Author Topic: How do i use an ADC with diffrent grounds?  (Read 943 times)

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Offline FlimFlam89Topic starter

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How do i use an ADC with diffrent grounds?
« on: November 26, 2018, 08:15:32 am »
I just wanted to start with thanks for the help in my other threads regarding this project, it’s much appreciated!

I’m made a thread earlier about my school project loop powered sensors and this is the final piece in my puzzle to completing this!

I’ve got the power supply, micro and all complementary electronics to work but there is still a problem with the measuring.
The ground of the micro controller and OP-AMP are different witch prevents the micro from reading the voltage of the OP-AMP.

Is there some way to get around this and still use next to no power?
Is there some sort of dual supply OP-AMP or could I use some type of octocopter?

I’m not really sure what to do here since I’ve never run into a problem like this...


Below is an attached image of the working principle.
The micro has to be in series with the load since this is a 4-20mA current loop.
I want to use the power supply IC (LTC3255)
OP-AMP is LT6106 (current sensing OP-AMP)
The "load" is a temp sensor from the 90's
 

Offline David Hess

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Re: How do i use an ADC with diffrent grounds?
« Reply #1 on: November 27, 2018, 08:23:45 pm »
As shown the current shunt, operational amplifier, and microcontroller all share a "common" which is the negative power input to the microcontroller.  Configure a standard single supply operational amplifier as an inverting amplifier, and the negative value from the current shunt will become a positive value referenced to the microcontroller's negative power input which is a common configuration for 4 to 20 milliamp sensors to measure their own output current.
 


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