I have a PXI 4070 DMM card, and I set the voltage measurement range to 1V. What happens, if the input gets 15V? Will the card be damaged, or is there any protection against higher voltages?
Normaly the card will be having Fuse so the input to the card will be passing through that so if any high voltage or a surge is comming the fuse will open and thus the card will be safe. Read the hardware manual for the ranges.
The PXI 4070 does have input protection that is designed to protect the device from overload conditions. In the NI Digital Multimeters Help there is a section called Handling High DC Voltages which says that the input protection will engage when the signal exceeds about 15V when on the 10V range or lower for the PXI-4070. The behavior is that the input will change and look like a constant current.
The input protection circuit will protect your board from damage however I would not recommend designing a test that would rely on this if you can avoid it. It will not damage the PXI 4070 but it will take a little time to recover from this overload state before you can continue to make low voltage measurements. There is a caution about regularly relying on the protection circuit if you have a switch in your system because there will be current transients that can degrade the lifetime of your switch.