Question for a circuit …

[Achelius]

Hello from Greece !!!

In this circuit, the variable air capacitor Cvar is used as a converter angular position in frequency

I need a small help for this a circuit. Can someone explain to me what job makes the amplifier of figure? Is it Wien bridge oscillator ? Function generator ? Is it something else ? What

Thank you !!!

 

[rahdirs]

@Achelius:Where is input to your circuit.I can only see supply voltage of +12V.

 

[Achelius]

he is a function generator

 

[keith1200rs]

I assume the variable capacitor is the 'input'. It looks like a square wave relaxation oscillator.

Keith

 

[Achelius]

i believe the circuit is wronk. No right. The feeback circuit of R2 and R3 must been placed at non inverting input of operational amplifier (3 pin) and not at pin 2 (inverting input

 

[rahdirs]

@Achelius: Shouldn't the variable capacitor be connected to inverting terminal(pin 2) keeping the feedback resistor R2 as it is and removing R3 & connect it from non-inverting terminal to ground so that it operates in positive feedback.

Then you will see a saw-tooth kind of wave at inverting input & square-wave at the o/p node.

 

[_Eduardo_]

The block corresponding to the operational amplifier is a capacity multiplier.

The 555's block is the traditional astable oscillator working with the capacitor "multiplied".

 

[Achelius]

but where is the input of the circuit and hοw this works ?

 

[keith1200rs]

There is no "input" - as you said yourself,

the variable air capacitor Cvar is used as a converter angular position in frequency

.

I am not sure it actually would work. rahdirs' suggestion looks good, although you might need to bias the resistors to the non-inverting input to be nominally mid rail if you want it to work off a single rail.

Keith

 

[Achelius]

These circuits are proposed from the manual of LM108. What is your opinion ? Are they functional ?

 

[_Eduardo_]

These circuits are proposed from the manual of LM108. What is your opinion ? Are they functional ?

Why not? The last circuit is the multiplier adopted in your schematic.

The need for a capacitance multiplier is because the capacitor formed by the plates which you senses the angle is of a few picofarads.

 

[Achelius]

For this circuit. Can someone explain the meaning of the expression "slope conversion 40 Hertz per Degree (angle)"?

Do you know the right equation?