Improved Quartz Crystal Microbalance Instrument
Original Publication Date: 1988-Jul-01
Included in the Prior Art Database: 2005-Feb-15
A frequency or phase-locked loop (PLL) is used to determine the resonance frequency, Q1, and shunt capacitance of a quartz crystal in a microbalance instrument. The crystal is placed in a transmission network, the output of which is proportional to the admittance Y (or impedance Z) of the crystal. This output is analyzed by two quadrature phase sensitive detectors whose outputs are used to measure the various parameters of the crystal. In addition, these outputs direct the PLL to lock onto the crystal's series resonant frequency. (Image Omitted) A particular implementation is show in Fig. 1. A constant amplitude V0, voltage controlled oscillator (VCO) sweeps its frequency over a small range +Wl about the _ crystal's series resonant frequency l0 .