frequency that the module uses.
Using this Function
The SCXI-1122 has one filter setting applied to all channels on the module; therefore,
you must set channel = –1. The SCXI-1122 only works with filterMode = 1; you cannot
configure the SCXI-1122 to bypass the filter or to use an external signal to set the cutoff
frequency. The default frequency setting for the SCXI-1122 is 4 Hz.