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Unable to achieve Stable Current acquisition using cDAQ9185 and NI 9227

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Hi everyone,

I am trying to acquire an Analog Current Signal in range of 4mA-20mA using cDAQ9185 and NI 9227. The acquired Signal is not stable. Please suggest me how to smooth or filter the Signal inorder to get a Stable Signal..?

Please find the attached graph below

Thanks in advance

 

Best Regards,

Deepa

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What is the frequency of your signal of interest?

 

9227 can sample up to 50,000 times per second. If you are interested in essentially a DC measurement, then you can arbitrarily average the 50,000 samples every second to reduce the noise by a factor of over 200 and produce one sample every second. The spec indicates that there is an input current error of .4mA at 50kS/s and also about .2% of the range is an offset error. So at a 5A range, we expect our signal to be polluted with noise of around 1mA, which is a lot for a 3.7mA signal. But averaging or filtering could reduce our noise bandwidth a lot and get the effective noise down to .01mA or less.

 

Look at the Statistics express vi or the Filter express vi for ideas about how to filter your data. If you want to cut straight to it, try the mean or FIR filter vis. Of course, it all depends on the bandwidth of the signal you are interested in.

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Are you following NI guidelines on best wiring practices and grounding?

These two papers should get you started.

Field Wiring and Noise Considerations for Analog Signals

Grounding Considerations - Intermediate Analog Concepts

 

More tips here: Five Tips to Reduce Measurement Noise

 

It might also be noise from nearby power lines, a better sampling rate will help. 

Eliminating Powerline Noise from DC Measurements in NI Software

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Frequency in the range of 10 - 10kHz

I will try the filters and averaging. Thanks a lot for your Inputs.

 

Best Regards

Deepa

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Thanks a lot for your Inputs.

 

Best Regards,

Deepa

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