• Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

optimization problem

Status
Not open for further replies.

Mateusz

New Member
Hello.
I need some help in solving a cicuit:
upload_2017-2-6_14-36-33.pngupload_2017-2-6_14-36-38.png

-Find Value R4 for which the voltage U34 = 21,6 [V]
-Create and describe the mathematical model of optimization problem using to describe the dependencies in the DC circuit, the method of nodal readable matrix

I add my solution, but in my teacher opinion everything is wrong ;)

upload_2017-2-6_14-46-58.pngupload_2017-2-6_14-48-12.png

I will appreciate any help with that.
With best regards,
Mateusz
 

Attachments

JimB

Super Moderator
Most Helpful Member
Ian,
I think that IZ1, IZ2 and IZ3 are current SOURCES rather than ammeters.

JimB
 

ericgibbs

Well-Known Member
Most Helpful Member
hi,
They are used to demonstrate the students grasp of thevenin and norton theorems in reducing circuits.

E
 

Ian Rogers

User Extraordinaire
Forum Supporter
Most Helpful Member
hi,
They are used to demonstrate the students grasp of thevenin and norton theorems in reducing circuits.

E
I Know.... But even when we did nodal analysis in A/C systems, they were more useful circuits..

I wasn't very good at these... I got 1.02 ohm for R4....
 

ericgibbs

Well-Known Member
Most Helpful Member
I would agree that the problems should be based on every day circuits and applications.

I am a professional engineer, but I prefer to approach and enjoy engineering in a practical way.

E
 

Ian Rogers

User Extraordinaire
Forum Supporter
Most Helpful Member
I have never given analogue electronics much of my time.... Even my projects back in Uni were semi digital even then..

When we sat down and did nodal analysis, I think I was asleep as its really boring to me.. As you know the nearest I get to analogue is a loadcel amp, 4~20mA output, LCD contrast voltage circuits and that's about it!!
 

Ratchit

Well-Known Member
Hello.
I need some help in solving a cicuit:
View attachment 104114View attachment 104115

-Find Value R4 for which the voltage U34 = 21,6 [V]
-Create and describe the mathematical model of optimization problem using to describe the dependencies in the DC circuit, the method of nodal readable matrix

I add my solution, but in my teacher opinion everything is wrong ;)

View attachment 104116View attachment 104118

I will appreciate any help with that.
With best regards,
Mateusz
I don't see that as a big problem. You have three unknowns, the current present in E1, V2, and R4. You can easily find three nodal equations to solve for those three unknowns, right? I can't follow what you are doing now, but it appears like you are calculating up a storm. Why don't you start over and write out those three equations so we can see if you are a right thinker. You can solve them later.

Ratch
 

ericgibbs

Well-Known Member
Most Helpful Member
hi M,
For ref only, LTSpice plot of your circuit

E
 

Attachments

MrAl

Well-Known Member
Most Helpful Member
Hi,

Check to see that the 5.998 is just due to a rounding during the calculations.

If we solve for the voltage U34 we get:
U34=((I3*R3-I2*R3+I1*R3-E1)*R4)/(R4+R3)

and this is interesting because it is independent of some of the components meaning you can look for reasons why this is so if you want to understand circuits better.

Solving that for R4 we get:
R4=(R3*U34)/((I3-I2+I1)*R3-U34-E1)

Plugging in the given values for the components we get:
R4=6 Ohms

That is an exact value not rounded.

The main idea here is that we first solved for the required voltage and then used that solution to solve for what we really wanted to know, which was R4.
 
Last edited:
Status
Not open for further replies.

EE World Online Articles

Loading
Top