Unformatted text preview: pacitor changes.
With capacitive proximity sensors, an RC resonant circuit is tuned in such way that a
sensor in the unactuated state produces a stray field in front of the active surface.
Only if an object enters into this zone, is it possible for the RC-oscillator to respond.
The change in capacitance leads to this response.
The capacitance change depends on the following factors:
• Distance and position of the object in front of the electrode
• Dielectric constant of the object
• Dimensions of the object
If a non-conductive object is introduced into the active zone, then capacitance
increases with the dielectric constant εr of the material and vice versa in proportion
with the distance from the disc-shaped capacitor electrode. The greatest switching
distance is achieved with either a water surface or with earthed, electrically
conductive materials. The smaller the relative dielectric constant of a nonconductive material, the smaller the switching distance.
As with inductive proximity sensors, it is possible to detect moving or stati...
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- Spring '12
- pH, proximity sensors, Festo Didactic GmbH, Festo Didactic GmbH & Co