Page 73 - Sensors and Systems - North American Catalog
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Proximity Sensors
1
Proximity Sensors,
Inductive Sensors
1
.1
Sensors and Systems for Factory Automation
Issue 2012
71
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Proximity Switches
Introduction
Slot-shaped inductive proximity sensors
These sensors have a U-shaped or slot-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 function
is triggered when the object (metallic target) enters the area between the
coils.
Ring-shaped inductive proximity sensors
These proximity sensors are shaped as a ring to detect metal objects that
pass through the loop. The electromagnetic AC field is concentrated inside
the ring. The switching 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, the F90,
F110, and F112 inductive positioning systems 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 provide analog output signals
relative to position. See the
Positioning Systems
section.
Step 2: Operating distance
The sensing range is the most important parameter for a proximity sensor
and is primarily determined by the sensor diameter (coil or capacitor). The
dimensions and material composition of the target as well as the ambient
temperature are also influencing factors. For magnetic proximity switches,
the alignment and field strength of the magnets are the key criteria to
determining the sensing range.
Definition of the operating distance
Standard EN 60947-5-2 defines the sensing range for all types of proximity
sensors other than slot and ring-shaped housing designs.
There are two options for actuating a proximity sensor:
•
Through an axial approach (head on)
•
Through a radial approach (side approach)
The following definitions apply first of all to axial actuation.
Nominal sensing range s n
The nominal sensing range (according to EN 60947-2-5 “Rated Sensing
Range”) is a standard value for defining the operating distance. It does
not take into account production tolerances or changes through external
influences such as voltage and temperature.
Standard measuring plate (target)
The following sensing ranges are determined using a standard target. This
target 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 target must be
grounded for capacitive proximity sensors.
Example 1:
.M18 proximity sensor
5 mm sensing range
.3 x operating distance = 15 mm < diameter
Therefore, the actuator dimensions must be 18 x 18 x 1 mm
Example 2:
.M18 proximity sensor
.8 mm sensing range
.3 x operating distance = 24 mm
Therefore, the target dimensions must be 24 x 24 x 1 mm
This standard measuring plate (target) is the optimal actuator for the
operation.
A reduction in the dimensions or change in material composition reduces
the sensing range.
Actual sensing range s r
The sensing range of an individual proximity sensor measured at ambient
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 sensing range s u
The sensing range of an individual
proximity sensor, 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
