The DI-2108 has differential analog inputs that are spec'ed as being able to measure +/- 10V, does this mean that they have an overall measurement range of 20V between the - and + terminals? If so, can I connect an 18V DC signal to an input by connecting the - (normally ground) of the signal to the - terminal of the DI-2108 input and the + of the signal to the + terminal of the DI-2108 input? Will this be a problem if I have other, lower voltage signals in my system that connect ground to the - input of a DI-2108 input?