Returns the COMTRADE ID of a given channel number.
        The number to be given is the same of the COMTRADE header.

def getAnalogID(self,num):
        """
        Returns the COMTRADE ID of a given channel number.
        The number to be given is the same of the COMTRADE header.
        """
        listidx = self.An.index(num) # Get the position of the channel number.
        return self.Ach_id[listidx]