Accelerometers by Brüel & Kjær

How to Maximize the Armature Life of a Shaker

The armature of a shaker is a living component that must be replaced sooner or later due to various influences. Nevertheless, some factors can be considered to maximize the lifetime of an armature.

While HBK LDS shakers are extremely robust, the armature is a living component, whereby the high numbers of stress cycles, high stresses and high temperatures will ultimately lead to failure and the need for replacement. The time taken for an armature to fail depends on:

  • The force level at which it is running
  • The type of test
  • Other factors that will influence its life 

The Force Level
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As a guide, HBK LDS shakers have an expected life of over 10,000 hours when running at 80% force. At force levels below 80% the expected life will be longer; at levels above 80% it will be shorter. This relationship is non-linear, being based on SN curves, which approximate to a straight line only on a log-log scale.


The Type of Test

Armature life is also affected by the type of test being run as shown below (higher values lead to reduced life):

Type of Test         Value        
 Sine Sweep             1
 Random broadband (20 - 2000 Hz)             1 
 Shock            1.5
 Shock response spectrum (SRS)             2
 Sine on Random             2 
 Narrowband random             2            
 Fixed frequency sine             3 


The expected armature life can be calculated by dividing the value of the type of test into the rated life for the force level used. For instance, the expected life of a fixed frequency sine test run at 80% force is approximately 10,000/3 = 3000 hours.


Other Risk Factors

Other risk factors that can lead to a reduction in armature life are as follows: •

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  • High temperature of raw cooling air or water
  • Distortion caused by ‘slapping’ components
  • High ‘g’ levels
  • Humid or dusty environments
  • High frequency > fn
  • Large displacement
  • Horizontal running
  • Running under a chamber
  • Large overturning moments applied
  • High velocity
  • Drive high
  • Lively payload
  • Poor control
  • Not keeping reference plots
  • Poor maintenance
  • Unattended operation
  • Large payloads 

The maximum armature life will be obtained when the above factors are avoided as much as feasibly possible, all while using the shaker within its specified performance range.