Re: [Electronics_101] Re: How to analyze change in frequency?
- 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 !!)
did i just answer my own post doh enjoy
- 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.
[mailto:Electronics_101@yahoogroups.com] On Behalf Of jeremy youngs
Sent: Monday, March 04, 2013 12:19 AM
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
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
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
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 :)
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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
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
The other Howard
On 3/2/2013 9:49 AM, A6intruder@... wrote:
> 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
> 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
> 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
> 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...
> -----Original Message-----
> From: 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
> Subject: Re: [Electronics_101] How to analyze change in frequency?
> A couple of questions: How many teeth are there on the gear that the
> 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
> 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
> wizard to plot your data.
> Does the graph of the frequencies look somewhat sinusoidal? That graph
> 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
> 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.
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