Page 74 - Sensors and Systems - North American Catalog
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Proximity Sensors,
Inductive Sensors,
cylindrical
1
.1.1
Proximity Sensors,
Inductive Sensors,
rectangular types
1
.1.2
Proximity Sensors,
Inductive Sensors,
slot type
1
.1.3
Proximity Sensors,
Inductive Sensors
1
.1
Proximity Sensors,
Inductive Sensors,
ring type
1
.1.4
Proximity Sensors,
Inductive Sensors,
Rotational Speed Monitors
1
.1.7
Proximity Sensors,
Inductive Sensors,
Dual Position Sensors for Valve Actuators
1
.1.5
Proximity Sensors,
Inductive Sensors,
Dual Sensors for Clamping Systems
1
.1.6
Proximity Sensors,
Inductive Sensors,
Valve Position Sensors ( Accessories)
1
.1.5
Sensors and Systems for Factory Automation
Issue 2012
72
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Refer to General Notes Relating to Product Information
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Copyright Pepperl+Fuchs
Proximity Switches
Introduction
Assured sensing range s a
Distance from the active area where actuation of the proximity switch is
assured under defined conditions:
.0 < sa ≤ 0.81 · s n
Repeatability R
Repeat accuracy is the change in the actual sensing range s r , measured
over a period of eight hours at a housing temperature of 23 ± 5 °C
(73 ± 9 °C), any level of relative humidity, and a supply voltage of Ue ± 5% or
any voltage within the rated operational voltage range ± 5%:
R ≤ 0.1 ·s r
Hysteresis H
Hysteresis is the distance between the switching points when the measuring
plate approaches and moves away from the proximity sensor. This value
is specified relative to the actual operating distance s r , measured at an
ambient temperature of 23 ± 5 °C (73 ± 9 °C), and the rated operational
voltage:
H ≤ 0.2 · s r .
Switched off
A proximity sensor is switched off with certainty when the distance between
the target and the active sensor face is at least three times the rated sensing
range sn .
Laterally/radially approaching objects
In addition to an axial approach, target objects can approach a proximity
sensor radially, through the active zone.When targets approach radially, a
different sensing range is obtained depending on the axial distance. This
relationship is described by the response curves shown.
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Different target sizes
Inductive sensors are often activated by machine parts. These very rarely
have the same size and shape as the standard measuring plate to which
the sensor’s technical data applies. The real application sensing range
depends on the size of the metal used to attenuate the sensor.
Generally, the sensing range increases only marginally with a larger object
surface, but reduces significantly for smaller objects.
If the application target is different in size to the standard measuring plate,
it is recommended that you verify the sensing range of the selected sensor.
Different actuator materials
In addition its dimensions, the material composition of the target is also
important. This is described by the reduction factor. The reduction factor
specifies by what factor the operating distance reduces based on different
materials compared to steel FE 360 (St37) for inductive proximity sensors
and against a grounded plate for capacitive proximity sensors.The lower the
reduction factor, the shorter the sensing range for the material in question.
Since the reduction factor for inductive proximity sensors depends upon the
housing and shielding material, this factor vary from type to type. Please
use the value in the respective data sheet.
For inductive proximity sensors, the conductivity/permeability ratio of the
target is the parameter for the reduction factor. Some typical reduction
factor values are provided below:
Material
Reduction factor
Construction steel
1
Aluminum foil
1
Stainless steel
0.85
Aluminum
0.4
Brass
0.4
Copper
0.3
Step 3: Mounting conditions
Inductive and capacitive sensors can be flush mounted or non-flush
mounted.
Sensors that cannot be flush mounted
Non-flush proximity sensors have the greatest sensing range relative to
sensor diameter. The coils used to generate electromagnetic fields in
inductive proximity sensors are placed in a ferrite core to produce a directed
field. But for non-flush sensors, a portion of this field is radiated laterally. A
lateral effect can also be observed in capacitive proximity sensors.
In order to prevent these high-range products from being damped by their
environment, a metal-free space must be left around the sensor element.
The space must conform to the minimum requirements shown below.
Sensors that can be flush mounted
Flush inductive and capacitive proximity sensors can be installed without
leaving a distance between the mounting surface and the sensor face. The
advantage is that they are better mechanically protected and less prone to
errors than non-flush types. The flush mounting is possible because of the
addition of an internal shield designed into the sensor. Flush sensors are
generally called flush mountable or embeddable sensors.
D
B
F
A
A = 2 x operating distance
Non-flush mountable
sensor, installed correctly
Flush mountable sensor,
installed correctly
B = 3 x diameter
Further details on the mounting conditions are included in the technical data
for the sensors.
active
(D)
