Author Topic: Reconstructing a waveform from its harmonics.  (Read 8008 times)

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Offline rstofer

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Re: Reconstructing a waveform from its harmonics.
« Reply #100 on: March 16, 2018, 05:04:34 pm »
Congratulations!

I have used Fourier Analysis exactly once since I graduated in '73.  I was looking at the 11th and 13th harmonics generated by a 10 MW 12 pulse rectifier.  It was interesting to get the expected FFT and not at all useful to the transformer manufacturer when I was questioning the heating effects.



 

Offline rstofer

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Re: Reconstructing a waveform from its harmonics.
« Reply #101 on: March 16, 2018, 05:15:10 pm »
I have The Fourier Transform and Its Application" 2nd ed.  I'm pretty sure they all have the dictionary of transforms.  It's one of the reasons it was so popular.  It's mathematically rigorous, though not at the level of "Operational Mathematics" by Churchill.  The latter consumed much of my life for two semesters. 

Book prices have gotten crazy.  Publishers like to push out new editions even though they are not justified in order to obsolete older editions.  But it makes the old edition cheap.  If you're building a personal library that's the way to go.


I have bought quite a few used books from Alibris and some new ones.  As you say, the prices are completely out of sight for new texts.  For my grandson's library, we are buying all textbooks as 'new' and planning to hold on to them forever.  I still have most of my college texts and I wish I hadn't sold a couple of them.  I also have duplicate copies of his textbooks.  Gotta try and keep up!

I have a couple of years to brush up before my grandson gets to signal processing.  In fact, his proposed major of computer engineering may not even get that far; I haven't seen the entire curriculum.  What I have seen of the lower division stuff is 4 computer science classes and only one circuit analysis course.  I don't know what the upper division stuff will look like.

He's vacillating between computer engineering and civil engineering.  Robots or dirt work.  I know which choice I would make.

 

Offline Simon

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Re: Reconstructing a waveform from its harmonics.
« Reply #102 on: March 16, 2018, 05:23:20 pm »
well I'm just skipping through resistor colour codes, so exciting this university level education.............
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Offline rhb

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Re: Reconstructing a waveform from its harmonics.
« Reply #103 on: March 16, 2018, 08:04:33 pm »
He's vacillating between computer engineering and civil engineering.  Robots or dirt work.  I know which choice I would make.

Civil engineering has the advantage that much of it can't be sent offshore.

I'm of the opinion that whatever the field, an MS is needed to do professional work.  Traditionally the MS has always been the professional degree in  geology.  A BS would just get you a lab technician job. And by the time I was in school, law was also a 2nd degree field just as medicine had become.  Now I look at how much math you need for any engineering field and I just don't see any way that someone can learn that and learn an engineering discipline in 4-5 years.  Sadly, all the universities, even Stanford, are producing an increasing number of crap graduates.   And according to some, "rigor is racist", though I suspect they would not like the consequences of applying that to aircraft engineering.

I'm glad Simon got through his travails OK.
 

Offline rstofer

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Re: Reconstructing a waveform from its harmonics.
« Reply #104 on: March 17, 2018, 12:23:22 am »
He's vacillating between computer engineering and civil engineering.  Robots or dirt work.  I know which choice I would make.

Civil engineering has the advantage that much of it can't be sent offshore.

This is true for all of the professional engineering fields.  An ideal career is one where you have to lay hands on the product.  Your field is also a good example!

Quote

I'm of the opinion that whatever the field, an MS is needed to do professional work.  Traditionally the MS has always been the professional degree in  geology.  A BS would just get you a lab technician job. And by the time I was in school, law was also a 2nd degree field just as medicine had become.  Now I look at how much math you need for any engineering field and I just don't see any way that someone can learn that and learn an engineering discipline in 4-5 years.  Sadly, all the universities, even Stanford, are producing an increasing number of crap graduates.   And according to some, "rigor is racist", though I suspect they would not like the consequences of applying that to aircraft engineering.

I'm glad Simon got through his travails OK.

I went through the same thought  process when I decided to go for an MSEE.  It was a sweet deal because my employer paid the bills.

One of the reasons for the 4 year internship for budding Professional Engineers is that you CAN'T really learn the profession in school.

There are a number of fields where rigor is required.  Nuclear (weapons or energy) is one of them.  Aviation, space flight (although there are stories...) and some others.  All of the professional engineering fields.  Automotive is another, we can't have steering wheels falling off - hey Ford!  Get it fixed!

 

Offline rhb

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Re: Reconstructing a waveform from its harmonics.
« Reply #105 on: March 17, 2018, 12:51:43 am »
Computer and electronics engineering can certainly be sent offshore.  They may not be any good, but they have "credentials".  I encountered a pair of Indian CS grads who spent 4 hours trying to redirect stderr from a program for which they did not have the source into a file.  They called to me as I was passing by.  It took me 5 minutes to write a program that wrote to stderr and stdout and a program to call it with stderr redirected to a file.

They'd been hired because a manager didn't want to hire me.  He told me to my face when we met at my interview.  He ultimately became my primary client in the company.  The Indians and everything they produced went away.  Unfortunately, India is not the only place producing such breathtakingly incompetent graduates.
 

Offline rstofer

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Re: Reconstructing a waveform from its harmonics.
« Reply #106 on: March 17, 2018, 01:13:11 am »
Computer and electronics engineering can certainly be sent offshore. 

They can and they are.  Even with all of that, the Bureau of Labor Statistics shows phenomenal job growth in these fields.  I have been pushing a little toward robotics and I will eventually nudge toward AI.  That's where I see the job growth.  You will either work on robots or be replaced by them.  Even burger flippers are becoming an endangered species.

OTOH, many graduating engineers don't actually work in their major.  One chip designer I met had a degree in Astrophysics.  Here he was designing chips (I don't recall if he was doing analog or digital).  At the BS level, all you really know how to do is work the math.  Turns out, math is useful in just about every field.
 

Offline rhb

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Re: Reconstructing a waveform from its harmonics.
« Reply #107 on: March 17, 2018, 01:39:38 am »
I'm a strong advocate of a liberal arts undergraduate program.  Not the fru-fru stuff popular now, but the liberal arts degree of 100 years ago which was roughly equal parts history, literature, mathematics and science.  My undergraduate degree was a bit short on math, just algebra and trig which bored me to tears as I had taught myself algebra in 5th & 6th grade and trig in 7th and 8th.  But lots of science and literature.  I read 4-5 full length novels a week.  About half were for a class and the others were because I'd read the author for a class and wanted to read more.  I made up for the math deficiency in my MS.  I was required to take Calculus I and it was so much fun I took II & III and DiffEq.  When I went to Austin fo pursue a PhD most of my effort was focused on math.  Now I look at "new" stuff and typically find it's just a familiar bit of math in new clothes.  Sparse L1 pursuits being the big exception.  It really is new.  People were doing it, but the rigorous justification didn't exist.  Much as it took the mathematicians a long time to  justify Fourier and Heaviside.
 

Online BrianHG

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Re: Reconstructing a waveform from its harmonics.
« Reply #108 on: March 17, 2018, 01:43:32 am »
Well I am sure you will all be surprised to know that I got a distinction on this assignment. Standards are really much lower than I thought. One question went unanswered and I blagged a few by explaining how I arrived at the answer without using the expected techniques.

My new module "digital and analogue electronics" looks like a bit of a joke from the assignments that I can mostly do without the study material.
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Offline amspire

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Re: Reconstructing a waveform from its harmonics.
« Reply #109 on: March 17, 2018, 01:59:52 am »
My new module "digital and analogue electronics" looks like a bit of a joke from the assignments that I can mostly do without the study material.
It is pretty normal to have an introductory course in Electronics - not everyone who starts an electrical engineering degree knows what an opamp or a 2-input NAND gate is. Hopefully, you will quickly get into the real electronics design courses. From the 2nd year on, the course usually gets a lot tougher.
 

Offline Simon

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Re: Reconstructing a waveform from its harmonics.
« Reply #110 on: March 17, 2018, 07:42:32 am »
My new module "digital and analogue electronics" looks like a bit of a joke from the assignments that I can mostly do without the study material.
It is pretty normal to have an introductory course in Electronics - not everyone who starts an electrical engineering degree knows what an opamp or a 2-input NAND gate is. Hopefully, you will quickly get into the real electronics design courses. From the 2nd year on, the course usually gets a lot tougher.

No I am doing a HNC, that is 1 year of uni. I wanted to do opamps, transistors, EMC and electronic design, but these are all level 5 modules and I am only allowed to do one for a HNC and the other 3 have to be level 4 which is the mamby pamby rubbish. I am just repeating my A levels........ once I am near the end I should speak to my employer about a HND (second year) and basically i just carry on to do another 8 modules presumably this time the level 5's are allowed.
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Offline Simon

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Re: Reconstructing a waveform from its harmonics.
« Reply #111 on: March 17, 2018, 07:43:59 am »
here, have a laugh on the UK education system.....
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Offline amspire

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Re: Reconstructing a waveform from its harmonics.
« Reply #112 on: March 17, 2018, 08:59:33 am »
here, have a laugh on the UK education system.....
Pretty mind-numbing. The IC informations seems to be from the 1970's. 1 million transistors is a large scale memory chip and 1-100 million transistors needs a whole wafer.  :-DD

According to that table, a single 15 Billion transistor nVidia Tesla chip would need 150 wafers to make! I don't even want to think about the biggest ram and SSD chips.

I do hate exams based on courses like that because they usually do not want accurate answers. If they asked if a diode was an active or passive device and you said it can be both active and passive, you would probably be marked as wrong.

It did start to get into some actual formulae at the end.

 

Offline Simon

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Re: Reconstructing a waveform from its harmonics.
« Reply #113 on: March 17, 2018, 09:06:13 am »
Well I am just reading about simetrix 6 with screenshots in windows XP, they do point out that the program might be a later version due to constant updates and indeed the version I downloaded is 8. It would be good to get to grips with "a" PSPICE program.

The first assignment i need to do is attached. the only question I can't answer off the top of my head I could probably learn about in 10 minutes on google.
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Offline amspire

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Re: Reconstructing a waveform from its harmonics.
« Reply #114 on: March 17, 2018, 09:58:01 am »
The nicest Spice program for beginners would be LTSpice. It is an excellent free tool.

http://www.linear.com/designtools/software/

I think there is a Student PSpice that can be used for free in a limited way.

The best opensource SPICE is probably ngSpice. There is a variant CUSPICE that can use recent models of nVidia GPU's to accelerate the calculations, but for the type of circuits in your course, Spice running on a CPU is totally fine.

Spice basically runs from a text file, and it may be your course will require you to run it this way.

The Spice with a GUI such as LTSpice automatically translate the circuit to a Spice text file, and automatically graphs the output. You can insert raw Spice directives from the GUI.
 

Offline Simon

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Re: Reconstructing a waveform from its harmonics.
« Reply #115 on: March 17, 2018, 10:08:33 am »
They use simetrix which is similar to LTspice which I have also used and found to be unrefined and clunky. They explained the concept of the concept of the text file (netlist ?) but no they are not that archaic. They failed te explain clearly that PSPICE is the simulator core that a number of programs use and provide an interface to.
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Re: Reconstructing a waveform from its harmonics.
« Reply #116 on: March 17, 2018, 11:28:17 am »
is it me or are they making hard work out of explaining op amps ? never heard it called "open loop amplification" before.
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Re: Reconstructing a waveform from its harmonics.
« Reply #117 on: March 17, 2018, 12:03:14 pm »
The explanation of the schmitt trigger comparator/op amp circuit is the most fucked up thing I have ever seen.........
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Offline Mechatrommer

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Re: Reconstructing a waveform from its harmonics.
« Reply #118 on: March 17, 2018, 12:04:10 pm »
is it me or are they making hard work out of explaining op amps ? never heard it called "open loop amplification" before.
https://en.wikipedia.org/wiki/Open-loop_gain the graph plot usually available in most opamp datasheet. we can estimate the opamp respond at desired closed loop gain (i'm not sure i'm not EE at any Degree)

here, have a laugh on the UK education system.....
i know your pain. the material mostly for kids who are eager to learn something. for adult who has touched something, those materials will be boring. just be patience ;)

I wanted to do opamps, transistors, EMC and electronic design, but these are all level 5 modules and I am only allowed to do one for a HNC and the other 3 have to be level 4 which is the mamby pamby rubbish.
be carefull of what you expect. solely just designing some opamps and transistors can be learnt from home alone with internet. i will expect you will be faced with something like, stability compensation in phasor or laplace domain trying to solve all holes and poles in number equations. not for the faint hearted. you may as well join the club of Donna Riley's campaign... Rigor is not good! ;D Good luck!
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Offline Simon

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Re: Reconstructing a waveform from its harmonics.
« Reply #119 on: March 17, 2018, 12:10:09 pm »
But this is year 1 at university.......... i did all this in my A levels........ and the explanations are confusing at best. yes I know opamps in general and yes the stability analysis will be a challenge but for what else does one go to university ? With a thorough grounding in op amps I can design a low drop out regulator without it oscillating. As i am i rely on intuition.
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Offline Mechatrommer

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Re: Reconstructing a waveform from its harmonics.
« Reply #120 on: March 17, 2018, 12:26:33 pm »
As i am i rely on intuition.
we know you can design something, even military grade, but this is not how academic institutions work, take your time to get acquainted. ;)
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Offline Mechatrommer

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Re: Reconstructing a waveform from its harmonics.
« Reply #121 on: March 17, 2018, 12:38:18 pm »
the only problem with education (at least at my place during my time) i saw is the facilitators, lecturers, teachers etc failed to relate what they are teaching with real life problems and application (contextual learning) but this is not entirely their fault, maybe due to lack of budget, time constraint, goverment or education policies etc. if someone can relate between theories and applications more, the gap between practitioners who never went to school, and students who never went to field can be closed together. having said that, practitioners should keep track what theories behind what they are doing to get some idea, students also should be exposed to real world field/work/problem environment more during their learning in college/university... the education is not at fault, usually the economy and politics is... imho..
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Offline Simon

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Re: Reconstructing a waveform from its harmonics.
« Reply #122 on: March 17, 2018, 12:46:30 pm »
yes well the problem in the UK is that universities have to self fund. and the government wants to trumpet how many more graduates they produced than the last administration so they allow a race to the bottom that solves both problems. the courses are easier so more students can complete them so the government get the figures they want and the universities get the money they need from students
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Offline rhb

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Re: Reconstructing a waveform from its harmonics.
« Reply #123 on: March 17, 2018, 01:11:31 pm »
The fundamental problem is the "everyone should go to university" model combined with the denigration of books in favor of electronic media.  So instead of the students having carefully vetted texts, they have sloppily produced videos and notes.  The result is ever more poorly trained graduates going out to train even more poorly trained graduates.  It's become a scam for the benefit of the faculty and staff.

Moreover, some people don't know the subject well enough to actually teach. I enrolled in an upper division  graduate level  electrostatics class.  The 2nd or 3rd meeting the instructor was deriving the equations for a charged particle in free space.   He was referring to his notes the whole time which is always a bad sign.  At one point he wrote out an equation which I didn't understand where it had come from.  So I asked him how he got that from the previous equation. "Oh, that's the way you do it."  After sitting in stunned silence for a few minutes I figured out that the transition was via a trig substitution.  I didn't need the course for anything.  I just picked it because it looked as if it would be interesting.  So after class, I went directly to the admin office and dropped the class. I did not get my doctorate because of a personality conflict that arose with my supervisor.  But a classmate who did not know Snell's law did get his.  I seem to recall he did a post doc at Stanford before finding a job.

The object of education is to convey the logic of the topic.  This guy was just writing his class notes on the board.  This was 30 years ago at UT Austin which is very highly ranked school.  I rather fear there are many more, even worse, examples now.

From your comments, you should definitely get a copy of "The Art of Electronics" and read it cover to cover a couple of times.   Don't bother with the problems on the first reading.  That's just for surveying the territory.  On the 2nd reading work selected problems and build circuits that interest you. Keep it all in a notebook with a sewn binding.  There's a lab manual for AoE, but I read that it is poorly edited and full of errors.  Read a bunch of articles  Jim Williams and Bob Pease wrote for EDN and other trade magazines.  Especially read, "Max Wien, Mr. Hewlett and a Rainy Sunday Afternoon".

Collect a personal library covering the material.  For example, get 2-3 books on op amps, 2-3 on network analysis, etc.  Look for books referenced by other books, especially H & H. I used to visit 3 used books stores every weekend when I lived in Dallas.  Over the course of 10 years I built a very good library doing that.  It's still a significant investment, but I've made my money back many times over.  The reason for multiple books is everyone leaves something out or bungles an explanation.  If you watch a really good professor as I have had the privilege of doing, they will cover the same thing from multiple few points during their presentation.

The ultimate goal is not to know the answer.  No one can remember everything.  The goal is to be able to find the answer to whatever questions come along.
 

Offline Simon

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Re: Reconstructing a waveform from its harmonics.
« Reply #124 on: March 17, 2018, 06:16:30 pm »


The ultimate goal is not to know the answer.  No one can remember everything.  The goal is to be able to find the answer to whatever questions come along.

Maybe that is why they gave me a merit for using intuition instead of the techniques i was supposed to.
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