USB-1208HS-2AO Noise

[jtar]

I am using the referenced DAQ for the first time and noticed increased measurement uncertainty using the analog input. See the attached image. A precision DC source was used at the input of an AI channel. Two data sets were taken.  For each input voltage, I acquired 100 and 1000 readings and calculated the mean and standard deviation of the measurements.

• The DAQ is configured for SE input (but the same is noted for Differential input)
• The data plotted in the attached images is for input voltages ranging from 0V to ~9.7V
• At periodic input voltages the measurement standard deviation is noticeably greater than nearby input voltages.
• These spikes are very repeatable. I can dial the input voltage to see the increased Std-Dev at will. 

I am hoping someone can help me understand the cause of this. Do I have a defective DAQ?

Thanks.

[DAQman]

Hello,

For the +/-10 volt range, the USB-1208HS-2AO accuracy is 6.23mV or 8.06mV depending on input mode.  Measure the AGND pin to get an idea of input noise and offset and to remove the dc source from picture. 

John