Hello friends,

Is it possible to join two instrumentation amplifiers in series without any groung shift in between?

I have attached a hand drawn circuit for reference.
If I give -1v to the input will i get -4v at the output? or do i need to ground pin 2 of the second amplifier for this to happen?

 

Why would you want to?
If you need more gain, just use a standard op amp circuit at the output of the instrumentation amp.

 

Why would you want to?
If you need more gain, just use a standard op amp circuit at the output of the instrumentation amp.

The second opamp(the INA114) is part of a larger circuit and i cannot change anything on that side.

So my only other option is to add an amplifier in between Vin and the INA114 to increase the gain before the signal reaches the INA114.
I chose the INA2128 because its just needs one gain resistor thats needed to be added ,instead of a typical differential amplifier circuit.
Notice that the Vin is referenced with a different ground(pin 1) than that the ground present on the output of the INA114(pin 5).
Will this be a problem in correctly amplifying the input signal?

PS:
I just tested the above circuit on a bread board and the INA114 does not seem to amplify the input signal,it is only when i short pin 2 and pin 5 of the INA114 , i get the desired output.I donot want to short these two so that the input and output remain isolated(by having two separate grounds.)Is there any other way around this?

 

i get the desired output.I donot want to short these two so that the input and output remain isolated(by having two separate grounds.)Is there any other way around this?

Not with those devices.
If you truly need separate, isolated grounds, then you will need to use an isolation amp that has galvanic isolation.

Why do you think you need separate grounds?

 

The input is comming from a high power non isolated current / voltage measuring circuit,so the isolation is done with the INA114,
I tested the ISO124 and seems to be working well but a separate DC DC converter for the output is required.
Anyways thanks for your help

AK

 

o the isolation is done with the INA114

That amp has a differential input with common-mode rejection but it does not provide isolation (in the usual engineering sense of that word).