The Importance of Dynamic Range in Vibration Control

Discussions about dynamic range are most often concerning dynamic signal analyzers.  However, a large dynamic range is perhaps even more beneficial for closed loop vibration control.

In vibration control applications, the most obvious benefit of dynamic range is the same benefit achieved by dynamic signal analyzer applications:  it allows for high accuracy of measurement and therefore high accuracy of control. As SignalStar vibration controllers evolved from one generation to another the benefit of high dynamic range manifested itself as accurate control of larger dynamic conditions, meaning control across high Q resonances with deep anti-resonances. The first generation DP540 vibration controllers offered 70 dB control range for random vibration while the current generation SignalStar Vector offers over 100 dB control range.

Unlike dynamic signal analyzers, vibration controllers always employ the use of an output channel to close the loop of vibration control. It is critically important to have a digital to analog converter (DAC) that is as accurate as the ADC.  The importance of a high dynamic range on both the ADC and DAC can be seen most clearly when looking at resonance situations. For example, a resonance dwell test might require only the smallest amount of voltage to excite a resonance without exceeding the test tolerances.

Consider a case of a random test that contains a sharp, high Q factor, resonance with sharp anti-resonances. At the frequencies where there are anti-resonances, the drive signal has to be extremely high while it needs to drop to the lowest possible values at the resonances. The ADC’s ability to measure this large dynamic range and the DAC’s ability to generate this large dynamic range will determine control quality of the instrument.

The example below illustrates a simple random test with an extremely sharp resonance just below 200 Hz. The bottom graph shows this drive signal, which is dropping to very low values at the resonance frequencies, and very high values at the anti-resonance frequencies.  Roughly 100 dB of range in the output (drive) signal can be seen in this particular plot.

The Importance of Dynamic Range in Vibration Control - Data Physics Corporation
A simple random test with an extremely sharp resonance just below 200 Hz

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