Kapasitive måleprinsipper

• Rene geometriske målinger som kan forstås fra elektrostatikk (gauss lov)

• Materialavhengige målinger kan forståes ut fra dielektrisitetskonstant og forskyvnings strøm i tillegg til elektrostatikk

Materiale fra• Fraden kap 3.1 og 3.2• Hyperphysics• Fraden kap 7 og 8

Capacitive displacement sensor 1

Capacitice displacement sensor 2

e

AC r 0

Capacitive displacement sensing 3

Cj

i

C

dti

C

QV

Capacitive spring based accelerometer

Capacitive finger accelerometer

Electric dipoles2 (3.10,3.11)

Ep

Near- and far field from dipole

Alonso/Finn: Fundamental univeristy physics Hyperphysics

Far field (dipole field) depend on:• Dipole moment (charge*separation)• Distance from dipole (->amplitude)• Angle with dipole (->direction)

Near field depend on:• Charge• Exact location of charges

Dipoles in an electric field

http://hyperphysics.phy-astr.gsu.edu/hbase/electric/dielec.html

Fraden p.47

Due to thermal agitation the alignment of the dipoles is proportional to the applied field!!

Displaced charge

S r

qSdE

0

rk Total dielectric constant

Capacitive level measurement

Humiditiy sensor

Occupancy

Monopolar capacitive probe

Driven shield proximity sensor