Download Sensors

Sensor
types
Automatic Control System
Automatic Control
System
Construction
•
•
•
•
•
•
•
•
•
•
Material or Power
Object
Output Signal
Sensor
Disturbances
Converter
Measuring Device
Controller
Industry Controller
Executive Device
Graphic Symbols- Sensors and
Detectors
– PROXIMITY SENSOR
– PROXIMITY DEVICE
(FUNCTIONAL SYMBOL)
– CAPACITIVE CRYSTAL SET
TACTILE SENSOR -
– TACTILE SENSOR WITH NORMAL
CLOSED CONTACT
– PROXIMITY SENSOR WITH
NORMAL OPEN CONTACT
CONTACTRON
– IRON SENSOR
SENSORS
SELECTION
(CLASSIFICATION)
1. Contact versus Non-contact
• Contact sensor : There is physical contact
betwen the sensor an the parametr it
measures
• Non-contact sensor : Also called
proximity sensors. Proximity indicates that
the object is near, but contact is not
required.
Contact Sensor
Non- Contact Sensor
2. Digital (binary) versus Analog
• Digital sensors
– Have two states: on or off
– Detect presence/absence of object
– Counting such as used in a rotary encoder
• Analog sensors
– They sense continuous variables (temp,
pressure) and provide a continuous (usually
linear) voltage or current according to an
input/output transfer function.
– More complex than digital and can provide
more information.
3. Principles and Designs
• Sensor principles
– Inductive
– Capacitive
– Resistive
• Sensor designs
– Extrinsic
– Intrinsic
4. Digital Sensors
•
•
•
•
•
•
Switches
Optical (photoelectric) sensors
Encoders
Ultrasonic sensors
Inductive sensors
Capacitive sensors
5. Industrial sensors
• Proximity
– Mechanical
– Optical
– Inductive/Capacitive
• Position/Velocity
–
–
–
–
Potentiometr
LVDT
Encoders
Tachogenerator
• Force/Pressure
• Vibration/Acceleration
Inductive
sensors
Types of inductive sensors
proximity
movement
Proximity sensors
I. Schematic diagram
metal
generator
liminal
output
construction amplifier
with hysteresis
output
signal
Proximity sensors
II. Principle of working
metal
generator
liminal
construction
with hysteresis
output
amplifier
output
signal
Proximity sensors
III. Parameters
Nominal zone of working
Trip - out
Switches on
Metal plate
Inductive sensor
Hysteresis
Zone of working
Frequency of jumpering
Sensor
Measuring plate St37
Traffic trend
Real zone of working
Working zone of action
Hysteresis of jumpering
Corrective coeficiences
Repeatability
Temperature of working
Admission
Residual voltage
Residual current
Movement sensors
I. Schematic diagram
Movement sensors
II. Principle of working
Movement sensors
III. Parameters
Zone of working
Trip - out
Switches on
Metal plate
Inductive sensor
Corrective coeficiences
Hysteresis
Zone of working
Hysteresis of frequency
Out
Increase speed
lowering
speed
Liminal frequencies
Maximum frequency of jumpering
Time of deceleration
IV. Symbol of inductive sensors
V. Examples of inductive sensor
VI. Inductive sensor in use
Quantity control
Detection unevenness
on packaging
VI. Inductive sensor in use
Control of screw tight the screws
Capacitive
sensors
Capacitive sensors
I. Schematic diagram
object
periphery of oscillator
active surface
screen
comparator
amplifier
Capacitive sensors
II. Principle of working
O
b
j
e
c
t
periphery of
oscillator
comparator
amplifier
III. Symbol of capacitive sensors
IV. Capacitive sensor in use
Silicon Wafer deposition & etching
Silicon Wafer proximity
Wafer cutting/processing
Robot arm control
Computer hard disc drive
Printing Press/Photocopiers
Tooling parallelism/alignment
IV. Capacitive sensor in use
Detection of movement
Detection of position
IV. Capacitive sensor in use
Counting of
rotational speed
Steering mechanical
process
Optical
sensors
Optical (Photoelectric) Sensors
• All optical sensors use light to sense
objects.
• Operation method:
- Lasers, Incandescend bulbs, or Light emitting diodes
(LEDs) are used as light source
- The light source is turned off and on (modulation) at a
high frequency (could be as hight as several kHz)
- A photodetector senses the pulsed light
- The light emitter and receiver are turned to the
modulation frequency.
Example of Sensor using LED as a
light source
Types of Optical Sensors
•
•
•
•
•
•
•
Reflective (Diffuse) Sensors
Retroreflective Sensors
Thru-beam Sensors
Polarizing Photo Sensors
Convergent Photo Sensors
Fiber Optic Sensors
Laser Sensors
Reflective (Diffuse) Sensors
T - Transmitter
R - Receiver
Transmitter and receiver are
combined into one casing
OBJECT
T
R
Work relies on the reflective surface on the target to
reflect the light from the transmitter to the receiver
Advantages
•
Singular casing (Transmitter +
Receiver)
•
Objects detection with high reflect
parameter (0,6 - 0,9)
Disadvantages
• Low detecting distance
• Sensitive to colour and quality
• Sensitive to background
• Dead zone
Retroreflective Sensors
Transmitter and receiver are combined into one
casing
Make use of a reflector to reflect the light from
the transmitter to the receiver
OBJECT
T
REFLECTOR
R
Advantages
• Easy instalation
• Singular casing ( Transmitter + Receiver)
• Good working zone
Disadvantages
• Sensitive to lights objects
• Use reflector
• Dead zone
Thru-beam Sensors
System has a separate transmitter and receiver
OBJECT
T
R
It’s capable of sensing very small
object by narrowing the light
beam
Advantages
•
•
•
•
Detection for long distance
Lack of dead zone
Detection light objects
Detection in several environment
Disadvantages
• Large separate casings
• Problems with instalation ( set- up
Transmitter and Receiver)
Typical Application
•
•
•
•
•
•
•
•
•
•
Detecting the presence or absence of an object
Positioning and counting
Detection the end of travel of an object
Packaging machinery
Sorting and labelling machinery
Textile machinery
Pharmaceutical
Small part detection
High speed detection
Door controls
Parameters
-
Operating Temperature (10°C - +50°C)
Vibration
Supply Voltage (10 – 30 VDC or 230 VAC)
Detecting Distance
Output Current
Max. Switching Frequency
Degree of Protection
Hysteresis
Encoders
An encoder is a device that senses a
modification of speed and position and
converts it to a digital value
There are two main types of rotary
encoders:
- Incremental
- Absolute
Principle of working
The light from Light Source shines through the lines on disk
and Grid Assembly and is then sensed by photo detector
Construction of encoder’s disk:
Incremental encoders:
An incremental encoder generates a series of
square waves
Encoders transform rotary movement into a sequence of
electrical pulses
There are two main types of incremental
encoders:
-Tachometer
- Quadrature
Absolute encoder
An absolute encoder provides a word of output with a
qunique pattern that represents each position.
The output is proportional to the angle of the shaft
Principle of working