Proximity Switches - Fayat Group BOMAG BW 900-50 Service Manual

Proximity switches

5.3 Proximity switches
Fig. 1 Proximity switches on travel control lever
B08 Proximity switch, travel lever "0"-position
B38 Proximity switch for vibration lock
General
In all automated sequences the use of sensors as a
source of information for the electronic control is indis-
pensable. The sensors deliver the necessary signals
about positions, end positions, filling levels or serve as
pulse transducers for counting tasks or speed detec-
tion. In industrial applications inductive and capacitive
proximity switches are today indispensable. Com-
pared with mechanical switches it provides almost
ideal conditions: contactless, wear-free working, high
switching frequencies and switching accuracies as
well as high protection against vibrations, dust and
moisture. Inductive sensors detect all metals without
contact, capacitive sensors detect almost all solid and
liquid media, such as metal, glass, wood, plastic, wa-
ter, oil, etc.
Working principle
Fig. 2
The working principle is based on the principle of the
dampened LC-oscillator. The coil of the oscillation cir-
cuit forms a high-frequency magnetic stray field.
This stray field leaks out from the active area of the
proximity switch. If metal or non-ferrous metal enters
into the response range energy is absorbed. The os-
008 921 86
cillator is thus dampened and the resulting change in
current consumption is evaluated.
PNP circuitry
Fig. 3 PNP circuitry
On sensors with PNP-circuitry the output stage con-
tains a PNP-transistor, which switches the load
against the positive operating voltage. The load is
connected between the output and the negative oper-
ating voltage. The switch is designed with a normally
open contact, i.e. the contact closes when the initiator
comes in "contact" with metal.
NPN circuitry
Fig. 4 NPN circuitry
On sensors with NPN-circuitry the output stage con-
tains a NPN-transistor, which switches the load
against the negative operating voltage. The load is
connected between the output and the positive oper-
ating voltage.
Breaking and making contacts
Fig. 5
Proximity switches are used as breaking or making
contacts. Depending on the design the switching dis-
BOMAG
5.3
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