3 phase 3 wire and 3 phase 4 wire circuit

Dear all,

I am trying to build 3 phase voltmeter that could measure L-L and L-N voltage during 3 phase 3 wire and 3 phase 4 wire connection. 3 phase 3 wire and 3 phase 4 wire connection are external connection. 

as we know in 3 phase 4 wire we will get neutral reference so we can get accurate reading for L-L and L-N.
but in case of 3 phase 3 wire we dont have neutral reference .In this case it will be difficult to get gnd reference. I would like use both connection type in common circuit,

I have seen one of the product where they using VXMH IC , can some one suggest me functionality of this iC. i have attached schematic for reference.

If any other suggestion with schematic will be appreciated. to differentiate 3 phase 3 wire and 3 phase 4 wire