Science of Test Measurement Accuracy - Data Sampling and Filter Selection during Data Acquisition
AIR FORCE TEST CENTER EDWARDS AFB CA
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Know how to specify our instrumentation requirements, especially the sample rates We all know about the Nyquist frequency and choosing sample rates that are at least twice the Nyquist to prevent aliasing. But did you know that your data may contain high frequency content that can alias down and muddle the frequencies you care about Once the aliased signal is digitized it can never be recovered. Your data might be ruined Your instrumentation engineers know about this, and that is why they added anti-aliasing filters to your data acquisition system. What is an anti-alias filter I don t know, but Im sure my instrumentation engineer knows exactly what I need Wrong. Your instrumentation engineer DOESNT know what you need and probably chose a 6-pole butterworth filter with a specific cutoff because thats what they used last time. To achieve quality measurements with accurate magnitude and frequency content, the test must start by using comprehensive signal processing principles during initial data acquisition e.g., correct data sample rates and anti-alias filter selection. To achieve quality measurements, the disciplined engineer must verify proper data sampling and filtering principles have been applied during the data acquisition process. Example of how to determine sample rate and filter selection during data acquisition are provided.
- Test Facilities, Equipment and Methods