Implementing Integration

If you need to perform measurements on velocity or displacement data when you have only acquired acceleration or velocity data, respectively, integrate the measured signal to yield the desired data.

You can perform integration either in the time domain as a form of signal conditioning or in the frequency domain as a stage of analysis. When performed in the frequency domain, integration is one of the extended measurements for frequency analysis.

Converting acceleration data to velocity or displacement data presents a pair of unique challenges. Measured signals typically contain some unwanted DC components. The second challenge is the fact that many transducers, especially vibration transducers, have lower-frequency limits. A transducer cannot accurately measure frequency components below the lower-frequency limit of the transducer.

  • DC Component—Even though a DC component in the measured signal might be valid, the presence of a DC component indicates that the device under test (DUT) has a net acceleration along the axis of the transducer. For a typical vibration measurement, the DUT is mounted or suspended in the test setup. The net acceleration of the DUT is zero. Therefore, any DC component in the measured acceleration is an artifact and must be ignored.
  • Transducers—Most acceleration and velocity transducers are not designed to accurately measure frequency components close to DC. Closeness to DC is relative and depends on the specific transducer. A typical accelerometer can accurately measure components down to about 10 Hz. A typical velocity probe can accurately measure components down to 2–3 Hz. Inaccurately measured low-frequency vibrations can dominate the response when the signal is integrated because integration attenuates low-frequency components less than high-frequency components.