This behavior is expected when your sensor requires a precise excitation voltage source to be low noise and you use the + 5 V output of your PCIe-6363 for this purpose. The output of the user +5 V line on the 6363 (and many X Series cards
) are not well conditioned, and the power supply that supplies power to that user +5 V line has sawtooth noise on it's output. Depending on the loading of the +5 V line the frequency and amplitude of that noise may change (larger loads, smaller amplitude, faster frequency noise).
But if you are looking for a precision 5 V line, an option on the X Series line is to use one of the AO channels to provide a continuous 5 V DC signal. The accuracy of that output will be specified in the specification sheet. Otherwise, you can use another external DC power supply.