basic sales tech training information
TRANSCRIPT
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PLC What is PLC
PLC is an abbreviation and stand
forProgrammable LogicController.
A Programmable LogicController is a device that a usercan program to perform a seriesor sequence of events.
PLC performs relays, timers andcounters equivalent functions
Designed for industrialenvironment
Common brand use in market :Omron, Siemens, Mitshubishi,Allen-Bradley, GE, Modicon,Telemecanique/Schneider, etc.
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PLC How it work
PLC is like a small computer containing :
CPU (central processing unit), Memory, Input module and Outputmodule
Application for controlling machine or certain process thru pre-programmed set of instructions for implementing specific throughdigital or analog inputs and outputs.
The inputs will provide machine condition and status at the specific
time.The CPU with pre-programmed instruction will analyze and computeall the inputs condition as well as operation requirement and willtake necessary actions thru outputs channel.
The outputs are used to do specific action on the machine orprocess according to program logic sequence.
The program logic sequence is a set of instructions, sequencing,timing, counting and arithmetic that is written for specific application.
Programming PLC can be done thru few different programminglanguage, depending on type of PLC and what feature available tospecific model.
The most popular and easy to use is called a Ladder Logic Diagram
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PLC Connection
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PLC Programming Language
Statement list Function block
Ladder diagram
The instructions are represented
by graphic symbols:
Contacts, Coils & Boxes
The ladder diagram is the most
popular programming language
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Digital signals are discrete, have 2 values like 0 or 1, ON
and OFF.Analog signals are continuous, and varying in value.
Typical analogue signals from 0-10 VDC or 4-20 mA.
Ued to represent changing values such as speed,
temperature, weight and level
PLC Digital and Analog
PLC Input and Output (I/O = eye-oh)
Input is kind of analog or digital signal from input devices
(photo sensor, limit switch, pushbutton, transducer, etc)to PLC input module
Output is kind of analog or digital signal sent-out from
PLC output module to output devices (solenoid,
contactor, relay, frequency inverter, lamps, etc)
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PLC Conventional Design Comparition
Disadvantage Many wirings to relays and timers
Modification can be quite difficult
Troubleshooting can be quitedifficult to trace for problem
Power consumption can be quitehigh as relay coils consumespower
Machine downtime is usually longwhen problem occur
Drawing are not easily updatedover the years due to changes,this causes longer downtime inmaintenance and modifications
Advantage: Components replacement
compatibility usually easy to findeventhough has been absolute
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Advantages : Cost effective for controlling
complex system Flexibe and be re-applied to
control other system quickly andeasily
Computational abilities allow moresophisticated control application
Trouble-shooting aids make
programming easier and reducedown-time
Reliable components is higherthan mechanical relays and timers
High speed PLC operationincreases productivity
Cost much less compare to
conventional system in situtionwhen number of I/Os is very largeand control functions are complex
Spare part for relays andhardware timers are greatlyreduced as compared toconventional control panel
Disadvantages:Due to long years operation
capability, in long termreplacements could be difficult ifthe model has been absolute inthe market, may required aspecialist who know details ofmachine operation andprogramming, will take high costto upgrade.
Need certain skill level oftechnician for trouble-shooting
PLC Advantage vs Disadvantage
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PLC When need it
Mainly used in complex process control, that may
require algorithm and performance.Now there are many small and compact PLCsavailable in market that significantly help to reducecost to build a simple process automation, soconventional control system with relays, timers andcounters has been drastically left behind.
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Term of Control Board here is
referring to customized controlboard, designed for specificmachine process orsequencing.
Control Board controlled bymicrocontroller, programmed
to execute certain instructions.Provide software protectionagainst pirate copy by othercompetitor, as well as supplierdependent for spare
Relatively faster execution ofinstruction comparing to PLCexecution time.
Widely used for more complexand fast machine processapplication
PLC vs Control Board
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Advantage Faster respond
DisadvantageSensitive against
temperatureDifficult totroubleshoot
High cost for sparedue to supplied only
by machine supplier
Control Board Advantage vs Disadvantage
Program written and stored in
this IC Microcontroller
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PLC - Operator Interface
Man Machine Interface = Human Machine Interface =
User Interface = Operator Interface consider termused for similar function/purpose althought in definitianslightly different each other.
User interface is a place (device) where interactionbetween humans and machines occurs, for effectiveoperation and control of the machine, and
feedback/status/alarm/fault indication from themachine which aids the operator in making operationaldecisions.
Built-in hardware and software components.
In machine industries application, usually used in
combine with PLC, it will help to reduce cost forhardware input and output devices like push-button,indication lights, status, switches, input and output forvalues, etc.
(contd next.....)
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PLC - Operator Interface (contd)
Help to reduce extra wirings for more complex
machine applicationFor more advance model, can be used to aids formaintenance trouble-shooting.
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Data Communication - 1
Serial RS232, RS422, RS485
Serial transmission involves the sending of data onebit at a time over a single communication line.
Low speed data transfer compare with other type ofcommunication.
Can be used for long distance data transfer (forcurrent-loop type), sometime up to several
kilometers, comparing with voltage type with only upto 50 meters.
Profibus A single multi-drop cable is used to connect all
devices, with high speed, bi-directional, serial
messaging used for transfer of information Offer huge savings on cabling cost when compare
with older methods, particularl for large plant sites.
Allow simple linking of devices from many differentvendors
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Data Communication - 2
Ethernet
The most common type of connection computersuse in a local area network (LAN)
Looks much like regular phone jack, has 8 pins,called RJ45
2 widely-used form of Ethernet are 10BaseT(10mbps) and 100BaseT (mbps=megabit per-
second)
USB Allow high speed data transfer, easy connection of
peripheral to a PC. When plugged in, everythingconfigures automatically.
Use for short length of distance, not suitable forlonger distance data transfer process as thevoltage will significantly drop over the longdistance.
USB has completely replace parallel ports in mostmodern PC now
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Data Communication - 3
Parallel
Parallel communication requires atleast as many lines as there arebits in a word being transmitted (foran 8-bit word, a minimum of 8 linesare needed).
For short distances or when highertransmission rates are required.
Mainly used for connectionbetween test instruments orcomputer and printer.
Less use in modern PC now sincethe USB found to be much fasterand more simple connection.
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Interfacing Devices Sensors & Actuators
A Sensoris an input device, transducer that converts a
physical stimulus from one form into a more useful form tomeasure the stimulus
An Actuatoris an output device that convert a controllercommand signal into a change in a physical parameter
Actuators
Controller or
PLC
Transformation Process
Sensors
DAC ADC
Input DevicesOutput Devices
Continuous and Discrete
VariablesContinuous and Discrete
Parameters
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Sensors - Function
Feedback on task completion
Information on the status of the process
Inspection and measurement data
Collect product or process data for quality monitoring
Sensors Types (1)
Contact versus Non-contact
Contact sensor : there is a physical contact between
the sensor and parameter to be measured Non-contact sensor: also called proximity sensors.
Proximity indicates that the object is near, but contact isnot required
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Sensors Non-contact
Non-contact sensors do not operate mechanically and
are more reliableLess likely to fail than mechanical ones
They are much faster than mechanical devices
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Sensors Digital vs Analog
Digital sensor:
Have two states : ON or OFF
Presence or absence of object
Counting such as used in a rotary encoder
Analog sensor:
It senses continues variables (such temperature,pressure) and provides a continuous (usually linear)voltage or current
More complex than digital and can provide moreinformation
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Sensors Digital Type
Switches
Optical (photoelectric) sensors
Encoders
Ultrasonic sensors
Inductive sensorsCapacitive sensors
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Sensors Digital Type - Switches
Pushbuttons andmanual switches(manual operators)
Limit switches
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Sensors Digital Type Switches
Manual Operatos
Push Buttons
Normally Open /Normally Closed
Spring returned versus
maintained
Selectror Switches
Specify number ofpositions : 2, 3, 4, etc
Can be spring returnedor maintained
Limit Switches
Advantages
Robust, made for harshenvironments
Can directly drive a load
(contact 15A+)
Disadvantages
Mechanical wear out
Large sizeMay require contact withproduct
Operating force may besignificant
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Sensors Digital Type Switches
Other Mechanical Switches
Level/Float Switch
Mechanical switch that is actuated by the level of a liquid
Pressure Switch
Mechanical switch that is actuated by the pressure influid system
Flow Switch
Mechanical switch that is actuated by the flow rate of afluid
Temperature Switch
Mechanical switch that is actuated above a settemperature (such a bimetallic element)
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Sensors Digital Type Optical/Photoelectric
All optical sensors use light to sense objects
Operating method: Lasers, Incandescent bulbs, or Light emitting diodes
(LED) are used as light source
The light source is turned off and on (modulation) at ahigh frequency (several kHz)
A photodetector senses the pulsed light
The light emitter and receiver are tuned to themodulation frequency
Refers to the normal state of the sensor, optical sensor
are either : Light sensing (light-ON): the output is energized (ON)
when the sensor receives modulated beam
Dark sensing (dark-ON): the output is energized (ON)when the sensor does not receive modulated beam
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Sensors Digital Type Optical/Photoelectric
All optical sensors function in the same basic
manner, the differences are in the way in which thelight source and receiver are package
Type of Optical Sensors
Reflective Sensors
Polarizing Photo SensorsRetroreflective Sensors
Thru-Beam Sensors
Convergent Photo Sensors
Fiber-Optic SensorsColor Mark Sensors
Laser Sensors
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Sensors Digital TypeOptical/Photoelectric : Reflective (Diffuse) Sensors
Transmitter and receiverare combined into oneunit
Relies on the reflectivesurface of the target to
bounce the light from thetransmitter to the receiver
Target must be somewhatperpendicular to thesensor axis
Used when it is notfeasible to mount areflector
Less sensing range (relyon the reflected light)
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Sensors Digital TypeOptical/Photoelectric : Polarizing Photo-Sensors
They sense only shiny objects using special reflector
The reflector vertically polarizes the light from the sensor
Reflections from shiny objects will be ignored
Only reflections from the polarizing reflector will trigger
this sensor
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Sensors Digital TypeOptical/Photoelectric : Retroreflective Sensors
Transmitter and receiver are combined into one unit
Makes use of a reflector to bounce the light from thetransmitter to the receiver
Have more sensing distance than reflective sensors
Have less sensing distance than thru-beam sensors
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Sensors Digital TypeOptical/Photoelectric : Thru-beam Sensors
Has a separate transmitter and receiver
Capable of sensing very small object by narrowing thelight beam
Fiber optics can be used to position the beam
transmitter and receiversTargets can be opaque but not transparent
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Sensors Digital TypeOptical/Photoelectric : Convergent Photo Sensor
Also called focal length sensor
The sensor emits the light to a specific focal length
The light must be reflected from the focal length to besensed
Only objects near the focal point are detected
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Sensors Digital TypeOptical/Photoelectric : Thru-beam Sensors
Has a separate transmitter and receiver
Capable of sensing very small object by narrowing thelight beam
Fiber optics can be used to position the beam
transmitter and receiversTargets can be opaque but not transparent
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Sensors Digital TypeOptical/Photoelectric : Fiber Optic Sensor
Same as the other types of photo sensors except fiber isused to transmit and receive the light
Allows the sensor to be used in very small tight areas
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Sensors Digital TypeOptical/Photoelectric : Color Mark Sensor
These sensors can differentiate between different colors
Used to check labels and to sort packages by color mark
Charts are used for propoer selection
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Sensors Digital TypeOptical/Photoelectric : Laser Sensor
Optical sensors can use laser as their light source
Laser sensors can be used for precise measurements(as small as few microns), example is a bar code reader
Outputs can be analog or digital