Data Acquisition (DAQ) and Control from Microstar Laboratories

Knowledge Base: Hardware

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Q10073 What is signal conditioning?

Tags: Help, Sampling, signal quality, measurement, conditioning, DAP, filtering, isolation

Applies to: All input sampling, but analog signals in particular

When discussing input signals and measurements, the term signal conditioning often appears. What does this mean?

The term signal conditioning describes the processes intentionally provided in a signal's path between its source and destination, typically within a measurement system. It is a very broad term... [1]

The twin purposes of signal conditioning are to preserve the information you desire from a signal, while excluding physical effects that can interfere with the capture of that information.

  • For a perfect sensor, the role of the signal conditioning is to represent the signal from that sensor in a form that best preserves accuracy during the measurement capture.
  • For a signal that is low level, or driven through a weak transmission path, hence vulnerable to interference, signal conditioning will provide amplifiers to boost the signal level, provide transfer power, and present a low impedance drive to measurement circuits.
  • For a signal that is too high level, signal conditioning will provide attenuation.
  • A signal can be converted to a form more conducive to measurement; for example, from a 4-20 mA current level to a voltage.
  • For a signal source that cannot be referred to a quiet and reliable reference ground voltage, signal conditioning can provide ground isolation.
  • For a lower-level signal that "floats" or is otherwise dominated by large voltage shifts, the signal conditioning can provide signal isolation.
  • For signals that provide only "AC" information with no "DC" component, the stray constant offsets can be suppressed by highpass filtering or capacitive coupling.
  • For signals vulnerable to high frequency noise interference and related aliasing problems, high frequencies can be removed from the signal by lowpass filtering.
  • For signal paths that tend to "ring and rattle" in response to transient and switching events, termination networks provide a bypass path where transient energy can discharge to ground.
  • For devices that exhibit a somewhat nonlinear electrical response to a physical process, for example a thermocouple, signal conditioning can "invert" the nonlinear effects, "linearizing" the signal to yield a modified signal more proportional to the original physical process.

The parts of signal conditioning that are vital to obtaining an accurately sampled signal must be done using hardware devices. Some other signal conditioning adjustments, such as removal of DC offsets, lowpass filtering, and signal linearization, can be done equivalently by pre-processing of the sampled data.


[1] Every DAQ System Deserves Well-Conditioned Signals, Tom Lecklider, Senior Technical Editor, Evaluation Engineering, July 2010, pp. 34-38.