You are here: NI Home > Support > Product Reference > Manuals > Sound and Vibration Measurement Suite 6.0 Help

This topic presents examples of and discussion about time-domain integration.

Single-Shot Acquisition and Integration

The following block diagram shows how you can use integration to convert acceleration data to displacement data in a single-shot acquisition and integration.

In the previous block diagram, the acquired waveform is sampled at 51.2 kHz and is double integrated.

Because the integration is implemented with filters, there is a transient response associated with integration while the filters settle. You must avoid the transient region when making further measurements. The following front panel shows the results of a single-shot acquisition and integration of a 38 Hz sine wave.

You can see the transient response in the first 200 ms of the integrated signal.

Continuous Acquisition and Integration

The more common case for time-domain integration occurs with continuous acquisition. The following block diagram shows a VI designed for continuous acquisition and integration.

In the previous block diagram, the highpass cut-off frequency used for the integration is 10 Hz. Additionally, the integration is explicitly reset in the first iteration of the VI and performed continuously thereafter. In this example, this additional wiring is optional because the SVL Integration VI automatically resets the first time it is called and runs continuously thereafter.

If you use the previous block diagram in a larger application that requires starting and stopping the data acquisition process more than once, National Instruments recommends that you set the reset filter control to TRUE for the first iteration of the While Loop. Setting the reset filter control to TRUE causes the filter to reset every time the data acquisition process starts. Set the reset filter control to FALSE for subsequent iterations of the While Loop.

The following front panel shows the results of the continuous acquisition and integration of the same 38 Hz sinusoid used in the single-shot acquisition and integration example.

As in single-shot acquisition and integration, continuous acquisition and integration has an initial transient response. Do not make additional measurements until the response of the filters settles. Once the filters settle, you can use the integrated signals for additional analysis.

The following front panel shows the frequency response for time-domain single integration.

You can see the characteristic 20 dB per decade roll-off of the magnitude response of the single integration.

The following front panel shows the frequency response for time-domain double integration.

You can see the characteristic 40 dB per decade roll-off of the magnitude response of the double integration.

Upper and lower frequency limits exist for which you can obtain a specified degree of accuracy in the magnitude response. For example, sampling at a rate of 51.2 kHz, the magnitude response of the integrator is accurate to within 1 dB from 1.17 Hz to 9.2 kHz for single integration and from 1.14 Hz to?.6 kHz for double integration. The accuracy ranges change with the sampling frequency and the highpass cut-off frequency. The attenuation of the single integration filter at 9.2 kHz is –95 dB. The attenuation of the double integration filter at 6.6 kHz is –185 dB. Accuracy at high frequencies usually is not an issue.