1. Sensors
May 25, 2013

2. Classification of Sensors
Sensors are classified as either :
Contact type
Non-contact type (proximity sensors)
Proximity sensors being the more commonly used sensor.

3. Classification of Sensors
Sensors are further categorized as either :
Binary
Analogue.
Binary sensors convert a physical quantity into a binary signal which means it has two switching states. The most common being an electrical signal ON or OFF.

4. Types of Sensors

5. Types of Sensors

6. Types of Sensors

7. Limit Switches
Limit switches are considered to be contact sensors, as it needs to be actuated to give a signal output

8. Reed Switches
Most Widely Known and Used as Cylinder Switches

9. Glass Tube filled with nitrogen
Reed contacts
LED indicator

16. 24v

17. 24v

19. Reed Switches

20. Sensor Switching Distance
Object
Sensor Sn
Sn = Switching Distance

21. Sn = Switching Distance
Sensor Hysteresis
Sensor
Object h Sn
Sn = Switching Distance
h = Hysteresis

22. Inductive Proximity Sensors

23. Inductive Proximity Sensors
High Frequency magnetic field (300 to 800 kHz) Active Surface
Resonant circuit coil
LED indicator
Connection cable

24. Target
Sensor
Oscillation
Amplitude
Sensor output signal ON
OFF

25. Target
Sensor
Oscillation
Amplitude
Sensor output signal ON
OFF

26. Target
Sensor
Oscillation
Amplitude
Sensor output signal ON
OFF

27. Target
Absorbtion of energy
Sensor
Oscillation
Amplitude
Sensor output signal ON
OFF

28. Target
Sensor
Oscillation
Amplitude
Sensor output signal ON
OFF

29. Target
Sensor
Oscillation
Amplitude
Sensor output signal ON
OFF

30. Target
Sensor
Oscillation
Amplitude
Sensor output signal ON
OFF

31. Target
Sensor
Oscillation
Amplitude
Sensor output signal ON
OFF

32. Target
Sensor
Oscillation
Amplitude
Sensor output signal ON
OFF

33. Target
Sensor
Oscillation
Amplitude
Sensor output signal ON
OFF

34. Inductive Proximity Sensors
The bigger the coil, the greater the active switching gap.
Inductive sensors can only detect metals.
Different switching distances for different metals

35. Inductive Proximity Sensors
Material
Reduction Factor
Mild Steel
1.0
Chrome Nickel
0.70 ~ 0.90
Brass
0.35 ~ 0.50
Aluminum
0.35 ~ 0.50
Copper
0.25 ~ 0.40

36. Inductive Proximity Sensors
Inductive sensors detect metals and operate quickly, reliably and tirelessly. They are used to:
Count
Identify
Detect
Switch
Control
Check
Distinguish
Sort
Position

37. Inductive Proximity Sensors
Sensing a Cam Controller

38. Inductive Proximity Sensors

39. Inductive Proximity Sensors

40. Inductive Proximity Sensors

41. Inductive Proximity Sensors

42. Capacitive Proximity Sensors
Sensor is looking for a change in capacitance in the active field
Electrostatic field
Active surface
Active electrode
Earth electrode
LED indicator
Adjusting screw
Connection cable

43. Capacitive Proximity Sensors
Almost similar to the inductive sensor.
Able to detect most materials.
Switching distance adjustable.
Able to detect fluid level through the wall of a bottle.

44. Target

49. Sensor is adjusted so that it does not ‘see’ the wall of the vessel.

50. As the level rises the fluid affects the sensor field.

51. To detect liquid filling level

52. Capacitive Proximity Sensors
Detection of matt, black objects.
Detecting fluid level, wall thickness must be limited.
Monitoring the winding of electrical wires and cables.

53. Capacitive Proximity Sensors

54. Capacitive Proximity Sensors

55. Capacitive Proximity Sensors

56. Capacitive Proximity Sensors

57. Optical Proximity Sensors
There are three different types of optical proximity sensors:
Through beam optical sensor
Retro-reflective optical sensor
Diffuse optical sensor

58. Optical Proximity Sensors

59. Through Beam Sensor

60. Through Beam Sensor
Transmitter
Receiver

61. Transmitter
Receiver

62. Target
Transmitter
Receiver

63. Transmitter
Receiver

64. Transmitter
Receiver

65. Transmitter
Receiver

66. Transmitter
Receiver

67. Transmitter
Receiver

68. Transmitter
Receiver

69. Transmitter
Receiver

70. Through Beam Sensor

71. Through Beam Sensor

72. Through Beam Sensor Advantages of through beam sensors
Enhanced reliability because of permanent light during operation.
Wide range.
Small objects can be detected even at large distances
Suitable for aggressive environment.
Good positional accuracy

73. Through Beam Sensor Disadvantages of through beam sensors
Two separate proximity sensor modules and separate electrical connections are required.
Cannot be used for completely transparent objects.

74. Through Beam Sensor Applications of through beam sensors
Used as safety devices.
Fast counting applications.
Monitoring for broken parts.

75. Through Beam Sensor

76. Retro-Reflective Sensor

77. Reflector (prismatic) Transmitter / Receiver

78. T R
Transmitter / Receiver
Reflector (prismatic)

79. Transmitter / Receiver Reflector (prismatic)

80. Transmitter / Receiver Reflector (prismatic)
Target T R
Transmitter / Receiver
Reflector (prismatic)

81. Transmitter / Receiver Reflector (prismatic)

82. Transmitter / Receiver Reflector (prismatic)

83. T R

84. Transmitter / Receiver Reflector (prismatic)

85. Transmitter / Receiver Reflector (prismatic)

86. Transmitter / Receiver Reflector (prismatic)

87. Retro-Reflective Sensor
Advantages of retro-reflective sensors
Enhanced reliability because of permanent light during operation.
Simple installation and adjustment.
Objects can be diffuse reflecting, mirroring or transparent as long as enough light is absorbed.
A greater range as compared to diffuse sensors.

88. Retro-Reflective Sensor
Disadvantages of retro-reflective sensors
Transparent, very bright or shiny objects may remain undetected.

89. Retro-Reflective Sensor

90. Retro-Reflective Sensor

91. Diffuse Sensor

92. Transmitter / Receiver
Target T R
Transmitter / Receiver

93. Transmitter / Receiver

94. Transmitter / Receiver

95. T R

96. Transmitter / Receiver

97. Transmitter / Receiver

98. Diffuse Sensor Advantages of diffuse sensors
Because the reflection on the object activates the receiver, an additional receiver is not required.
Diffuse sensors allows frontal detection.
Objects can be detected selectively in front of a background.

99. Diffuse Sensor Disadvantages of diffuse sensors
They are not as suitable as through beam sensors if accurate lateral response is crucial.
They do not react to objects with reduced reflection eg. Black objects

100. Diffuse Sensor

101. Diffuse Sensor

102. Fibre-Optic Cables Advantages of using fibre optic cables
Detection of objects in areas of restricted access.
Possibility of remote installation.
Accurate detection of small objects.
Sensing elements can be moved.

103. Fibre-Optic Cables

104. Fibre-Optic Cables

105. Fibre-Optic Cables

106. Fibre-Optic Cables

107. Fibre-Optic Cables

108. Fibre-Optic Cables
Needle detection

109. Fibre-Optic Cables

110. Ultrasonic Sensors
Distance meas.

111. Ultrasonic Sensors Advantages of ultrasonic sensors
Relatively large range.
Object detection irrespective of colour and material.
Safe detection of transparent objects.
Relatively dust and dirt insensitive.
Fading out of background possible.
Outdoor application possible.

112. Ultrasonic Sensors Disadvantages of ultrasonic sensors
Object surface should be at right angles.
They react slowly.
Generally more expensive than optical sensors.
They cannot detect sound absorbing materials.

113. Ultrasonic Sensors

114. Ultrasonic Sensors

115. Ultrasonic Sensors

116. Pneumatic Sensors
With pneumatic proximity sensors the presence or absence of an object is detected by means of contactless sensing with air jets.
A signal pressure change occurs which is further processed.

117. Selection Criteria
They can be selected according to the material which they are to detect.
Metals of any kind can be detected easily and economically with inductive sensors if short switching distances only are required (eg. 0.4 …. 10 mm)
For greater distances, optical sensors of varying designs are available. The greatest distances can be spanned by means of through beam sensors.

118. Selection Criteria
Capacitive proximity sensors are suitable for the detection of a wide range of materials, but again only for relatively small distances, similar to inductive proximity sensors.
Ultrasonic and optical diffuse reflective proximity sensors are able to detect a wide range of different materials over greater distances. However, the detection of reflecting objects with tilted surfaces may create problems.

119. Selection Criteria
Further criteria for the selection of proximity sensors are the conditions under which the object is to be detected, what the installation requirements for the proximity sensors are and the environment factors to be taken into account

120. Selection Criteria Object material
Conditions for the detection of objects
Installation conditions
Environmental conditions
Safety applications
Options/features of proximity sensors

121. Sensor Exercise
A Conveyor transports three different coloured workpieces to a sorting station. At the sorting station, the workpieces will be sorted according to their colour and directed to their respective paths.
The workpieces are :
Red
Black
Metal
How many sensors and which sensors are required at the sorting station?

122. Sensor Exercise
Sorting
Station
Red
Metal
Black