zebris Medical GmbH
FDM Technical Data and Operating Instructions
Page 8/36
1.8 Measuring principle
The system contains a measuring matrix consisting of capacitive pressure sensors that
are arranged in columns and lines running closely next to each other. For determining
the force distribution over the measuring matrix the capacity proportional to the force
exerted is determined for each individual sensor. To do this, the drive logic generates a
number of sinus burst signals equivalent to the number of columns via the column
decoder
,
and transmits them to the respective measuring column. The analog signal
coupled into the shift register over the lines is proportional to the pressure-dependent
capacity and is passed on for further processing to the control and signal-processing
electronics and transmitted to the PC from there and shown on the display.
Schematic circuit diagram of the measuring system
C
a
p
a
c
iti
v
e
m
e
a
s
u
rin
g
m
a
tr
ix
Column
decoder
driver
Diode
switch
shift
register
Diode
switch
shift
register
...
Burst generator, control logic
Rectifie, Amplifier,
8-Bit ADC
Data bus
Calibrating data
Calibrating - Flash
RAM
Optocoupler & electrical
insulation with rectifier
PC
external
AC Power pack
according
IEC 601
USB
CPU
Program data
CPU-internal
Flash
Diode
switch
shift
register
Diode
switch
shift
register
...
