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The following information is for the EMANT300**

# Convert an electronic personal weighing scale to measure center of pressure (Posturography)

Warning: This application note illustrates a typical strain gage application and is not for actual medical use.

One use of Center of Pressure
measurement is in the study of standing posture - Posturography. By measuring the
position of the Center of Pressure at regular intervals, a plot
called a spaghetti diagram can be generated. By calculating the mean
and standard deviation of the center of pressure, an indication of
sway is derived^{1}.

In the paper **Context Acquisition
Based on Load Sensing**^{2}, an algorithm is given to
measure the center of pressure using four load cells. If the total
force exerted at x,y by the load is F_{L } and assuming
static forces, the sum of all 4 load cells F_{1}, F_{2},
F_{3}, and F_{4} is equal to F_{L } as given
by eq 1

Similarly, the no load force F_{0L}
is the sum of the forces on each load cell F_{01}, F_{02},
F_{03}, and F_{04} - eq 2. The position of the load
can be calculated by eq 3 and 4 using the load and no load forces.

An electronic Personal Weighing Scale (we used the Soehnle 62867 Hawaii Monotronic Scale) commonly uses 4 half bridge strain gages to measure weight. By using these 4 gages, the strain application adaptor and the EMANT300 USB DAQ module, we are able to measure the center of pressure in a low cost way.