Solution
The noise floor is the lowest level at which we can no longer discern signals. In NI DSA, this specification is referred to as spurious free dynamic range (SFDR), which can be found in the specifications document for each device. As an example, an excerpt from the NI 447x Specifications document is shown below to highlight SFDR.
If you want to measure or verify the spurious free dynamic range yourself, you can apply a pure sinusoidal tone into an analog input channel at 0 dB gain. In the frequency domain, calculate the difference between the applied tone and the next smallest peak (called spurs). This is the spurious free dynamic range.
Note: It is important to use a pure sinusoidal tones to avoid seeing additional noise that is not caused by the DSA device.