Why is the amplitude smaller when using the Extract Single Tone VI to measure the amplitude of a signal?

Whenever I measure the amplitude of a signal using the Extract Single Tone VI, the amplitude is smaller than if I measured the signal by hand by positioning the top and bottom cursors to the highest and lowest peaks of the captured waveform. Should I not use the Extract Single Tone VI to measure amplitude? I'm using Labview 6i.

I'm not exactly sure but I think the amplitude from the Extract Single Tone vi is in peak volts (Vp). When you use the cursors on a scope set to the top and bottom peaks, you are measuring volts peak to peak (Vp-p). If the Extract vi amplitude is one half of your scope reading, then this is true. Just double your Extract vi amplitude to get the peak to peak voltage. It also depends on the signal. If your signal is a square wave from 0 to 5 volts (TTL), this is usually measured in peak voltage. A sinewave going positive and negative (from -5 to +5) is usually measured in peak to peak.
- tbob
Inventor of the WORM Global

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What does the extract single tone vi do?

When using an extract single tone vi, what does it actually do? Does it give the frequency, phase and amplitude of the HIGHEST amplitude wave? Say we provide a waveform of 400 samples of an undermined number of sine waves.....Are there any documents with block diagrams that explains this?

TooEagerToLearn wrote:
My head started hurting when I opened and went deep into all the subvis. All I would like to know what does the output represent?
1. Just the dominant frequency?
2. Amplitude corresponding to that frequency?
3. Phase (relative to what?)
yes, the strongest frequenc
Yep
A tone is assumed to be a sine wave. So if the first point is the positive peak, you would get 90 degrees.
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> Thanks Vix, Joe, and Mad Dog for responding, the site is
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Measuring frequency or amplitude using extract single tone information

Hi All,
I'm trying to read speed of a drill and was hoping that I could use the information extracted from Extract Single Tone Information to get to the speed. However, when I run the attached code while the drill is still off I get Inf for frequency and 0 for amplitude (the waveform chart shows numbers in the 0.21 range - see attached picture). When I turn on the drill the signal amplitude as viewed on the waveform chart jumps to ~4 range, but the frequency continues to read Inf and the amplitude 0. Am I missing something, or using the Extract Single Tone Information incorrectly?
Thanks!
Attachments:
Drill Encoder Test.vi ‏21 KB
Drill Turned Off.JPG ‏38 KB
Drill Turned On.JPG ‏40 KB

Hi,
Thanks so much for your quick response.
As to point 1, I actually see data come in, over time. I could only capture a snapshot of it, hence the photo, but if I continue the run data continues to come in over time. I believe I've fixed the array vs waveform issue (see my modified code). I ended up with that because I was trying (out of desperation) different Analog Wave form function. I'm seeing lots of data, but no actual numberical values for frequency of amplitude.
Thanks again!
Attachments:
Drill Turned Off 2.JPG ‏42 KB
Drill Turned On 2.JPG ‏40 KB
Drill Encoder Test.vi ‏21 KB

Does the Extract Single Tone Information.vi only find the fundamental harmonic?

I capture a waveform that only has 1 frequency. If I use the Extract Single Tone Information.vi to extract a single tone, is this single tone the fundamental harmonic? And if I feed the residual portion of the waveform into the Extract Single Tone Information.vi, will the next tone be the second harmonic? And so on? Is it possible to compute the total harmonic distortion just by feeding the the waveform into the Extract Single Tone Information.vi over and over again (only feed the residual waveform into the vi continously)?
Message Edited by solitude on 08-18-2005 09:28 AM

Notice the title of the vi: Extract SINGLE Tone. It is expecting only one frequency. This vi is not intended to handle a carrier frequency or audio with harmonics. You say that you capture a waveform that has 1 frequency. If this is so, then there should be no harmonics. To measure harmonic frequencies, you must perform spectral analysis. To measure total harmonic distortion, there exists a THD vi in the Waveform Analysis palette.
- tbob
Inventor of the WORM Global

Using Extract Single Tone Information to detect phase

Dear all,
I have problem using Extract Single Tone Information vi to detect phase angle of a sine wave.
I posted similar question a few days ago regarding using the same vi to determine phase angle of a square wave and realised it couldn't be done because square wave is not single tone. I modified my program slightly and use it to examine a sine wave but I still couldn't get reliable results.
Please find the attached for the program code. When I set frequency to 5 Hz, everything worked fine but when I set it to 5.17 Hz with 20 degree phase, the detected phase value keeps changing. Appreciate if you could help me on this matter. Thank you very much!
Best regards
Attachments:
SineWavePhaseAngleTest.vi ‏28 KB

Hi looloo,
Sorry for slow response! Here's the VI back-saved to LV8.2
(in case It's not too late to help...)
The "phase" output reflects the "angle" associated with the beginning value in the Y-array (when Y = amplitude, Phase is 90deg.)
Phase is changing because sine-wave (Y-input) is shifting each time single-tone is called...
Cheers!
"Inside every large program is a small program struggling to get out." (attributed to Tony Hoare)
Attachments:
SineWavePhaseAngleTest[1,LV8.21].vi ‏38 KB

Extract Single Tone Information using Flat Top Windowing

Beginner here - Does anyone have any ideas on what would be the easiest way to create a function that would essentially perform the same function as the built in "Extract Single Tone Information.vi" only that instead of using Hanning windowing (as I noticed that this Vi does) I would be able to use Flat Top (or selectable windowing)? I basicly need to set something up that will accept an incoming Sine wave and apply FFT using Flat Top windowing then output the measured frequency and the amplitude of that frequency. I need to still be able to input the "advanced search" criteria into the VI and give it a frequency and tolerence to look for as I don't want to just look for the peak signal but at specific frequencies.

I am running Labview 7.1.1 (that's what my company uses and they refuse to upgrade). I can't open files built under anything newer than LV7.1.1.
I really don't want to just do a peak search of the entire spectrum and would rather enter a specific frequency to look for and the tolerance window (find peak at say +/- 2% tolerance away from known recorded frequency. This test is targeted as a production test we will be shipping to several parteners around the world to use in production. This will be a test fixture to perform testing on electret boom microphones. The fact that it will be used in a production environment there is potential for high levels of background noise (radios, floresent lights, people talking, etc) and therefore I need as much filtering as possible to only the frequency i am trying to measure. I will be outputting a specific frequency from a speaker and recording it back through the microphone under test via a NI USB-6211 DAQ.
Can anyone tell me if "Extract Single Tone Information fron Hann Spectrum.vi" has anything in it which would limit me to only inputting a Hann windowed FFT into the signal input of that VI? This is the VI which is password protected in my 7.1.1. copy of Labview. If it doesn't and I could feed it a Flat Top windowed FFT signal into it without problem I am golden. I can modify the other sub-vi ("FFT with Hanning") and the main "Extract Single Tone Information 1CH.vi".
Thanks for you continued input.
P.S. I am fairly new to Labview (<2yrs)

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Hello,
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<cfset date1 = DateConvert("Local2UTC", now())>
<cfset date2 = '2014-03-06'> 
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I’m wishing to compare a dateTime that I want something to stop being displayed on the remote server.
<cfset myDate = CreateDateTime(2014,08,05,17,0,0)>
<cfset myDateInUTC = DateAdd("s", GetTimeZoneInfo().UTCTotalOffset, myDate)>
<cfdump var="#myDateInUTC#">
This produces the string: {ts '2014-08-15 07:00:00'} .
I then generate currentUTCDateTime from:
<cfset currentUTCDateTime = DateAdd("s", GetTimeZoneInfo().UTCTotalOffset, now())>
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DateCompare(currentUTCDateTime, "{ts '2014-08-07 15:00:00'}" )
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Why is the amplitude smaller when using the Extract Single Tone VI to measure the amplitude of a signal?

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