Hi,

If there is an instrumentation amplifier circuit, and I have R1= R2= 10k and R3= 20k
Vo= 100(v1-v2)

My question how to find Rx?
If R1=R2=R3, I can use 1+2R/Rx=100, and then I can figure out Rx,
But if R3 is different from R1&R2, what should I do in this case?

 

Sorry, I can't imagine what your "If there is an instrumentation amplifier circuit" looks like.
Post the circuit schematic.

 

Sorry, I can't imagine what your "If there is an instrumentation amplifier circuit" looks like.
Post the circuit schematic.

If you go to this link, the second figure
http://www.allaboutcircuits.com/technical-articles/practical-uses-of-instrumentation-amplifiers/

 

Which resistor is Rx?

Didn't the paragraph above the drawing give you any ideas?

 

Figure out the gain of the output differential op amp for your given values of R2 and R3, and then go from there.

 

Hi,

If there is an instrumentation amplifier circuit, and I have R1= R2= 10k and R3= 20k
Vo= 100(v1-v2)

My question how to find Rx?
If R1=R2=R3, I can use 1+2R/Rx=100, and then I can figure out Rx,
But if R3 is different from R1&R2, what should I do in this case?

Hi,

Where are you getting this Vo=100*(v1-v2) from?
With all resistors equal the gain is not 100.

As has been mentioned, when the resistor R3 is changed (assuming both are changed) the gain increases by the gain of the output stage. When it had all resistors equal it had a gain of 1, so if R3 is changed it will have a new gain of R3/R2, so that should tell you what to do.