Siglent 1104X-E Automatically capture frequency of max voltage of sweep of coil? - Page 1
Forum section: electronics / testgear

author: t1d
author_rank: Super Contributor
timestamp: January 05, 2023, 03:37:49 am
content: Scope Skill Level = Novice. But, I have a rather nice lab and equipment.Goal: I want to find the resonate frequency of a coil.Method: I will inject a frequency sweep and investigate the output’s maximum voltage amplitude.I know that my scope can easily capture the max voltage and tell me what it is. But, can it also automatically tell me at what frequency the max voltage was encountered? If so, what are the scope settings.All of the methods that I have studied have the operator watching the sweep and noting the maximum him/herself, visually. I would think that the scope would have a mathematical function that would make the determination automatically (and more precisely,) but I do not know how to set up my specific scope. The scope setup is what I need help with.Please and thank you.PS: I apologize for this being poorly written, but I am not feeling well.

author: noisyee
author_rank: Contributor
timestamp: January 05, 2023, 09:09:20 am
content: Scopes don't know what max voltage is but we know (or we can predict). So the trick is how to capture what we want.Sorry I don't have a coil to demonstrate, but I have a very high Q crystal filter.Just set trigger level high enough (to where the scope can barely trigger) to capture only the resonate in a sweep, then the scope can easily measure the frequency.If we want observe the whole sweep while measure the resonate frequency, we can use the same trick to set trigger (to “freeze” the sweep to a certain position) and use gate mode to measure certain part of the captured waveform.Or try bode plot to measure the resonate property.

author: t1d
author_rank: Super Contributor
timestamp: January 06, 2023, 04:48:55 am
content: Quote from: noisyee on January 05, 2023, 09:09:20 amThanks, noisyee; that's good information. My scope does have a set of math functions that will find the max/min voltage. I was hopeful that it would have the ability to tell me the frequency at the moment of highest/lowest amplitude. But, your methods are very clever and I do like them. I will try them and add them to my skill set. I have never used the FFT function. I wonder if it might be useful for this application?

author: noisyee
author_rank: Contributor
timestamp: January 06, 2023, 10:13:07 am
content: Quote from: t1d on January 06, 2023, 04:48:55 amFFT is a powerful tool, it's also helpful in this application.Use the Max Hold display mode in the FFT while continuous sweeping, we can get frequency response (or to be strict, amplitude response rather than magnitude response) of the DUT. I use this trick all the time.But it require some setting tweak to get better result. e.g, if we want more frequency resolution, we need more FFT points, which increase calculate time and slow down the measurement.

author: t1d
author_rank: Super Contributor
timestamp: January 06, 2023, 11:11:24 am
content: Quote from: noisyee on January 06, 2023, 10:13:07 amThat is a good trick, noisyee, and I will give it a go.I briefly scanned my scope's manual and it looks like I may have a Bode Plot function. But, there may be caveats... 1) The manual clearly states that this function only works if you have a Siglent function generator. Mine is a Rigol. But, there may be a hack to work around this. So, I will need to investigate that. 2) This may be a pay-to-play add on feature and I did not buy any of those.I did try just using manual methods to sweep the frequency. And, yes, that is not a particularly hard thing to do. But, as said, I would like to learn to do it automatically, if my scope is capable of doing that.My results are posted below, in a separate post. There, I will just sharing the fun that I am having.

author: t1d
author_rank: Super Contributor
timestamp: January 06, 2023, 11:19:06 am
content: Here is where I played with learning the previously mentioned testing protocol for determining the resonate frequency of a coil = Pix3.First, I DIY’d the LED light indicator = Pix1/Blue board = One of my 1206 breakout boards, with the needed protection resistor and the two LEDs in polar opposition.Second, I DIY’d a random coil = Pix1/White cylinder = 24ga magnet wire wound on a nylon cylinder.Third, I set up the test rig on a breadboard = Pix1 = Notice that I did not use a Near Field Probe. More on this, later.Forth, I manually swept the bandwidth. I immediately noted a large amount of noise and added a 0.1uF cap across the LEDs = Pix1/Yellow Cap. This greatly reduced the noise and increased the output voltage amplitude. More on this, later.ResultsThe coil’s resonate frequency was determined to be approximately 19.23MHz = Pix4. The input voltage amplitude was 2.3Vpp = Pix2. The output voltage amplitude was 12.4Vpp (Pix4,) being a ratio of 12.4/2.3 = 5.4:1.ConclusionsA breadboard always adds unknown and undesirable influences.The test rig was highly sensitive to ambient influences. Even touching the scope controls added capacitance and greatly changed the output voltage amplitude reading. Increasing the scope’s voltage amplitude sensitivity exacerbated the problem. A more precise reading of the resonate frequency would likely require lab isolation equipment beyond my hobbyist level.Adding the cap across the coil may be a violation of testing protocol. Meaning, I may have created a different type of circuit, entirely. Might this be called a LC Tank Circuit? If so, the test results may be wholly useless. It comes to mind that changing the cap value might have changed the resonate frequency. Thoughts?You may have noted that in Pix1 the LEDs are not illuminated. The circuit was running, but my frequency generator can only output 2.3Vpp at 19.23MHz. That is not enough voltage to illuminate the LEDs. As the LEDs do not provide visual feedback, they will be removed for future testing. This will also remove any influence that they might contribute.I forgot to use a Near Field Probe. This surely influenced the test results, likely to the point of wholly negating them. I plan to test again with the a NFP. I will let you know of my future findings.Anyway, I am learning and having fun. Cheers.

author: t1d
author_rank: Super Contributor
timestamp: January 10, 2023, 11:42:30 pm
content: Quote from: noisyee on January 06, 2023, 10:13:07 amI am homing in on your trick...- Math Button- Operator = FFT- Tools- Type = Peaks- Show Table = On- Show Frequency = OnThis displays a chart of frequencies and their amplitudes.Next step is to find the Max Hold function. This is good progress! Thanks noisyee!

author: t1d
author_rank: Super Contributor
timestamp: January 11, 2023, 12:27:33 am
content: I did discover that the Bode Plot function requires that I have a Siglent Function Generator. Oops, I already said that.

author: ozkarah
author_rank: Regular Contributor
timestamp: January 11, 2023, 01:09:21 am
content: There are some gateway projects simulating Siglent AWG using different branded AWGs.SCPI is used for that. You might wanna check out.

author: t1d
author_rank: Super Contributor
timestamp: January 11, 2023, 11:20:43 am
content: Quote from: ozkarah on January 11, 2023, 01:09:21 amThank you for your help, ozkarah. Much appreciated. I could use some help with your terminology, please. I am not familiar with "gateway projects," though I guess that the term is somewhat self-explanatory. And "SCPI?"

author: pope
author_rank: Frequent Contributor
timestamp: January 11, 2023, 12:19:39 pm
content: Something like this.

author: t1d
author_rank: Super Contributor
timestamp: January 11, 2023, 03:02:40 pm
content: Quote from: pope on January 11, 2023, 12:19:39 pmExcellent! Thank you.