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Avoid Aliasing When Using a 12-Bit or 16-Bit DAQ Board with SCXI-1141/1142/1143

Hardware: SCXI>>Modules>>SCXI-1141, SCXI>>Modules>>SCXI-1142, SCXI>>Modules>>SCXI-1143

Problem:
What sample rate should I choose if I am using a 12-Bit or 16-bit DAQ board with a SCXI-1141, 1142, or 1143 to avoid aliasing?

Solution:
In order to prevent aliasing on DAQ systems with 12 bits of precision or less, the high-frequency signal components must be attenuated by 80 dB or more. On systems with more than 12 bits of precision or systems with extremely high amounts of out-of-passband noise, higher sampling rates or lower cutoff frequencies are necessary to prevent aliasing.

In order to prevent aliasing on DAQ systems with 16 bits of precision, the high-frequency signal components must be attenuated by 96 dB or more. Below is a table with the -96dB cutoff points for the three SCXI modules. In order to prevent aliasing, you need to sample at twice this rate.

SCXI Module	-80 dB Cutoff	Minimum Sampling Frequency	-96 dB Cutoff	Minimum Sampling Frequency
SCXI-1141	1.5 * Fc	3 * Fc	9.55 * Fc	19.1 * Fc
SCXI-1142	6 * Fc	12 * Fc	7.78 * Fc	15.56 * Fc
SCXI-1143	3.2 * Fc	6.4 * Fc	4.02 * Fc	8.04 * Fc

For more information on using the SCXI-1141/1142/1143 module as an antialiasing filter, please see the User Manual linked below.
For more information on how dB measurements are calculated, please see the Measurement Encyclopedia entry on dB linked below.


Related Links:
Product Manuals: SCXI-1141/1142/1143 User Manual and Specifications
Developer Zone Tutorial: decibel (dB)

Attachments:





Report Date: 10/07/2005
Last Updated: 09/06/2007
Document ID: 3Q6E7S0K

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