if I have a ideal op-amp of an instrumentation amplifier with 2R1, R2, R3, and R4. with v1=Vcm-Vd/2 and v2=Vcm+Vd/2.

Finding Ad and Acm:
Ad=.5[(R4/(R2+R3) ) (R4/R1 + 1) + (R4 / R1) ]
Acm=(R4/ (R2+R3) ) (R4/R1 + 1) ( R4/R1)

Would those equations be correct?

or Acm=0?

 

if I have a ideal op-amp of an instrumentation amplifier with 2R1, R2, R3, and R4. with v1=Vcm-Vd/2 and v2=Vcm+Vd/2.

Finding Ad and Acm:
Ad=.5[(R4/(R2+R3) ) (R4/R1 + 1) + (R4 / R1) ]
Acm=(R4/ (R2+R3) ) (R4/R1 + 1) ( R4/R1)

Would those equations be correct?

or Acm=0?

It would help us better understand your equations if you would post a diagram of your circuit.

hgmjr

 

It would help us better understand your equations if you would post a diagram of your circuit.

hgmjr

Agreed. I am baffled by posts like these. What are they thinking?

 

Agreed. I am baffled by posts like these. What are they thinking?

I figured everyone knew what an ideal op-amp instrumentation amplifier looked like. Let me google it for you:

http://www.electronics-tutorials.ws/opamp/opamp21.gif

With R1=2R1.

 

Link does not work. How about a schematic with all those resistors placed and labeled?

 

Link does not work. How about a schematic with all those resistors placed and labeled?

what about now? I used the insert link button.

 

what about now? I used the insert link button.

Before you post, click on the Go Advanced button, post your link, then click on the Preview button and test your link before you click on Submit Reply.

 

I figured everyone knew what an ideal op-amp instrumentation amplifier looked like. Let me google it for you:

http://www.electronics-tutorials.ws/opamp/opamp21.gif

With R1=2R1.

I know what the circuit looks like, but I haven't memorized the resistor reference designators. In fact, I doubt that they are standard.

 

Before you post, click on the Go Advanced button, post your link, then click on the Preview button and test your link before you click on Submit Reply.

my link works when I click on it in my post. So not sure what the problem is.

 

my link works when I click on it in my post. So not sure what the problem is.

When I click on your link, I get a blank page with this text in the upper left corner:

/opamp/opamp21.gif

 

OK, I got the schematic.
In your original post, what does 2R1 mean?
You can find the gain equation on the Internet.

 

OK, I got the schematic.

Ok, so if 2R1=4k, R2=100k, R3=10k, and R4=10k, Find differential gain and common mode gain, would I use those equations in first post? Assumming V1 and V2 what I put.

 

Ok, so if 2R1=4k, R2=100k, R3=10k, and R4=10k, Find differential gain and common mode gain, would I use those equations in first post? Assumming V1 and V2 what I put.

I still don't get the 2R1 thing. Why didn't you just say R1=2k?

 

I still don't get the 2R1 thing. Why didn't you just say R1=2k?

that is the case, by my circuit has 2R1 instead of R1. SO R1=2k

 

Have you searched for the gain equation?

 

Have you searched for the gain equation?

No, Acutally I believe Ad=R4/R3(1+R3/R2). I have a problem in my book that states.

For instrumentation amplifier a designer proposes R2=R3=R4=100k, 2R1=10k. For ideal components, what is difference mode gain, common mode gain.

The solution uses Ad above to get 21V/V and Acm=0. So, not sure what Acm equation is but doesn't look like my equations on original post are correct.

 

No, Acutally I believe Ad=R4/R3(1+R3/R2). I have a problem in my book that states.

For instrumentation amplifier a designer proposes R2=R3=R4=100k, 2R1=10k. For ideal components, what is difference mode gain, common mode gain.

The solution uses Ad above to get 21V/V and Acm=0. So, not sure what Acm equation is but doesn't look like my equations on original post are correct.

That equation doesn't even contain R1, so it can't be correct.
The correct equation is all over the internet.

 

That equation doesn't even contain R1, so it can't be correct.
The correct equation is all over the internet.

Ad=R4/R3(1+R2/R1), wrote the equation wrong

 

Ad=R4/R3(1+R2/R1), wrote the equation wrong

Ad=R4/R3(1+2R2/R1)

 

Ad=R4/R3(1+2R2/R1)

how is it 2R2? Confused now, as the solution that was provided for the problem I mentioned in previous post, we used the Ad I posted. With Acm=0, so would Acm=0 here?