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Use the Torsional Vibration Measurement VIs to measure and monitor torsional vibration in a rotating system. You can measure the torsional vibration of the rotating components from the change in angular position, angular velocity, or angular acceleration. The Torsional Vibration Measurement VIs measure torsional vibration from the change in angular velocity, or the rotational speed, of the rotating components. You can use either analog or digital tachometer signals as the input signals. When you use analog tachometer signals as the input signals, set the sampling rate of the analog tachometer higher than the sampling rate calculated in the following equation:

sampling rate_tacho = 10 * samples per revolution * max speed (RPM)/60

The tachometer system you use to obtain tachometer signals might have geometric imperfections. For example, suppose you use an optical transducer to observe pieces of reflective tape attached to a shaft. The intervals between two pieces of reflective tape might vary. The variation of the intervals can affect the accuracy of the rotational speed profile that the tachometer measures. The Torsional Vibration Measurement VIs can compensate for these geometric imperfections.

Note  If you use an encoder that can generate several hundred or more pulses per revolution, you do not need to compensate for geometric imperfections using the Torsional Vibration Measurement VIs. An encoder can generate accurate speed profile results, so you can ignore the geometric imperfections in the tachometer system.

The Torsional Vibration Measurement VIs can return torsional vibration signals as either waveform signals or even-angle signals. Use the Waveform Output instances of these VIs to measure torsional vibration that is at fixed frequencies. Rotating systems like compressors, turbines, and electric motor drives usually generate torsional vibration at fixed frequencies. Use the Even-Angle Signal Output instances of the Torsional Vibration Measurement VIs to measure torsional vibration that changes with rotational speed or torsional vibration at fixed orders. Rotating systems like combustion engines usually generate torsional vibration that changes with rotational speed or generate torsional vibration at fixed orders.

You can use the SVFA Power Spectrum VI to measure the power spectrum of a waveform torsional vibration signal. You can use the OAT Order Power Spectrum VI to measure the order power spectrum of an even-angle torsional vibration signal.

By measuring the torsional vibration of a rotating system, you can monitor the condition of the system to identify faulty components and avoid system failure. You also can perform noise, vibration, and harshness testing on the rotating system to identify unwanted vibrations and improve system performance.

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