CHAPTER 3 INTRODUCTION TO PROGRAMMABLE LOGIC CONTROLLER BY: Salsabila Ahmad

INTRODUCTION TO PLC History of PLC Advantages of PLC 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?

Conventional series circuit SERIAL CIRCUIT Can also be referred as AND logic function where all switch must be closed (ON) for output to energized (ON) SW1 SW2 Battery LMP1 Conventional series circuit

Series circuit represented in conventional ladder rung Or it can be represented In schematic ladder diagram As: LMP1 SW1 SW2 L1 L2 Series circuit represented in conventional ladder rung

LADDER DIAGRAM To energized LMP1 SW1 and SW2 need to be closed 05 PLC representation of previous rung using Allen- Bradley MicroLogix1000

Program listing / Mnemonic Code LOAD I1 AND I2 OUT 05 for Allen-Bradley MicroLogix1000 Note: The instructions tell the processor to load input (I1) into memory, AND it with input2 (I2), then output the result to output5 (O5) Notice the operands for input differ OMRON use 00001 Allen Bradley use I1 (for input 1) While operands for output OMRON use 01000 Allen Bradley use O1 (for output 1)

AND TRUTH TABLE ? A B C 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’ SW1 SW2 SW3 LMP1 I1 I2 I3 01 Three- input PLC ladder rung

PARALLEL CIRCUIT Can also be referred as OR logic function where at least one switch must be closed (ON) for output to energized (ON) SW1 SW2 LMP1 Battery Conventional parallel circuit

Or Or it can be represented In schematic ladder diagram As: LMP1 SW1 L1 L2 SW2 Parallel circuit represented in conventional ladder rung

LADDER DIAGRAM ? To energized LMP1 SW1 OR SW2 need to be closed 02 ? SW2 I2 PLC representation previous rung using Allen- Bradley MicroLogix1000

OR TRUTH TABLE ? A B C 1

CONSIDER…. What is the Mnemonics Code for OMRON CPM1A? LD 00001 LMP1 SW1 02 I1 SW2 I2 SW3 I3 Three- input OR logic What is the Mnemonics Code for OMRON CPM1A? 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 Decimal System 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 10s), the third column represents the number of hundreds and so forth and so on. Decimal System 100,000s 10,000s 1000s 100s 10s 1s

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

BINARY SYSTEMS Binary System 1 1 0 0 1 1 0 1 2 Used by computers and PLCs Use only two digits; 0 and 1 Base 2 Works similarly to decimal systems Binary System 32s 16s 8s 4s 2s 1s 1 1 0 0 1 1 0 1 2 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

16-BIT GROUP BINARY NUMBER Most Significant Byte Least Significant Byte 1 0 1 1 0 0 1 1 1 0 0 1 1 1 1 0 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 Octal System Use only 8 digits; 0,1,2,3,4,5,6 and 7 Base 8 Octal System 32,768s 4,096s 512s 64s 8s 1s 3 2 0 7 8 Octal number 7 x 80 = 7 0 x 81 = 0 2 x 82 = 128 3 x 83 = 1536 Decimal number 167110

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

HEXA DECIMAL 2 0 D 16 Hex number D x 10 = 13 0 x 161 = 0 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 hexadecimal 0111 1101 0011 1111 binary 0111110100111111 0111 1101 0011 1111 hexadecimal 7 D 3 F

EXAMPLE 1 16 Bit Binary 1001 0010 1011 0101 Grouped Binary Hexadecimal Equivalent 16 9x163 2x162 11x161 5x160 36, 864 512 + 176 5 37,55710 1 0 0 1 0 0 1 0 1 0 1 1 0 1 0 1 9 2 B 5 DECIMAL?

EXAMPLE 2 Most Significant Number (MSD) Least Significant Number (LSD) Middle Digit, MD BCD number 23222120 23222120 23222120 0+0+2+0 0+0+2+1 8+0+0+1 2 3 910 =23910 0 0 1 0 0 0 1 1 1 0 0 1 DECIMAL?

COMPARISON BETWEEN THESE NUMBER SYSTEMS

Decimal Hexadecimal Octal Binary 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 1 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 1 2 3 4 5 6 7 8 9 A B C D E F 8s 1s 1 2 3 4 5 6 7 8s 4s 2s 1s 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 Boolean equation; A + B = C OR Truth table C A B OR gate A B C 1 OR Truth table

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

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

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

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

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

Structure of a Ladder Diagram 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 Power Rail Rung 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? if NC is chosen Doorbell will continuously ringing until someone pushes the button So, when is NC used? 24V Current flow allow bell to ring 0V

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 L1 M d.c input Motor ? L2 Wiring diagram But this wiring is not suitable/relevant Why? L2 L1 Switch Motor M No safety. Ladder diagram How to include safety? BASIC STOP/START CIRCUIT

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 PB1, PB2 L1 for components

This wiring scheme is done for safety reasons. 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 LAMP2, 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 and 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 M 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 Control device- Switches, Solenoids, Coil and Relays. Power device- Valves, Motors and Cylinders (these shown separately in power diagram) Output Devices Located On Right Output device- Solenoids, lamps and control relays. Input Devices Located On Left Input device- Pushbuttons, Limit Switches etc. All conductor numbered All rungs numbered

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