# Help me with PSpice, please.

Discussion in 'Homework Help' started by wiz0r, May 7, 2008.

1. ### wiz0r Thread Starter Active Member

May 2, 2008
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Hello,

On the first attachment you will see the RLC circuit that I drew with PSpice. What I need to do is to plot V(t) of the resistance number 4 (R4) on a 10 sec interval starting at t = 0 using a 100 m sec step size.

The switch is closed, and it will open at t = 0.

On the second attachment, you will see each value that I'm using to plot V(t). Is everything right here?

On the third attachment is the plot of V(t), which doesn't seem to be right in my opinion. Is it just 4? No change over time?

Can anyone tell me what I'm doing wrong? It doesn't seem to be right, so please, help me out.

Any help will be gladly appreciated.

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2. ### JoeJester AAC Fanatic!

Apr 26, 2005
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Did your instructor state that the capacitor was fully charged?

If the capacitor is not charged at just before t0, then everything to the left of the switch is not consequential to the circuit, just superfluous parts.

Since your meter only shows a straight line voltage, it appears you didn't have the initial conditions of zero.

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3. ### wiz0r Thread Starter Active Member

May 2, 2008
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Greetings JoeJester,

First of all, thanks for the responce.

Second, no, the capacitor is not fully charged just before t=0.

Now, what do you mean by setting the initial conditions to zero? Is that double clicking on both the L, and C and make the IC to 0V? If so, I already did that.. if that's not it could you please explain it further?

Thanks a lot.

Last edited: May 8, 2008
4. ### JoeJester AAC Fanatic!

Apr 26, 2005
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I started the transient analysis with "zero initial values". I could have choosen use initial conditions or calculate operating point.

Your plot indicates the transient analysis has calculated the operating point.

I'm not familiar with pSpice to give you the absolute correct answer. Your pSpice reference should have the solution. Look at the options under transient analysis.

5. ### wiz0r Thread Starter Active Member

May 2, 2008
64
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Dang, there's definitely something wrong with what I'm doing. All of the plots (VR1, VR2, IR1, IR1, etc, etc) they all are straight lines.

I tried what you said JoeJester, and put nothing on the initial condition of both the Capacitor and the Inductor, and nothing changed.

So, bleh, I don't know what to do. My book says to put the initial conditions to zero, I did that, and still, nothing changed. They are all straight lines.

I attached the Transient analysis, again, if you could check it that'd be great.

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6. ### wiz0r Thread Starter Active Member

May 2, 2008
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Mm, well I figured I have a problem with my switch. If you can, JoeJester could you post the attributes of your switch?

Thanks a lot.

7. ### JoeJester AAC Fanatic!

Apr 26, 2005
3,315
1,109
Switch is always open.

If at t=0 the switch opens ... it's useless. That's why I asked about the initial charging on the capacitors.

You could redo the circuit with an additional switch that closes at t=0 between the current source and R3. Then your plot might work.

Like I said, I am not familiar with the pSpice program. A pSpice reference should tell you how to do it with every initial value at zero. It might be as simple as starting the current source and voltage source with an initial value of 0.

What does "skip initial transient solution" do to the plots?

Last edited: May 8, 2008
8. ### wiz0r Thread Starter Active Member

May 2, 2008
64
0
Hello JoeJester,

For my case "skip initial transient solution" does nothing. However, I did found the initial conditons.

Before the switch opens, the voltage of the Capacitor is 3.2V, and the current of the Inductor is 1.6A.

How would that change the plot you made?

Hope you can answer me today, because the work is due tomorrow at 7:30 AM.

Thanks a lot.

9. ### JoeJester AAC Fanatic!

Apr 26, 2005
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1,109
make the initial conditions on the two supplies also zero.

At t0, everything should be zero. At t0 plus 1 attosecond, the two supplies can be at their rated values. The switch opens at t0, so the voltage at the junction of R1 and R2 will not reach the junction of Isource and R3.

What program are you using?

replace that time activated switch with a normally open switch. See if that get's you the proper plot.

I had my time activated switch both closing and opening at t=0.

10. ### wiz0r Thread Starter Active Member

May 2, 2008
64
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Mm, well, how can I set the initials conditons of the sources to 0? The program only lets me to put the DC Voltage/Current.

I'm using PSpice 9.1 Student Edition, it is free you can download it here;

The only switches I can use with this PSpice is a time activated Open or Closed switch. :X Dang, I would do anything to have the correct plot.

11. ### JoeJester AAC Fanatic!

Apr 26, 2005
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First ... kill all the initial conditions you've set.

Attached is the schematic, the plot, and the transient analysis settings I used.

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• ###### Plot_pSpice.PNG
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Last edited: May 9, 2008
12. ### wiz0r Thread Starter Active Member

May 2, 2008
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O:

God, I owe you so big. Thank you so much, JoeJester.

I'll try to fix everything now, thank you, thank you. :]

One last question, did you edit any of the attributes of the switch?

13. ### JoeJester AAC Fanatic!

Apr 26, 2005
3,315
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No. I just looked at the switch and saw that it OPENED at t=0.

14. ### wiz0r Thread Starter Active Member

May 2, 2008
64
0
YES, I GOT IT. WOOT, I love YOU JoeJester!

Thank you so much, you are my hero. YOU made my day. :]