Sensors May 25, 2013
Classification of Sensors Sensors are classified as either : Contact type Non-contact type (proximity sensors) Proximity sensors being the more commonly used sensor.
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.
Types of Sensors
Types of Sensors
Types of Sensors
Limit Switches Limit switches are considered to be contact sensors, as it needs to be actuated to give a signal output
Reed Switches Most Widely Known and Used as Cylinder Switches
Glass Tube filled with nitrogen Reed contacts LED indicator
24v
24v
Reed Switches
Sensor Switching Distance Object Sensor Sn Sn = Switching Distance
Sn = Switching Distance Sensor Hysteresis Sensor Object h Sn Sn = Switching Distance h = Hysteresis
Inductive Proximity Sensors
Inductive Proximity Sensors High Frequency magnetic field (300 to 800 kHz) Active Surface Resonant circuit coil LED indicator Connection cable
Target Sensor Oscillation Amplitude Sensor output signal ON OFF
Target Sensor Oscillation Amplitude Sensor output signal ON OFF
Target Sensor Oscillation Amplitude Sensor output signal ON OFF
Target Absorbtion of energy Sensor Oscillation Amplitude Sensor output signal ON OFF
Target Sensor Oscillation Amplitude Sensor output signal ON OFF
Target Sensor Oscillation Amplitude Sensor output signal ON OFF
Target Sensor Oscillation Amplitude Sensor output signal ON OFF
Target Sensor Oscillation Amplitude Sensor output signal ON OFF
Target Sensor Oscillation Amplitude Sensor output signal ON OFF
Target Sensor Oscillation Amplitude Sensor output signal ON OFF
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
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
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
Inductive Proximity Sensors Sensing a Cam Controller
Inductive Proximity Sensors
Inductive Proximity Sensors
Inductive Proximity Sensors
Inductive Proximity Sensors
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
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.
Target
Sensor is adjusted so that it does not ‘see’ the wall of the vessel.
As the level rises the fluid affects the sensor field.
To detect liquid filling level
Capacitive Proximity Sensors Detection of matt, black objects. Detecting fluid level, wall thickness must be limited. Monitoring the winding of electrical wires and cables.
Capacitive Proximity Sensors
Capacitive Proximity Sensors
Capacitive Proximity Sensors
Capacitive Proximity Sensors
Optical Proximity Sensors There are three different types of optical proximity sensors: Through beam optical sensor Retro-reflective optical sensor Diffuse optical sensor
Optical Proximity Sensors
Through Beam Sensor
Through Beam Sensor Transmitter Receiver
Transmitter Receiver
Target Transmitter Receiver
Transmitter Receiver
Transmitter Receiver
Transmitter Receiver
Transmitter Receiver
Transmitter Receiver
Transmitter Receiver
Transmitter Receiver
Through Beam Sensor
Through Beam Sensor
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
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.
Through Beam Sensor Applications of through beam sensors Used as safety devices. Fast counting applications. Monitoring for broken parts.
Through Beam Sensor
Retro-Reflective Sensor
Reflector (prismatic) Transmitter / Receiver
T R Transmitter / Receiver Reflector (prismatic)
Transmitter / Receiver Reflector (prismatic)
Transmitter / Receiver Reflector (prismatic) Target T R Transmitter / Receiver Reflector (prismatic)
Transmitter / Receiver Reflector (prismatic)
Transmitter / Receiver Reflector (prismatic)
T R
Transmitter / Receiver Reflector (prismatic)
Transmitter / Receiver Reflector (prismatic)
Transmitter / Receiver Reflector (prismatic)
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.
Retro-Reflective Sensor Disadvantages of retro-reflective sensors Transparent, very bright or shiny objects may remain undetected.
Retro-Reflective Sensor
Retro-Reflective Sensor
Diffuse Sensor
Transmitter / Receiver Target T R Transmitter / Receiver
Transmitter / Receiver
Transmitter / Receiver
T R
Transmitter / Receiver
Transmitter / Receiver
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.
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
Diffuse Sensor
Diffuse Sensor
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.
Fibre-Optic Cables
Fibre-Optic Cables
Fibre-Optic Cables
Fibre-Optic Cables
Fibre-Optic Cables
Fibre-Optic Cables Needle detection
Fibre-Optic Cables
Ultrasonic Sensors Distance meas.
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.
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.
Ultrasonic Sensors
Ultrasonic Sensors
Ultrasonic Sensors
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.
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.
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.
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
Selection Criteria Object material Conditions for the detection of objects Installation conditions Environmental conditions Safety applications Options/features of proximity sensors
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?
Sensor Exercise Sorting Station Red Metal Black