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+--- Thread: magnetic spectrum versus time (/showthread.php?tid=505)
magnetic spectrum versus time - julien - 12-19-2019
Hello,
I am playing with a hand spinner. I have magnetized one of its arm. This way i can use the magnetic spectrum to find out its speed of rotation.
I would like to draw a chart of the values of the peak frequencys versus time. But i don't know how to do it.
Is there any way to perform this kind of measurement ?
Thank you !
RE: magnetic spectrum versus time - Sebastian Staacks - 12-20-2019
You probably have already seen the color plot under "history", so this is probably not what you are looking for. Instead, you probably only want a simple graph with the peak of each analyzed time interval.
In fact, this can be done quite easily with out editor (https://phyphox.org/editor). You just need to add a timer-module to get the x axis (time) and connect the peak-frequency (output of the max module) to the y axis of the graph. The tricky part is that both connections need to be set to an infinite buffer (size 0) and clearing needs to be disabled, so the data is collected.
However, this works so well and is so easy to implement, that I will add it to the next version of phyphox. For those, who do not want to wait, just open the following links to the development version of the spectrum experiments in phyphox (for example by clicking the link and scanning the QR code from within phyphox):
https://raw.githubusercontent.com/Staacks/phyphox-experiments/development/acc_spectrum.phyphox
https://raw.githubusercontent.com/Staacks/phyphox-experiments/development/mag_spectrum.phyphox
https://raw.githubusercontent.com/Staacks/phyphox-experiments/development/audio_spectrum.phyphox
RE: magnetic spectrum versus time - julien - 12-21-2019
Excellent !
This is exactly what i was looking for.
I definitly need to learn how to use your editor, it seems to be very usefull !
Thanks !
Julien
RE: magnetic spectrum versus time - julien - 12-21-2019
Here is the results.
We can see an exponential decay and a half-life of 16s !
RE: magnetic spectrum versus time - Physikator - 12-25-2019
I don't know about the sprectrum at low frequencies, but this experiment might be adapted to become a speedometer for a bicycle. These usually work with a magnet in the spokes. Maybe it might be more feasible to measure the time between two pulses?
RE: magnetic spectrum versus time - Sebastian Staacks - 12-26-2019
Yes, I would also think that measuring the time inbetween would work better. In fact, this should work right away, if you use the "magnetic ruler" experiment and enter the circumfence of the wheel as a distance. However, due to the way, phyphox tries to figure out the threshold of the magnet signal, you need to make sure that your phone is mounted such that the distance to the magnet is perfectly constant.