signal filtering

[Steve Blackwell]

The signal input is made up of many 100HZ sine waves containing multiple phase shifts. I need to extract the individual sine waves at varying phase angles. The project will be used to balance model car motors.

[LocalDSP]

Steve,

If your signal is composed of only one 100 Hz sine wave (at a time), you can extract the absolute phase information using, for example, the Extract Single Tone Information LabVIEW VI (in the Waveform Measurements palette).

If your signal is composed of the sum of multiple sine wave having all the exact same frequency (but different phases), there will be no way for you to decompose your signal and find the different components. Your signal will just be a simple sine wave.

If your signal is none of the above, I would suggest you to post a simple VI with for example a waveform graph showing your actual signal

Alain

[SachaE]

Hi Steve,
as said by Alain, you're not going to be able to strip out the individual components even with FFT.
What if you took the program one step further though.
I assume that a balanced motor would produce a single 100Hz sinewave. Why not use the limit checking capabilities of LV 6.x and tweak until you're inside acceptable limits? (Or does each sine wave refer to a particular part of the motor, so you can see the effect of each one as you tweak?)

just my 2 cents worth.

S.

[Tims]

Hi Steve,

You can find the instantaneous phase by referencing your signal agains a
continous100Hz Sinewave. If this Sinewave is at the same length as you
original data you can use the arctan function to return the relative
phase (in radians) between the two signals at all points.

Tim

Steve Blackwell wrote:

> The signal input is made up of many 100HZ sine waves containing
> multiple phase shifts. I need to extract the individual sine waves at
> varying phase angles. The project will be used to balance model car
> motors.

[Urs Bögli]

Steve,

If your signals all have exactly the same frequency you have no chance to
find one component of it - a sum of the sine waves of the *same* frequency
is just one sinewave.
I guess you mean these motors have a frequency almost at 100 Hz. Try to get
a reference frequnecy (ie ignition) and use the lock-in technology find the
phases of the different components. This is decribed very well in the
classic Gary Johnson's Labview book.

Good Luck
Urs

Tim Streeter schrieb:

> Hi Steve,
>
> You can find the instantaneous phase by referencing your signal agains a
> continous100Hz Sinewave. If this Sinewave is at the same length as you
> original data you can use the arctan function to return the relative
> phase (in radians) between the two signals at all po
ints.
>
> Tim
>
> Steve Blackwell wrote:
>
> > The signal input is made up of many 100HZ sine waves containing
> > multiple phase shifts. I need to extract the individual sine waves at
> > varying phase angles. The project will be used to balance model car
> > motors.

[Steve Blackwell]

I have a model car motor supported on two legs (one each end)fitted with piezo sensors producing a sine wave caused by the deflection in the leg. The idea was to look at these two sine waves and the components there in, then calculate where counter weights are required on the motor itself. Due to the difficulty of decomposing sine waves of the same frequency, maybe I need a different approach to my problem. Any ideas chaps, would be very greatfull ?

[LocalDSP]

Now it sounds like you are able to measure your two sine tones independantly. If this is true you should be no problem extracting the phase difference(s).
Could you describe your measurement setup a little bit more in details? How many sensors do you have? how many acquisition channels? what signal(s) do you apply to each input? are they acquired simultaneously? What hardware and sample rate? etc...

Thanks
Alain

[Steve Blackwell]

The model car motor sits on two arms and is spun at several thousand rpm. The two arms (one on each end of the motor) have sensors to measure the vibrations. A perfectly balanced motor would give two flat lines (no sine wave) on either end of the motor. An out of balance motor will give varying sine waves depending on how far out of balance the motor actualy is. Remember it can be out of balance in more than one place. How to look at the two waveforms from each end and decide where to put the conter balance is the problem. An expert on the thory of balancing motors is what I need! Anyway, let me know what you all think.

[Ben]

I am not an expert at motor balancing but I would like to through out a thought.

Can't this be handled like "quadraphonic stero" and the like?

Use the two signals A and B to create to additional signals "A+B" and "A-B".

In perfect balance all 4 would be zero.

If out at A end, the "A", "A+B", and "A-B" would be non-zero, but "B" would be zero.

Similarly for "B" end.

If "A" and "B" where equal and oposite all signals would have magnitude except "A+B" and "A-B" would be largest.

If Equal and in-phase "A+B" would be largest.

So if you give each of teh above sets of values a direction similar to,

A Plus X direction
B Minus X direction
A+B Plus Y direction
A-B Minus Y direction

You could add them together vectorally and the resulting vector wou
ld indicate the magnitude of the imbalance and the phase.

You may have to set up your sensors such that they measure forces that are perpendicular to each other.

Just my thoughts,

Ben

[Ben]

After letting my coffee take effect...

Go with 4 sensors. Two at each end, 90 out of phase.

Plot the horizontal on the X, verticle on the Y and you should be in buisness.

Ben