Class Notes - Year 4 - 2020-2021
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Year 4

Lesson 408

Counters and Sensors

IEC Manual 408

Operation and Uses for Counters

Can count up or count down from preset number
Inputs are supplied by sensors
When # of signals (pulses) reaches preset #, SPDT contacts operate
Application example: track items for packaging

ECM5 16-5 - Counters and Totalizers

Account for # of events in system
Products made
Required to fill carton
Rejected parts
Gallons through pipe

Totalizers

Can be used only total number is required to be known
Only displays total number, no output

Counters

Count inputs and provides output
Provides output at predetermined count
2 types
Up counter
Down counter

Up Counters

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Two types - One count inputs / One count input and one reset input
One count input
Removing power resets count
One count input and one reset input
Activating reset input resets count input
One count added each time count input is closed
When preset count is reached, contacts are activated

Up/Down Counters

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Counts input from two different inputs
One adds a count
One subtracts count
Provided output when certain count is reached
Third input for reset input
Example: parking garage

ECM5 21-5 - Flow Detection Sensors

Detects movement of liquid of gas
Operates using thermal conductivity
Detection head is heated slightly higher than medium to be detected
When flowing, heat is conducted away from head
When not flowing, heat is not conducted away
Thermistor translates temp into resistance
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There will be slight delay (30 sec)
Short time will pass before operating
LED indicators are usually included to indicate state of flow

ECM5 21-6 - Hall Effect Sensors

Sensor that detects proximity of magnetic field
Named for Edward H Hall in 1879

Theory of Operation

Constant control current passed through T\this strip of semiconductor
When magnet is brought near, small voltage (Hall voltage) appears at contacts
Voltage varies depending on proximity of magnet
When magnet removed, voltage is 0
Hall voltage is dependent upon magnetic field and current flow
No magnetic or no current flow, output is 0

Sensor Packaging

Configurations:
Cylinder
Proximity
Vane
Plunger
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Cylinder and proximity used to presence of magnet
Vane include sensor on one side and magnet on other, used to detect object passing through
Plunger includes magnet moved by external force against lever

Sensor Actuation

Head-On

Magnet is oriented perpendicular to surface of sensor and usually centered over the point
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Direction of movement is toward or away

Slide-By

Magnet is moved across face of sensor at constant gap
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Pendulum

Combination of head-on and slide-by
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Can be single pole or multiple-pole

Vane

Iron vane shunts or redirects magnetic field away from sensor
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Sensor Applications

Used to detect presence or proximity of objects

Conveyor belts

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Hall effect sensor mounted to frame
Magnet mounted to conveyor pulley
Signal is sent every time magnet passes
Shut down of conveyor interferes with normal signal and alerts operator

Liquid Level Monitoring

Mount magnet to cork
Cork floats in tube
As level goes down, magnet passes sensor
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Security Systems

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Beverage Guns

Used because of small size and sealed construction
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Length Measurement

Mount disk with 2 notches on extension of a motor drive shaft
Vane sensor is mounted so disc passes through gap
Each notch represents fixed distance
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Level/Degree of Tilt

Magnets installed above sensor in pendulum fashion
If magnets are directly over sensor, machine is level
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Joysticks

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EMC5 21-7 - Proximity Sensors

Detects presence of object my means of electronic sensing field
Object does not contact sensor
Can detect almost any solid or liquid
Can detect very small or very large objects
Two types

Inductive Proximity Sensor

Operate on eddy current killed oscillator (ECKO) principle
An oscillator produces an alternating magnetic field that varies in strength depending whether or not a metallic target is present
When metallic target is in front of inductive proximity sensor, RF field causes eddy currents to be set up on the surface of target material
Eddy currents upset AC inductance or sensor oscillator circuit, causing oscillation to be reduced
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Detect ferrous materials more readily than non-ferrous
Sensing distances range from .5 mm to 40 mm
Applications:
Positioning of tools and parts
Metal detection
Drill bit breakage detection

Capacitive Proximity Sensors

Measures change in capacitance that is caused by approach of an object to the electric field of capacitor
Detects all materials that are good conductors as well as insulators with relatively high dielectric constant
Plastic, glass,water, moist wood
Operation
2 small plates that form capacitor are located directly behind front of sensor
When object approaches, dielectric constant of capacitor changes, changing oscillator frequency
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Distances range from 3 mm to 15 mm

EMC5 21-8 - Ultrasonic Sensors

Can detect presence of object by emitting and receiving high frequency sound waves
Can detect solids or liquids
Can detect up to 1 m distance
Soft objects are more difficult to detect
Can detect clear objects

Operating Modes

Direct Mode

Emitter and receiver are placed opposite each other
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Diffused Mode

Emitter and receiver are in the same enclosure
Receiver listens for sound wave bouncing back
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EMC5 24-2 - Photoelectric Sensors

Can detect presence of object without touching object
Detects by means of beam of light

AC Photoelectric Sensors

Sensor connected in series with load it controls
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Considerations
Load Current
Operating Current
Minimum Holding Current
Minimum load current to hold sensor closed
Series/Parallel Connections
AND logic - series
OR logic - parallel
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DC Photoelectric Sensors

EMC5 24-3 - Fiber Optics

Uses thin, flexible glass or plastic optical fiber to transmit light
Most commonly used as transition link

Optical Fibers

Consists of:
Core
Cladding
Protective jacket
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Fiber Connectors

Fibers held together by connector or splice that squarely aligns them
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EMC5 24-4 - Photoelectric Sensor Applications

Can detect most materials
Have longer sensing distance than ultrasonic and proximity sensors
Several mm to over 100’
Many sensors include adjustable sensing distance
Uses:
Counting
Positioning
Sorting
Providing safety
Usually used as inputs into timers, relays, counters, programmable controllers, and motor control circuits

Scanning Techniques

2 major components
Light source
Emits beam of light
Photosensor
Detects beam of light
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Factors to determine best scanning technique:
Distance
Size of target
Reflectance
Target positioning
Differences in color and reflective properties
Changes in ambient light
Condition of surrounding air

Direct Scan

Transmitter and receiver placed opposite each other
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Retroreflective Scan

Transmitter and receiver placed in same housing
Beam is reflected back
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Polarized Scan

Receiver responds only to depolarized reflected light
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Specular Scan

Transmitter and receiver placed at equal angles from highly reflective material
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Diffuse Scan

Light reflected back from target
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Convergent Beam Scan

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Modulated and Unmodulated

Modulated
Sources is turned on and off quickly
Unmodulated
Source is constant

Response Time

# of pulses per second a controller can detect
Must be considered if high speed is needed

Sensitivity Adjustment

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Dark Operated/Light Operated

Dark Operated

Energizes output switch when target is present
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Light Operated

Energizes output switch when target is absent
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EMC5 24-5 - Photoelectric Control Applications

Truck Loading Bay / Height and Distance Monitoring

Schematic

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Step by Step Animation

Full Speed Animation

Product Monitoring

Schematic

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Step by Step Animation

Full Speed Animation

Mounting Photoelectric Sensors

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