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H.l.p. Hurkmans
12-09-2001, 10:15 PM
Dear Biomch-L members,

I'm a PhD student and working on a project to measure, for a long
term period, the ground reaction force during standing and walking
of THP patients. At my department we use an insole system with
capacitive pressure sensors. Static test measurements showed an
amount of drift depending on the amount of weight and duration of
loading.

During the long term measurements we are going to perform with
THP patients the data will show variation in the amount and
duration of loading during walking, which could lead to a large
amount of drift.
During the swing phase of walking the amount of force should be
zero; a zero setting is performed when the insoles are in the shoes
before starting the measurements.
A possible way we were thinking of to correct for this drift is by
subtracting the force data measured during the swing phase from
the force data measured during the stance phase.

Questions I have regarding the drift correction are:

1. Is drift correction, in general, done after measurements when
working with capacitive or other type of sensors?(so, is it generally
accepted to correct data afterwards when measuring with
sensors/transducers)

2. Does anyone know another way to correct for the drift described
in the situation above?

I also would like comments on the correction method I described
above.

I thank all of you in advance for your help.

Henri Hurkmans


Hurkmans, H.L.P, MSc.
University Hospital Dijkzigt
Dept. of Physical Therapy
P.O.Box 2040
Dr.Molewaterplein 40
3015 GD Rotterdam
The Netherlands
Phone: +31 10 4633950
Fax: +31 10 4634501
Email: hurkmans@fyth.azr.nl

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