Hi,

This is getting funny now. You guys seem to refuse to read all the posts so you miss information presented.

Electrician:
I agree with Mike on the resonance and power factor correction. Note that the inductor draws the same current with or without the cap being present for all frequencies.

Mike:
I agree with Electrician in that there is still some behavior we might call resonance. Note that if you use the formula for resonance, you can come up with the cap value!

Both:
You guys will argue these points forever because you both cant accept that there are at least two types of what we call resonance. One of you 'believes' that the opposite definition is the only true one. This isnt religion here, it's science.

Here is the current amplitude function:
I(w)=100*sqrt((9*w^2)/625000000+25.0/w^2-83/90000)

There is an amplitude min at f=32.5 approximately (and w=2*pi*f) equal to 1.66667 amps.
I might add that it is not a very sharp response, but it is still a dip meaning that the current is greater than the min of 1.66667 amps for frequencies lower and higher than the center frequency.

 

Hi,

This is getting funny now. You guys seem to refuse to read all the posts so you miss information presented.

Electrician:
I agree with Mike on the resonance and power factor correction. Note that the inductor draws the same current with or without the cap being present for all frequencies.

You've missed the point, which is not whether the capacitor changes the current in the inductor. The capacitor changes (minimizes) the current drawn from the voltage source (the grid).

In the tutorial circuit which is the subject of this thread, it's also true that "the inductor draws the same current with or without the cap being present for all frequencies.", but that is not the relevant point. What is relevant to the question of whether the circuit exhibits resonance of any kind is the total current drawn from the voltage source driving the circuit.

The load on the grid with PF correction is the same circuit as the parallel resonant circuit from the tutorial--parallel R, L and C--simplified of course. MikeML wanted an example of something useful to do with the circuit, and PF correction on the grid is such an example. Even though it's usually described as PF correction, it's still a parallel resonant circuit. The current from the driving voltage source gets minimized by the correct value capacitor, just like a parallel resonant circuit.

In fact, the usual definition of resonance is that the circuit exhibits zero phase angle at the resonance frequency--that's power factor correction. Why limit ones understanding of circuit operation by only considering one way of looking at it?

Mike:
I agree with Electrician in that there is still some behavior we might call resonance. Note that if you use the formula for resonance, you can come up with the cap value!

Both:
You guys will argue these points forever because you both cant accept that there are at least two types of what we call resonance. One of you 'believes' that the opposite definition is the only true one. This isnt religion here, it's science.

Where did I ever suggest that I don't think there are "at least two types of what we call resonance"? I have repeatedly used the terms "voltage resonance" and "current resonance".

In post #17, I said:

"If you apply a voltage source across a parallel RLC circuit, you won't see a "voltage resonance", but you will see a "current resonance".

If you apply a current source to a series RLC circuit, you won't see a "current resonance", but you will see a "voltage resonance".

The word "resonance" standing alone can describe can describe any kind of resonance."

This is explicit acknowledgement that there are at least two kinds of resonance.

I have emphasized the importance of being precise about what one is saying. If there are indeed at least two types of resonance, then when discussing a circuit that has only one, a person should not use the unqualified term "resonance" lest it be unclear which of the two is meant.

Here is the current amplitude function:
I(w)=100*sqrt((9*w^2)/625000000+25.0/w^2-83/90000)

There is an amplitude min at f=32.5 approximately (and w=2*pi*f) equal to 1.66667 amps.
I might add that it is not a very sharp response, but it is still a dip meaning that the current is greater than the min of 1.66667 amps for frequencies lower and higher than the center frequency.

Did you miss the simulation in post #12 where I show the clear resonance in the current from the voltage source?

 

I'm going to start a new thread in General Chat. We've taken the OP's question far afield.

 

I think that we have got bogged down with the easy test of resonance which you might use in your lab using a Signal Generator & an Oscilloscope.
You hang the LC network across the output of the Gen,tweak the frequency till you see either a dip or a peak on the 'scope,depending on whether the LC network is Series or Parallel Resonant.

With real world Generators it is sometimes difficult to get a nice sharp dip,as the 50 Ohm output impedance of the Gen is << smaller than the Z of the LC network.
(If Z is very large,the Sig Gen output voltage will be so close to the no-load value as to make it impossible to discern a peak or a dip)
The quick fix is to insert a higher value resistor in series with one leg of the feed.

An ideal Signal Generator,with zero Ohms output impedance will be able to present the same output voltage at its terminals for loads from zero Ohms to Infinity,so that the voltage across any external load will not be affected by any change in Z of that load.

LTSpice presents just such an ideal device.
A simple check is to connect a variable resistor across the LT Spice source & vary its resistance.
The source voltage will not change.
Commonsense tells us that something must change,& indeed it does.
From Ohm's Law,it is obvious that the current changes,as it does if you replace this load with a LC network & tune the source through the Resonant frequency of the network.

In many cases it is easier to monitor the current through an LC network than to observe the voltage across it.
This was,in fact the normal method for many years.

In tube type Radio Frequency Amplifiers the average value of anode current,which contains both AC & DC components dips as the anode tuned circuit (which is often a parallel tuned circuit) is tuned through resonance.
Sometimes the circuit is more complex,containing elements of both Series & Parallel circuits,but in any case,the indication of resonance is current,not voltage.