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Proximity Sensors
1
Proximity Sensors,
Inductive Sensors
1
.1
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Slot-shaped inductive proximity switches
These have a U-shaped housing made out of PBT. The electromagnetic
AC field is generated between two coils that are positioned opposite each
other in the sides of the U. The switching element function is triggered
when the object (metallic switching target) appears in the area between
the coils.
Ring-shaped inductive proximity switches
These proximity switches are designed as a ring. The electromagnetic
AC field is concentrated inside the ring.The switching element function is
triggered when a metallic object moves into the ring.
The housing is made of PBT.
Inductive PMI positioning systems
Based on the very precise evaluation of multiple coil systems, inductive
positioning systems F90, F110, and F112 are able to determine exact
positions along linear travel ranges. The PMI360D inductive positioning
system is optimized for continual angle determination on valve actuators
and valves. Inductive positioning systems are included in
Step 2: Operating distance
The operating distance is the most important parameter for a proximity
switch. It primarily depends on the sensor diameter (coil or capacitor).
The dimensions and material composition of the actuator as well as the
ambient temperature are also influencing factors. For magnetic proximity
switches, the alignment and field strength of the magnets used must also
be taken into account.
Definition of the operating distance
Standard EN 60947-5-2 defines the operating distance for all types of
proximity switch other than slot and ring-shaped housing designs.
There are two options for actuating a proximity switch:
•
Through an axial approach
•
Through a radial approach
The following definitions apply first of all to axial actuation.
Rated operating distance s n
The rated operating distance (according to EN 60947-2-5 "Rated Sens-
ing Range") is a conventional size for defining the operating distance.
It neither takes into account production tolerances nor changes through
external influences such as voltage and temperature.
Standard measuring plate
The following operating distances are determined using a standard mea-
suring plate.This plate is square with a thickness of 1 mm and is made of
steel, e.g., type FE 360 (ST37) with a smooth surface.
Its side lengths are either
•
1
x inner circle diameter of the active area or
•
3
x s n .
The greater value applies in each case. The standard measuring plate
must be grounded for capacitive proximity switches.
Example 1:
.
M18 proximity switch
5
mm operating distance
.3
x operating distance = 15 mm < diameter
Therefore, the actuator dimensions must be 18 x 18 x 1 mm
Example 2:
.
M18 proximity switch
.8
mm operating distance
.3
x operating distance = 24 mm
Therefore, the actuator dimensions must be 24 x 24 x 1 mm
This standard measuring plate is the optimal actuator for the operation.
A reduction in the dimensions or change in material composition reduces
the operating distance.
Actual operating distance s r
The operating distance of an individual proximity switch measured at am-
bient temperature of 23 ± 5 °C, at a voltage within the operating voltage
range and the defined mounting conditions:
.0.9 ·
s n ≤ s r ≤ 1.1 · s n
Usable operating distance s u
The operating distance of an individual proximity switch, measured at an
ambient temperature range between -25 °C and +70 °C, with a supply
voltage between 85% and 110% of the rated operational voltage:
.0.9 ·
s r ≤ s u ≤ 1.1 · s r
s
n
s
r min
s
r max
s
u max
s
r max
s
n
s
r min
s
u min
s
umax
s
umin
switched off with
certainty
Target
+ Hysteresis
+ Hysteresis
+ Hysteresis
active face
switched on
with certainty s
a
Sensor
+ Hysteresis
+ Hysteresis
Introduction, Inductive Sensors
