Hi, I'm Sam Foster, an R&D engineer at Keysight Technologies. Today I'll be talking about
the IntegraVision Power Analyzer's harmonics, topics which I did not cover in my first harmonics
video which can be found – if you missed it – at a link in the video description.
Today I have my harmonics already set up and I will be talking about the DFT trace, how
to scale its X and Y axes, and also a discussion about inner harmonics and how we actually
bucket our harmonics. If you are interested in getting at frequency content above 30 KHz.
I will show you how to do that with the math FFT. A DFT trace is actually this purple trace
down here. Now I'll run a single. This tells you a lot of interesting information about
the actual frequency spectrum. Looking at the left side bar here, we see the total harmonic
distortion, the source, fundamental, number of harmonics, and harmonic duration measurement
period. All the numbers below here are actually specific to the DFT trace. We have the DFT
peak, which is the maximum value – usually the fundamental. We have 13.98 dB here. The
Y scale, which is 36.7 dB per division; the X scale, 240 hertz per division, and then
a frequency reference which is the maximum value of the Y axis here. To be able to scale
this, I will simply click on the math button and you will get some controls to be able
to move things around. This knob here will scale the math DFT up and down. I can change
the offset up and down, and if you are interested in seeing this as an RMS value, you can change
the Y units. Because I am using a 60 Hz signal, I would like to zoom in a little bit on the
fundamental. So, I'll change the top frequency here to 200 Hz. You can see the waveform is
scaled for you. I will be defining a term here, referring to this figure. I'll be defining
the pure tone as the frequency content at exactly the harmonic frequency. The inner
harmonics I will define as all the frequency content between pure tones, and a harmonic
group is what this picture shows as half of the inner harmonics to the left, half of the
inner harmonics to the right, some together with the pure tone. That is actually how we
bucket our harmonics and are the values that you see in the table view here. If you wanted
to get an idea of what your pure tone and inner harmonics are, that is where the IntegraVision's
cursor and waveform tracking mode come in handy. I will click here on cursors, flip
the mode to track waveform, and change my X1 and X2 source to that math 4 waveform.
Here, what will happen in tracking waveform is I'll move my X cursor and the Y cursor
will snap to the value there. Here, I've placed my first X cursor on the pure tone, and here
on the Y1 cursor readout we see 13.96 dB. To get an idea of inner harmonics, I can go
and look at the 65 Hz bin and I can see in the Y2 a value there for the 70 Hz,
75 hertz, and so on and so forth until you get to the next pure tone. This will be a
very useful tool for you to look at your inner harmonics. If you are interested in looking
at things about 30 KHz, which is the frequency limit to the DFT, I will go ahead and click
on math again and actually look at the screen FFT rather than the DFT. Putting my box back
in run mode and adjusting my horizontal, I will run another single. Exactly the same
controls for scaling the Y and X are available to you for the math FFT. So, I will go ahead
and set my scale and offset appropriately and you can see the start and stop frequency
are the same as before, but now we have a stop frequency of much higher – 2.5 MHz.
If you wanted something above 30 KHz, you could easily set the start frequency to, say,
30 KHz, and maybe the stop to 200 KHz. You can see the waveform scaled on the screen
for you and all of that higher frequency content is available. That is all I have for you today
on the DFT trace, harmonic bucketing and inner harmonics, and the math FFT trace for higher
frequency content. Until next time, thanks for watching.