Instrumentation Amplifier exercise

[alex123]

If the site's Ad gain is 1000 (times). Determine the resistive components of the circuit.


I came to the conclusion that vo / (V1-V2) = (R3 / R2) (1+ {2R1 / Rgain}) Take the traditional 3-opamp instrumentation amplifier, keep in mind that operational amplifier 1 is inverted

[gbaddeley]

FYI , it is Instrumentation, not Instrumental (pertains to music)

[Jwillis]

G= R3/R2 (1+2R1/R_gain)

R3=100K
R2=10K
R1=9k9
R_gain=100

[magic]

keep in mind that operational amplifier 1 is inverted

Indeed, this is some nonsense circuit with positive feedback. A1 output will randomly saturate into either of its supply voltages. I suppose that has to be a mistake.

[Circlotron]

The upper opamp is wrong. Various websites have copied and pasted without looking closely. Most have it right though.

https://www.google.com.au/search?q=3+op+amp+instrumentation+amplifier&source=lnms&tbm=isch&sa=X&ved=2ahUKEwihyduTya3pAhXZHDQIHZK_A8MQ_AUoAXoECBAQAw&biw=1264&
bih=951

Edit -> seems the same set of images don't come up every single search...

[Jwillis]

The upper opamp is wrong. Various websites have copied and pasted without looking closely. Most have it right though.

https://www.google.com.au/search?q=3+op+amp+instrumentation+amplifier&source=lnms&tbm=isch&sa=X&ved=2ahUKEwihyduTya3pAhXZHDQIHZK_A8MQ_AUoAXoECBAQAw&biw=1264&
bih=951

Edit -> seems the same set of images don't come up every single search...

Your right . Shouldn't both inputs be non-inverting ? So my calculations would be wrong.

[anvoice]

FYI , it is Instrumentation, not Instrumental (pertains to music)

I had a class in uni called "Instrumental Chemistry". We played 0 music.

[alex123]

https://www.elprocus.com/what-is-an-instrumentation-amplifier-circuit-diagram-advantages-and-applications/

[chris_leyson]

keep in mind that operational amplifier 1 is inverted

Reminded me of this:-

[Jwillis]

https://www.elprocus.com/what-is-an-instrumentation-amplifier-circuit-diagram-advantages-and-applications/

If you read the paragraph   .   Instrumentation Amplifier using Op Amp

"The instrumentation amplifier using op-amp circuit is shown below. The op-amps 1 & 2 are non-inverting amplifiers and op-amp 3 is a difference amplifier. These three op-amps together, form an instrumentation amplifier. Instrumentation amplifier’s final output Vout is the amplified difference of the input signals applied to the input terminals of op-amp 3.Let the outputs of op-amp 1 and op-amp 2 be Vo1 and Vo2 respectively."

This leads me to believe that the circuit is drawn wrong on that web sight.  Op amps 1 and 2 must be non-inverting.