1. Writ Write e a report for Programmabl Programmable e Logic Controllers Controllers (PLC), (PLC), the solutio solution n should includes but not limited to: a. NO and and NC Electr Electroma omagne gnetic tic relay relay Elecromagnetic relays Relay is Relay is an electrical sitch. !t opens and closes under control of electric curent applied. "he sitch is operated by an electromagnet to open or close sets of contacts. When a current flos through the coil, the generated magnetic field attracts an armature, mechanically lin#ed to a mo$ing contact. "he mo$ement either ma#es or brea#s a connection ith a fi%ed contact.
"he contacts are either &ormally 'pen (&'), &ormally Closed (&C), or ouble "hro (also #non as *orm C or change+o$er (C')) contacts. •
&ormally+open contacts connect the circuit hen the relay is acti$ated and disconnect hen the relays is deacti$ated.
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&ormally+closed contacts disconnect the circuit hen the relay is acti$ated the circuit is connected hen the relay is inacti$e.
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Change+o$er contacts control to circuits: one normally+open contact and one normally+closed contact ith a common terminal. -imply spea#ing they ust sitch in+beteen circuits
b. PLC definitions / Programmable Logic Controller (PLC, or Programmable Controller) is a ruggedi0ed, microprocessor+based system hich pro$ides factory or plant automation by monitoring sensors and controlling actuators in real time.
/ programmable logic controller, PLC, or programmable controller is a digital computer used for automation of typically industrial electromechanical processes, such as control of machinery on factory assembly lines, amusement rides, or light fi%tures. PLCs are used in many machines, in many industries. PLCs are designed for multiple arrangements of digital and analog inputs and outputs, e%tended temperature ranges, immunity to electrical noise, and resistance to $ibration and impact. Programs to control machine operation are typically stored in battery+bac#ed+up or non+$olatile memory. / PLC is an e%ample of a hard real+time system since output results must be produced in response to input conditions ithin a limited time, otherise unintended operation ill result. efore the PLC, control, se2uencing, and safety interloc# logic for manufacturing automobiles as mainly composed of relays, cam timers, drum se2uencers, and dedicated closed+loop controllers. -ince these could number in the hundreds or e$en thousands, the process for updating such facilities for the yearly model change+o$er as $ery time consuming and e%pensi$e, as electricians needed to indi$idually reire the relays to change their operational characteristics.
igital computers, being general+purpose programmable de$ices, ere soon applied to control of industrial processes. Early computers re2uired specialist programmers, and stringent operating en$ironmental control for temperature, cleanliness, and poer 2uality. 3sing a general+purpose computer for process control re2uired protecting the computer from the plant floor conditions. /n industrial control computer ould ha$e se$eral attributes: it ould tolerate the shop+floor en$ironment, it ould support discrete (bit+form) input and output in an easily e%tensible manner, it ould not re2uire years of training to use, and it ould permit its operation to be monitored. "he response time of any computer system must be fast enough to be useful for control the re2uired speed $arying according to the nature of the process.415 -ince many industrial processes ha$e timescales easily addressed by millisecond response times, modern (fast, small, reliable) electronics greatly facilitate building reliable controllers, especially because performance can be traded off for reliability.
!n 1678 9 ;ydra+atic (the automatic transmission di$ision of 9eneral otors) issued a re2uest for proposals for an electronic replacement for hard+ired relay systems based on a hite paper ritten by engineer Edard <. Clar#. "he inning proposal came from edford /ssociates of edford, assachusetts. "he first PLC, designated the =8> because it as edford /ssociates? eighty+fourth proect, as the result.4@5 edford /ssociates started a ne company dedicated to de$eloping, manufacturing, selling, and ser$icing this ne product: odicon, hich stood for odular igital Controller. 'ne of the people ho or#ed on that proect as ic# orley, ho is considered to be the father of the PLC.4A5
"he odicon brand as sold in 16BB to 9ould Electronics, later ac2uired by 9erman Company /E9, and then by *rench -chneider Electric, the current oner. 'ne of the $ery first =8> models built is no on display at odicon?s head2uarters in &orth /ndo$er, assachusetts. !t as presented to odicon by 9, hen the unit as retired after nearly tenty years of uninterrupted ser$ice. odicon used the 8> moni#er at the end of its product range until the 68> made its appearance. "he automoti$e industry is still one of the largest users of PLCs.
c. Block diagram of PLC
/ simplified bloc# diagram of a PLC shon in abo$e *ig. !t has three maor unitssections. • • •
!' (!nput'utput) odules. CP3 (Central Processing 3nits). Programmeronitor.
"he input section con$erts the field signals supplied by input de$icessensors to logic+le$el signals that the PLC?s CP3 can read. "he Processor -ection reads these inputs, Processes the signal, and prepares the output signals. "he output section con$erts the logic le$el output signals coming from processor section to high le$el signals and used to actuate $arious output field de$ices.
"he programmermonitor is used to enter the user?s program into memory and to monitor the e%ecution of the program.
d. Processor and power supply
/ poer supply unit (P-3) con$erts mains /C to lo+$oltage regulated C poer for the internal components of a computer. odern personal computers uni$ersally use a sitched+mode poer supply. -ome poer supplies ha$e a manual selector for input $oltage, hile others automatically adapt to the supply $oltage.
ost modern des#top personal computer poer supplies conform to the /"D specification, hich includes form factor and $oltage tolerances. While an /"D poer supply is connected to the mains supply, it alays pro$ides a F standby (F-) $oltage so that the standby functions on the computer and certain peripherals are poered. /"D poer supplies are turned on and off by a signal from the motherboard. "hey also pro$ide a signal to the motherboard to indicate hen the C $oltages are in spec, so that the computer is able to safely poer up and boot. "he most recent /"D P-3 standard is $ersion @.A1 of mid+@==8. "he des#top computer poer supply changes alternating current from a all soc#et to lo+$oltage direct current to operate the processor and peripheral de$ices. -e$eral direct+current $oltages are re2uired, and they must be regulated ith some accuracy to pro$ide stable operation of the
computer. / poer supply rail or $oltage rail refers to a single $oltage pro$ided by a poer supply unit (P-3). /lthough the term is generally used in electronic engineering, many people, especially computer enthusiasts, encounter it in the conte%t of personal computer poer supplies.
*irst+generation microcomputer and home computer poer supply units used a hea$y step+don transformer and a linear poer supply. odern computers use sitched+mode poer supplies (-P-) ith a ferrite+cored high fre2uency transformer. "he sitched+mode supply is much lighter and less costly, and is more efficient, than an e2ui$alent linear poer supply.
Computer poer supplies may ha$e short circuit protection, o$erpoer (o$erload) protection, o$er$oltage protection, under$oltage protection, o$ercurrent protection, and o$er temperature protection.
"his standby $oltage is generated by a smaller poer supply inside the unit. !n older P-3 designs, it as used to supply the $oltage regulator, located on the lo+$oltage side of the transformer, alloing the regulator to
measure output $oltages. "he regulator controls the sitching transistors insulated by optocoupplers or pulse transfomers. "he standby poer source as a small linear poer supply ith con$entional transformer, hich as later changed to a sitching poer supply, sharing some components of the main unit due to cost+ and energy+sa$ing re2uirements.
Poer supplies designed for orldide use ere e2uipped ith an input $oltage selector sitch that alloed the user to configure the unit for use on local poer grid. !n the loer $oltage range, around 11 F, this sitch is turned on changing the poer grid $oltage rectifier into a $oltage doubler in delon circuit design. /s a result, the large primary filter capacitor behind that rectifier as split up into to capacitors ired in series, balanced ith bleeder resistors and $aristors that ere necessary in the upper input $oltage range, around @A= F. Connecting the unit configured for the loer range to a higher+$oltage grid usually resulted in an immediate permanent damage. When the poer factor correction (P*C) as re2uired, those filter capacitors ere replaced ith higher+capacity ones, together ith a coil installed in series to delay the inrush current. "his is the simple design of a passi$e P*C.
/cti$e P*C is more comple% and can achie$e higher P*, up to 66H. "he first acti$e P*C circuits ust delayed the inrush. &eer ones are or#ing as an input and output condition+controlled step+up con$erter, supplying a single >== F filter capacitor from a ide+range input source, usually beteen 8= and @>= F. &eer P*C circuits also replace the &"C+based
inrush current limiter, hich is an e%pensi$e part pre$iously located ne%t to the fuse.
e. Programming device
!n the field of computer hardare, the term programmer, chip programmer or de$ice programmer refers to a de$ice that configures programmable non+$olatile digital circuits such as EP<'s, EEP<'s, *lashes, P/Ls, *P9/s or programmable logic circuits. *or programming a circuit, it is either inserted into a soc#et (often I!*) on top of the programmer, or the programmer is directly connected by an adapter to the circuit board (!n+-ystem Programming). /fterards the data is transferred into the circuit by applying signals to the connecting pins. -ome circuits ha$e a serial interface for recei$ing the programming data (J"/9 interface). 'ther circuits re2uire the data on parallel pins, folloed by a programming pulse ith a higher $oltage for programming the data into the circuit.
3sually de$ice programmers are connected to a personal computer through a printer connector, 3- port or L/& interface. / softare program on the computer then transfers the data to the programmer, selects the circuit and interface type, and starts the programming process.
f. nput and output interface
!nput+output interface pro$ides a method for transferring information beteen internal storage and e%ternal !' de$ices. Peripherals connected to a computer need special communication lin#s for interfacing them ith the central processing unit. "he purpose of the communication lin# is to resol$e the differences that e%ist beteen the central computer and each peripheral. "he maor differences are:
Peripherals are electromechanical and electromagnetic de$ices and their manner of operation is different from the operation of the CP3 and memory, hich are electronic de$ices. "herefore, a con$ersion of signal $alues may be re2uired.
"he data transfer rate of peripherals is usually sloer than the transfer rate of the CP3, and conse2uently, a synchroni0ation mechanism may be needed.
ata codes and formats in peripherals differ from the ord format in the CP3 and memory.
"he operating modes of peripherals are different from each other and each must be controlled so as not to disturb the operation of other peripherals connected to the CP3.
"o resol$e these differences, computer systems include special hardare components beteen the CP3 and peripherals to super$ise and synchroni0e all input and output transfers. "hese components are called interface units because they interface beteen the processor bus and the peripheral de$ice.
&eed for !' interface
Peripherals are electromechanical de$ices.ut CP3 and emory are electronic de$ices. "herefore con$ersion of signal $alues may be re2uired.
ata codes and formats in peripherals differ from the ord format in CP3 and memory. ata transfer rate of peripherals are sloer than CP3, -o synchroni0ation may be needed. "he operating modes of peripherals are different. -o they must be controlled so as not to disturb the operation of other peripherals that are connected to CP3.
g. input and output devices wiring.
'ne of the many ad$antages to using a PLCP/C is the simplicity of the !' iring. !' de$ices are ired to !' points on a fi%ed !' unit and to !' modules in a modular unit. !nput de$ices such as sitches, pushbuttons and sensors are ired to input module points and output de$ices such as indicator lights, solenoids and motor starter coils are ired to output module points. !' modules can accept /c$, CF or a combination of /CF and CF. ost modern automation systems use CF !', therefore e ill focus on CF. C $oltage has a polarity. We already #no that current flo is from negati$e to positi$e. "his current flo is also referred to as electron flo and is also the current that is measured hen ma#ing measurements ith a meter. "here is also another current flo. "his current flo is called ?con$entional current? and is the current flo that solid state physis use. "his current flos from positi$e to negati$e. When electrons flo from one atom to another they lea$e a hole behind on the atom that they lea$e. !f you could atch the electrons mo$ing from atom to atom, the electrons ould be mo$ing in one direction (negati$e to positi$e) and the holes ould loo# li#e they are mo$ing in the opposite direction (positi$e to negati$e).
CF !' module polarity is referenced using the terms sin# and source. "he terms are deri$ed from con$entional current flo, but e ill e%plain sin# and source in terms of electron flo. Why should e care hat direction current is floingK echanical sitches, indicator lamps and solenoids don?t care hat polarity the current is floing. ut sensors such as photoelectric, inducti$e and capaciti$e pro%imity sensors are also ired to PLCP/C !' modules. "hese sensors are solid state, using diodes and transistors in their internal or#ings. "hese de$ices re2uire current to be floing in the right direction.
@. Write a report for PLC ladder diagram programming, the solution should includes but not limited to:
2.a) The different between PLC physical ladder diagram and PLC programmed ladder diagram
A ladder diagram is a symbolic and schematic representation of both the process hardware and process control. It is called ‘ladder’ because all the devices are connected across the supply lines making it looks like a ladder. Each parallel connection is named as ‘Rung’ and it can contain many inputs but only one output. The physical ladder diagram made of switches and relays which are connected to devices to give desired output. The programmed ladder diagram is made of electronic gates such as A! gate and A! gate.
PLC physical ladder diagram
"igure #$ E%ample of ladder diagram
PLC programmed ladder diagram
The first& and still most popular programming language& is ladder logic. 'sing e%amples& the language is developed from the electromechanical relay system(wiring diagram.
"igure )$ *adder diagram& Truth table and *ogic gate
+ 2.b) Types of relay use in ladder diagram • • • • •
Input relays ( ,contactsInternal utility relays ( ,contactsounters relay Timers relay /utput relays ( ,coils-
!ata storage Analogue model • 'ser interface input • etworking modules • •
2.c) NO and NC relay in ladder diagram
"igure 0$ 1ymbol of / and relay in ladder diagram
2.d) Input relay output relay internal relay timer relay and counter relay •
I2'T RE*A31(,contacts-$ These are connected to the outside world. They physically e%ist and receive signals from switches& sensors& etc. Typically they are not relays but rather they are transistors. These inputs are called discrete or logic inputs.
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ITERA* 'TI*IT3 RE*A31(,contacts-$ These relays do not receive signals from the outside world nor do they physically e%ist. They are simulated relays and are what enables a PLC to eliminate e%ternal relays. There are also some special relays that are dedicated to performing only one task. 1ome are always on while some are always off. 1ome are on only once during power(on and are typically used for initiali4ing data that was stored.
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/'TER1$ These again do not physically e%ist. They are simulated counters and they can be programmed to count pulses. Typically these counters can count up& down or both up and down. 1ince they are simulated they are limited in their counting speed. 1ome manufacturers also include high(speed counters that are hardware based. 5e can think of these as physically e%isting. 6ost of the time these counters can count up& down or up7down.
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TI6ER1$ These also do not physically e%ist. They come in many varieties and increments. The most common type is an on(delay type. /thers include off(delay and both retentive and non(retentive types. Increments vary from 8ms through 8s.
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/'T2'T RE*A31(,coils-$ These are connected to the outside world. They physically e%ist and send on7off signals to solenoids& lights& etc. They can be transistors& relays& or triacs depending upon the model chosen.
!eferences
http$77www.electronics(tutorials.ws7io7io9#.html http$77www.amci.com7tutorials7tutorials(what(is(programmable(logic(controller.asp
