Use a simulator to produce a resonance curve for this RLC circuit

[leejohnson222]

Homework Statement

RLC series circuit

Vs (10 +j20) R = 100 Xl = +300 Xc = -j200

use a simulator to produce a resonance curve for the circuit between 800 Hz
and 4.5 kHz.

Relevant Equations

i would convert the given numbers so they can be used in a sim,
so
impedance Z = R + j (lL - Xc)
Xl = 2pifL
Xc = 1/ 2pifC1

Then i think you would need to convert Xl and Xc into L and C using the formulas
L = Xl/ 2pif

C = -1 /2pifXc

my issue here is what would i put in for frequency ? unless i use the formula to find the resonance frequency
i have only used multisim live and you cant put in Vs 10 +j20

 

[gneill]

my issue here is what would i put in for frequency ? unless i use the formula to find the resonance frequency
i have only used multisim live and you cant put in Vs 10 +j20

You could pick an arbitrary frequency between the given values, such as the midpoint, 2650 Hz. Then solve for the components from there. You weren't given a specific value of frequency, only a range that (presumably) the resonance would occur in.

As for the voltage source, $V_s$, that specifies a magnitude and angle (not the frequency!)
So find the magnitude and angle from the given value. You should be able to specify the magnitude and angle in the source voltage in multisim?

 

[leejohnson222]

ok makes sense to pick the mid point of the frequency for the formulas as this is what the questions wants me to look at. I think the imedance of the circuit is (100 + j100) and i think Current = (0.149 + j0.049)a
so V = I x Z ?

 

[gneill]

ok makes sense to pick the mid point of the frequency for the formulas as this is what the questions wants me to look at. I think the imedance of the circuit is (100 + j100) and i think Current = (0.149 + j0.049)a
so V = I x Z ?

You've already got the voltage, no? The current is just $I = V_s/Z$.

 

[leejohnson222]

i have the given Voltage but i can see how i can enter that form into multism, it wants voltage and freq
unless im missing some options, i need to do the maths to work out the L and C then draw up the circuit in the sim

 

[gneill]

i have the given Voltage but i can see how i can enter that form into multism, it wants voltage and freq
unless im missing some options, i need to do the maths to work out the L and C then draw up the circuit in the sim

In LTSPICE the voltage source gives you the option of SINE and you can specify the AC voltage and Frequency, as well as a value for Phi, the angular offset.

I don't know what Multisim gives (I don't have it installed, or signed up for the online version). But surely there must be some option for specifying the angle of the source? If you can do a screenshot of the options for the source voltage, maybe we can take a look?

Edit: Changed Theta to Phi.

 

[leejohnson222]

LT spice sounds like a good option, i can not get it to install on my mac

 

[leejohnson222]

Vs magnitude is this the formula ? Sq root (102 + 202) i think i am getting myself mixed up, multism wont allow me to not enter a frequency for voltage, not sure what to use for that

i think i have made an error here as the question says L = +300 ohms C = -j200ohms
so they are not Xl and Xc

 

[gneill]

Vs magnitude is this the formula ? Sq root (102 + 202) i think i am getting myself mixed up, multism wont allow me to not enter a frequency for voltage, not sure what to use for that

For a Bode plot (sweeping through multiple frequencies) you'll want to specify the voltage and frequencies in a different way. There should be some entries equivalent to LTSPICE's 'Small signal AC analysis' in the setup for the voltage source, probably shown as magnitude and phase?

For the bode plot you'll have to work out how Multisim does that. Probably some setting for AC Analysis, as opposed to Transient Analysis. You'll specify the frequency range there I think.

i think i have made an error here as the question says L = +300 ohms C = -j200ohms
so they are not Xl and Xc

I think that those are impedances (Z), and there's a typo for the inductance: Should be L = +j300 ohms. Inductances have +j impedances and capacitance have -j impedances. They really shouldn't have used L and C for those values, as those symbols represent the real values of inductance and capacitance (henries and farads), not their impedances.

 

[leejohnson222]

yes this is where i am getting mixed up as the circuit says L and C but no units for L or C, so as you say they may be impedance rather than henries or farads.
I will get spice running on my computer and see how i get on, thank you

 

[Baluncore]

Something is missing from this puzzle, lost in translation.
Is there a link somewhere to the original question or challenge ?

 

[leejohnson222]

yes here,
use a simulation and produce a resonance curve for the circuit between 800h and 4.5 kHz.