Post subject: Fast Frequency Measurement Posted: Sat May
20, 2006 12:47 am
Joined: Sat May 20,
2006 12:29 am
I need to track resonant frequency
changes in a resonator. The resonant frequency is about 230 kHz.
I would like to measure resonant frequency changes with noise level
on the order of 1-5 mHz with a large dynamic range, and I would
like to sample this frequency at about 100 Hz or better.
I was wondering if a PLL could help me. Essentially, I would like
to take my signal (230kHz), convert it to a voltage proportional
to the resonant frequency, so that I can measure this output voltage
with a DAQ card. I'm not very competent when it comes to electronics,
so it would be great if someone could suggest circuits and components.
Thanks in advance!
subject: Posted: Sat Jun 10, 2006 6:07 am
Joined: Fri May 19, 2006 5:01 am
Just a thought, might be silly..
you could heterodyne the drifting 230KHz signal with a PLL'ed 230KHz
(the calibration frequency so to speak). If the frequencies differ,
their difference frequencies will be produced. This frequency should
be so low that it's easily measurable.
Post subject: Posted: Mon Jun 12, 2006
Joined: Mon Jun 27, 2005 2:02
What I woud
suggest is simply to use an FM detector. The detector provides a
voltage relative to the frequency offset from the carrier (The center
frequency of 230kHz in your case). You can adjust the center frequency
by means of an inductor and capacitor (Variable). I worked with
such an IC 8 years ago in an FM receiver circuit. I am sure that
since then there are many new IC's availabel. Simply run a search
in Google I am sure you will get up on something.