We are looking for implementing the weighting as a digital filter, if possible, but are not sure how to do it - any ideas?
The ISO 2631-1 standard, regarding vibration, explains the procedure, but states that a digital filter designer understands it - we are not filter designers, but we do know how to apply a filter using MATLAB and PYTHON.
In the ISO they have different frequency bands. How are they defined?
First thought is to apply FFT to the acceleration signal and then apply the weighting factors to each of the frequencies, but for that we need to define the different frequency bands.
Any good advise?
Thank you :)
Hello Mathias,
1) "In the ISO they have different frequency bands. How are they defined?"
If you refer the ISO2631-1 standard, it itself refer to another standard "IEC1260:1995 - Electroacoustics - Octave-band and Fractional-octave-band filters.
2) The Frequency weighting factors
I am just trying to present what I have collected from the discussion of the frequency weighting as per the standard. Kindly forgive me if there is anything wrong from my side.
The frequencies are weighted for the acceleration values in respective axis. Or in other words, when we are sensing the vibrations we shall use and interpret the frequencies to represent that particular acceleration level the driver or whole-body may be experiencing at the time of measurement.
Now as you might be well aware that these vibrations in different directions of the subject body have different effects on the body such as Health, Comfort, Motion Sickness etc. The standard states the various frequencies and their acceptable levels.
Therefore, if you are simply using your MATLAB or Python script, you need to find the level of those frequency components as stated in the ISO2631-1 standard.
May be you will require even a proper calibration and understanding of frequency response of your measurement system is needed and then compensate in your software for any errors or deviations.
I hope this will be helpful to you.
Wish you success in your trials.
-PRASANNA WAICHAL
to Mathias Bech :
I refer you to my my former director of Rehabilitation Engineering at the University of Tennessee,
Dr. Douglas Hobson, as linked below.
I am not suggesting that your research
will gain a simple answer.
Dr. Hobson has many published articles.
This is a start.
Good Luck.
Glen Ellis
http://web.stanford.edu/group/resna/Fellows/Hobson.html
http://www.wheelchairnet.org/WCN_WCU/SlideLectures/Lectures/lectures.html
http://www.resna.org/support-resna/founders/founders
https://www.researchgate.net/profile/Douglas_Hobson
Just a quick thought. Frequency weighting is used to assess hearing since we are more sensitive to hearing sounds in some frequency bands vs others. So if you like a sound will appear to be louder at frequencies in the middle of the hearing range rather than at frequencies at the edge of our hearing range, even though technically the actual intensity of the sound is the same. The same issue may be true for whole body vibration where our physiological response to vibration is stronger (maybe more pathological) at some frequencies compared to others. To determine acceptable dose of vibration we would therefore need to weight the dose (intensity*time) for the frequencies of vibration the wheelchair user is being exposed to.
Mathias,
I propose we talk and you call +1 206-276-7525 or skype me (peterwj11). The topic is involved and talking would be the best way to discuss your matter. Please e-mail me ([email protected]) and we can set a time to meet.
Pete
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