Unformatted text preview: ice life of the contacts.
When switching inductive loads, a high voltage peak is created at the moment of
switch-off. For this reason a protective circuit must be provided for the proximity
sensor unless one is already built in.
The protective circuit can either be a suitable RC element or a corresponding diode
or varistor (see circuit diagram Fig. 3.1.5). The electrical values of these components
depend on the following power component (e.g. relay, contactor etc).
If a relay or contactor is to be actuated, the technical data of both the proximity
sensor and the relay or contactor must be observed.
The pull-in power of a relay or contactor is considerably higher (8- to 10-fold) than
that of the holding power. Therefore, it is important to take the pull-in power as a
reference. +24 V DC RL L V
0V +24 V DC RL L C V R
0V Load resistor (RL) Protective resistor (R) Inductance of load (L) Protective diode or Varistor (D) Protective capacitor (C) Fig. 3.1.5: Protective circuits for reed contacts © Festo Didactic GmbH & Co. KG • FP 1110...
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- Spring '12
- pH, proximity sensors, Festo Didactic GmbH, Festo Didactic GmbH & Co