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

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  • jeremy youngs
    ... on this project though if you dont have a magnitude of impulse (accelerometer) or the frequency of vibration (transducer pick up) one will not be able to
    Message 1 of 23 , Mar 3, 2013
      >
      > john
      >


      > yes without going into the strategies and engine controller uses
      > quadrature encoding in the crank sensor to monitor instantaneous crankshaft
      > acceleration for misfire detection. which is exactly what you have outlined
      > here.
      >
      on this project though if you dont have a magnitude of impulse
      (accelerometer) or the frequency of vibration (transducer pick up) one
      will not be able to properly calculate the data for proper fourier analysis
      and will be lacking enough detail to have any substantial quantitative
      results , you can measure 0 drive train harmonics by traking rotation or
      acceleration ther is simply not enough information to calculate the other
      polynomial variables. Simply in order to do what the o.p is aking 3 sensors
      will be needed and the crank seneor would be very easy to just access at
      the engine controller by simple back probing. arduino shields are available
      with accelerometers and transducers availabe it is possible an electret
      with enough frequency spectrum would work as well.



      --
      jeremy youngs


      [Non-text portions of this message have been removed]
    • Jan Kok
      Regarding using a Hall effect sensor to measure rotational resonance: it may work if the resonant frequency is substantially lower than the frequency of the
      Message 2 of 23 , Mar 3, 2013
        Regarding using a Hall effect sensor to measure rotational resonance: it
        may work if the resonant frequency is substantially lower than the
        frequency of the square wave that you get from the Hall effect sensor. If
        the resonant frequency you're looking for is close to or higher than the
        frequency of the sensor square wave (and actually, if there are strong
        frequency components above the frequency of the square wave), then the Hall
        effect sensor won't give you reliable info about the frequency variations,
        i.e. small, high-frequency changes in the rotation rate.

        It has to do with sampling theory. Suppose you use an A/D converter to
        sample a 900 Hz sine wave at a 1000 samples per second rate. In 10 ms the
        sine wave goes through 9 cycles, and you take 10 samples. The result is
        that the samples, if plotted, look like a single cycle of a sine wave at
        100 Hz. So 900 Hz looks like 100 Hz after sampling. The signal you are
        sampling must not have frequency components greater than 1/2 the sampling
        frequency, in order to avoid seeing spurious frequencies in the sampled
        data.

        With the Hall effect sensor, you can sample on the rising and falling edges
        of the sensor square wave, and what you are sampling is the width of the
        pulses. If you get 500 Hz from the sensor, then you can sample 1000 times
        per second and the maximum resonant frequency you can see accurately is
        below half that rate, i.e. less than 500 Hz.



        On Sun, Mar 3, 2013 at 4:38 PM, jeremy youngs <jcyoungs76@...> wrote:

        > >
        > > john
        > >
        >
        >
        > > yes without going into the strategies and engine controller uses
        > > quadrature encoding in the crank sensor to monitor instantaneous
        > crankshaft
        > > acceleration for misfire detection. which is exactly what you have
        > outlined
        > > here.
        > >
        > on this project though if you dont have a magnitude of impulse
        > (accelerometer) or the frequency of vibration (transducer pick up) one
        > will not be able to properly calculate the data for proper fourier analysis
        > and will be lacking enough detail to have any substantial quantitative
        > results , you can measure 0 drive train harmonics by traking rotation or
        > acceleration ther is simply not enough information to calculate the other
        > polynomial variables. Simply in order to do what the o.p is aking 3 sensors
        > will be needed and the crank seneor would be very easy to just access at
        > the engine controller by simple back probing. arduino shields are available
        > with accelerometers and transducers availabe it is possible an electret
        > with enough frequency spectrum would work as well.
        >
        >
        >
        > --
        > jeremy youngs
        >
        >


        [Non-text portions of this message have been removed]
      • AlienRelics
        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
        Message 3 of 23 , Mar 3, 2013
          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

          --- In Electronics_101@yahoogroups.com, Jan Kok <jan.kok.5y@...> wrote:
          >
          > Regarding using a Hall effect sensor to measure rotational resonance: it
          > may work if the resonant frequency is substantially lower than the
          > frequency of the square wave that you get from the Hall effect sensor. If
          > the resonant frequency you're looking for is close to or higher than the
          > frequency of the sensor square wave (and actually, if there are strong
          > frequency components above the frequency of the square wave), then the Hall
          > effect sensor won't give you reliable info about the frequency variations,
          > i.e. small, high-frequency changes in the rotation rate.
          >
          > It has to do with sampling theory. Suppose you use an A/D converter to
          > sample a 900 Hz sine wave at a 1000 samples per second rate. In 10 ms the
          > sine wave goes through 9 cycles, and you take 10 samples. The result is
          > that the samples, if plotted, look like a single cycle of a sine wave at
          > 100 Hz. So 900 Hz looks like 100 Hz after sampling. The signal you are
          > sampling must not have frequency components greater than 1/2 the sampling
          > frequency, in order to avoid seeing spurious frequencies in the sampled
          > data.
          >
          > With the Hall effect sensor, you can sample on the rising and falling edges
          > of the sensor square wave, and what you are sampling is the width of the
          > pulses. If you get 500 Hz from the sensor, then you can sample 1000 times
          > per second and the maximum resonant frequency you can see accurately is
          > below half that rate, i.e. less than 500 Hz.
          >
          >
        • jeremy youngs
          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
          Message 4 of 23 , Mar 3, 2013
            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]
          • 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 5 of 23 , Mar 3, 2013
              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 6 of 23 , Mar 4, 2013
                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 7 of 23 , Mar 6, 2013
                  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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