hello

I have this

the values are
1uF
151mH
4700 ohm

I put this together on multisim to find resonance using the ac analysis option but all that happened was a high pass filter. does the capacitor short circuit as the frequency increases. I have to calculate the resonant frequency and im not sure how to do that.

 

Why do you need to put it togerher on multisim to find the resonant frequency? If associative learning kicked in, you already know the resonant frequency.

Start your bode plot at 1 hz or 0.1 hz

If your starting it higher it will look like low pass filter.

You have another fine example of low Q circuit.

 

Why do you need to put it togerher on multisim to find the resonant frequency? If associative learning kicked in, you already know the resonant frequency.

Start your bode plot at 1 hz or 0.1 hz

If your starting it higher it will look like low pass filter.

You have another fine example of low Q circuit.

thanks Joe!
what I meant to say was, I have a nice picture from the AC analysis function on multisim that shows bandwidth and resonant frequency. I cant get the bandwidth or resonant frequency. I know that at resonant the impedance will be maximum so it should look the opposite of what I have for the series circuit. I think I know how to calculate the resonant frequency. I already know the values, I think the formula is different than series but there is a resistor in there. I am thinking, work out the RL circuit first, then that in parallel with the capacitor?

cheers!!!

simon

 

The current will be minimum at resonace in this circuit. In my youth, this was an antiresonant circuit while the series RLC was called resonant .... With maximum current flow.

 

The current will be minimum at resonace in this circuit. In my youth, this was an antiresonant circuit while the series RLC was called resonant .... With maximum current flow.

hello Joe

thanks for your help!

I have put this in multisim and tried to get an AC analysis, this is what I get. so this is a low pass filter?

 

Please start your AC analysis from 0.1Hz

 

That circuit has a damping factor much greater than 1 so will show no resonant peak. R must be less than 777Ω to reduce the damping below 1, to where you can see a peak (reduction) in the generator current at resonance.

 

hello

tried 0.1Hz and 0.001Hz, the same result
change resistance to less than 777 ohms and same problem

shouldn't it look like a "U" shape when I have magnitude and frequency?

 

Here is the "resonance" of your network as a function of the values of R1 = 10, 100, 1000, and 4700Ω. What happens to the Q between 100Ω and 1000Ω?

 

tried 0.1Hz and 0.001Hz, the same result
change resistance to less than 777 ohms and same problem

shouldn't it look like a "U" shape when I have magnitude and frequency?

Are you looking at the source current?

 

hello

I have this
View attachment 77172
the values are
1uF
151mH
4700 ohm

I put this together on multisim to find resonance using the ac analysis option but all that happened was a high pass filter. does the capacitor short circuit as the frequency increases. I have to calculate the resonant frequency and im not sure how to do that.

You haven't given any indication of what you are using as the parameter that you are trying to find the resonance for? Is it a voltage? If so, what voltage? Is it a current? If so, what current?

 

One thing, by experiment, your oscillator or signal generator will have an impedance ... probably 50 ohms.

Attached is the sweep using a signal generator with an impedance of 50 ohms and the inductor has zero resistance.

 

One thing, by experiment, your oscillator or signal generator will have an impedance ... probably 50 ohms.

Attached is the sweep using a signal generator with an impedance of 50 ohms and the inductor has zero resistance.

hello joe

would I have to include the 50 ohms in the calculations then. I seem to get voltage readings that are a little off. I put this down to poor test equipment.
is the 50 ohms in series with the circuit?

thanks

simon

 

You need to publish in the forum your recorded readings. It would be best if you annotated the schematic and indicate your reference point (i.e. ground or across the component.)

Help the members help you.