User Guide for FSR Sensor

Page 6 FSR Integration Guide and Evaluation Parts Catalog
with Suggested Electrical Interfaces
At the high force end of the dynamic
range, the response deviates from the
power-law behavior, and eventually
saturates to a point where increases in
force yield little or no decrease in
resist-ance. Under these conditions of
Figure 2, this saturation force is
beyond 10 kg. The saturation point is
more a function of pressure than force.
The saturation pressure of a typical
FSR is on the order of 100 to 200 psi.
For the data shown in Figures 2, 3 and
4, the actual measured pressure range
is 0 to 175 psi (0 to 22 lbs applied
over 0.125 in
2
). Forces higher than
the saturation force can be measured
by spreading the force over a greater
area; the overall pressure is then kept
below the saturation point, and
dynamic response is maintained. However, the converse of this effect is also true, smaller actuators will
saturate FSRs earlier in the dynamic range, since the saturation point is reached at a lower force.
Force vs. Conductance
In Figure 3, the conductance is
plotted vs. force (the inverse of
resistance: 1/r). This format allows
interpretation on a linear scale. For
reference, the corresponding
resistance values are also included on
the right vertical axis. A simple
circuit called a current-to-voltage
converter (see page 21) gives a
voltage output directly proportional
to FSR conductance and can be
useful where response linearity is
desired. Figure 3 also includes a
typical part-to-part repeatability
envelope. This error band determines
the maximum accuracy of any
general force measurement. The
spread or width of the band is
strongly dependent on the repeatability of any actuating and measuring system, as well as the repeatability
tolerance held by Interlink Electronics during FSR production. Typically, the part-to-part repeatability
tolerance held during manufacturing ranges from ± 15% to ± 25% of an established nominal resistance.
Figure 3:
Conductance vs. Force (0-10Kg)
Figure 4:
Conductance vs. Force (0-1Kg) Low Force Range