What is the minimum noise level of 9263 AO? And how to reduce the noise?

[hoonyu]

Hello, I used many 9263 analog output modules. Most output signals control current servo circuit. The current servo is designed for 1 V output voltage = 1 A. However my output current from current servo has white noise and peak noise on 60 Hz harmonics. Now I'm trying to figure out the noise source.

Here is my question. As my measurement by using spectrum analyzer, the output voltage from 9263 module has white noise. The noise level is 5 uV. Of coure this noise level is a problem in my experiment. So..What is the minimum noise level of 9263 module? If I have more noise than minimum level, how can I eliminate it?

[johnsold]

According to the data sheet the noise level of the NI 9263 is 260 uVrms. It appears that your observed noise level is quite a bit lower than the specified maximum.

A system where 5 ppm noise is a problem will likely take a significant amount of effort to identify and eliminate or compensate the effects of the noise.

The first thing you can do to minimize noise is to make sure that you have no excess bandwidth.  The device supports sampling rates to 100 kS/s so its analog bandwidth is probably wider than your servo system requirements.  A filter with a bandwidth matching your servo bandwidth will reduce the noise components at higher frequencies.

Next, you mention 60 Hz harmonics. Are you using the isolation capability of the NI 9263 or does everything share a common ground?  Power line frequency interference typically is coupled into a system by induction or by shared grounding conductors.  Capacitive coupling is possible but most systems do not have enough capacitance to provide a low impedance path at 60 Hz.  If various parts of your system are isolated, then inductive coupling is most likely.  It is rather difficult to troubleshoot this type of problem without seeing how the whole system is connected.

Lynn