Author Topic: What you do with math channels on oscilloscope?  (Read 8609 times)

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Offline David Hess

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Re: What you do with math channels on oscilloscope?
« Reply #25 on: September 29, 2018, 01:12:40 pm »
If you have access to a very fast-rise step (square wave) generator then you can almost instantaneously measure the frequency response of the scope from DC to its bandwidth limit. You can do the same for any device under test between the step generator and the scope (a filter, etc).

This requires measuring the step, averaging that to remove noise, taking the derivative of the average, and finally taking the FFT of that derivative.

And if the FFT also returns the phase information, then aligning the trigger correctly will produce a full Bode plot with amplitude and phase.
 

Offline Smokey

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Re: What you do with math channels on oscilloscope?
« Reply #26 on: September 29, 2018, 01:36:17 pm »
Hello Everyone...  I'm just starting out (but I'm SUPER excited about electronics!) and I heard on a web form that beginners should get an analog oscilloscope for their first scope so I picked up a Tek 465 for a really good deal.  None of the knobs are missing!  Here's a picture!


Anyways... All this math channel talk sounds really interesting, but I'm having a really hard time trying to figure out how to get my Tek 456 math functions to work. 
Can someone please help me find the FFT button on my scope.. I've looked everywhere!!

Thanks!
 

Offline bsfeechannel

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Re: What you do with math channels on oscilloscope?
« Reply #27 on: September 29, 2018, 03:09:32 pm »
I used AxB in this video to calculate the instant power and derive the real power consumed by the isolation transformer I built a while ago. Since my scope is a Rigol DS1052E, I had to calculate the integral using the old school technique of measuring the area under the curve by hand.

.

In this other video I used A-B to get a three-phase reading out of a car alternator, using the only two channels my Rigol has.



In the video I just posted today I used FFT. So even with a humble scope like the venerable Rigol DS1052E, math is quite a handy tool.

« Last Edit: September 29, 2018, 03:18:14 pm by bsfeechannel »
 
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Offline dazz1

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Re: What you do with math channels on oscilloscope?
« Reply #28 on: September 29, 2018, 06:58:46 pm »
Hello Everyone...  I'm just starting out (but I'm SUPER excited about electronics!) and I heard on a web form that beginners should get an analog oscilloscope for their first scope so I picked up a Tek 465 for a really good deal.  None of the knobs are missing!  Here's a picture!


Anyways... All this math channel talk sounds really interesting, but I'm having a really hard time trying to figure out how to get my Tek 456 math functions to work. 
Can someone please help me find the FFT button on my scope.. I've looked everywhere!!

Thanks!

You will find it is the grey, white or red knob.  Occasionally it is the silver one but in all cases they may or may not have numbers and letters.    On this particular model of scope, the FFT knob is not actually called FFT.  Often it is easier to find the correct knob with all the lights out and with the room is in complete darkness.    If you have any further questions, feel free to ask someone else.  Hope this all helps in your quest.
 

Offline MrW0lf

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Re: What you do with math channels on oscilloscope?
« Reply #29 on: September 29, 2018, 10:09:32 pm »
This requires measuring the step, averaging that to remove noise, taking the derivative of the average, and finally taking the FFT of that derivative.

I wonder if any of the low- to midrange knobbed DSOs could do that? I can dot it both on AD2 (required GUI script) and Picos (required custom math).

None of the knobs are missing!

You are not missing a knob but magic mushrooms. Back in the wild days one would consume them until reaching state of free conversion between time and frequency domains.


 

Offline David Hess

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Re: What you do with math channels on oscilloscope?
« Reply #30 on: September 30, 2018, 02:30:23 pm »
This requires measuring the step, averaging that to remove noise, taking the derivative of the average, and finally taking the FFT of that derivative.

I wonder if any of the low- to midrange knobbed DSOs could do that? I can dot it both on AD2 (required GUI script) and Picos (required custom math).

None that I know of.  Most mid range DSOs cannot either.  Some 20+ year old DSOs can though.

Anyways... All this math channel talk sounds really interesting, but I'm having a really hard time trying to figure out how to get my Tek 456 math functions to work. 
Can someone please help me find the FFT button on my scope.. I've looked everywhere!!

FFTs on the Tektronix 465 require option 1401.
« Last Edit: September 30, 2018, 02:36:24 pm by David Hess »
 

Online nctnico

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Re: What you do with math channels on oscilloscope?
« Reply #31 on: September 30, 2018, 09:11:02 pm »
This requires measuring the step, averaging that to remove noise, taking the derivative of the average, and finally taking the FFT of that derivative.
I wonder if any of the low- to midrange knobbed DSOs could do that? I can dot it both on AD2 (required GUI script) and Picos (required custom math).
Not that I know of. On most scopes FFT is a seperate mode and not a math operation.
There are small lies, big lies and then there is what is on the screen of your oscilloscope.
 

Online rstofer

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Re: What you do with math channels on oscilloscope?
« Reply #32 on: October 01, 2018, 02:26:03 am »
I tried to help someone over at Pico forum with some math stuff that ended up with creating excessive test environment :P Thought share it here also maybe useful to someone.
<snip>

Your projects look like an excellent demo for Pico Scope!  Which model are you using?
My Analog Discovery is nice and it can be scripted but on its best day I'm not sure it will do the things you are doing.  It's pretty clear my Tek 485 won't do anything other than add/subtract.  The DS1054Z is a lot better but, if math is the issue, it's nowhere near what you are doing with the Pico Scope.

I think I am beginning to want one!

 

Offline MrW0lf

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Re: What you do with math channels on oscilloscope?
« Reply #33 on: October 01, 2018, 04:33:41 am »
Your projects look like an excellent demo for Pico Scope!  Which model are you using?
My Analog Discovery is nice and it can be scripted but on its best day I'm not sure it will do the things you are doing.  It's pretty clear my Tek 485 won't do anything other than add/subtract.  The DS1054Z is a lot better but, if math is the issue, it's nowhere near what you are doing with the Pico Scope.

Hi, thanks for kind words, I just did choose to help get low- to midrange scoping out of the dark ages, not because this is easy, but because it is hard |O Fighting with most fierce bugs hidden deep in the math core lair and measuring thins far beyond measure :-/O

Over the time I had several models. Phase formula investigation was done on oldest 25MHz 2205. So all that circus was working on top of 2ch scope with 16k of memory :) When need more power I have 2408B 4ch 100MHz 128MS and for ultimate challenges something bit faster also. Considering what toys you have there I would not look for something ordinary but perhaps more specialized. 5000D FlexRes is 8...16bit but need read specs carefully because higher bit modes drop in sampling rate. Then there is 4444 differential 1000V CAT III. 4000 series has other specialized scopes also, for example 8 channel non-differential.
If compare to AD2 they similar yet quite different. Software in general is much easier to use for "normal" tasks. There are special modes (ETS, DPO, rapid sequential). Main mode I would call "analytical" and this similar to AD2 only operation mode in its pros and cons vs ordinary knobbed DSO. Creating complex scoping environment with many windows is much easier with Pico and all the zooming etc more handy. However in-GUI post-processing wise one is "limited" to math channels which do have bugs and tricks that need to know if doing heavy stuff. Think that post-processing is main thing going for AD2 if directly compare. Scripting is scripting. You cannot do everything with just formulas. However raw power is of course not there with AD2 so for me it is mostly a learning tool. In fact just finishing little derivation/integration/phase angle scripts for it since there are no built in functions for that. As by product managed to do TDT. Will post these also sooner or later.
« Last Edit: October 01, 2018, 05:57:17 am by MrW0lf »
 

Offline Scratch.HTF

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Re: What you do with math channels on oscilloscope?
« Reply #34 on: October 02, 2018, 10:46:02 am »
Following Ohm's Law, (Voltage / Current) calculates dynamic resistance at a given point and (Current * Voltage) calculates dynamic wattage at a given point (both are done using a current probe).
And when you FFT dynamic AC wattage, you can get information on produced harmonics.
If it runs on Linux, there is some hackability in it.
 

Offline MrW0lf

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Re: What you do with math channels on oscilloscope?
« Reply #35 on: December 19, 2018, 03:46:39 am »
On some scopes one cannot manually set vertical reference level for pulse width calculation and some other functions. On my scope it is automatic and defaults to middle of the signal: positive_peak - (peak_to_peak / 2). Below is workaround for setting calculation reference level to 0V, so reference can be steered around with DC offset. Two functions for each case, one for scopes with abs(x) function, other without.

Clip signal -100mV...+100mV:
((abs(A-0.1)-(A-0.1))-(abs(A+0.1)-(A+0.1)))/-2+0.1
((sqrt((A-0.1)*(A-0.1))-(A-0.1))-(sqrt((A+0.1)*(A+0.1))-(A+0.1)))/-2+0.1


Some other potentially useful functions:

Extract positive part from signal:
(-abs(A)+A)/-2
(-sqrt(A*A)+A)/-2


Extract negative part from signal:
(abs(A)-A)/-2
(sqrt(A*A)-A)/-2




As can see LowPulseWidth(Clip) matches cursors on zero level.
« Last Edit: December 19, 2018, 03:49:34 am by MrW0lf »
 

Online vk6zgo

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Re: What you do with math channels on oscilloscope?
« Reply #36 on: December 19, 2018, 02:45:36 pm »
Hello Everyone...  I'm just starting out (but I'm SUPER excited about electronics!) and I heard on a web form that beginners should get an analog oscilloscope for their first scope so I picked up a Tek 465 for a really good deal.  None of the knobs are missing!  Here's a picture!


Anyways... All this math channel talk sounds really interesting, but I'm having a really hard time trying to figure out how to get my Tek 456 math functions to work. 
Can someone please help me find the FFT button on my scope.. I've looked everywhere!!

Thanks!
I don't know quite why earlier posters thought it was funny to tell you a lot of nonsense, but here is the answer to your question.

On Analog Oscilloscopes, the maths functions are limited to "A-B" & "A+B" , where "A" & "B" denote two vertical channels.
This was done in hardware, so the more complex mathematical functions would have been prohibitively costly to implement.

With DSOs, all such functions can be done in firmware, in most cases, or loaded as software in some others.

FFT also is something relatively easy to do in DSOs, & extremely difficult to do in Analog 'scopes.for the same reason.
The FFT function in DSOs can be good, or quite poor, depending upon the implementation.

A real Spectrum Analyser still offers superior performance.
Some Analog 'scopes had SA "plugins"or adaptors as accessories, like the 4401 adaptor for your 465.
 

Offline Smokey

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Re: What you do with math channels on oscilloscope?
« Reply #37 on: December 19, 2018, 03:47:07 pm »
Hello Everyone...  I'm just starting out (but I'm SUPER excited about electronics!) and I heard on a web form that beginners should get an analog oscilloscope for their first scope so I picked up a Tek 465 for a really good deal.  None of the knobs are missing! 

Anyways... All this math channel talk sounds really interesting, but I'm having a really hard time trying to figure out how to get my Tek 456 math functions to work. 
Can someone please help me find the FFT button on my scope.. I've looked everywhere!!

Thanks!
I don't know quite why earlier posters thought it was funny to tell you a lot of nonsense....
>:D
.... Because their sarcasm detectors were set a little more sensitive than yours :)
 

Online vk6zgo

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Re: What you do with math channels on oscilloscope?
« Reply #38 on: December 19, 2018, 06:26:49 pm »
Hello Everyone...  I'm just starting out (but I'm SUPER excited about electronics!) and I heard on a web form that beginners should get an analog oscilloscope for their first scope so I picked up a Tek 465 for a really good deal.  None of the knobs are missing! 

Anyways... All this math channel talk sounds really interesting, but I'm having a really hard time trying to figure out how to get my Tek 456 math functions to work. 
Can someone please help me find the FFT button on my scope.. I've looked everywhere!!

Thanks!
I don't know quite why earlier posters thought it was funny to tell you a lot of nonsense....
>:D
.... Because their sarcasm detectors were set a little more sensitive than yours :)

Your posting sounded so much like many ones we get, so the sarcasm detector didn't pick it up in the noise.
The master stroke was "disappearing" for a while, exactly as a knowledge challenged "noob" would.
That convinced me.-----Well Played!
 


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