Shaker Controllers

Shaker controllers are units designed to control shaker tables. The simplest types of shaker controllers are controlled manually and depend on the operator to read and evaluate the feedback signal and adjust the amplifier signal input voltage accordingly. This type of system can be as simple as a sine wave signal generator and an accelerometer monitored by a voltmeter. It is left to the operator to manually make the necessary gain compensation for changes in frequency or desired level specifications.

Since most modern accelerometers require a constant current source/buffer amplifier and most voltmeters read in either average or RMS voltage for AC signals, it can be difficult to read and adjust for peak acceleration with this setup. If the accelerometer has a sensitivity that is not convenient for conversion to voltage, mistakes are easy to make. Random acceleration can be monitored in this fashion more directly because of the RMS nature of most random acceleration specifications. However, the RMS calibrated meter will inject another error when monitoring Gaussian signals. If the vibration specification involves displacement, it becomes virtually impossible to use this method.

Shaker controllers vary in sophistication, but usually provide feedback calibrated in acceleration and displacement units useful to vibration testing. Simple manual units are available and provide for frequency and gain adjustment while providing a calibrated acceleration signal in peak G’s. More complex units will feature automatic servo controlled levels with programming and frequency sweep capabilities. Top end controllers utilizing computer technology are available and can control to almost any specification with multiple accelerometers, etc.

The most critical specifications for shaker controllers are number of inputs and outputs, output dynamic range and frequency range, and what types of testing the user needs performed. The types of tests include simple outputs such as a random Gaussian output signal, classical shock and arbitrary transients. More complex signals are available as well.  Sine on random is a test signal in which narrowband sine waves are combined with broadband random waves for a complex vibration signal. Random on random produces a test signal that has narrowband random waves combined with broadband random waves. A shock response system calculates the responses of a large number of theoretical, single-degree-of-freedom spring-mass systems to a given shock pulse.

• Control Dynamic Range
  A critical performance attribute for a digital vibration control system is its control dynamic range. Unless the controller has a wide dynamic range, the dynamics of shaker and test article cannot be...
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