How do Sinusoidal output comes out in the Wein-Bridge Oscillator

[davenn]

I seem to remember circuits that incorporated a thermistor, to achieve stability in a similar way. Something of the sort is essential is you want to make the oscillator frequency sweepable over a wide range for lab work.

yeah that is an alternative to a bulb.
I used a thermistor in my construction

Dave

 

[Averagesupernova]

I don't think a wein bridge oscillators bulbs are EVER supposed to glow.

 

[skeptic2]

But my experiments with a pea bulb revealed, from memory, that its best sensitivity occurred below where it had begun to glow.

It seems to me that the operating point could be altered by adjusting the value of R4.

http://hypertextbook.com/facts/2004/DeannaStewart.shtml

 

[darkxponent]

If you are familiar (at a sufficiently high level) with the maths of mechanical oscillators then you only need to replace Masses with Ls and Spring constants with Cs (in principle) etc. etc. to translate your knowledge into electrical oscillators. Oscillators and feedback systems of all types share exactly the same analyses. Could there ever be any surprise that the sinewave appears in both contexts?

Glad you put forward this point. I have studied Control Systems, where we replace mechanical systems by a circuit in Force-Voltage or Current-Voltage analogy. Now let's see this problem(the Wein-Bridge Oscillator) in a different way. The question is to draw the equivalent mechanical system for the wein-Bridge oscillator. Can this be done.

I haven't studied the equivalent mechanical thing for an op-amp. Moreover the op-amp is made up of transistors. Do transistors have a mechanical equivalent?

 

[technician]

Now you're getting there.

Mother Nature loves sines - they're the only function I know of whose shape does not change when you differentiate or integrate them. So pendulums and other harmonic systems produce them.

So I think of it this way - a sinewave appears for the same reason it does in a spring/mass system - the feedback system is linear(until amplitude grows to point it hits limits as pointed out above) and contains a restoring force that's proportional to rate-of-change of perturbing force.
a quick search took me to this page which shows the principle:(I'll not attempt the derivation right now)
http://www.calpoly.edu/~rbrown/Oscillations.pdf

Any help ?

Jim...you see where others see dark ! you are spot on...mother nature is simple

 

[technician]

I don't think a wein bridge oscillators bulbs are EVER supposed to glow.

whether they glow or not is irrelevant...they are non-linear

 

[Averagesupernova]

But there are parts of that curve that are more linear than others.

 

[technician]

But there are parts of that curve that are more linear than others.

The word is non- linear

 

[carlgrace]

Glad you put forward this point. I have studied Control Systems, where we replace mechanical systems by a circuit in Force-Voltage or Current-Voltage analogy. Now let's see this problem(the Wein-Bridge Oscillator) in a different way. The question is to draw the equivalent mechanical system for the wein-Bridge oscillator. Can this be done.

I haven't studied the equivalent mechanical thing for an op-amp. Moreover the op-amp is made up of transistors. Do transistors have a mechanical equivalent?

There is no mechanical equivalent for an op amp directly. You need to think in terms of macromodels. So think of it as a device with infinite gain and you go a long, long way to understanding its behavior.

You know, these types of circuits are called analog circuits because they are electrical analogs to mechanical systems, since both mechanical and electrical systems can typically can be described by a set of differential equations.

So yes, the mechanical equiv or the Wein-Bridge oscillator can be drawn. The mathematics are identical.

 

[sophiecentaur]

There are plenty of examples of 'mechanical amplifiers' , of course. They can be incorporated into mechanical oscillators to maintain oscillations - such as the escapement system in a clock (essentially a non-linear amplifier), which meters a small amount of energy into the pendulum / hairspring at the right phase, to maintain the oscillation. the Q of the pendulum is very high and acts as a filter to 'smooth' the impulses of energy into the sinusoidal motion of the oscillator. There are fluid and also magnetic amplifiers which are fairly linear and which can give a Wien equivalent oscillator function.

 

[darkxponent]

There is no mechanical equivalent for an op amp directly. You need to think in terms of macromodels. So think of it as a device with infinite gain and you go a long, long way to understanding its behavior.

You know, these types of circuits are called analog circuits because they are electrical analogs to mechanical systems, since both mechanical and electrical systems can typically can be described by a set of differential equations.

So yes, the mechanical equiv or the Wein-Bridge oscillator can be drawn. The mathematics are identical.

suppose i want to draw the mechanical equivalent of an op-amp in Force-Voltage or Torque-Voltage analogy. How do i start?

There are plenty of examples of 'mechanical amplifiers' , of course. They can be incorporated into mechanical oscillators to maintain oscillations - such as the escapement system in a clock (essentially a non-linear amplifier), which meters a small amount of energy into the pendulum / hairspring at the right phase, to maintain the oscillation. the Q of the pendulum is very high and acts as a filter to 'smooth' the impulses of energy into the sinusoidal motion of the oscillator. There are fluid and also magnetic amplifiers which are fairly linear and which can give a Wien equivalent oscillator function.

I want to draw the mechanical equivalent of Wein-bridge oscillator with springs, masses etc. Can this be done?

 

[carlgrace]

suppose i want to draw the mechanical equivalent of an op-amp in Force-Voltage or Torque-Voltage analogy. How do i start?

The opamp is there to make the circuit more ideal, that is to approximate a mechanical system more closely. You wouldn't need the mechanical equivalent of an opamp in your drawing.

I think this is what you're looking for:

http://lpsa.swarthmore.edu/Analogs/ElectricalMechanicalAnalogs.html

Have fun! :)

 

[darkxponent]

The opamp is there to make the circuit more ideal, that is to approximate a mechanical system more closely. You wouldn't need the mechanical equivalent of an opamp in your drawing.

I think this is what you're looking for:

http://lpsa.swarthmore.edu/Analogs/ElectricalMechanicalAnalogs.html

Have fun! :)

I tried this in a Force-current analogy. The mechanical system i got was a first order differential equation for velocity. For velocity stands for voltage, it should have been a second order equation in v for the solution to be sine. Where am i doing wrong?

 

[sophiecentaur]

Voltage corresponds to displacement and force (aka acceleration) is the second derivative. That ends up as a second order equation to solve.