Is it true that you forgot all about mesh, nodal, KCL, KVL, Thevenin, Norton and don't use them as an engineer?

Thread Starter

hanhan100

Joined Apr 8, 2022
6
The excerpt is taken from this. I completely agree with most of the part he said there.
However, I want to discuss about the yellow part with real engineers.
Is it true that you forgot all about mesh, nodal, KCL, KVL, Thevenin, Norton stuff and don't use them as an engineer?

1672759437994.png
 

nsaspook

Joined Aug 27, 2009
12,749
Yes, and no. You don't usually sit down with a quill pen and calculate. It's intrinsic to the thought process of how you see circuits at the circuit theory level. You black-box (using knowledge gained from experience and intuition from that experience) nodes as an abstraction of the needed total functionality..
 

ZCochran98

Joined Jul 24, 2018
303
I still use these analyses myself, though like others have said, you grow an intuition for things and don't necessarily have to sit down and put pen to paper. The concepts are still used, even if I'm not exactly calculating the node voltage here or the branch current there.
Of course, some of these principles start getting REALLY hard to properly use if you're doing things in RF frequencies, as things aren't just nice, lumped elements or wires.
 

MrChips

Joined Oct 2, 2009
30,448
It is like asking, do you forget all about geometry, trigonometry, algebra, calculus, differential equations when you become an engineer?
The answer is no. You still use all of the above in your career.

What the writer Peter Hand said is total crap!
 

drjohsmith

Joined Dec 13, 2021
850
The excerpt is taken from this. I completely agree with most of the part he said there.
However, I want to discuss about the yellow part with real engineers.
Is it true that you forgot all about mesh, nodal, KCL, KVL, Thevenin, Norton stuff and don't use them as an engineer?

View attachment 284383
Id go even further
The majority of bits I've learnt over the decades, i do not regularly use

BUT
I know they exist,
what I have learnt affects how I aproach and analyse
I know where to find the information when I do need it

example recently
I've note used smith charts for almost half a century
just before Christmas had a problem that was solved by smith charts,
took a few days to get up to speed, but got there and found the answer,
 

WBahn

Joined Mar 31, 2012
29,843
I strongly disagree with that particular claim. I used all of those on a very regular basis when designing ICs and the larger systems that used them.

While I definitely agree that much more time should be devoted to using and learning to read data sheets, his approach, goes way too far and is, sadly, all too common. What does he do when the output of the 7805 is not 5 V because the external circuit gets loaded down so that the input voltage no longer satisfies the dropout voltage requirement. Sure, he can look at the data sheet all day long to see what the dropout voltage requirement is, but if he can't perform basic circuit analysis on the surrounding circuitry, how will he figure out that he is violating it? His answer is probably to run a simulation -- but aside from the let-the-computer-do-my-thinking-for-me attitude, that will only work to the degree that the simulation is faithful to the circuit, including the behavior of the 7805 when the dropout voltage requirements aren't satisfied.
 

dcbingaman

Joined Jun 30, 2021
1,065
Being they are tools used for circuit analysis they are almost always used to some degree, during my career as an EE:
Mesh - Rarely
Nodal -Almost never
KCL - All the time! Both intuitively and mathematically
KVL - All the time! Both intuitively and mathematically
Thevenin - All the time, intuitively and mathematically
Norton - Rare to never

You never mentioned 'super-position' but I use that probably most of all being most circuits contain multiple sources and tend to be LTI.

We do it all the time at least intuitively, like the following:

1672786672509.png
If I gave this to an EE who could not tell me what Vout is in terms of V1 and V2 without a calculator, I probably would not hire them.
 

nsaspook

Joined Aug 27, 2009
12,749
I still use these analyses myself, though like others have said, you grow an intuition for things and don't necessarily have to sit down and put pen to paper. The concepts are still used, even if I'm not exactly calculating the node voltage here or the branch current there.
Of course, some of these principles start getting REALLY hard to properly use if you're doing things in RF frequencies, as things aren't just nice, lumped elements or wires.
You don't need to even be in the RF domain with the non-conservative nature of E fields involving induction.

https://www.physicsforums.com/insights/circuit-analysis-assumptions/
 

drjohsmith

Joined Dec 13, 2021
850
My first job was as a microwave engineer. Waveguides at 200 MHz.
Now days I design boards with digits at 400 Gbps .
I still use striplines etc, and talk about en fields , it's just digits now ,and I have SW that allows us to design ,
Then it was a lot more intuitive .
Still have to teach youngsters why they can't put GHz signals down ribbon cable.
Don't use the maths , but it's there as backup.
You have to learn the maths to know it's there for when you do need it .
 

KeithWalker

Joined Jul 10, 2017
3,026
The mathematical tools that we learn and understand are available to us for the rest of our lives, even if we rarely use them. As an example, in my youth I struggled to understand calculus as it was taught by a very unapproachable theoretical math teacher. Fifty years later I was writing a very complex vibration analysis program using Fourier analysis. While transposing data from velocity to acceleration and back, I suddenly realized that I was using and understanding the calculus I had been taught, for the very first time, to actually do something in the real world.
 

MrChips

Joined Oct 2, 2009
30,448
Sadly, so much depends on the ability and enthusiasm of your teacher.
In a similar and positive vein, I had a fantastic teacher in Latin class in grade school.

How much Latin do I use today?

You would be amazed how much Latin is used daily in everyday language, especially as I am learning to speak French and Spanish (Italian is next on the list).
 

ErnieM

Joined Apr 24, 2011
8,374
A couple of jobs ago I was being interviewed by the Engineering Manager and his chief engineer who I knew from a previous job where he was the Engineering Manager.

Anyway, the manager drew out a circuit with several sources and resistors and asked me what some voltage was. I proceeded to section it off into Thevenin equivalents to get a much easier problem to solve. While I did not get "his answer" they were both impressed I took this approach and they figured I just bumbled the math due to interview jitters.

Aside: I also mentioned I was working on a job the chief engineer did back in the day and what I took from it was his use of capacitors. Circuit took two values multiple times and he selected different voltage ratings to give them two different sizes of what today would be called SMD caps. That impressed them both.

Summation: back at home I reworked the problem given, and if you actually did the math as I did you got my answer, as opposed to eyeballing it to get the wrong answer.

BTW, I outlasted that manager who was "retired" (with cause) a year later. Smart man, but did not check his own work.
 

MisterBill2

Joined Jan 23, 2018
17,754
Those methods described are a foundation, and they are handy tools when the need arises. The one part I never used is matrix math but I can see where it may have uses. Superposition is very handy if it can be applied correctly, it is too easy to get signs wrong so care is needed. KVL is occasionally vital, likewise KCL, but not during most weeks. Usually to explain things to some who do engineering for a living, not being engineers. Thermodynamics and kinetics are also vital, at least the concepts and the realities they describe.
What has been very valuable, which I did not anticipate, were the writing classes, especially technical writing, and public speaking. Standing in front of a room full of CEOs and making sense is very important when it has to be done. No second chances there.
 

BitsNBytes

Joined Mar 22, 2021
35
Being they are tools used for circuit analysis they are almost always used to some degree, during my career as an EE:
Mesh - Rarely
Nodal -Almost never
KCL - All the time! Both intuitively and mathematically
KVL - All the time! Both intuitively and mathematically
Thevenin - All the time, intuitively and mathematically
Norton - Rare to never

You never mentioned 'super-position' but I use that probably most of all being most circuits contain multiple sources and tend to be LTI.

We do it all the time at least intuitively, like the following:

View attachment 284403
If I gave this to an EE who could not tell me what Vout is in terms of V1 and V2 without a calculator, I probably would not hire them.
I agree. I use and I encourage my team to keep their skills sharp. I use KVL, KCL, and, Superposition, and Thevenin almost daily.

I will say though, it honestly depends on your role as a practicing engineer. Since I am in the semiconductor industry, I am always analyzing customer circuits, and building my own. I can see other positions in engineering that you may not use these skills. We can mull over if this is unfortunate or not, but the reality is the career choice does help to dictate the skills you need. Personally I find the "You should know this!" a little bothersome. We all have unique skill sets and levels of knowledge.

There are a lot of topics that I am aware of, and by no means an expert. At least I can ask the good questions and seek assistance.
 

MrChips

Joined Oct 2, 2009
30,448
I find this attitude prevalent among students who are bored and unmotivated in class. They don't see the reason for having to learn something that they will never use in a later career. Learning the fundamentals and having to use them daily on the job are two different things. We see the same attitude towards having to learn how to code in ASM.
 

panic mode

Joined Oct 10, 2011
2,644
when it comes to actual job, some things may not be used much while also one may need to learn a lot that university program did not cover. things that i do not use i may not remember much from top of my head but i may be able to quickly derive it and if not, i know how to look them up when needed. but i strongly disagree with comment of Peter Hand that most of the things are forgotten within a month. that may be his case but he should not generalize or speak on behalf of others. for example KVL, KCL, superposition, voltage divider etc are so basic they are part of any electrical work including troubleshooting. one may not need to write the equations out on a piece of paper, most of the time things can be processed in the head.
about math... i do a lot of robot programming and math involves 3D transforms, forward and inverse kinematics etc. without matrices this would be way harder. in my job algebra, trigs, calculus, physics etc all come in handy. i would like to see him find and read datasheet that has tabulated results of all 3D transforms etc.

then he ends it by blaming others... smh
 
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MisterBill2

Joined Jan 23, 2018
17,754
Consider that just because somebody has a really good word processing writing program on a computer, and a skilful way with words, does not mean that they have any sense or actually a clue as to what they are talking, or writing, about.
 
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