DIGITIZERS:

Measurement settings chosen for the digitizers can create two potential noise problems: digital noise and aliasing.

Digital noise occurs when the digitizing range is set too high, or when the signal is too low. If the signal is reasonable (about 10-100 mV), but the digitizing range has been set too high, simply set the range lower to increase resolution. This is done using a control on the LabVIEW virtual instrument on the computer screen.

If the signal is too low, try increasing the gain of pre-amplifier. Typical amplifier gain is 100-1000 mV.

Aliasing occurs because of an incorrect sampling rate setting. If the sampling rate is too low, you get what looks like a lower frequency oscillation. This is not a real oscillation. Since there are not enough sampling points, if one were to connect the sampling points of a sine wave, the points would be so greatly spread that they would often miss the peaks and valleys of the sin wave. This would result in a poor reproduction of the sin wave with inaccurate curves, and a low frequency. This effect goes away when the sampling rate is increased.