Large Fluctuation When Acquiring at a High Data Rate Using NI9253 in FPGA Interface Mode

Issue Details

I am using the NI9253 in our measurement system. When I change the Data Rate settings of the NI9253, I observed fluctuations in the measurement values.

What is the possible causes of this phenomenon and how to solve it?

Solution

The fluctuation is cause by the incoming signal that have a high fluctuation at a higher frequency portion.

By default, the NI9253's Filter Frequency setting follow the Data Rate setting. For example, when Data Rate is set to 2.000 kS/s the frequency above 2 kHz is cut off by NI 9253 built in filter.

On the other hand, when the Data Rate is set at 1.000 kS/s, the Filter Frequency is set at 1 kHz which will filtered out the fluctuated 1 kHz and above portion of the signal.

In order to get the same result as Data Rate 1 kS/s when running at Data Rate 2kS/s, you can change the Filter Frequency setting to Data Rate / 2 (1.000 kHz) as shown below.

Additional Information

The NI 9202, NI 9252, and NI 9253 use a combination of analog and digital filtering to provide an accurate representation of in-band signals while rejecting out-of-band signals. The filters discriminate between signals based on the frequency range, or bandwidth, of the signal. The filtering is always enabled and the filter configuration applies to all channels on the module.