Better Filter VI?

Question

I am working on a VI to read voltage inputs from a USB 6210 that vary from +/- 5 mV. I understand I will have noise, but there are instances where that noise can get up to +/- 1mV. It usually last for only a few milliseconds before settling down back to the normal +/- 0.2 mV. I have attached my VI with my idea to filter this noise out. Is there a better method than this?
Attachments:
PlainVIv1.vi ‏130 KB

Answer 1

Plenty of ways to filter - depends upon your application as to what is acceptable:
If you are not bothered about phase shift or dynamics of your filtered signal - then a simple averaging / low pass filter might work if the separation between the frequency of the noise and the signal you want to keep is sufficient.
If this is a problem, but you are not using as part of an online system - i.e the filtering can be done once all (or part) of the data has been gathered then there are multi-pass filters that preserve the phase shift (there is filtfilt command in Mathscript)
If you are bothered about phase shift and it needs to be filtered online - then you have to design your filter carefully, and may need something far more advanced, but depends upon the performance you need and frequency separation you have. If you are doing filtering within a control loop be careful the phase shift doesn't destabilise the control loop.
REMEMBER: The best way to deal with noise is identify the source, and reduce it at source before resorting to filtering - for example timing / synchronisation issues can make things look noisy.
Consultant Control Engineer
www-isc-ltd.com