I've been putting together a geophysics resistivity unit (see my other threads) and I have a question, given the block diagram below is there a high common mode voltage across the ADXL1115 or is it floating if the Inverter isolates the battery from the 120V side?

 

Hi Sirch,
Please add the 0V/Common lines to your block diagram, this should help highlight any problems, including any 0V copper tracking on the modules
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Here's a revised block diagram with the -ve rail shown, as I mentioned the Inverter isolates its input and output

 

given the block diagram below is there a high common mode voltage across the ADXL1115 or is it floating if the Inverter isolates the battery from the 120V side?

Basically it's floating so its common-mode voltage would be determined by any leakage currents between the input and output of the inverter.

 

I thought so, just wanted to check

 

hi sirch,
If I am reading your circuit correctly, when C1 is 0V and C2 is 168Vdc, P1/A0 analog input pin will be a -Vin wrt to GND pin on the ADS1115, if the Soil/Earthing electrodes are in the alignment show in your diagram???

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Well spotted, that's an error with the diagram. There is actually a change over relay for both current and voltage to average out self potential so they do swap but the A0 would be above ground

 

hi sirch,
I assume you have voltage overload protection circuit on the ADC inputs, to cover an event where the Earth resistance between A0 and Gnd, probes is very high.?
E