Zhou,
If you want to use the 5V source of the board it is not isolated... that means, if you over charge the board with more than 1A you may burn it (fuse). In case you may want more than 1A you can use an external power supply or even if you want an isolated supply. In the manual it means the board power for the non-isolated mode... and for external power supply if you want either an isolated or more than 1A source.
Take a look to the specs of your switch, how much amps does it takes when activating?... common switches uses 100 mA range currents so probably your switch does also... in that case you may use the board 5V source... isolation means protection against... take a look to the picture in that page you mention, there is an optical isolator there, it funct
ions like a relay or like a transistor where the electronic circuitry is going to be "isolated" or protected from the power circuit (external)...
Good luck!...
Nestor Sanchez
Applications Engineer
National Instruments
Nestor
