FAQ: My colleague who is trying to build a generator tells me that maximum vibration is observed at 19.85 kHz for the assembly (Transducer+Booster+Horn) that I measured as 20.00 kHz with TRZ® Analyzer. Both of them were not mounted. Why do we observe such a difference?
A few Hertz difference is expected because of the measurement uncertainties and nonlinearities at high power, but 150 Hz is far too much. The SonicSniffer uncertainty is ±8 Hz and the TRZ® Analyzer is ±0.03 % (±6 Hz @ 20 kHz), these uncertainties combined (geometric mean) is equal to ±10 Hz at 20 kHz.
The difference you observed (150 Hz) may be due to an issue with the power generator tuning or impedance matching. The generator output should also be tuned to the converter frequency and capacitance.
Learn more about testing converters and acoustic stacks.