MH's ideal coil and voltage question

[poynt99]

Also off topic but I read the comments about solid state vs tubes so I assume some here are pickers and/or audiophiles. I researched the differences nearly fifty years ago as best one could with a single channel kit scope, and determined the main difference was the output impedance or damping factors. I found tube outputs to be soft or poorly regulated with the changes in speaker impedance over a given frequency range, where s/s was highly regulated with high damping factors. By using a combo of negative voltage and current feedback in a s/s bipolar power amp, one can approach the ideal tube type output impedance tracking which yields the fat, warm tube sound. Other factors played a role as well like depletion mode j-fets in preamps, passive tone networks,  and phasing the output so the attack transients from a string pushed the cone forward, etc.

Aren't all JFETs depletion mode?

I prefer enhancement mode MOSFETs for my pre-amp designs, hi-fi and guitar/bass.

[minnie]

Is it sort of near field coupling, or am I barking up the wrong tree?
      John.

[tinman]

For this analogy to work, lets tie the carts together so they act as a single cart and lets point the rocket engines' thrusts away from each other so they oppose.  Engine #1 has a fixed and continuous thrust (EMF).  Engine #2 has an identical thrust that can be turned on or off (CEMF).  A sensor and control mechanism is used to determine the acceleration (rate of change) of the cart in the direction determined by engine #1's thrust.  We have set the desired acceleration rate to 800 feet per second .

Engine #1 fires and the cart accelerates.

1.  When the cart's acceleration reaches 800 feet per second, engine #2 fires

2.  When engine #2 fires, the cart's acceleration decreases

3.  When the cart's acceleration becomes less than 800 feet per second, engine #2 is cutoff

4.  When engine #2 is cutoff, the cart's acceleration increases (return to 1, loop forever)

Again, this is a step wise description.  If engine #2 could respond instantaneously, and the time between steps were made infinitely small, there would be a smooth and continuous acceleration of the cart at a rate of 800 feet per second in the desired direction.

PW

And there is the problem PW.
Engine 2s thrust dose not just start only when engine 1 has reached a point of acceleration of 800 feet per second,nor dose engine 2s thrust simply switch off when engine 1s acceleration drops below 800 feet per second. Engine 2s thrust matches that of engine 1 at every instant,and so there is no motion between the two.
I see the same thing with the EMF induced current,and the CEMF induced counter current,where every change made by the forward current is counteracted by the CEMF induced reverse current.
Why dose this action/reaction have to start only when a rate of change has reached a level of 800mA per second?
The value in question here,is the 800mA per second,and it seems that your self and Poynt keep using this very value to justify the value in question it self.
This feed back system i believe should represent a situation where if you push against a concrete wall,the concrete wall will push back just as hard at the very same time,and the net result is no motion. The way i see you explaining thing's,is that some how,the person is able to move the concrete wall,even though the concrete wall is pushing back just as hard.

The ideal coil becomes a power source it self in this case,and it matches that which was induced into it,only with opposition.

Anyway,i am going to leave it at that,as i dont think it is going to go anywhere,when the value in question is being used to confirm the value in question,when the conversation is about that very value it self.


Brad

[picowatt]

And there is the problem PW.
Engine 2s thrust dose not just start only when engine 1 has reached a point of acceleration of 800 feet per second,nor dose engine 2s thrust simply switch off when engine 1s acceleration drops below 800 feet per second.

First, its an analogy, but as I have modified it, it is a very close to describing the action of an inductor.  It has the same negative feedback and just like the inductor, and the step wise description has no CEMF, or counter thrust. until the rate of change reaches the desired rate.  As stated over and over, it is only being _described_ to you in a step wise fashion.  It is actually a smooth and continuous process.  As stated in the analogy, try to envision those steps being separated by an infinitely small amount of time and engine #2 having instantaneous response.

Engine 2s thrust matches that of engine 1 at every instant,and so there is no motion between the two.

When does this happen, in either the analogy or the inductor?

If the two thrusts are equal, acceleration decreases.  If acceleration is less than 800f/s, engine#2 fires again.

This is the same as what happens when CEMF=EMF which causes the current flows rate of change to decrease.  But when the rate of change is less than .8A/s, the CEMF is no longer equal to the EMF so the rate of change again increases.  The rocket engine analogy is a very good example of a similar feedback mechanism.   

I see the same thing with the EMF induced current,and the CEMF induced counter current,where every change made by the forward current is counteracted by the CEMF induced reverse current.

You are not working with an inductor.  You are working with an inductor in series with a reaistor with a capacitor connected across the two.

Why dose this action/reaction have to start only when a rate of change has reached a level of 800mA per second?

It does not "only start" when the .8A/s is reached.  .8A/s is the rate of change that produces a CEMF of 4 volts in a 5H inductor.  It is the rate of change that current is limited to when 4 volts is placed across a 5H inductor. 

The value in question here,is the 800mA per second,and it seems that your self and Poynt keep using this very value to justify the value in question it self.

Seems like the there is much more "in question"..

Perhaps if you were to study the basic units of the Volt, Ampere, Ohm, Farad, and Henry, this would be more clear to you.

The definition of a Henry specifies what value the generated CEMF will be for a given value of inductance with a given rate of change of current flowing thru that inductance (actually, it is with regard to the rate of change of the magnetic flux.  However, in an inductor, the current flowing thru it creates the magnetic field and the rate of change of the current flow is also the same as the rate of change of the magnetic field created by that current flow).

One Henry will generate a CEMF of 1 volt when the current flowing thru it is changing at 1A/s.

A 5H inductor will generate a CEMF of 4 volts when di=.8A/s. 

A 5H inductor will generate a CEMF of 5volts when di=1A/s.  So, if a 5H inductor is connected across a 5 volt source, current flow thru the inductor will rise at 1A/s.

Put 10volts across a 5H inductor and current will rise at 2A/s, because a 5H inductor with current rising at 2A/s will generate a CEMF of 10Volts.

The CEMF is what limits the current flow's rate of change, and the CEMF is well defined for a given inductance and rate of change.

It is somewhat similar to the defined relationship of 1 volt across 1ohm causing 1amp to flow.

This feed back system i believe should represent a situation where if you push against a concrete wall,the concrete wall will push back just as hard at the very same time,and the net result is no motion. The way i see you explaining thing's,is that some how,the person is able to move the concrete wall,even though the concrete wall is pushing back just as hard.

I am not explaining it that way...

It pushes back only as hard as necessary to limit the rate of change to .8A/s.

Perhaps you are just not familiar with negative feedback.  The rocket engine analogy was a very good example of a negative feedback loop.  As I have stated over and over, although described in a step wise fashion, it is a smooth and continuous process.

The ideal coil becomes a power source it self in this case,and it matches that which was induced into it,only with opposition.

And that opposition only allows the inductor's current to change at a rate of .8A/s (4V across 5H)

Anyway,i am going to leave it at that,as i dont think it is going to go anywhere,when the value in question is being used to confirm the value in question,when the conversation is about that very value it self.

It is indeed obvious that it is not going anywhere...

Regarding the "value" you are so concerned with, perhaps time spent studying the definitions of the most basic units used in electronics would be of help (Volt, Amp, Ohm, Farad, and Henry).

PW

[poynt99]

The feedback system,, well that would have an oscillation,, an extremely small amplitude and high frequency sure,, but an oscillation anyway, and as such invalidates the results.

It is clear that many can not get their heads around negative feedback. There would be no oscillation, at any frequency or amplitude.

Imagine a centrifugal clutch. In a way it can be thought of as a rpm regulator. At a certain rpm, the clutch, due to the centrifugal force engages, and if we anchor the axle so that it can not move, this is obviously going to cause drag on the motor. The harder the motor tries to turn the axle, the more the clutch engages (if the rpm increases), etc. There is no oscillation there.

It is a very similar case with the inductor and the feedback mechanism, except that process begins the instant even minute currents begin to flow. It is an instantaneous reaction that limits the rate of rise. Can you see that the current would rise very quickly upon connection? Can you also see that the cemf would be induced instantly in conjunction with that current?