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Resquesting help with Sinewave voltage measurement.

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N-743, I went through that thread and still ask myself what you want to measure:

Amplitude of a single sine with offset  or the angle (over time) of a shaft with a mounted encoder (giving sine&cosine and probably Z)?

 

Can you read both signals (sine & cosine) at the same time ?

Can or have you establish a differential measurement if your encoder provide differential outputs?  (that helps agains noise 😉 )

 

If you want shaft/encoder angle over time and sample sine and cosine things get easy 🙂  

 

Put it to the edge: For the offsets and sine and cosine amplitude errors/differences there is a nice method  called Heydemann correction

P. L. M. Heydemann, Determination and correction of
quadrature fringe measurement errors in interferometers,
Applied Optics 20, 3382 (1981)

(should have some vis for that .. somewhere ...)

 

Greetings from Germany
Henrik

LV since v3.1

“ground” is a convenient fantasy

'˙˙˙˙uıɐƃɐ lɐıp puɐ °06 ǝuoɥd ɹnoʎ uɹnʇ ǝsɐǝld 'ʎɹɐuıƃɐɯı sı pǝlɐıp ǝʌɐɥ noʎ ɹǝqɯnu ǝɥʇ'


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Solution
Accepted by topic author N_743

Interesting abstract Henrik, can you link the full paper? 

 

Unfortunately, this actually appears to be a mechanical allingment problem. Hence the approach to moving the signal into Polar coordinates.

 

There will be at several sources of error;

  • Shaft angle not normal to drive plane.  This will show on the Polar plot as offset from origin opposite of the error angle and proportional to the sin of the error angle and the shift elasticity
  • Shaft imbalance. This will appear as correlated spikes on rho and again opposite the angle of lowest weight (just like balancing a tire) and will vary over shaft speed maximizing at the shafts natural resonance frequency with a bandwidth related to shaft stiffness.
  • Sympathetic vibrations. Will appear as random noise on rho.  Properly tightened fasteners and mounting plates of good quality will fix those.
  • Drive train discontinuities.  Like a frozen chain link, chipped gear tooth, or even a pothole. 

Imagine riding a bicycle with no springs, no rear tire, rusty chain, with broken sprockets on a rear wheel out of true and missing spokes over railroad ties.

 

You have to pay attention to the hardware!


"Should be" isn't "Is" -Jay
Message 12 of 14
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Hi Jpb,

 


You have to pay attention to the hardware!

I agree with you. Only issue there is, in my situation, is difficulty in getting responsible person to admit it.  There are issues with grounding, physical mounting etc. But I guess I am only supposed to call out if there is "spike/noise" or not. 

 

I will mark your post as solution since there is not enough one can do without resolving hardware issues. For now I will just raise a flag if voltage values go out of bound.

 

Thanking all of you for your input on this.

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Message 13 of 14
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@N_743 wrote:

Hi Jpb,

 


You have to pay attention to the hardware!

I agree with you. Only issue there is, in my situation, is difficulty in getting responsible person to admit it.  There are issues with grounding, physical mounting etc. But I guess I am only supposed to call out if there is "spike/noise" or not. 

 

I will mark your post as solution since there is not enough one can do without resolving hardware issues. For now I will just raise a flag if voltage values go out of bound.

 

Thanking all of you for your input on this.


Show them the Polar plot.  If faced with empirical evidence they can try to explain its causes themselves.  A responsible person would own up to the mistakes or oversights.

 

You are welcome.


"Should be" isn't "Is" -Jay
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