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.
Steve B
