Measuring Voltage Mean and Standard Deviation simultaenously using VIs for a Tektronix DPO 3034 Oscilloscope and other measurements

[rexreignbeaux]

Hi all,

I am currently trying to measure Voltage Mean and Standard Deviation simultaenously with the LabVIEW 2013 Tektronix DPO MSO 2000 4000 Series Fetch Waveform Measurement VI. After the initialising and configuration VIs I have two different instances of the Fetch Waveform Measurement VI; one to measure voltage mean, one to measure standard deviation. However, I am aware that they will not run simultaneously in the described arrangement of VIs because of race conditions. Would this mean that I am measuring the values for two different waveforms, measured at (ever so slightly) different times? If so, is there a way I can obtain the Voltage Mean and Standard Deviation  at the same time for the same waveform using/by modifying the Tektronix VIs? The waveforms I am measuring are of a pulse train from a laser of constant rep rate and (roughly) constant amplitude, so the data is periodic.

I would also be interested in knowing if I could measure the voltage peak height of each individual pulse using the Tektronix VIs.

Thank you for any help/advice!

[RTSLVU]

Without seeing your code we can only guess, so here goes...

How about doing a single sweep and taking all your measurements on the single sweep waveform? 

[Kyle97330]

I had a similar problem but I was using a DPO2014 scope.  I think they're pretty similar in capability.

Basically I did what RTSLVU suggested.  Instead of using "Read waveform measurement" to get one value, use just the "Read" VI to get the whole waveform.  After that, you can use that waveform output with all of the standard waveform measurement VIs (found in Programming --> Waveform --> Analog waveform --> Measurements) to get multiple measurements.  Or analyze the waveform array directly.

The other option is that you can turn off continuous acquisition.  That should leave the last waveform on the screen, you can take multiple measurements, then enable one more acquisition.  Repeat.

[crossrulz]

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@Kyle97330 wrote:

The other option is that you can turn off continuous acquisition.  That should leave the last waveform on the screen, you can take multiple measurements, then enable one more acquisition.  Repeat.

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This is what I've always done for automated test where the scope is doing the actual calculation.  Using the continuous acquisition introduces way to many variables to the measurements.

[rexreignbeaux]

Sorry I was in such a rush yesterday evening. I've attached the screenshot of the VI (Screenshot of Two Waveform Measurements VI.jpg) to this reply.

I have tried your (and Kyle97330's) suggestion (single sweep) and am using the Amplitude and Levels.vi (implemented as shown in Screenshot of Edge-Triggered Waveform Measurements VI.jpg) found in Programming --> Waveform --> Analog waveform --> Measurements to get the amplitude, high state level and low state level values of the waveform I am recording. Are these values averages calculated from the whole waveform? If not, is it even possible to calculate the averages for the amplitude, high state level and low state level values for each pulse period of the waveform using any of the waveform measurement VIs?

Thanks again to everyone who has replied.

[Kyle97330]

The "Amplitude and levels" VI checks the whole waveform.  

If you want to check just one pulse at a time, you'll need to slice the waveform into pieces.  There's a "Get waveform subset" function on the Programming --> Waveform palette.  

If your pulses have predictable timing, you can use this to slice up your one waveform into X waveforms and analyze each separately.  If it's irregular pulses, you can try using the "Peak detect" VI in the Programming --> Waveform --> Analog waveform --> Measurements --> Waveform monitoring palette twice (once for peaks, once for valleys) to get an array of Amplitudes and either use that as your pulse heights array or use that for the timing of when to slice up the waveform to analyze separately.