Fig.7. UUT resonance pickup
ii). Stabilization of Reference source
a). Mechanical Stabilization
Vibration isolators (dampers or special class of rubber) are used to
isolate reference source from UUT in which PLL system resides inside. It
gives free floating stress less assembly to reference module which makes
reference source to experience lesser level of vibration in comparison
to vibration level experienced by UUT. Fig. 8 shows an implemented
arrangement of reference source assembly. Selection of vibration
isolator is very critical as these are vibration profile dependent
special class of rubber; also make sure that it qualifies other
environmental test profiles requirements i.e. temperature, shock,
acceleration, humidity, etc. To check the effective performance
improvement with vibration isolators, vibration sensors has been used to
access reduction in intensity level (PSD) or damping effect of random
vibration on reference source. Fig. 9 shows a very significant
improvement in damping effects by mechanically stabilizing it
[6]-[8].