Mechanical shock is the exposure of the quartz resonator to an impact. Mechanical shock can occur in a wide range. Dropping a crystal onto the floor onto the floor is one example. An example of extreme mechanical shock would be a crystal utilized in the electronic circuit of an proximity fuse of an artillery shell fired from a 155 mm gun.
Mechanical shock has two components, intensity measured in Gs and duration measured in milliseconds. Dropping a crystal from table-top height onto a hard floor can result is shock in excess of 1,000 g’s over a period of about 3 milliseconds. The crystal in the artillery shell experiences about 16,000 g’s for 12 milliseconds. Higher shock levels usually have shorter duration, 0.25 milliseconds and lower shock levels can have a duration as long as 20 milliseconds.
The effects of mechanical shock range from frequency shifts, intermittent operation an/or total destruction due to the stress sensitivity of the resonator. Stress sensitivity is a function of the mechanical design of the resonator and shock survivability is a consideration when developing the design. Design, selection of material, internal mounting structure and processes can all be optimized to enhance a resonators ability to survive mechanical shock. A resonator’s ability to tolerate mechanical shock can be tested by exposing the device to a calibrated shock, then measure and compare the pre- and post-test performance.
Military specifications, MIL-PRF-3098/H and MIL-STD-202F Method 213 TC C&D, set the typical standard and test conditions for mechanical shock for crystals:
< 4.0 MHz: 100g, 6 mS, half-sine, 3 blows each plane
> 4.0 MHz: 500g, 1 mS, half-sine, 3 blows each plane
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