ME 445 INTEGRATED MANUFACTURING TECHNOLOGIES
EXPERIMENT 1
"PROXIMITY SENSORS"
OBJECTIVE
Increasing automation of complex production systems necessitates the use of components
which are capable of acquiring and transmitting information relating to the production
process. Sensors fulfill these requirements and have therefore in the last few years become
increasingly important components in measuring and in open and closed loop technology.
Sensors provide information to a controller in the form of individual process variables.
Proximity sensors are the most basic data acquisition devices in automation. They measure /
detect physical input such as temperature, pressure, force, length, and proximity of an object.
Transducers are typically a sensorial system capable of signal processing, equipped with
electronic instrumentation. Position sensors give a “yes” or “no” response according to the
place of the object.
The aim of this experiment is to illustrate the aspects of different types of proximity sensors,
their properties, and to compare them. For this, a setup table containing Magnetic, Inductive,
Capacitive, and Optical sensors is used. A positioning slide coupled with a vernier caliper is
used to measure switching distances.
Figure: Proximity sensors setup table
1
GENERAL INFORMATION
Sensors are the first of the four milestones of Automation:
1. Sensing
2. Signal Processing
3. Planning and Response
4. Memory
They usually convert some physical data into a voltage difference for further processing by a
Computer, PLC or I/O Card. The advantages of proximity sensors are:
 They determine the geometrical positions automatically and sensitively.
 They do not need of a direct contact with the workpiece.
 They do not have movable parts that can wear out.
 They are usually equipped with electronic circuits for failure protection.
 They have various types that can be used under different situations.
 They provide the secure working of the process.
 They are used for the system failure analysis.
Their typical usage areas are:
 Automotive industry,
 Packaging industry,
 Printing and paper industry
 Ceramic industry
 Wood-working industry
 Food processing industry
CATEGORIES
According to I/O processing:
 Binary: Convert a physical measurement value to a binary code (in the form of ON/OFF
signals in a selected voltage range)
 Analog: Convert a physical measurement into an analog signal (e.g. temperature readings
to variable voltage differences)
According to physical considerations:
 Mechanical switches
 Magnetic (with/without contacts, pneumatic output)
 Inductive (inductive sensors)
 Capacitive (capacitive sensors)
 Optical (light barriers, reflection sensors)
 Ultrasonic (ultrasonic barriers, ultrasonic sensors)
 Pneumatic (back-pressure nozzles, air reflection sensors, air barriers)
2
TYPICAL USAGE
Detecting whether an object exists in a defined position:
Positioning of an object:
Counting the number of parts:
3
Determining the rotational speed:
Determining the linear speed:
4
TYPES
1. Mechanical switches:
Mechanical switches are simple GO/NoGO indicators. They have physical contact with the
object, usually coupled with relays and contactors to drive a circuit. Widely used in the
industry to mark the end-start points of cylinders, pistons, linear and rotary drives, to sense
doors. They are less sensitive and have lower maximum switching frequency compared to
proximity switches. Because of the physical contact with the object, they require maintenance
and replacement.
2. Magnetic Proximity Switches:
Magnetic switches (also called as Reed-contacts) use the distortion of the magnetic field. If a
ferromagnetic material (Fe-Ni compound) comes in the vicinity, the magnetic field distorts
and gives an input to the switch. Thus, they are only sensitive to ferromagnetic materials and
magnetic fields. Dirt and humidity is of little importance. They preserve high hysteresis
(undefinite range of physical input). They are widely used in pairs of machine parts such as
piston-cylinder arrangements.
3. Inductive Proximity switches:
Inductive proximity switches also work on the principles of magnetic fields and induction.
They response to conductive materials, typically metals. The tabular data on switching
distance depends on mild steel (usually Fe37); thus, a reduction coefficient must be defined
for different metals. For the metals such as Cr-Ni, brass, aluminum, and copper this value
must be modified with the experimental reduction coefficient found usually in the range of
0.25-0.9. Also the reduction coefficient depends on the size of the measured object. They are
widely used in the mass production lines and conveyors to detect metallic workpieces,
moving parts of machinery, for measuring linear, rotational speeds, presses, and encoders.
4. Capacitive Proximity switches:
Unlike the magnetic and inductive types, capacitive proximity switches response to all types
of materials. The reduction coefficient is determined experimentally in the range of 0.1 to 1
(metals =1 and water =1). Note that liquids can also be detected by capacitive switches. They
are very sensitive to environmental factors such as dust, dirt and humidity. Therefore they can
be used to distinguish object properties such as color, thickness, water column height, and
vibration. Sample application areas are in production lines and conveyors to count
workpieces, sense packaging defects etc.
5. Optical Proximity switches:
Optical proximity switches use the presence of visible (with wavelength of 660nm -red-) or
invisible (with wavelength of 880nm -ultra-red-), light for input. They give a NPN or PNP
output to the circuit. Here, instead of the reduction coefficient the operation reserve is defined
as the ratio of signal intensity in the input of the sensor to the required intensity for switching.
Note that in correct working conditions, operation reserve must have a value of greater than
one. The operation reserve depends on ambient conditions such as dust, dirt, ambient light
color and intensity, distance from part, reflect-angle etc.
Optical sensors are divided into two main parts:
5


Light sensors (can be equipped with fiber-optic cabling for long distance transmission,
may use ambient light or the light produced in a coupled unit)
Reflected light sensors (can be equipped with fiber-optic cabling for long distance
transmission, uses the reflected light produced in the same unit from the part or a reflector
sheet)
Optical sensors have a relatively greater switching distance. Therefore they may be used in
detecting surface irregularities, failure detection, detection of transmissive surfaces, colors
etc. Fiber optic cabling for transmission also gives a flexibility to use small units at difficult
locations.
6. Ultrasonic Proximity switches:
They use the reflected sound power for input. Note that above the sensors stated here,
ultrasonic proximity switches have the greatest switching distance and frequency. Therefore,
they are used to detect distant objects with very high speeds. They are usually insensitive to
ambient conditions and should be preferred in very extreme conditions, while they are very
expensive.
7. Pneumatic Proximity switches:
They use the reflected back-pressure supplied from a nozzle at or distant from the switch unit.
Generally preferred in the areas of:





Very dirty and dusty places,
At high temperatures,
In the vicinity of explosive materials where electrical currents may be dangerous,
At places where intensive magnetic fields are present, in the vicinity of big motors,
pumps, turbines etc.
The sensor unit and nozzle unit may be built in one package or as different units. Can be
used to drive a pneumatic piston directly.
6
SELECTION CRITERIA
7
PROTECTION CLASSES
The protection classes of the mechanical elements are defined in DIN 40050. For example,
IP67 represents a device with protection against contact and foreign material according to 6
(Table A1) and against water and humidity according to 7 (Table A2).
First
digit
0
1
2
3
4
5
6
Second
digit
0
1
2
3
4
5
6
7
8
Protection Class
No special protection
Protection against solid objects larger than 50 mm diameter. Unprotected against
forced contacts (eg. via hand). Should be kept apart from the body
Protection against solid objects larger than 12 mm diameter. Should be kept apart
from the fingers
Protection against solid objects larger than 2.5 mm diameter. Should be kept apart
from the devices (wire, hand tools etc.)
Protection against solid objects larger than 1 mm diameter. Should be kept apart
from the devices (wire, hand tools etc.)
Protection against hazardous dust accumulation. Dust protection is not totally
achieved, but inner dust accumulation does not affect functioning of the device. Full
protection against forced contact.
Full protection against dust accumulation. Full protection against forced contact.
Table A1: Protection against dust & forced contact.
Protection Class
No special protection
Protection against vertically tipping water. The water has no hazardous effects
(tipping water).
Protection against vertically tipping water at 15  to the normal of the device
surface. The water has no hazardous effects (inclined tipping water).
Protection against water tipping at 60 to the normal of the device. The water
has no hazardous effects (sprinkling water)
Protection against water from any direction to the device. The water has no
hazardous effects (flowing water)
Protection against water from a nozzle coming from any direction to the device.
The water has no hazardous effects (flowing water)
Protection against water forced water coming from any direction to the device.
The water has no hazardous effects (forced water)
Protection against water in case of immersion at certain pressure for a specific
time Leakage of the water into the device is avoided.
Full protection against water in case of immersion for a predetermined period of
time (permanent immersion).
Table A2: Protection against water
8
DEFINITIONS
Object material: The material of the object to be sensed. Note that under non-ideal
circumstances reduction factors are defined. All tabular data about the properties of the sensor
are based on identifying the indicated object under ideal circumstances.
Switching Voltage: The operating supply/output voltage of the sensor. The sensor must
definitely be operated at the permitted voltage range. For most industrial applications
typically 5V DC, 12-24V DC, 110-220V AC.
Switching Distance: The maximum distance of the object to be sensed from the head of the
sensor. Reduction factors about the environment and object properties not applied.
Max. Current: The maximum allowable current at the sensor output. To avoid excess
currents a protection circuit may be necessary.
Protection Class: The physical protection of the industrial device against foreign material,
dust, water and humidity. Defined in DIN 40050. Generally related with the construction.
Life: The theoretical life of the device. Indicated as time or in operating cycles.
Switching Frequency: The maximum occurrence of the object material at the switching
distance of the sensor in one second.
Reduction factor: The ratio of switching distance of metals (typically Fe37) to other
materials at the same ambient conditions. Some guide values are given in the table:
Material
All metals
Water
Glass
Plastic
Cardboard
Wood (depends on humidity)
Oil
Reduction factor
1.0
1.0
0.3 to 0.5
0.3 to 0.6
0.3 to 0.5
0.2 to 0.7
0.1 to 0.3
Table: Reduction factor of some materials
Hysteresis: The distance between switch-on and switch-off position of a sensor.
9
EXPERIMENTAL DATA
The following equipment is contained on the setup table. In the experiment, you may use this
list as a reference to distinguish between equipment.
Component
Proximity Sensor, non-contact, inductive-magnetic
Reed switch
Optical proximity sensor with fiber optic connector, block shaped (2 pieces)
Diffuse reflective optical sensor, block shaped
Optical sensor with fiber optic connector, cylindrical, M18
Inductive Proximity Sensor, cylindrical, M12
Inductive Proximity Sensor, cylindrical, M18
Capacitive proximity switch, cylindrical, M18
Ultrasonic proximity sensor, cylindrical, M18
Designation
167055
167056
167065
167068
167166
177464
177466
177470
184118
Table: List of sensors
Component
Reflector unit for reflex light barrier
Optical fiber for one-way light barrier (2 pieces)
Optical fiber for diffuse reflective optical sensor
One way light barrier, transmitter
One way light barrier, receiver
Designation
150504
150505
150506
167064
167067
Table : List of optical fibers & barriers
Component
Set of test objects
Graph paper, mm grid
Positioning slide
Adapter set
Vernier caliper
Digital multimeter
Ruler
Distributor unit
Counter unit
Rotary unit
Designation
034083
034085
034094
035651
035653
035681
035697
162248
162252
167097
Table: List of auxiliary equipment
10
Part no
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
Material, Dimensions (mm)
Magnet 1
Magnet 2
Mild steel (St 37), 90 x 30
Stainless steel, 90 x 30
Aluminium, 90 x 30
Brass, 90 x 30
Copper, 90 x 30
Cardboard, 90 x 30
Rubber, 90 x 30
Plastic, transparent, 90 x 30
Mild steel (St 37), 30 x 30
Mild steel (St 37), 25 x 25
Mild steel (St 37), 20 x 20
Mild steel (St 37), 15 x 15
Mild steel (St 37), 10 x 10
Mild steel (St 37), 5 x 5
Kodak gray card, 100 x 100
Plastic, transparent, 100 x 100
Plastic, red, 100 x 100
Plastic, blue, 100 x 100
Plastic, black, 100 x 100
Cardboard, white, 100 x100
Plastic, 2.0 mm thick, 90 x 30
Plastic, 3.0 mm thick, 90 x 30
Plastic, 4.0 mm thick, 90 x 30
Plastic, 8.0 mm thick, 90 x 30
Plastic, 11.0 mm thick, 90 x 30
Plastic, 14.0 mm thick, 90 x 30
Plastic, 17.0 mm thick, 90 x 30
Holder for fiber optic cable
Base plate with gear wheels
Holding bracket for liquid level measurement, through-beam sensor
Beaker
2 test screws
Valve housing
Screw driver
Table: List of test objects
11
PART 1 (Switching characteristics of a contacting magnetic proximity sensor)
The objective of the experiment is to learn about the switching characteristics of a contact
based magnetic proximity sensor (Reed contact) as a function of position and orientation of a
magnet.
Setup
Mount the distribution plate (1), the positioning slide (2), and the magnetic Reed sensor (3,
Designation 167056) on the assembly board. Mount the magnetic sensor laterally offset by 5
cm to the center of the positioning slide. Plug in the electrical power supply and connect the
sensor to the distribution plate. Note that the red color represents (+24V), the blue (0 V or
natural) and the black is the sensorial output (either +24V or 0, ON/OFF). Mount the test
object (Magnet 1) on the positioning slide. Adjust the distance from 0 to +18 mm with 2 mm
increments and at a constant distance adjust the stroke from -50 to +50 mm manually to detect
on/off positions. Enter the response points into the data sheet provided in the following pages.
Repeat the same procedure with the test object 2 (Magnet 2).
Figure: Setup for part 1
12
Conclusion
When working with magnetic proximity sensors, one has to take into account that there may
be several switching areas. This can lead to multiple counting when counters are employed.
This effect depends on the field strength of the permanent magnet used, and/or the distance of
the magnet to the proximity sensor.
As can be seen from the response diagram, two or even three switching areas may be
observed, depending on the orientation of the axis of the magnetic poles. This ambiguity of
the output signals can be prevented by attaching the magnet with the correct orientation of the
axis and, given a specific field strength, at the correct distance.
Discussion
Which orientation of the magnet would be appropriate if the magnet is located on a wheel and
for each rotation it should count only once? Is there a similarity of the response diagram and
magnetic field lines, why?
13
Data sheet for Part 1
Distance
Stroke (On/Off)
Table: Response positions for magnet 1
Distance
Stroke (On/Off)
Table: Response positions for magnet 2
14
PART 2 (Switching characteristics of different types of sensors)
The objective of the experiment is to learn about the switching characteristics of different
types of sensors, their interaction with material, thickness, color. The reduction factors and
hysteresis will be investigated.
Setup
Mount the distribution plate (1), the positioning slide (2) on the assembly board. In this
experiment you will use all other sensors (3) available:
Figure: Setup for Part 2
15
Data sheet for Part 2
Component
Workpiece
Inductive
Proximity
Sensor, cylindrical, M12
(177464)
Inductive
Proximity
Sensor, cylindrical, M18
(177466)
Mild
Steel
(St 37), Part
3
Mild
Steel
(St 37), Part
3
Component
Workpiece
Inductive
Proximity
Sensor, cylindrical, M18
(177466)
""
Mild
Steel
(St 37),
Part 3
Stainless
Steel,
Part 4
Aluminium,
Part 5
Brass,
Part 6
Copper,
Part 7
""
""
""
Switch-On
Point
SwitchOn
Point
Switch-Off
Point
SwitchOff
Point
Hysteresis
Hysteresis
Reduction
Factor
1.0
16
Component
Workpiece
Optical sensor with fiber
optic connector, cylindrical,
M18 (167166)
""
Kodak grey
card, white
side, part 17
Kodak grey
card,
grey
side, part 17
Plastic,
transparent,
part 18
Plastic, red
part 19
Plastic, blue,
part 20
Plastic, black
part 21
Cardboard,
white, part 22
Mild
steel
(St37), part 3
Rubber,
part 9
""
""
""
""
""
""
""
Component
Workpiece
Switch-On
Point
Switch-Off
Point
Hysteresis
Switch-On
Point
Switch-Off
Point
Hysteresis
Capacitive
proximity Mild Steel (St
switch, cylindrical, M18, 37), Part 3
(177470)
""
Stainless Steel,
Part 4
""
Aluminium,
Part 5
""
Brass,
Part 6
""
Copper,
Part 7
""
Cardboard,
Part 8
""
Rubber,
part 9
""
Plastic,
transparent,
part 10
17
Discussion
Industrial solutions are highly problem dependent so that the selection of sensor for particular
cases is very important. Which sensor would you prefer in an installation if you were to count:
1. Automobile tyres,
2. Tiny industrial metallic chips,
3. Plastic cups,
4. Bottles to determine either filled or empty.
18
PART 3 (Determining the rotational speeds)
The objective of the experiment is to learn about the differences and the application criteria of
rotational speed detection with optical and inductive proximity sensors.
Setup
Mount the distribution plate (1), the counting unit (2), rotary unit (3), Optical sensor with
fiber optic connector, cylindrical, M18, (4, 167166) and Inductive Proximity Sensor,
cylindrical, M12 (6, 177464) on the assembly board. Mount the Optical fiber for diffuse
reflective optical sensor (150506) to the Optical Sensor. The inductive sensor unit is to be
mounted approximately 2 mm away from the perforated disc. You will use the counting unit
to read the output pulse frequency and to determine the speed. Use the digital multimeter to
read the motor voltage. Adjust the speed such that the motor voltage is increased in 2V
intervals.
Figure 6. Setup for Part 3
19
The rotational speed is determined by the formula:
RS 
60  f s
n
where,
RS: Rotational speed (rpm)
n: Number of actuations per rotation (=8 pulse/rpms for the disc)
fs: Pulse frequency of the output signal (pulse/s)
Data sheet for Part 3
Motor
Output pulse frequency
Voltage of optical sensor (167166)
(V)
(pulse/s)
4
6
8
10
12
14
16
18
20
Speed RS
(rpm)
20
Output pulse frequency
of inductive sensor
(177464) (pulse/s)
Speed RS
(rpm)
INSTRUCTIONS FOR THE EXPERIMENT
Before the Experiment
1. Read your lab manual carefully.
2. You can use the data sheets in your manual provided, or you take photocopies of the data
sheets and fill them.
During the Experiment
1. Note that the experiment will be conducted by the group members, so be prepared and
familiar with the setup. The assistant should not answer all your questions or mount items
to help you.
2. You should take notes in the experiment to prepare a good report.
3. Time is short, be quick to finish everything required.
Grading
1. Your individual contributions in the laboratory will be assessed and graded.
2. Prepare a lab report according to the report outline that will be provided to you as a word
document.
3. Submit your report one week after the lab date until 17:30 to your assistant.
21