Operation
5.2.1 Balance (Posturography)
Important:
It is imperative the charge amplifier is switched to
OPERATE before the subject steps on the force plate.
Otherwise Center of Pressure COP can not be calcu-
lated correctly.
5.3 Time Constant
Some charge amplifiers have a time constant (TC) function.
A time constant is a high pass filter (AC mode) which al-
lows dynamic measurement without the static (DC) com-
ponent.
Time constant is rarely used for biomechanical meas-
urements.
5.4 Effective Frequency Range
The force plate Type 9287C… has a natural frequency of
750 Hz in shear and 520 Hz in vertical direction. The fre-
quency response curve indicates how strongly each fre-
quency is amplified or attenuated. See chapter 8.5 "Fre-
quency Response".
Impacts like those which occur in sports have a large pro-
portion of high frequencies. The more rapid and abrupt an
impact is, the greater the proportion of high frequencies.
The force plate as a mechanical system oscillates at its
natural frequency when excited. Certain frequency com-
ponents of an impact are amplified whereas others are at-
tenuated.
The lowest natural frequency of a force plate is deter-
minant for its performance. For example 200 Hz is the
relevant natural frequency of a force plate which:
1 000 Hz natural frequency in vertical direction
200 Hz natural frequency in shear direction
9287C
_002-462e-03.11 Page 21
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