CHAPTER 3 INTRODUCTION TO PROGRAMMABLE LOGIC CONTROLLER BY

CHAPTER 3 INTRODUCTION TO PROGRAMMABLE LOGIC CONTROLLER BY: Salsabila Ahmad

INTRODUCTION TO PLC • • History of PLC Advantages of PLC Operations Serial and Parallel Circuit – Serial Circuit – Parallel Circuit • Numbering System • Boolean Algebra • Ladder Logic Diagram Q&A

HISTORY OF PLC • In the early days; all stages in a process were done by hand • As depicted in figure – the filling – capped – labeling – packing processes are done totally manually

• After the industrial revolution – entire processes were automated – filling, labeling and packing are all being done by machines controlled electro-mechanically

• Then invention of computers brought – a new method of automation control, the Programmable Controller. – That time, a more efficient PC is managing the bottling process – Substituting the old relay control system.

• As technology expands further, today – the same bottling processes – use a central control system – linking many PCs together

ADVANTAGES OF PLC • • • Flexibility Large quantities of contact Lower cost Ease of pilot running Visual observation Speed of operation Reliability Security Ease of documentation Ease of changes by reprogramming

PLC OPERATIONS CHECK INPUT STATUS EXECUTE PROGRAM UPDATE OUTPUT STATUS

• PLC can continuously perform the cyclical task of scanning, a process which involves – reading the inputs, – executing the user program – updating the outputs without requiring a user program to direct it to do so.

• A PLC is designed to perform logic functions previously done by – electromechanical relays, – mechanical timers/counters to control the manufacturing process.

• The operator enters a sequence of instructions – program into the PLC memory. • The controller then monitors the inputs and outputs according to the program • The controller carries out the control rules

Step 1 CHECK INPUT STATUS First the PLC takes a look at each input to determine if it is on or off. In other words, is the sensor connected to the first input on? How about the second input? How about the third. . . It records this data into its memory to be used during the next step.

Step 2 EXECUTE PROGRAM Next the PLC executes your program one instruction at a time. Maybe your program said that if the first input was on then it should turn on the first output. Since it already knows which inputs are on/off from the previous step it will be able to decide whether the first output should be turned on based on the state of the first input. It will store the execution results for use later during the next step.

Step 3 UPDATE OUTPUT STATUS-Finally the PLC updates the status of the outputs. It updates the outputs based on which inputs were on during the first step and the results of executing your program during the second step. Based on the example in step 2 it would now turn on the first output because the first input was on and your program said to turn on the first output when this condition is true. After the third step the PLC goes back to step one and repeats the steps continuously. One scan time is defined as the time it takes to execute the 3 steps listed above.

HOW TO APPLY HERE?

SERIAL CIRCUIT Can also be referred as AND logic function • where all switch must be closed (ON) • for output to energized (ON) SW 1 SW 2 Battery Conventional series circuit LMP 1

Or it can be represented In schematic ladder diagram As: L 1 SW 2 LMP 1 Series circuit represented in conventional ladder rung L 2

LADDER DIAGRAM To energized LMP 1 • SW 1 and • SW 2 need to be closed SW 1 SW 2 I 1 I 2 LMP 1 05 PLC representation of previous rung using Allen- Bradley Micro. Logix 1000

Program listing / Mnemonic Code LOAD I 1 AND I 2 OUT 05 Notice the operands for input differ • OMRON use 00001 • Allen. While operands (for output 1) Bradley use I 1 for input • OMRON use 01000 • Allen Bradley use O 1 (for output 1) for Allen-Bradley Micro. Logix 1000 Note: The instructions tell the processor to • load input (I 1) into memory, • AND it with input 2 (I 2), • then output the result to output 5 (O 5)

AND TRUTH TABLE ? A B C 0 0 1 1 1

Can we have more than 2 inputs for AND logic? • Yes • We can have more than 2 inputs for AND logic but the outcome will still be the same – when all inputs ‘ON’. – output will only be energized ‘ON’ SW 1 SW 2 SW 3 I 1 I 2 I 3 Three- input PLC ladder rung LMP 1 01

PARALLEL CIRCUIT Can also be referred as OR logic function • where at least one switch must be closed (ON) • for output to energized (ON) SW 1 SW 2 Battery Conventional parallel circuit LMP 1

Or it can be represented In schematic ladder diagram As: Or L 1 SW 1 LMP 1 SW 2 Parallel circuit represented in conventional ladder rung L 2

LADDER DIAGRAM To energized LMP 1 • SW 1 OR • SW 2 need to be closed SW 1 I 1 LMP 1 02 ? SW 2 I 2 PLC representation previous rung using Allen- Bradley Micro. Logix 1000

OR TRUTH TABLE ? A B C 0 0 1 1 1 0 1 1

CONSIDER…. LMP 1 02 SW 1 I 1 SW 2 I 2 SW 3 I 3 Three- input OR logic What is the Mnemonics Code for OMRON CPM 1 A? LD 00001 OR 00002 OR 00003 OUT 01002

NUMBERING SYSTEMS • In our daily, we use the decimal numbering system • But, besides decimal, knowledge of – Binary • 16 bit group binary number • Binary Coded Decimal – octal – hexadecimal numbering system is essential when using the PLCs • EXAMPLE 1 • EXAMPLE 2 • Comparison of the Number Systems

DECIMAL SYSTEMS • Uses in daily life • Uses only ten digits ; – 0, 1, 2, 3, 4, 5, 6, 7, 8 and 9 • • The first column can hold up to 9 the second column can hold up to 90(nine 10 s), the third column represents the number of hundreds and so forth and so on. Decimal System 100, 000 s 1000 s 10 s 1 s

For example, 328 represents • three 100 s • two 10 s • and eight 1 s 3 2 8 10 Decimal number 8 x 100 = 8 2 x 101 = 20 3 x 102 = 300 Decimal number 32810

BINARY SYSTEMS • Used by computers and PLCs • Use only two digits; – 0 and 1 • Base 2 • Works similarly to decimal systems Binary System 32 s 16 s 8 s • 1 1 0 0 1 1 0 1 4 s 2 2 s Binary number 1 x 20 = 1 0 x 21 = 0 1 x 22 = 4 1 x 23 = 8 0 x 24 = 0 0 x 25 = 0 1 x 26 = 64 1 x 27 = 128 Decimal number 20510 1 s

16 -BIT GROUP BINARY NUMBER Most Significant Byte Least Significant Byte 10110011110 Nibble Word • 1 nibble= 4 bits • 1 byte= 8 bits • Size of word depends on the processor; – 16 -bit processor has 16 -bit word while a – 32 -bit processor has a 32 -bit word

BINARY CODED DECIMAL • In BCD, 4 binary bits are used to represent a decimal digit. • These 4 bits are used to represent the number 0 through 9. • Note: BCD is not the same as binary! • The decimal number of 205 is – In BCD 0010 0000 0101 – but in Binary 1100 1101 (refer binary note)

OCTAL SYSTEM • Use only 8 digits; – 0, 1, 2, 3, 4, 5, 6 and 7 • Base 8 Octal System 32, 768 s 4, 096 s 3 2 0 7 512 s 8 64 s Octal number 7 x 80 = 7 0 x 81 = 0 2 x 82 = 128 3 x 83 = 1536 Decimal number 167110 8 s 1 s

HEXADECIMAL SYSTEM Hexadecimal 0 0 1 1 2 2 3 • Used 16 digits • but with an unusual twist Decimal 3 4 4 5 5 6 6 7 7 8 8 9 9 A 10 B 11 C 12 D 13 E 14 F 15

HEXA DECIMAL 2 0 D Hex number 16 D x 10 = 0 x 161 = 13 0 2 x 162 = 512 Decimal number 52510

HEXA BCD HEXA Each hex digit is simply converted to its four-digit binary (BCD) equivalent and vice versa 7 D 3 F 0111 1101 hexadecimal 0011 1111 binary 0111110100111111 0111 1101 0011 7 D 3 F 1111 hexadecimal

EXAMPLE 1 16 Bit Binary Grouped Binary 1001 0010 1011 0101 10010010101 Hexadecimal Equivalent 9 2 B 5 16 DECIMAL? 9 x 163 36, 864 512 + 176 5 37, 55710 2 x 162 11 x 161 5 x 160

EXAMPLE 2 Most Significant Number (MSD) Middle Digit, MD Least Significant Number (LSD) BCD number 0 0 1 0 0011 1001 DECIMAL? 2 32 22 12 0 0+0+2+1 8+0+0+1 2 =23910 3 910

COMPARISON BETWEEN THESE NUMBER SYSTEMS

Decimal Hexadecimal Octal Binary 8 s 1 s 8 s 4 s 2 s 1 s 0 0 0 0 1 1 0 0 0 1 2 2 0 0 1 0 3 3 0 0 1 1 4 4 0 1 0 0 5 5 0 1 0 1 6 6 0 1 1 0 7 7 0 1 1 1 8 8 1 0 0 0 9 9 1 1 1 0 0 1 10 A 1 2 1 0 11 B 1 3 1 0 1 1 12 C 1 4 1 1 0 0 13 D 1 5 1 1 0 1 14 E 1 6 1 1 1 0 15 F 1 7 1 1

BOOLEAN ALGEBRA • Mathematical system of logic • Used only – two digits (0, 1) – 2 states (true, false) are used in logic problem • Types of functions – – – OR AND NOT NOR NAND XOR

OR relationship • A and B wired in parallel C A B OR gate • Boolean equation; A + B = C • OR Truth table A B C 0 0 1 1 1 0 1 1 OR Truth table

AND relationship • A and B are wired in series. A C B AND gate • Boolean equation; A. B = C • AND Truth table A B C 0 0 1 1 1 AND Truth table

NOT relationship A B NOT gate • Boolean equation; Ā = B • NOT Truth table Ā B 0 1 1 0 NOT Truth table

NAND function A C B NAND gate • Boolean equation; Ā + B = C • NAND Truth table A B C 0 0 1 1 1 0 NAND Truth table AND of NOT

NOR function A C B OR of NOT NOR gate • Boolean equation; Ā. B = C • NOR Truth table A B C 0 0 1 0 1 0 0 1 1 0 NOR truth table

XOR function A A C B B XOR gate • Boolean equation; A. B + Ā. B = C • XOR Truth table A B C 0 0 1 1 1 0 XOR truth table

LADDER LOGIC DIAGRAM • Introduction • Objectives • Ladder Logic Fundamentals – Electrical Ladder Diagram – Basic Symbols in Ladder Logic • Ladder Logic Programming – Transform – Programming • Basic STOP/START circuit

INTRODUCTION • Is an electrical machine diagrams drawn using a standard format • Used to – show the electrical relationship of the components – to speed understanding of how the circuit works

OBJECTIVES • To describe the basic process of ladder logic • To define terms such as contact, coil, rung, scan, normally open and normally closed in symbols • Simplified ladder logic for simple applications

FUNDAMENTALS OF ELECTRICAL LADDER DIAGRAM • Beginning with the control transformer, we add a protective fuse on the left side, which is often part of the transformer itself • From the transformer/fuse combination, horizontal lines are extended to both sides and then drawn vertically down Control Transformer

• These vertical lines are called power rails or simply rails or uprights • All wires in a control system are numbered – the left rail is often wired as 1 – and the right rail is wire number 2 (hot side) Basic Power Circuit Power Rail Rung Power Rail Line Branch Structure of a Ladder Diagram

• The voltage difference between the two rails is equal to the transformer secondary voltage • Therefore, any component connected between the two rails will be powered. • Ladder logic program for PLCs is similar to electrical ladder diagrams. • Electrical Ladder Diagram is different from power diagram. Refer to the following Figure • There are some basic rules to follow to make the diagram. Refer Ladder Diagram Rules

Ladder Diagram and Power Diagram

BASIC OF LADDER LOGIC Basic symbols found • Contact • Coil

CONTACT Used to represent input conditions to be evaluated by processor to solves program Two common symbols for contacts • Normally Open ][ – Will not pass current until it is pressed • Normally Closed ]/[ – Will allow current flow until it is pressed When to decide using NO or NC?

CASE 1 • Think of a doorbell switch. • Would you choose the NC switch? 24 V Current flow allow bell to ring 0 V if NC is chosen Doorbell will continuously ringing until someone pushes the button So, when is NC used?

CASE 2 • Previously, we learn that NC is often used when safety is concerned. Take for example • Production line • Hazardous machine • Always on unless sense object

COIL Please Recall ? • Represent output • Only appear only on the right side of the rung

WIRING TO LADDER DIAGRAM Switch L 1 d. c input Motor M ? L 2 Wiring diagram But this wiring is not suitable/relevant L 1 Switch Motor Why? M No safety. How to include safety? BASIC STOP/START CIRCUIT Ladder diagram L 2

PROGRAMMING • To represent the circuit in in form of ladder logic diagram – we would utilize the power from the rails and simply add the two switches and lamp in series between the rails • Added along are few details – such as wire numbers – reference designators PB 1, PB 2 – L 1 for components

• Also note that the switches are on the left, and the lamp is on the right • This wiring scheme is done for safety reasons. • If we put the lamp on the left side and the switches on the right. If there is – a short to ground in the wire from the lamp to the switches the lamp would light without either of the switches being pressed

• For a lamp to inadvertently light is not a serious problem • but assume that instead of a lamp we had the coil of a relay that started the machine – This would mean that a short circuit would start the machine without any warning.

• By properly wiring the controlled device (called the load) on the right side, a short in the circuit will cause – the fuse to blow when the rung is activated – thus de-energizing the machine controls – and shutting down the machine

• Rung 2 has two branches on the input side of the rung • It is also possible to have branches on the load side. • For example, we could place another lamp in parallel with LAMP 2, thereby creating a branch on the load side

• It is important to note – it is possible to exchange rungs 1 and 2 without changing the way the lamps operate – This is one advantage of using ladder diagramming. The rungs can be arranged in any order without changing the way the machine operates • It allows the designer to compartmentalize and organize the control circuitry so that it is easier to understand troubleshoot

• However, keep in mind that, when beginning PLC ladder programming, the rearranging of rungs is not recommended – since in a PLC, the ordering of the rungs is critical – and it could change the way the PLC program executes.

BASIC STOP/START CIRCUIT START STOP M M HOLDING SWITCH • When power is applied, motor coil not energized • When START button is pressed, motor starts • When START released, it remain energized, by the holding contacts.

NOTE: • Should power fail while the machine is ON – the latch rung will de-energize • When power is restored, the machine will not automatically restart – this is a safety feature that is required on all heavy machines

Q&A

Ladder Diagram Rules There are some basic rules to follow when drawing ladder diagrams • to make the diagram easy to read • to provide a properly drawn circuit.

Show Only Control Devices Not Power Device Output Devices Located On. Solenoids, Coil and Relays. Right Input device- Switches, numbered Control Devicesconductor. On Left All Located All rungs numbered Output device- Solenoids, and Cylinders (theseetc. Input Valves, Motors lamps and control relays. Power device- Pushbuttons, Limit Switches shown separately in power diagram)

All Components rung At Least one Switch per Line Only 1 load per Labeled Functions- always be If no switches- outputi. e. STARTon. If necessary 2 load; Then does. Abbreviation purposeare control output not serve its i. e. 1 PB to Shown • Never wired loads Only Contacts Actually usedin series -Voltage deficient • Loads in parallel