Bertec FIT - Calculating Load Values

Bertec Corporation Instrumented Treadmill Manual 23
The analog data acquisition procedure can be summarized as follows:
> Check all the cables, and make sure that they are properly connected.
> Turn on the ampliers, and allow the system to warm up at least for 5 minutes.
> For the 6504 and 6800 series ampliers, set a proper gain value for the data channels using the gain switch.
> Press the auto zero button to remove any load offset from the signals.
> Using the control software, set the speeds for the right and left sides of the treadmill.
> Collect analog data using software. Remember to remove a baseline reading from the signals in order to set the signal
mean values to true zero.
Calculating Load Values
Each force plate is calibrated individually and the calibration matrix is stored digitally in the force plate. Therefore, the analog
output from the amplier provides full-scale calibrated output (±5 V) per rated load range of the attached force plate. The voltage
output of each channel is a scaled form of the load in the units of N and N•m for the forces and moments respectively. The scale
factor for each channel for a gain of unity is given in the product data sheet supplied with the transducer. The force and moment
values are calculated by multiplying the signal values with corresponding scale factors, as given in the following equation:
where, F’s and M’s are the force and moment components in the force transducer coordinate system (Figure 11), and S’s are the
output signals corresponding to the channels indicated by their subscripts, in volts, divided by the respective channel gain. The
origin of the coordinate system is centered at the inner corner of the outer back roller support block of the corresponding (right
or left) treadmill half (Figure 11 and Figure 12). The standard coordinate system is such that the positive y-direction points
forward; x-axis is to the left when looking in the y-axis direction; and the z-axis is dened downwards by the right hand rule.
Data Acquisition and Load Calculations
F
x
= C
1
• S
1
F
y
= C
2
• S
2
F
z
= C
3
• S
3
M
x
= C
4
• S
4
M
y
= C
5
• S
5
M
z
= C
6
• S
6
Force and signal scale factors