Signal Information - Frequency

Signal Information - Frequency, a forum discussion on Cleverscope Mixed Signal USB Oscilloscopes. Join us for more discussions on Signal Information - Frequency on our Questions forum.

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timothy.coulter

12th April
Posts: 9

I have noticed that the signal information window will sometimes give incorrect frequency measurements when I am looking at only a few cycles in the waveform. When you increase the time scale to see more cycles, the frequency will jump to the correct value.

Using the cursors is the best way to measure a frequency of interest, but the signal information should also be accurate for a few cycles.
rhcarter rhcarter

12th April
Posts: 114

Hi Tim,
I have just tried it here with the latest build and the frequency is calculated at about 1.6 cycles and does not change no matter how many more cycles are added. Is there a lot of noise on your signal? Can you perhaps share a screen shot or send the apc file to support at cleverscope.com

Regards,
Roger
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timothy.coulter

25th April
Posts: 9

Hopefully these snippets attach to this post. I thought I originally attached the images to my first post. The signal information gives different results for the frequency of the square wave, depending on how many cycles are in view.

bartschroder

25th April
Posts: 481

Hi Tim,
Sadly I do not see any snippets. What I can say is that we calculate the frequency by doing an FFT on the signal, and then finding the highest amplitude component, and then displaying that as the frequency.
Some waveforms can be quite complex.

If you are measuring a square wave, and you have only one and a bit cycles, then there is a lot of high frequency information in there that dominates. You will need at least two full cycles to see the frequency. greatest accuracy on a square wave is achieved with three or more cycles. With a sine one just a bit more than one full cycle is enough.

If you are interested in the pulse frequency, which uses edges instead of an FFT, then on the Signal Information display, on the bottom centre titled 'Time Info' select Pulse as the signal type. You will still need one complete cycle, but now frequency is calculated using edges.

I hope this helps.

timothy.coulter

25th April
Posts: 9

Hi Bart,
For some reason I cannot see the images that I am attaching to my post. Regardless, we will be sure to view multiple cycles of the square wave when determining the frequency in the signal information window.
bartschroder

26th April
Posts: 481

Hi Tim,
We will investigate the images problem.
Did you see that if you use Pulse Information, and the signal is a square wave of some sort, then you'll get the frequency with just one cycle. It uses edges to calculate the frequency.
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