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Unformatted text preview: he permissible voltage supply
of the proximity sensor and which, depending on the time constant, fade away
relatively slowly. In the case of unfamiliar power supply units, it is recommended to
check the voltage switch-on behaviour by means of a storage oscilloscope.
Depending on the specification given in the data sheets for proximity sensors, the
supply voltage ripple must not exceed a certain limit value. 154 © Festo Didactic GmbH & Co. KG • FP 1110 11. Physical fundamentals 11.1
Fundamentals of inductive
and capacitive proximity
sensors Inductive and capacitive proximity sensors are based on the use of oscillators, their
oscillating amplitude being affected by an approaching object.
In order to generate sinusoidal oscillation, LC-oscillators (consisting of a coil and an
capacitor), quartz oscillators and RC-oscillators (consisting of a resistance, a
condenser and an amplifier, e.g. Wien bridge oscillators) are used.
The following denote:
L = Inductance
Unit: Henry (H)
C = Capacitance
Unit: Farad (F)
R = Resistance
Unit: Ohm Ω 1 H = 1 Vs/A
1 F = 1 As/V
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- Spring '12