Reading a PSD, can I get a mean frequency from this plot?
Reading a PSD, can I get a mean frequency from this plot?
(OP)
Hi!
I´ve tried to analyze the plot attached for a while now, but it does´nt make any sense to me. I´ve never encountered a PSD plot before and I need a frequency (mean) to continue my calculation on vibrations, but the PSD just makes me confused. Could anyone extract some information from it to me?
Acceleration data: http://files.engineering.com/getfile.aspx?folder=7...
PSD for the acceleration data: http://files.engineering.com/getfile.aspx?folder=b...
Kindly //
I´ve tried to analyze the plot attached for a while now, but it does´nt make any sense to me. I´ve never encountered a PSD plot before and I need a frequency (mean) to continue my calculation on vibrations, but the PSD just makes me confused. Could anyone extract some information from it to me?
Acceleration data: http://files.engineering.com/getfile.aspx?folder=7...
PSD for the acceleration data: http://files.engineering.com/getfile.aspx?folder=b...
Kindly //





RE: Reading a PSD, can I get a mean frequency from this plot?
I suggest you go back to whoeever asked you for a better definition. It is not an expression i have come across in 30 years of vibration analysis.
Cheers
Greg Locock
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RE: Reading a PSD, can I get a mean frequency from this plot?
RE: Reading a PSD, can I get a mean frequency from this plot?
Tobalcane
"If you avoid failure, you also avoid success."
“Luck is where preparation meets opportunity”
RE: Reading a PSD, can I get a mean frequency from this plot?
RE: Reading a PSD, can I get a mean frequency from this plot?
Tobalcane
"If you avoid failure, you also avoid success."
“Luck is where preparation meets opportunity”
RE: Reading a PSD, can I get a mean frequency from this plot?
RE: Reading a PSD, can I get a mean frequency from this plot?
Your time-history accel. is not enough flat ( many peaks).
In my opinion, your signal is not enough stationary to perform a PSD...
RE: Reading a PSD, can I get a mean frequency from this plot?
What exactly are you trying to calculate with your "mean" frequency? The only thing I can imagine using a single frequency is to determine whether a particular mechanical frequency overlays on top of an isolator frequency, which is undesirable.
TTFN
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RE: Reading a PSD, can I get a mean frequency from this plot?
The plot is from a test vehicle, and I need the frequency to complete some calculations within piezoelectrics.
RE: Reading a PSD, can I get a mean frequency from this plot?
TTFN
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RE: Reading a PSD, can I get a mean frequency from this plot?
What Im looking for in terms of frequency is the bandwidth where the most of the frequency is. Since I need to order piezoelements that work in that specific frequency range.
Is that easier to outline from the PSD? Thanks in advance (again!)
RE: Reading a PSD, can I get a mean frequency from this plot?
TTFN
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RE: Reading a PSD, can I get a mean frequency from this plot?
The only data I have is the acceleration graph and the PSD for it. They have been measured by someone else, and was given to me since Im doing studies that require an operating frequency. I need to pinpoint a frequency from which I could harvest the most energy from (piezoelectrics), and I have no idea how to read the PSD and what the strange unit (m/s2-rms^2)/Hz tells me.
Sorry, but my knowledge within electronics and vibrations are highly limited..
RE: Reading a PSD, can I get a mean frequency from this plot?
It seems to me, reading between the lines, you are actually needing to use the amplitude for a particular frequency to determine the amount of power your "piezoelectrics" produce? You then integrate with respect to frequency, and divide by the average bandwidth.
You do have a problem in that your PSDs are not rolling off, so there's no information about where the input energy actually starts to fall off.
TTFN
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RE: Reading a PSD, can I get a mean frequency from this plot?
RE: Reading a PSD, can I get a mean frequency from this plot?
I do actually have one more PSD from another measurement. I´ll post it here as soon as I get into the office tomorrow.
BrianE22: I tried to get hold of the guy who passed along the PSDs for me on order to see if they have other PSDs to get my hands on. I´ve checked other information graphs and I think the frequencies should be around 20Hz. Could the two peaks be about resonance frequencies?
Flat response through 100Hz minimum? And the circuitry I´ve planned on following uses a simple rectifying bridge to get DC, how does this determine the low end of the response?
ps. I really appreciate your time & thanks for the responses even though my replies tend to be a bit slow. Different time zones makes it hard for me to answer right away.. I´ll post the other PSD tomorrow
RE: Reading a PSD, can I get a mean frequency from this plot?
TTFN
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RE: Reading a PSD, can I get a mean frequency from this plot?
That´s the reason Im doing this, I can´t order any piezoelectric devices if I don´t have anything pointing out that I actually can get somewhere close the power output I need (with current being the limiting one).
Here is another graph with acceleration data and the PSD for it:
RE: Reading a PSD, can I get a mean frequency from this plot?
Conversely, your "current" requirement may simply exclude this approach completely. Piezoelectric devices are not high-current sources.
TTFN
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RE: Reading a PSD, can I get a mean frequency from this plot?
The piezoelectronic will be mounted as a cantilever, which bends back and forth due to the vibrations. This is where my need for average frequency bandwidth comes in :)'
ps. Im not trying to achieve high current, I just mentioned current as the limiting one which I´ll have to investigate closer than the other factors.
RE: Reading a PSD, can I get a mean frequency from this plot?
TTFN
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RE: Reading a PSD, can I get a mean frequency from this plot?
I´m currently halfway through the book "Energy Harvesting Technologies" by Priya & Inman, and I´ve read countless of articles. And the most of the equations rely on the electronics within the circuit and the surrounding kinetic energy (amplitude and frequency). Unfortunately the piezoelements are a bit too expensive for try-and-error solving, thats why Im bound to the calculations.
Btw, atm Im looking into this harvesting kit. And I´ve managed to sqeeze in two of them within my device (with CAD). Unfortunately it also has a higher frequency demand than I think I´ll have if the PSD would give me some actual frequency data.. So currently Im looking for a solution that offers a broad frequency band for energy harvesting.
I think that the average frequency bandwidth would lie around 20Hz, or am I totally lost now? :P
(My assumption is based on other data on the net about normal car driving accelerations & frequencies)
ps. It´s really hard to find anyone to rely on with discussions within piezoelectronics, so you are actually the one I´ve had the longest discussion with.
RE: Reading a PSD, can I get a mean frequency from this plot?
That's precisely what I'm saying when I talk about the response curve. You simply multiply the response curve against the input PSD to get the weighted output PSD. The integral of that is the average power expected from the transducer.
TTFN
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RE: Reading a PSD, can I get a mean frequency from this plot?
If your signal is supposed to be random but not stationnary, then ERS is a good indicator for analysing random vibation.
RE: Reading a PSD, can I get a mean frequency from this plot?
Of course, your device only puts out 7mW at rated frequency and deflection, which is pretty miniscule, when you get right down to it.
TTFN
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RE: Reading a PSD, can I get a mean frequency from this plot?
For the PSD: do I get the equation of integration interest from doing a "reversed bode plot" on the PSD? (it´s many years ago I had a course with bode plots, but its the only thing I remember where I´ve constructed equations from a curve)?
"Of course, your device only puts out 7mW at rated frequency and deflection, which is pretty miniscule, when you get right down to it."
Is it possible to achieve these two requirements with three of the devices coupled together:
(1) overcome the required power to start charging a small battery (around 120mAh)?
(2) to charge it in a reasonable time (Reasonable time = matter of hours, not days)?
Or is it completely out of question?
RE: Reading a PSD, can I get a mean frequency from this plot?
Even in an ideal case, you would need something like 10 of these piezoelectric devices in parallel to get enough current to charge a fully drained battery within 2 hours, with no additional load.
Seems to me that you've not presented a sufficiently enough detailed operational scenario and requirements to even begin to figure out what you need to do.
TTFN
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RE: Reading a PSD, can I get a mean frequency from this plot?
At my first try Im going with a Ni-Mh battery since it doesnt need extra circuitry to allow charging. The electronics are not going to be on at the same time as the battery is being charged (with and exception with the standby power of the circuitry ~1mA). The consumption of the electronics will hopefully not be over 50mA, but that is a bit uncertain for now with a choice of LEDs (the number of these has to be around 10 totally).
The 2 hours is a dream scenario, hopefully the idea is at least feasible and shows some charging activity which would allow more development and optimization.
The requirement of the lights today is that they can be activated 20times/day (8seconds/time) + one long term activation (60seconds), those are the main requirements for the energy source to handle.
Btw, I managed to get hold of the guy who produced the PSD today. He said that the PSD was constructed for one purpose only, and he has no idea why the data was sent to me since it cant be translated to something useful by anyone else. He is going to send me some PSDs and frequency data plots in the coming days that I actually can work with. But probably Im gonna need some help with those also :)
RE: Reading a PSD, can I get a mean frequency from this plot?
220s*50mA = 3 mAh plus 1mA standby
So there you have it. Your device puts out 1.4 mA at rated performance, and since you cannot have 100% charging efficiency, you'd need more than 8 hrs to recharge battery.
TTFN
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RE: Reading a PSD, can I get a mean frequency from this plot?