I just wonder about calibration for Pierce oscillator circuit in openQCM. Please link to this hyperlink to view schematic circuithttp://openqcm.com/openqcm-community-develops-and-shares-the-new-electronic-design-using-kicad.html
In basically, R3 & C2 make a "Low pass filter" with frequency cut-off Fc=1/2*pi*RC, when I try this circuit with my QCM sensor (5MHz) from MATEX, in air the frequency output is OK, but in liquid the frequency was not proper because my frequency counter ( Aligent 53230 ) can not detect the signal from this circuit. I try to replace 2 capacitors C1&C2 in circuit. as consequenlty, the circuit is proper operation with value of 130pF.
This is my situation and my solution for this case.
And I think I have a interesting question about the rule of R3 and C2 in this circuit. That is:
" Are the function of R3 and C2 same in calibration of output frequency ? " what happen if we change the value of R3 and remain the value of C2 ?
As far as I know the R3 & C2 make a "Low pass filter" with frequency cut-off Fc=1/2*pi*RC, change in value of R3 or C2 will be change the Gain and Phase of output frequency. So when we increase C2 the Gain will also increase so the level of voltage driving QCM will be increased.
Anyway my question is only a different thinking about aspect of design QCM circuit.
Nhannd from UNIST, Korea