Data Acquisition and Related Terms
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See also: Glossary
data acquisition - basics
Data acquisition refers to the process of digitizing an analog signal: converting a continuous waveform into a time series of digital values. Each value represents the signal voltage at that instant.
data acquisition - Nyquist frequency
To map the original analog signal at all well requires a data acquisition sampling rate high enough to provide several values for each cycle. Once the sampling rate falls below two samples per cycle, data acquisition breaks down: the time series of digital values provides no useful information about the analog signal. Signals with frequencies above the Nyquist frequency (half the sampling rate), when digitized, appear identical to lower frequency aliases.
data acquisition - filtering
If a signal contains frequencies above Nyquist, these frequencies will corrupt the acquired data. Digital filters work very well in data acquisition systems, but naturally they require valid data in the first place. Only analog filters can remove frequencies above Nyquist.
data acquisition - hardware triggers
Data acquisition on one or more channels can start or stop on an external hardware trigger event on a dedicated hardware triggering line. Also, an external hardware trigger event connected to one of the normal signal inputs can act as a software trigger - and return the block of data surrounding a trigger event. See below.
data acquisition - software triggers
Data acquisition on one or more channels can start or stop on a software trigger event on any channel. Trigger events include a specified level, slope, maximum or minimum, range, etc. By sampling all the time - and writing values into a circular buffer - a system can report pre-trigger as well as post-trigger values.