osp07 programmable logic controller
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Departemen Teknik I ndustri FTI-ITB
TI-3222: Otomasi Sistem Produksi
Programmable Logic Controller
LaboratoriumLaboratorium SistemSistem ProduksiProduksi
www.lspitb.orgwww.lspitb.org
20042004
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Hasil Pembelajaran
Umum Mahasiwa mampu untuk melakukan proses perancangan
sistem otomasi, sistem mesin NC, serta merancang danmengimplementasikan sistem kontrol logika.
Khusus Memahami fungsi PLC serta komponen-komponen PLC
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PURPOSE OF Programmable
Logic Controllers (PLCs)
Initially designed to replace relay logic boards Sequence device actuation
Coordinate activities
Accepts input from a series of switches Sends output to devices or relays
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PURPOSE OF ProgrammableLogic Controllers (PLCs)
Initially designed to replace relay logic boards Sequence device actuation
Coordinate activities
Accepts input from a series of switches Sends output to devices or relays
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FUNCTIONS OF CONTROLLERS
1) on-off control,
2) sequential control,
3) feedback control, and
4) motion control.
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CONTROL DEVICES
1) mechanical control - cam, governor, etc.,
2) pneumatic control - compressed air, valves,etc.
3) electromechanical control - switches, relays,a timer, counters, etc,
4) electronics control - similar toelectromechanical control, except useselectronic switches.
5) computer control.
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PROGRAMMABLE LOGIC
CONTROLLER
Invented in 1968 as a substitute for hardwired relay panels.
"A digitally operating electronic apparatus which uses aprogrammable memory for the internal storage ofinstructions by implementing specific functions such as logicsequencing, timing, counting, and arithmetic to control,through digital or analog input/output modules, varioustypes of machines or processes. The digital computer whichis used to perform the functions of a programmablecontroller is considered to be within this scope. Excludedare drum and other similar mechanical sequencingcontrollers."
National Electrical Manufacturing Association (NEMA)
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VENDORS
Rockwell
GE/Fanuc
Schnieder MODICOM - GOULD ALLEN-BRADLEY Honeywell SQUARE-D
etc.
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PLC
CPU
System
User LadderDiagram
Workingmemoryregisters
Input
Flag
Output
InputModule
OutputModule
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PLC Configuration
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What devices does a PLC interact with?
INPUT RELAYS-(contacts)These are connected to the outsideworld. They physically exist and receive signals from switches,sensors, etc. Typically they are not relays but rather they aretransistors.
INTERNAL UTILITY RELAYS-(contacts) These do not receivesignals from the outside world nor do they physically exist.They are simulated relays and are what enables a PLC toeliminate external relays. There are also some special relaysthat are dedicated to performing only one task. Some arealways on while some are always off. Some are on only onceduring power-on and are typically used for initializing datathat was stored.
COUNTERS-These again do not physically exist. They aresimulated counters and they can be programmed to countpulses. Typically these counters can count up, down or bothup and down. Since they are simulated they are limited in
their counting speed. Some manufacturers also include high-speed counters that are hardware based. We can think ofthese as physically existing. Most times these counters cancount up, down or up and down.
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What devices does a PLC interact with?Continued
TIMERS-These also do not physically exist. They come in manyvarieties and increments. The most common type is an on-delaytype. Others include off-delay and both retentive and non-retentive types. Increments vary from 1ms through 1s.
OUTPUT RELAYS-(coils)These are connected to the outside world.They physically exist and send on/off signals to solenoids, lights,etc. They can be transistors, relays, or triacs depending upon themodel chosen.
DATA STORAGE-Typically there are registers assigned to simplystore data. They are usually used as temporary storage for math
or data manipulation. They can also typically be used to storedata when power is removed from the PLC. Upon power-up theywill still have the same contents as before power was removed.Very convenient and necessary!!
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SWITCHES
DPSTSPDT
Non-locking Locking
Normally Open Normally Closed
Multiple Throw
P1
P2
Multiple Pole
Break-before-make Make-before-break
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TERMSThrow - number of states
Pole - number of connecting moving parts (number ofindividual circuits).
DPST
A serial switch box (A-B box) hastwo 25 pin serial ports to switch from.
InputOutput
A B
Knob
How is this switch classified?
SPDT
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TYPES OF SWITCHES
1. Basic switch, operated by a mechanical level,
2. Push-button switch,
3. Slide switch,
4. Thumbwheel switch,
5. Limit switch,
6. Proximity switch, and
7. Photoelectric switch.
RATING: voltage, current
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RELAYSA switch whose operation is activated by an electromagnet is called a "relay"
contact
coil
input
Relay coil Output contact
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COUNTER
Digital counters output in the form of a relay contact when apreassigned count value is reached.
Register
Accumulator
contact
input
reset
output
Input
Reset
Output
Count 0 1 2 3 4 5 0 1
5
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TIMERA timer consists of an internal clock, a count value register, and an
accumulator. It is used for or some timing purpose.
Clock
Accumulator
contact
reset
output
Register
Contact
Time 5 seconds.
Clock
Reset
Output
Count 1 2 3 40 5
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AN EXAMPLE OF RELAY LOGIC
L1
LS1 PB1 LS2 R1
R1
R1TIMER
R2
PR=5
For process control, it is desired to have the process start (by turning on amotor) five seconds after a part touches a limit switch. The process isterminated automatically when the finished part touches a second limitswitch. An emergency switch will stop the process any time when it ispushed.
LS1
PB1LS2
R1
TIMER
5MotorR2
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PLC ARCHITECTUREProgrammable controllers replace most of the relay panel wiring by
software programming.
ProcessorI/OModules
MemoryPowerSupply
ProgramLoader
Printer
Cassette
Loader
EPROMLoader
Switches
Machines
Peripherals External Devices
PC
A typical PLC
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PLC COMPONENTS
1. Processor Microprocessor based, may allow arithmeticoperations, logic operators, block memory moves,computer interface, local area network, functions, etc.
2. Memory Measured in words.
ROM (Read Only Memory),
RAM (Random Access Memory),
PROM (Programmable Read Only Memory),
EEPROM (Electronically Erasable ProgrammableROM),
EPROM (Erasable Programmable Read Only Memory),
EAPROM (Electronically Alterable Programmable
Read Only Memory), and
Bubble Memory.
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PLC COMPONENTS3. I/O Modular plug-in periphery
AC voltage input and output,
DC voltage input and output,
Low level analog input,
High level analog input and output,
Special purpose modules, e.g.., high speed timers,
Stepping motor controllers, etc. PID, Motion
4. Power supply AC power
5. Peripheral Hand held programmer (loader),
CRT programmer,
Operator console,
Printer,
Simulator,
EPROM loader,
Cassette loader,
Graphics processor, and
Network communication interface. MAP, LAN
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LADDER DIAGRAM
A ladder diagram (also called contact symbology) is a means ofgraphically representing the logic required in a relay logicsystem.
A
R1
PB1 PB2
R1
R1
start emergency stop
Rail
Rung
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Ladder Representation
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PLC WIRING DIAGRAM
01 02 20
20
20 11
01
02
03
11
12
A
PLCInput Output
Externalswitches
Stored program
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SCAN
begin
Input
Output
Resolvelogic
Idle
A PLC resolves the logic of a ladder diagram (program) rung by rung, fromthe top to the bottom. Usually, all the outputs are updated based on thestatus of the internal registers. Then the input states are checked and thecorresponding input registers are updated. Only after the I/Os have beenresolved, is the program then executed. This process is run in a endlesscycle. The time it takes to finish one cycle is called the scan time.
Scan cycle
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PLC INSTRUCTIONS
1) Relay,
2) Timer and counter,
3) Program control,
4) Arithmetic,
5) Data manipulation,
6) Data transfer, and
7) Others, such as sequencers.
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LOGIC STATES
ON : TRUE, contact closure, energize, etc.
OFF: FALSE, contact open , de-energize, etc.
(In the notes we use the symbol "~" to representnegation. AND and OR are logic operators. )
Do not confuse the internal relay and program with the externalswitch and relay. Internal symbols are used for programming.External devices provide actual interface.
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AND and OR LOGIC
PB1 R1PB2
R2
R1 = PB1.AND.PB2
R2 = PB2.AND.~PB4
PB3 PB4
PB1 R1
PB2
R1 = PB1 .OR. PB2
AND
OR
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COMBINED AND & OR
R1 = PB1 .OR. (PB2 .AND. PB3)
PB1 R1
PB2 pb3
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Relay diagram symbols
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Relay diagram symbols
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RELAY
A Relay consists of two parts, the coil and the contact(s).
Contacts:
a. Normally open -| |-
b. Normally closed -|/|-
c. Off-on transitional -||-
d. On-off transitional -| |-
Coil:
a. Energize Coil -( )-
b. De-energize -(/)-
c. Latch -(L)-
d. Unlatch -(U)-
( )
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TIMERS AND COUNTERS
Timers:
a. Retentive on delay -(RTO)-
b. Retentive off delay -(RTF)-
c. Reset -(RST)-
Counter:
a. Counter up -(CTU)-
b. Counter down -(CTD)-
c. Counter reset -(CTR)-
RTO
RTF
PR value in 0.1 second
stopcountingstop
Input
TrueFalseTrue
RTO reach PR value, output ON
RTF reach PR value , output OFF
counting
resumestopcounting
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SEQUENCER
Sequencers are used with machines or processes involvingrepeating operating cycles which can be segmented intosteps.
Output
Dwell timeCBAStep
9 secOFFONOFF4
3 secONOFFOFF3
10 secOFFONON2
5 secOFFOFFON1
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A-B PLC
I/O points are numbered, they correspond to the I/O slot onthe PLC.
For A-B controller used in our lab
I/O uses 1-32
Internal relays use 033 - 098
Internal timers/counters/sequencers use 901-932
Status 951-982
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Programming a PLC
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Ladder Logic for Tank
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Logic for Ladder Solution
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How does it work?
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PROGRAMMING EXAMPLE 1
machine busy1input from machineC3
stopper up1output to stopperR4
robot busy1input from robotC2
unloading cycle1output robotR3
scan the part1output to bar code readerR1
loading cycle1output robotR2
task complete1input from machineC4
right part1input from bar code readerC1
part arrive1micro switchMSI
ExplanationStateDescriptionid
Part
microswitch
Bar code reader
Stopper
Conveyor
MachineRobot
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SOLUTION01
02
03
04
05
11
12
13
14
15
InputOutput
ProgrammableControllerPLC
MS1
C1
C2
C3
C4
R1
R2
R3
R4
01 1411
02
14 04 03
14
12
1305 03
Rung 1. If partarrives and no part isstopped, trigger thebar code reader.
Rung 2. If it is aright part, activate thestopper.
Rung 3. If thestopper is up, themachine is not busyand the robot is notbusy, load the part
onto the machine.
Rung 4. If the task iscompleted and therobot is not busy,unload the machine.
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EXAMPLE 2 TRAFFIC LIGHTS
Main street
Jefferson
street
Cycle time
215Jefferson
413Main
GreenYellowRedStreet
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WIRING DIAGRAM
64
65
66
67
70
71
ProgrammableController
input output
Jefferson Red
Jefferson Yellow
Jefferson Green
Main Green
Main Yellow
Main Red
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PROGRAM (1)
RUNG1
RUNG2
RUNG3
RUNG4
RUNG5
RUNG6
RUNG7
RUNG8
RUNG9
RUNG10
RUNG11
RUNG12
20
67
RTO
90366
RTO
901
80
RTO
902
30
901 90267 M. Red
901 90366 J. Green
902 90471 M. Green
904 90570 M. Yellow
RST
RST901 904
RTO
904
40
71
RST901 903
RST901 902
901 901
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PROGRAM (2)
RUNG13
64 RTO
907
50
65RTO
906
10
70RTO
905
10
903 90665 J. Yellow
90264
907J. Red
RST901 907
RST901 906
RST901 905
RUNG14
RUNG15
RUNG16
RUNG17
RUNG18
RUNG19
RUNG 20