TIDA-01513: Insulation monitoring resistance calculation

Part Number: TIDA-01513

Tool/software:

Dear team,

I want to use TPSA2140 for my insulation monitoring. I have gone through TIDA 1513 document but I am not sure about calculating RISO_POS and RISO_NEG value individually.

As per one forum, below equations are mentioned. 

Positive Error    S1 open, S2 closed RISO= (Rs2(HV_BATT+VREF))/(ISO_NEG-VREF)-Rns2-Rns1
Negative Error  S1 closed, S2 open RISO= -Rs1(HV_BATT+VREF)/(ISO_POS-VREF)-Rps1-Rps2

 Here, Positive error gives RISO_POS?  Negative error gives RISO_NEG? Is my assumption correct?

Are these equations correct

What is the purpose of S1 and S2 closed scenario?

It would be really helpful if anyone can clarify