Automatic frequency control in chemical etching of quartz crystal blanks

A method and system for measuring the resonance frequency of piezoelectric resonators in conductive fluids are described. One of its applications is in the chemical etching of quartz crystal blanks, where it can be used to monitor and control either the etch rate of the etchant or the etching of blanks to a targeted thickness or frequency. The system is composed of a crystal etch monitor in conjunction with special electrodes that are designed to take account and advantage of the conductive nature of the etchant. It can etch a load of blanks or a monitor blank different from the etch load but immersed in the same etchant. When the blank reaches a predetermined target, an etch-termination signal is triggered that can be used to alert an operator or to initiate action for automatic etch termination