Crystal unit

Abstract

A crystal unit includes: a crystal blank; an excitation electrode formed on the crystal blank and excites a main vibration of the crystal blank; a housing that accommodates the crystal blank; and a sub-vibration electrode formed on the housing and excites a sub-vibration of the crystal blank. And a method for inspecting a crystal unit, the method includes: generating a sub-vibration in a crystal blank by applying an input signal to a sub-vibration electrode formed on a housing, which accommodates the crystal blank, via external electrodes which are electrically coupled to the sub-vibration electrode and formed on the outer surface of the housing; obtaining an output of the crystal unit via the external electrodes; obtaining frequency characteristics of impedance between the external electrodes based on the output; and comparing the obtained frequency characteristics with the reference frequency characteristics indicating the quality of the crystal unit.

What is claimed is: 
     
         1 . A method for inspecting a crystal unit, the method comprising:
 generating a sub-vibration in a crystal blank by applying an input signal to a sub-vibration electrode formed on a housing, which accommodates the crystal blank, via external electrodes which are electrically coupled to the sub-vibration electrode and formed on the outer surface of the housing;   obtaining an output of the crystal unit via the external electrodes;   obtaining frequency characteristics of impedance between the external electrodes based on the output; and   comparing the obtained frequency characteristics with the reference frequency characteristics indicating the quality of the crystal unit.   
     
     
         2 . The method according to  claim 1 , further comprising: obtaining at least one of a peak frequency and a peak value according to the sub-vibration based on the output. 
     
     
         3 . The method according to  claim 2 , further comprising: comparing at least one of the peak frequency and the peak value according to the sub-vibration with the corresponding reference value or reference range.