Crystal parameters calculation/display

[vadim-dem]

Do you think adding crystal parameters calculation from their scans would be a good feature? The attached a PDF printout of a simple curve-fitting algorithm implemented in Mathcad, and zipped Mathcad file. It fits a circle into admittance B/G plot (Y=G+jB) and a line into tan(arg(Y)), thus allowing a good accuracy at reasonable frequency step of scans. Actually the fitting starts at page 7 of the printout, two other readings are also listed there: 4,782,281 US patent, http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&p=1&u=/netahtml/PTO/srchnum.html&r=1&f=G&l=50&d=PALL&s1=4782281.PN. and the best description of the circle fitting algorithm by Randy Bullock, https://dtcenter.org/met/users/docs/write_ups/circle_fit.pdf . All the scans used are on Google drive https://drive.google.com/drive/folders/1GLG88LrIcKK4O_8i7OJdPFRQF1mSgs48?usp=sharing and I would be happy to answer your questions

With best regards,

Vadim msmt_hc49u_4m9152_07.zip

msmt_hc49u_4m9152_07.pdf

[mihtjel]

It's certainly an interesting suggestion! I will tag it as a requested enhancement :-)

[paulh002]

I do this by using the bandpassfilter analysis. Then use excel to calculate Rs and Cm based on 3db bandwith. You could simple enhance the bpf analysis option. Cm = BW / (2PIFc^2*(2Rg + Rs)), where Rg is the resistance of the generator or detector, 12.5 ohms most of the time Lm = 1 / (39.48 * Fc^2Cm) (39.48 is 4PI^2) Rs = 2Rg (10^a/20 -1) where a is attenuation of peak of crystal

[vadim-dem]

Yes, I agree completely, you can start with 3dB bandwidth or with +/- 45 degree phase points. The problem is in getting these points at reasonable accuracy. Here the circle fitting method works well even when you use a single scan of 101 points covering both serial and parallel resonances of a crystal, then besides Rs and Lm (Cm) you can also get C0. And you can use reflection measurement as well, just converting its result to G+jB first

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