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Re: [Electronics_101] Re: How to analyze change in frequency?

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  • jeremy youngs
    DOH !!!! :)) simple cheap effective had to remeber bak to the first nvh class here this is the down and dirty old school tool !!! ( maybe a little ot as its
    Message 1 of 23 , Mar 3, 2013
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      DOH !!!! :))

      simple cheap effective had to remeber bak to the first nvh class here
      this is the down and dirty old school tool !!!
      ( maybe a little ot as its not electronic !!)
      http://www.treysit.com/16.html


      did i just answer my own post doh enjoy

      --
      jeremy youngs
    • A6intruder@myo-p.com
      I am the OP and I have tried to be completely forward as to my goal, I stated this earlier: I am trying to figure out the basic
      Message 2 of 23 , Mar 4, 2013
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        I am the OP and I have tried to be completely forward as to my goal, I
        stated this earlier:

        "I am trying to figure out the basic sensor/processing/display/record
        process now on my car so that later I can use it to analyze another
        combination of engine/gearbox/load."

        The point is to be able to test a given combination of engine/gearbox/load
        for destructive resonant frequencies in the full range of operation, engine
        RPM varying from idle (700 RPM) to max RPM (5500 RPM). I figured my turbo
        charged V-8 Mustang would be a good development test bed since I can load
        the engine very heavily to see "normal" power pulses with this process
        which aren't resonant in this parts combination. If there were a
        destructive resonant frequency in the operational range it would surface as
        a much larger magnitude than the regular power pulses from the engine, at
        whatever frequency it exists.

        So if we can see the "standard" power pulses with this process on my car
        then when I bolt a similar engine to different gearbox and load (say a
        propeller) on a test stand then I can monitor to see if the new combination
        has an resonant frequency within the normal range of operation.

        I really doubt my car has a resonant frequency in its range of operation as
        I have flogged that car on the street and at the drag strip throughout the
        full range of operation and it hasn't self-destructed.

        Everyone has been very helpful on this discussion, thank you. I have no
        doubt the information I am seeking can be determined from the gear teeth
        sensor, it is just a matter of processing that data stream. Jan has pointed
        out some of the numerical limitations to that process.

        Thanks,

        Dan

        -----Original Message-----
        From: Electronics_101@yahoogroups.com
        [mailto:Electronics_101@yahoogroups.com] On Behalf Of jeremy youngs
        Sent: Monday, March 04, 2013 12:19 AM
        To: Electronics_101@yahoogroups.com
        Subject: Re: [Electronics_101] Re: How to analyze change in frequency?

        I believe he said the resonance he is looking for would be at 1/4 the
        rotational frequency.

        Why not measure the period between gear teeth, and compare how it changes?
        It seems to me that what you are looking for is FM impressed on the pulses
        from the gear teeth.

        Steve Greenfield AE7HD

        steve i believe accel decel curve could be extrapolated via demodulation as
        you suggest. however this would assume abunch of ommitted truths that need
        reconciliation. just a few i wil miss them as i dont wish to write a thesis
        here :)

        1 this meaure is taken at the flywheel

        2 what exactly are we looking for ? just the 8 impulses in 2 revolutions?

        ( the op hasnt been as forward on what he is looking to do here as would be
        required)

        3 there will be MANY resonances as anything attached to the crankshaft will
        have a natural resonant frequency

        4 there will be 1st and second order harmonics dominating this analysis

        some means of isolating the suspect resonance is needed ( also to note what
        IS the suspect resonance? this has not been defined !!!!)

        (without definition i cannot help lead to a resolution :)

        5 what are the particulars of the test method i e under load ? going down
        the road? idling in the driveway? these conditions will radically affect the
        identifying of suspect parameters and will lead to different results

        in short i think an arduino with accelerometer, transducer and ignition
        pulse pick up is required. i believe in essence a 100 dollar eva could be
        built to experiment.

        if i were limited to only looking at one characteric the most info can be
        derived with a transducer monted to the engine to get precise frequency
        measurements to back calculate what component is causing the resonance.
        further the second most important thing is being able to quantify the
        magnitude of the imulse so you can identify which resonance is THE one that
        you are looking for .

        last is rotational tracking this is the least useful and the first
        recommended as all other parameters can be calculated using the above two
        methods, however being that crankshaft pulse is readily available to
        backprobe at the ecm connector it would be very handy to compare these three
        in a dso type arduino box and graph them in synchrony to paint the whole
        picture and make the resonance readily identifiable.


        What I really want to know is what exactly is the O.P. trying to do ie why
        are we measuring resonances and comparing them to other vehicles?

        As an auto tech i have never fixed a vehicle in my life :)

        What i do is resolve concerns and i find this concern to not currently be
        defined enough to resolve :)

        ( oh p.s rate of resolved conerns 97 percent in 7 yrs withh chrysler :)


        --
        jeremy youngs


        [Non-text portions of this message have been removed]



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      • Howard Hansen
        Hello Dan, A popular Frequency to Voltage Converter IC is the LM2907-N/LM2917-N IC. See: A recommended
        Message 3 of 23 , Mar 6, 2013
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          Hello Dan,

          A popular Frequency to Voltage Converter IC is the LM2907-N/LM2917-N
          IC. See: <http://www.ti.com/lit/ds/snas555b/snas555b.pdf>
          A recommended application circuit is Figure 16 on page 14. To be able
          to detect variations in frequency you need a frequency to voltage
          converter with a low output ripple. Hence this is why I recommended a
          frequency to voltage converter with 2 pole Butterworth Filter to reduce
          ripple.

          To select component values for the Butterworth Filter one needs to know
          the range of possible resonant frequencies. What is the range of
          possible resonant frequencies? My guess is 43 to 367 Hz. This guess
          comes from an engine RPM range of 650 to 5500 and 4 power pulses per
          revolution.

          The other Howard


          On 3/2/2013 9:49 AM, A6intruder@... wrote:
          >
          > OK,
          >
          > Just answering Jan and Jeremy got me thinking.
          >
          > Without looking at any data sheets let's say we have an IC that converts
          > frequency to voltage. The Hall effect sensor puts out a square wave signal
          > with equal high and low durations. So each time the sensor waveform
          > crosses
          > a certain voltage (say 2 volts) it allows the IC to determine
          > frequency and
          > output the corresponding signal voltage.
          >
          > With a completely smooth turning gear wheel at a steady RPM we will get a
          > very steady signal voltage. Any time the frequency starts to vary the
          > signal voltage will go up or down. In the case of four power pulses per
          > revolution the IC should see four areas of changing voltage in each
          > rotation
          > of the gear wheel. If you hooked an oscilloscope to the output of this IC
          > you would see a steady horizontal line for a steady RPM with no power
          > pulses. With power pulses you would start to see those four areas of
          > changing voltage.
          >
          > The peak amplitude of the changing voltages would signify the magnitude of
          > the resonance. Large resonance would be a faster change in frequency since
          > the mechanical amplitude of the disturbance has to happen in the same
          > amount
          > of time...
          >
          > I'm thinking out loud here. I need to dig into some data sheets and
          > see how
          > fast these IC's really are...
          >
          > Thanks,
          >
          > Dan
          >
          > -----Original Message-----
          > From: Electronics_101@yahoogroups.com
          > <mailto:Electronics_101%40yahoogroups.com>
          > [mailto:Electronics_101@yahoogroups.com
          > <mailto:Electronics_101%40yahoogroups.com>] On Behalf Of Jan Kok
          > Sent: Saturday, March 02, 2013 12:09 AM
          > To: Electronics_101@yahoogroups.com
          > <mailto:Electronics_101%40yahoogroups.com>
          > Subject: Re: [Electronics_101] How to analyze change in frequency?
          >
          > A couple of questions: How many teeth are there on the gear that the
          > sensor
          > senses? And, is there some way to tell where the "0" position of the
          > flywheel is?
          >
          > I would suggest buying or borrowing a digital storage oscilloscope with a
          > large memory (say 1 million samples or so) that can store waveform
          > data to a
          > USB key.
          >
          > Capture a bunch of waveforms from the sensor, and analyze them at your
          > leisure on your computer.
          >
          > You'll get a frequency modulated square wave from the sensor. The
          > higher the
          > RPMs, the higher the frequency and the shorter the period of the square
          > wave.
          >
          > Write a program to measure the period of each pulse, and plot the
          > frequencies of the pulses (inverse of periods). You can use the Excel
          > graph
          > wizard to plot your data.
          >
          > Does the graph of the frequencies look somewhat sinusoidal? That graph
          > would
          > show the frequency modulation of the sensor square wave, and the cycles in
          > the sinusoid should correlate with the power strokes of the pistons. The
          > sinusoid should have much larger amplitude when the engine is under load.
          >
          > The amplitude should also be larger at certain RPMs where there is
          > rotational resonance, compared with RPMs where there is no resonance.
          > However, my hunch is that it will be hard to see any resonance, for
          > several
          > reasons: the resonant frequency may be higher than the sensor squarewave
          > frequency, friction in the engine and drivetrain will act to dampen any
          > resonance, and the resonance may be buried in random noise.
          >
          > Sounds like a fun project. I'll be curious to hear how it turns out.
          >
          > [Non-text portions of this message have been removed]
          >
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          >



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