sound and vibration; integration and filter problems - real time analysis

[Klemen]

Hello,

i am building (i have already built) a program for vibration analysis. It consists of data acquisition (DAQ card), data processing and data display (and saving).There are two modes - offline and online (real-time) analysis. Everything works as it should, the only problem i get is with the filter and integration functions (more with the filter part, because the integration also has option for selecting cutoff frequencies, and i think this is prat of the problem).

Integration function is a part of sound and vibration toolkit, where filter is a part of waveform conditioning.

Here is my problem:

When a signal comes throug the integration or filter function, my real - time analysis doesn't update as it should. There is always a filter settling time which oscilates with amplitudes far greater than the signal's. Does the filter sets itself everytime it gets a new set of data from the DAQ card?If i skip the filtering and integration, the signal updates as it should.

I attached the picture of the processing .vi.

Thank you for your help,

Klemen P.

[Henrik_Volkers]

Looks like your first Express filter doesn't keep it's former values.  Even worse: If you choose a IIR Filter you might gain processing speed due to lower order, BUT you have to check it's stability. 

Try replace it with the FIR Filter from the sound &vibration or the advanced FIR Filter from signal processing that keep old values for the next chunk of data (good indicator is the boolean input INIT ) and read the help 😉

[Henrik_Volkers]

Another point: your velocity chart show acceleration right ?

[Klemen]

Thank you for your answer!

About velocity chart - yes it does show acceleration - i was just tring to show, that the unfiltered signal updates as it should, where as the filtered doesn't.

Thank you again i will try your solution and report.

Klemen P.

[preston_johnson]

Does your low pass filter work to provide alias protection?  A delta-sigma 24 bit based ADC has this built into hardware. 

The integration functions have the high pass filters built in to allow for integration.  I see you have some multiplication and division along the integration path.  These are not necessary, if you first scale your signal to engineering units with the sound and vibration scale to engineering units function.  Once this is done, the integration units will know that you have acceleration coming in and will do the calculation to convert to velocity, etc. 

Regards.

Preston

[Klemen]

Hello,

i tried but failed. So i used butterworth bandpass filter (point-by-point) and it works ok. The problem i think was, when a filter got a new set of data, it reseted itself. 

I still have to integrate though - will try it with point-by-point integration also...

regards,

Klemen