First thanks for everyone who gives me any reply!My problem is this:
1.We have desighed a power meter of 5(60)A with MSP430FE4242(current sample from a shunt~250uohm),but we found that its small signal is not good and the linearity of the erro curve is not well.Particularly,phase difference of1.0L and 0.5L becomes bigger with signal size.In fact,at 0.2A,the phase difference is about 1%.We have excluded the influence of transformer,and the problem is nothing when we replaced the mcu with MSP430FE427(NOT FE427A).At last,we used a LIERDA's demo meter for test,when we replaced the mcu with FE4242,the same problem came. So we thought that the 4242A's AD has some problems.At last,we calibrated the offset of current and opened the common-mode rejection function.Now we get the better the erro curve,but the erro variation at 0.2A does surpass 0.2%(about 0.3%).
2.And then recently,we found a good erro line by changing current gain from 16 to 8.when I calibrated power gain,the line was good.But when I calibrated the phase erro with your excel form,the small signal erro changed large.I don't know why?
3.In the reference meter code of MSP430FE42X,there is a parameter(SD16CONFx_FUDGE).What meaning is it?For MSP430FE4242,how can I assign a value to it?