instrumental amplifier

[emperror123]

i have only 2 problem

i have been done the question regarding instrumental frequency

which is Vo = (V2-V1)((R2/R1)((2*R3/Rg)+1))

a question ask

resistors can be choosen from ordinary range so that Vo = 10^6(V2-V1)

how do i Calculate the range for the resistors

and 2nd question is that how to i get the resistors value?

 

[audioguru]

Since you didn't post a schematic and didn't say which parts you are using then we don't know what you are talking about.

 

[emperror123]

sorry for not upload the schematic

here are the schematic

**broken link removed**

 

[Jony130]

The voltage gain is equal

[LATEX]\frac{Vout}{V1-V2}=(1+\frac{2*R3}{Rg}) * \frac{R2}{R1}[/LATEX]

And to get Voltage gain equal 1M[V/V] we could use this values
R2 = 100K; R1=1K; R3=500K; Rg = 100Ω

 

[emperror123]

if i would like to get the range get R3, R2 R1 and Rg, how do i do it?

2nd is if i substitute it (the value u gave) in to all the resistor. how do i prove it?

sorry for my weak in analogue electronics

 

[crutschow]

The gain is the ratio of the resistors shown in the equation. If you calculate those ratios you can show that those are obtainable by using resistors of normally obtainable values.

If you want to show the derivation of the gain equation you will have to show how to calculate the gain of each stage and then combine those to get the complete equation. Do you know how to calculate the gain of a single op amp, and how to do simple algebra?

This type of amplifier is an Instrumentation amp not an instrumental amp.

 

[emperror123]

which mean i have to get like vout/vin = - r2/r1

 

[crutschow]

which mean i have to get like vout/vin = - r2/r1

That's true for an inverting amp.

I mean do you know how to calculate the gain of an op amp for any configuration? That involves understanding how op amp (feedback) circuits work and how to generate the equations for calculating gain. If you are just copying gain equations from a tutorial, that's not sufficient.

The thing to understand is that, with an op amp connected with negative feedback, the op amp, due to its high open loop gain, will always try to keep the voltage across the two inputs very near 0V. Thus you do your calculations based upon that. This means that the sum of the currents into the minus (-) op amp node through all the resistors connected to that node must equal zero. So you write the gain (nodal) equations to make that happen.

If you do not understand nodal current equations, then you need to learn that first, such as here.

 

[emperror123]

i understand the nodal analysis

but when come to the op amp especially form equation on any type of op amp, then it would be hard for me

 

[crutschow]

Well, doing something hard is the way we learn.

If you can do nodal analysis then just do the analysis so that, for a negative feedback circuit, all the currents into the summing (-) junction equals zero.

For example, for a simple inverting op amp circuit with an input resistor Ri and a feedback resistor Rf, then for the current into the summing junction to equal zero, Vin/Rin must equal -Vo/Rf. Translating terms gives Vo/Vin (the voltage gain) = -Rf/Rin (The - means the circuit is inverting). You just do that for any feedback circuit and you will come up with the gain.