I couldn't understand how come the voltage in V1P and V2N line is 355 mV rms.I see that if we transform the 80 Amp due to 1/1800 maximum current on CT sensor is 44 mA RMS but i can't understand how to split the resistors to see voltage calculation in V1P-V1N line for proper values. Could you explain me detailed ?

 

CT current is 1800x smaller so 80A/1800 = 0.044444A or 44.45mA

since that current flows through two 4 Ohm shunts that are in series (combined resistance is 8 Ohm), voltage across them is
44.45mA* 8Ohm = 0.3555555 V
current through 1k resistors and the inputs is negligible.

 

CT current is 1800x smaller so 80A/1800 = 0.044444A or 44.45mA

since that current flows through two 4 Ohm shunts that are in series (combined resistance is 8 Ohm), voltage across them is
44.45mA* 8Ohm = 0.3555555 V
current through 1k resistors and the inputs is negligible.

Why 4 Ohm resistors are in series ?Both are connected to the ground from different point

 

yes... that is an additional connection but - this is not a factor in computing the output.
CT current must pass both of the shunt resistors. the center point is tied to GND in one point only - just for reference. no current is supposed to flow through it. so for analysis purpose this can be disconnected.

maybe it is better if drawn like this.


then open the jumpers (also no current here) and you get this:

the voltage you measure is not across 4Ohm shunt, it is across 8 Ohm. The net result is as if the resistors are in series...

 

or draw equivalent circuit, identify sources, solve for currents... something like this...
Pretty sure I1=I5 and all others are practically zero (MUCH smaller than I1 or I5).
so you end up with Rsh=SH1A+SH1B=8 Ohm.

Also I2 and I4 are not really zero but they are very small. But... ask yourself what could make currents I3 and I6 non-zero.

 

I see now thanks a lot and if you don't mind i want to ask another question
What is the purpose of splitting the shunt resistors ? What would be changed if SH1A=8 and SH1B=0 (vice versa) ?

 

you can but that would make it single ended. your ADC has differential input for a reason.

 

Okey, Thank you