Introduction to Industrial Automation

Figure 2.29  The metallic environment affects the operation of a non-shielded inductive prox-

imity switch: (a) non-shielded switch presenting field scattering, (b) safety distance for field 

scattering avoidance, (c) shielded switch in metallic environment without scattering.

Magnetic proximity switch

N

S

N

S

Pickup coil

Pole piece

Permanent magnet

Ferrous gear

wheel

V

coil

V

coil

V

coil

t

Figure 2.30  Typical variable reluctance magnetic proximity switch.

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  Introduction to Industrial Automation

Various other types of proximity switches exist in the market and may give the industrial 

engineer a better solution, depending on the distinctiveness of the application. For example, there 

are ultrasonic proximity sensors which use reflected or transmitted ultrasonic waves to detect the 

presence or absence of a target object. A deep knowledge of the available equipment in the market 

is a fundamental path toward the optimal solution to each application. In this case, optimality 

should be considered not only as a correct solution, but it should also be given with respect to the 

corresponding cost.

Applications of proximity switches: Proximity switches are used in manufacturing processes, e.g., 

to detect the position of machine components, to count objects on a conveyor, to monitor normal 

operation of a machine, and numerous other industrial applications. They are also used in robot-

ics in order to monitor the distance of a robot from the surrounding objects and in safety systems, 

where a simple application can detect the opening of an access door in an industrial cell. The most 

common industrial applications of proximity switches are shown in Figure 2.32. Some of the most 

Magnetoresistive

element

Trigger

stage

Amplifier and

output switching

circuit   

Magnetoresistive proximity switch

MR

Non-ferromagnetic

objects don’t affect

switch operation

Permanent magnet

N

S