Show a resonant curve in a simulation between 800hz and 4.5khz

[leejohnson222]

Homework Statement

Vs = 10 V @ 1.5 kHz, R = 15 Ω, L = 2.7 mH and C = 1.8 μF
produce a resonance curve for the circuit between 800 Hz
and 4.5 kHz.

Relevant Equations

no equations are needed

i have created the circuit but i am not sure what to do from here, this program is new to me

 

[Baluncore]

You have a voltage source, probably with zero internal resistance. A current will flow through the individual parallel RLC components, but there will not be resonance, because the components are short-circuited by the voltage source.

If you replaced the voltage source with a current source, LC resonance would be possible.

 

[leejohnson222]

ok i can change the VS but what would i set the current to? and would it be Peak or RMS ?
i tried a few times and it keeps giving me errors, i dont know how to use this simulation correctly

 

[berkeman]

Was this assigned schoolwork? Or did you make the whole question up as part of trying to learn SPICE simulations? As Baluncore says, the circuit will not experience resonance as drawn. You could experiment with adding source resistance to your AC voltage source, which is another way to start getting some resonant behavior out of that parallel "tank" circuit.

 

[leejohnson222]

yes is school work, but i have never used multisim before so its a learning curve even using it,
there were a few other questions before this one

 

[berkeman]

yes is school work

And that circuit was given in this resonance assignment? Probably time to have a talk with the instructor... (do you understand what Baluncore and I are saying about the problem with that schematic?)

i have never used multisim before

Neither have I. But I've used several SPICE packages over the years.

 

[leejohnson222]

i see what your saying and i have answered all the previous questions, which are as follows,

a.To what frequency would the voltage source, VS, need to be adjusted to in order for the circuit to be 
resonant? 

b. Given resonance in this circuit, what will be the current drawn from the voltage source? 

c. What would happen in this circuit if the power source was changed from AC to DC?
d. Use a simulator to produce a resonance curve for the circuit between 800 Hz 
and 4.5 kHz.

i have never used a sim before, so its all new

 

[berkeman]

i see what your saying and i have answered all the previous questions, which are as follows,

a.To what frequency would the voltage source, VS, need to be adjusted to in order for the circuit to be 
resonant? 

b. Given resonance in this circuit, what will be the current drawn from the voltage source? 

c. What would happen in this circuit if the power source was changed from AC to DC?
d. Use a simulator to produce a resonance curve for the circuit between 800 Hz 
and 4.5 kHz.

i have never used a sim before, so its all new

Well, the answer to a. is "To infinity, and beyond!" J/K

But seriously, the only way that circuit can go resonant is if there is some reasonable internal series resistance specified for the voltage source. Do you see the $R_s$ option for that voltage source in Multisim? Are you sure that the only specification for the AC voltage source for this problem is $V_s = 10V @ 1.5 kHz$?

 

[Baluncore]

ok i can change the VS but what would i set the current to? and would it be Peak or RMS ?

You have a simulator, so you can try several different values. Start with 1 mA, or 1 amp.

Why did you select that simulator?
Simulation allows you to quickly try many possibilities at low cost, it can be like a video game.

When you get errors reported, try to find out why. You can make the game easy. I would reduce the complexity of the simulation circuit until something works, then build on that.

We do not know what errors are being reported, you have not asked us, so we cannot help. Where can we find the user manual for the simulator version you are using?

 

[berkeman]

Here is an image of the configuration page for an AC independent voltage source in LTSpice. Note the availability of $R_s$ on the right-hand side...

https://spiceman.net/ltspice-voltage-source-setting/

 

[leejohnson222]

You have a simulator, so you can try several different values. Start with 1 mA, or 1 amp.

Why did you select that simulator?
Simulation allows you to quickly try many possibilities at low cost, it can be like a video game.

When you get errors reported, try to find out why. You can make the game easy. I would reduce the complexity of the simulation circuit until something works, then build on that.

We do not know what errors are being reported, you have not asked us, so we cannot help. Where can we find the user manual for the simulator version you are using?

i used this one as its an online version and it works, i was recommended LTspice but my mac wouldnt install it, kept saying the HD would not allow it or something strange

 

[berkeman]

i used this one as its an online version and it works, i was recommended LTspice but my mac wouldnt install it, kept saying the HD would not allow it or something strange

It would be weird if it were a certificate error, since the install is from a large and well-known company. Can you try again and post the error you are seeing?

 

[leejohnson222]

yeah of course, here you go, i tried the 2nd HD and it said you can only install where the OS is installed

 

[berkeman]

Weird. I know nothing about Macs, but those disk names don't look valid to me. Don't you have something like a C: drive? Those look like virtual drives or something? We may need to repost this issue in the PF Computing/Software forums if it's not easy to figure out here...

 

[leejohnson222]

i would be happy to get LT spice working to get some direct advice and help with this question.
I did have an issue with the hd a few months back and i was told the name is incorrect and i need to change it as i couldnt install the new OS, i will try that first, but i need to back up everything as it will possibly wipe my drive. Thinking about it, i have a work laptop, maybe i could install it on there

 

[berkeman]

Thinking about it, i have a work laptop, maybe i could install it on there

Windows or Mac?

 

[leejohnson222]

Windows or Mac?

oh sorry windows

 

[berkeman]

Oh, yay! Hopefully that install goes better. Let us know what you find.

For an initial value for $R_s$ in LTSpice, I'd use a value around the parallel resistance value, and then step that up to 10x and 100x that value to see how much the Q of the resonance grows...

 

[The Electrician]

Homework Statement: Vs = 10 V @ 1.5 kHz, R = 15 Ω, L = 2.7 mH and C = 1.8 μF
produce a resonance curve for the circuit between 800 Hz
and 4.5 kHz.
Relevant Equations: no equations are needed

i have created the circuit but i am not sure what to do from here, this program is new to meView attachment 334691

Your problem as you have stated it wants you to "produce a resonance curve". It's not asking you for a curve of any particular property of the circuit, such as a voltage appearing somewhere in the circuit.

How about a plot of the impedance vs. frequency as seen by the voltage source? Or a plot of the current vs. frequency supplied by the voltage source?

 

[leejohnson222]

ok its installed, i managed to create the circuit, but will need some help as i have even less of a clue on how to use this program, maybe its as you said, it may not be about the actual circuit with the settings given,
maybe they just want me to create a resonance curve ??

 

[Baluncore]

The LTspice learning curve is steep, and the help is cryptic.
Ask questions here for help.
Here is a starter circuit to get you going.
Remove the extra .txt extension to make it into a .asc file
Click on the resonance_1.asc file to load it with LTspice.
Run it.
Click with mouse on the 'out' label to plot out voltage and phase; V(out).
Hover mouse over L1, click to get a plot of L1 current and phase; I(L1)
Change the resistor values and try again.

 

[leejohnson222]

ok so this has an added level of frustration as i have not used a windows computer for years,
on the windows laptop it doesnt show the full extension .txt so i can not change it, i checked in properties and cant see how to do it anywhere else. could you maybe upload and provide a sendspace.com link here?
see the picture of the first circuit i created for this question

 

[Baluncore]

Go to the Windows pull down menu for that folder
Tools, Folder options, View,
Uncheck "Hide extensions for known file types".

 

[leejohnson222]

great so i have it working now, right i see the resonance, so basically there are 2 parts being looked here, is this current and voltage across the frequency and magnitude scale

 

[Baluncore]

This is the homework forum, so we should not do the work for you.
One circuit is excited by 1 amp, the other is excited by 1 volt.
Voltage sources have zero output resistance, so the LC circuit is driven through R.
Current sources have infinite output resistance, so the RLC circuit has R in parallel.

You have the simulator working now, so you can change the component values and look at different currents, voltages, and differential voltages.
To edit things, right-click on values or command text.
Change the L and C values to change the resonant frequency.
R sets the Q of the circuit, try different values.

Be productive, play LTspice simulation of circuits, not video games.

 

[leejohnson222]

ok i see what your saying this is very helpful, especially as i was already struggling with multisim, Ltspice is another program with different ways of doing things, so it is very helpful to me, as you say i will play with this and see what i can learn from it. One more question i noticed the way the C value is 1pico8 is this how you input different values with the SI unit in the middle

 

[berkeman]

One more question i noticed the way the C value is 1pico8 is this how you input different values with the SI unit in the middle

Sorry, where are you seeing this? For C1?

I would expect the value field to show 1.8u for C1...

https://ltwiki.org/LTspiceHelp/LTspiceHelp/A_General_Structure_and_Conventions.htm

 

[leejohnson222]

it shows up on both capacitors and the inductors, with the SI in the middle like 1K5 i assumed it was 1.5K ?

 

[Baluncore]

One more question i noticed the way the C value is 1pico8 is this how you input different values with the SI unit in the middle

On schematics, the decimal point is replaced with the SI multiplier, so 1.8uH becomes 1u8, 1.8u would also work.
NEVER enter the unit H or F as part of the value.
Only the first alpha character is significant.
A 1F5 capacitor is 1.5 femtofarad, not 1.5 farad.
1.5 picofarad is 1p5
1.5 milliohm is 1m5
1.5 megohm is 1MEG5

 

[leejohnson222]

very useful information, thank you, helps me avoid making mistakes with this sim

 

[leejohnson222]

this is what i have so far, looks like a very wide curve here

 

[Baluncore]

this is what i have so far, looks like a very wide curve here

The Q of the resonance is low, because the resistor value is too low.
Work out the reactance of the L or the C at the centre frequency, give the resistor that value in ohms. Then increase that resistor value by 10, 100, 1000, to reduce the damping of the resonance, to see a sharper resonance with higher Q.

 

[berkeman]

Then increase that resistor value by 10, 100, 1000, to reduce the damping of the resonance, to see a sharper resonance with higher Q.

Also, a tip for you as an early SPICE user is that you can set up simulations to run in "steps", so that you get multiple plots on the same graph for multiple step values...

https://qucs-help.readthedocs.io/en/spice4qucs/ASim.html

 

[The Electrician]

You have a voltage source, probably with zero internal resistance. A current will flow through the individual parallel RLC components, but there will not be resonance, because the components are short-circuited by the voltage source.

If you replaced the voltage source with a current source, LC resonance would be possible.

So called "resonance curves" can be concave up (like a notch filter) or concave down. If a simulation is run on the circuit of post #1 and the current supplied by the voltage source (call it Is) is plotted, the result will be a low Q, concave up, "resonance curve". Plotting the reciprocal of Is (1/Is) will result in a concave down "resonance curve". Increasing the value of R1 to 150 ohms gives nicer looking "resonance curves". The 1/Is curve will have the same shape as plotting the impedance seen by the voltage source.

 

[The Electrician]

Here's what I get for various plots. I plotted over a wider frequency range. The red curve is the impedance seen by the voltage source in post #1. The blue curve is Vo from the right hand circuit of post #31. The green curve is the current supplied by the voltage source in post #1.

If I increase the value of all the 15 ohm resistors to 150 ohms I get these curves: