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Figure 33
Behaviour of the switch in negative stroke.
A
: the magnetic field begins to act on the switch but the Force generated is not sufficient to move the electric
contact. (hysteresis
H
).
B
: the proximity switch is located in the zone of maximum attraction of themagnetic field; the electrical contact
closes and remains closed for the length
b
.
C
: themagnetic fieldmoves away from the proximity switch but the strength is still sufficient to keep the contact
closed.
H
b
b
A
B
C
Fig. 33
The contact strokes can be found in the cylinder manufacturer catalogues.
The following information is useful for the use of magnetic proximity switches:
• the life of the switch depends on the load applied and the number of switching operations,
• themaximum current value is related to closed contacts,
• the switch may be influenced by magnetic fields generated by large electrical motors, or electrostatic charges
from objects inmotion.
Special purpose cylinders
The cylinders we have analyzed, characteristically consist of a single piston rod and a single piston. We examine
the different versions and their varying characteristics.
Figure 34
Opposed cylinders
From a standard cylinder it is possible to obtain two positions defined by each stroke of the rod/piston. By rigidly
connecting the rear heads of two cylinders, we can achieve:
A
: three positions if the stroke lengths are the same
B
: four positions if the stroke lengths are different.
A
B
Fig. 34
3
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