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instrumentation amplifier configuration

Question asked by ALIREZA7 on Apr 6, 2018
Latest reply on Apr 10, 2018 by ALIREZA7

hi

first of all my application is based on these articles :

Electromagnetic Flow Meters Achieve High Accuracy in Industrial Applications | Analog Devices 

Electromagnetic Flow Meters: Design Considerations | Analog Devices 

 

i want to configure an instrumentation amplifier in order to amplify the induced signal of my electrode probes and i encountered this problem :

 

if i want to have an ac coupled input then i should use a resistor from each input to the ground for dc bios current return path. as illustrated in this picture:

this configuration will reduce input impedance which have contradict with one of the reasons of using an in-amp (having a G ohm input impedance) . but i saw some circuits that use this configuration for this application .

 

the other possible configuration is the one introduced in the articles that i mentioned above which is a dc coupled configuration . in those articles analog devices suggested to connect electrodes directly to the input of in amp.

but indeed am not sure about using a dc coupled configuration (my main reason is that i think if the measuring liquid have a high dc voltage imposed by operating environment it may damage the in-amp).

 

I still could not choose between these two configurations(or any other configurations if there is).

 

i would be grateful for any help that makes me able to configure my in amp in the best way .

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