Introduction to PLC Presentation

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INTRODUCTION TO PROGRAMMABLE LOGIC CONTROLLERS

Nikini Automation Systems (Pvt.) Ltd. Introduction to PLC

© Nikini Automation Systems (Pvt) Ltd

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Overview • • • • • • • • • Introduction to PLC

Introduction to automation technology Introduction to micro PLC systems General Structure of PLC System Installing PLC and configuring hardware CPU memory and data types Basic programming concepts Programming languages Programming instructions Programming of control systems © Nikini Automation Systems (Pvt) Ltd

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Automation Technology

Introduction to PLC


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Introduction to PLC


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What is automation?

Manual Process

Mechanized Process

Automation is aimed at reducing human effort in performing a task. Introduction to PLC


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What is automation? • Automation (ancient Greek: = self dictated) or industrial automation is the use of electronic controllers to control industrial machinery and processes, replacing human operators. • It is a step beyond mechanization, where human operators are provided with machinery to help them in their jobs. Introduction to PLC


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Where used? • • • • • • • • Introduction to PLC

Production Industry Offices Buildings Construction Industry Medical field Household equipment Aerospace Industry ??? © Nikini Automation Systems (Pvt) Ltd

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Example of a Manual process

Drilling machine Clamping device

Work piece Manual Process of Drilling a work piece Introduction to PLC


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Processes carried out • • • • • •

Introduction to PLC

Keeping the work piece Clamp the work piece Drill the work piece Un clamp work piece Remove the work piece Sensing each operation


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Elements of the manual system • Actuators

• Decision making element

• Sensors Introduction to PLC


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Automating the Process: • Step 1 :Replacement of human’s muscles (hands) by some actuators, e.g. the pneumatic cylinders • Step 2 :Replacement of human’s brain by a logic signal processing device, e.g. PLC, electrical relay circuit. • Step 3 :Replacement of human’s senses (eyes, ears, etc.) by some input devices (electrical sensors). • Step 4 :Use set of instructions to control output element according to the signal inputs present. Introduction to PLC


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Automated System Drill Cylinder

Limit switches/ sensors to detect end limits of cylinder movement

Clamp Cylinder

Operator panel Introduction to PLC

Signal Processor © Nikini Automation Systems (Pvt) Ltd

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Industrial Automation

Pentagon of Automation

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Signal Processors Hard-wired Control Electrical Pneumatics Hydraulic

Programmable Control Programmable Logic Controller (PLC) Embedded Controller

Digital Electronics

Micro controller (PIC) Industrial PC

Introduction to PLC


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Hardwired Control & Programmable Control

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• Hard-wired control – Wiring of mechanical, electrical, electromechanical or electronic components to obtain desired control

• Programmable control – Programming and reprogramming of an electronic component to obtain desired control

Introduction to PLC


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Introduction to PLC

Introduction to PLC


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What is PLC? • PLC is an abbreviation for Programmable Logic Controller. • PLC is a microprocessor-based electronic device. • This equipment controls a process/ machine. – a printing machine for printing newspapers, a bagging plant to bag cement, a press for pressing plastic-shaped parts, …

• This process occurs according to the instructions of a program in the memory of the equipment. Introduction to PLC


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What is PLC? • PLC is primarily used as an Industrial Machine Controller. • PLC is a small, but powerful Computer which is designed for industrial Controlling. • To control process/ Machine – Sensors Signal Inputs – Control switches (Push buttons, Switches) Signal – Actuators (Solenoid Valves, Motor controllers) Outputs should be wired to the PLC – Program with instructions stating how the process/ machine works should be written into the PLC memory Introduction to PLC


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What is PLC? Program loaded into the memory of PLC.. …routed to the machine

Program with instructions PLC Introduction to PLC


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Basic Principle of a PLC

Program (Instructions)

Input Signals

Introduction to PLC

Signal Processing


Output Signals

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What PLC can do? PLCs have inbuilt.. 1. Logic controls 2. Timers 3. Counters 4. Analogue Signals 5. Closed loop Control 6. Arithmetic Functions…etc.

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Advantages of PLC • Greater Flexibility and reliability – Changes to the design can easily be made on the program. • Easy debugging – Error detection program available. • Low power consumption & space requirement – Based on solid-state electronics rather than electromechanical technology. • Little maintenance – No moving parts. Introduction to PLC


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Advantages of PLC • No special programming skills required – Computer programming knowledge is not required. • Low Cost – Prices of microprocessor-based devices reduced more than those of electro-mechanical devices. • Easy Archiving & Documentation – Programming, Parameter changes, etc. can be noted and stored in the computer and documented without effort.

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Advantages of PLC • Less project planning work – tested programs and subprograms can be used for a number of different control setups – but each relay control circuit has to be wired and tested from scratch • Faster control development – programming and wiring can be carried out in parallel • Simpler monitoring of stations by a higher-level host computer – a programmable logic controller can easily exchange data with the host computer

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PLCs Vs Other Microprocessor Based Devices

• Modularity – Expansion possible. • Dedicated Input/Output Units – Inputs & outputs can be easily connected without interfacing. • Programmability – User friendly. No prior computer language required. – IEC 1131-3 Languages • Predictability – Designed to fail predictably. Outputs will turn off when program fails. • Single-Source Support – Most PLC manufacturers have complete range of input & output devices.

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Major PLC manufacturers • • • • • • • • • • • Introduction to PLC

ABB Koyo Honeywell Siemens Modicon Omron Allen-Bradley General Electric Tesco Controls Panasonic (Matsushita) Mitsubishi © Nikini Automation Systems (Pvt) Ltd

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SIEMENS SIMATIC S7 • SIEMENS SIMATIC S7 consists of 3 families. – S7-200 – S7-300 – S7-400

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S7-200

Introduction to PLC


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S7-200 • The SIMATIC S7-200 is the CPU for the lower level performance range. • It is available in various grades. – The CPU is qualified for open and closed loop control tasks in machines and system construction. – It is real time capable and offers extensive communication possibilities over a PROFIBUS or PC/PPI cable and over a free programmable interface protocol. – The SIMATIC S7-200 offers modular extensibility and integrated PID closed loop control functions. – The program software STEP 7 Micro/Win enables a quick introduction in the programming and configuration. Introduction to PLC


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S7-300

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S7-300 • The SIMATIC S7-300 family offers the automation solutions for the lower and middle performance range. • Properties of the SIMATIC S7-300 – Program memory up to 85 K instructions – Up to 1024 digital in- and outputs – Multipoint capable interface for the configuration of smaller networks and for configuration with help of a PC/PG. – Quick execution time in which the performance capable CPU executes 1024 binary instructions inside of 0.1 ms. – Modular configuration and quick enhancements are possible through interface modules with an integrated back plane bus.

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S7-400

Introduction to PLC


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S7-400 • The CPUs of the family SIMATIC S7-400 build the solutions for the middle and higher performance range (e.g. automobile and machine tool construction or instrumentation and control). • Properties of the SIMATIC S7-400 – Program memory up to 660 K instructions. – Up to 131056 digital in- and outputs. – Multipoint capable interface for the configuration of smaller networks and for configuration with help of the PC/PG. – Quick execution time that the performance capable CPU executes 1024 binary instructions inside of 0.1 µs. – Modular configuration and quick enhancements are possible through interface modules with integrated back plane bus. Introduction to PLC


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Components of a PLC system

Introduction to PLC


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PLC Components

PLC - Program

Input Module

Central Processing Unit

Sensors

Introduction to PLC

Modular PLC Compact PLC

Output Module

Actuators


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Hardware Components of a PLC • A PLC is made up of two basic sections – Input/Output (I/O) Interface – Central Processing Unit (CPU)

• CPU consists of two main parts – Processor – Memory

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Firmware • Firmware is the software part, which is permanently installed and supplied by the PLC manufacturer. • This includes fundamental system routines, used for starting the processor after the power has been switched on. • Additionally, there is the operating system in the case of programmable logic controllers, which is generally stored in a ROM, a read-only memory, or in the EPROM. Introduction to PLC


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Software Components • Firmware – Keeps information about hardware – Should be stored in CPU for proper use of hardware

• Operating System – Controls the basic functions of PLC

• User Program – Instructions written by the user (programmer)

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Structure of a S7-200 (CPU 222)

Introduction to PLC


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Mode Selector Switch • RUN • TERM • STOP

Introduction to PLC


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Expansion Modules

Introduction to PLC


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Cartridge • Portable EEPROM • Battery • Real Time Clock

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Steps to follow •

Steps to follow when using a PLC for the first time 1. Wire PLC and all the modules 2. Configure Hardware 3. PLC Programming

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Wiring PLC • Follow the instructions/ manual given by the manufacturer • Correctly connect the power supplies, etc. • Find the required type of inputs (Voltage, current, etc) • Connect all the modules and wire the modules as pre given instructions Introduction to PLC


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Introduction to PLC


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Introduction to PLC


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Hardware Configuration • Configuring connected hardware units and downloading the firmware into CPU. • Enables CPU to identify the connected hardware modules and their capabilities. This is essential for using the modules. • S7 200 provides facility to read the PLC rather than manually configuring each connected unit. Introduction to PLC


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Hardware Configuration 1. Connect wired PLC to Computer 2. Set PLC & PG (Computer) Interface (Identify the correct connecting cable) 3. Set communication with PLC 4. Configure connected components (or identify PLC type) 5. Download the settings to PLC Introduction to PLC


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Introduction to PLC


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PLC Programming

Introduction to PLC


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Programming Concept 1. Specification: Description of the task 2. Design: Description of the solution 3. Realisation: Implementation of the solution 4. Integration/commissioning: Incorporating into environment and testing the solution

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Programming Concept 1.

Prepare flow chart or Ladder diagram according to the functional specifications of the machine 2. Assign Input/ Output terminal addresses to the PLC as per the wiring diagram and List of symbols 3. Write program in to the PLC using the software 4. Simulate operation and debug program (with PLC programming software, if possible, or with switches and bulbs) 5. Is Program correct? – : Go to step 6 – : Modify program and go to step 4 6. Connect external devices such as Operator panel switches, sensors of the machine, relays, solenoids, etc. 7. Trial Run monitoring the functions closely 8. Is Program correct? – : Go to step 9 – : Modify program and go to step 7 9. Store Program 10. Run Introduction to PLC


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Nikini Prepare flow chart or ladder program

Assign Input/ Output terminal addresses

Write program into PLC

Simulate operation and debug program

Introduction to PLC

Correct program


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No

Yes

Connect external devices

Trial Run

Is program correct?

Correct program

No

Yes

Store program

Run Introduction to PLC


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Programming Method Console or Programming Keypad Peripheral Device Connecting Cable

PLC

Link with Console / Programming Keypad Programming Software

Computer

Link with Computer Introduction to PLC


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Programming Languages • IEC 61131-3 Languages – – – – –

Introduction to PLC

Ladder diagram (LD) Function block diagram (FBD) Instruction list (IL) Structured text (ST) Sequential function chart (SFC)


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Comparison of Programming Methods Graphical Programming (LD, FBD, SFC) • Windows-based graphical programming environment on a computer, to compose the ladder diagram. • Equipped with good monitoring tools and programming aids. • Good for program development. Mnemonic Code Programming (IL, ST)

• Compact handheld device to key in programming instructions in mnemonic codes. • Ideal for on-site debugging and minor circuit modification. • Requires knowledge of the programming codes. Introduction to PLC


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Ladder Diagram Programming

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Example • Actuation of a push button (S1) is to cause a lamp (B1) to be switched on. • The lamp is to be illuminated as long as the push button is actuated.

S1 B1 Introduction to PLC


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YES Function +24V

START

Input

Output

0 (Off)

0 (Off)

1 (On)

1 (On)

0V

Truth Table Electrical Circuit Introduction to PLC


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Introduction to PLC


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YES Function

Ladder Diagram Introduction to PLC


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Symbolic Addressing • For symbolic addressing, the symbol table must be filled in. • Select the symbol table from the operations tree or by selecting Symbol table in the View menu.

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Symbol Table • A window is displayed in which you can edit the symbol table. • Enter the element that you want to appear as plain text later on under “name”. • Under address, enter the operand that you want to have replaced by a symbolic name. • Under comment, you can enter a text that you find helpful.

Introduction to PLC


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Ladder Diagram • The ladder programs allow the CPU to emulate the flow of electric current from a power source through a series of logical input conditions that in turn enable logical output conditions. • The logic is separated into networks. • The program is executed as dictated by the program, one network at a time, from left to right and then top to bottom. • Once the CPU has reached the end of the program, it starts over again at the top of the program. Introduction to PLC


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Elements of Ladder Diagram • Contacts Represent a switch through which power can flow. • Coils Represent a relay or output that is energized by power flow. • Boxes Represent a function (for instance, a timer, counter, or mathematical operation) that is executed when power flow reaches the box. • A network is composed of these elements and represents a complete circuit. • Power flows from the left power rail (represented in the LAD editor by a vertical line on the left side of the window) through the closed contacts to energize the coils or boxes.

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Example of a Ladder Program Coil

Contact

Networks

Box

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Memory Addressing

Introduction to PLC

Inputs

Outputs

• I0.0 • I0.1 . . . . • I0.7

• Q0.0 • Q0.1 . . . . • Q0.5


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Statements • Control Statements • The control statement is the smallest unit of a PLC user program. A statement consists of an – operation part – operand part

Introduction to PLC

(I0.0, I0.1, Q0.4)


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Ladder Programming Rules • Rules about Placing Contacts – Each network must begin with a contact. – You cannot terminate a network with a contact

Introduction to PLC


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Ladder Programming Rules • Rules about Placing Coils – You cannot begin a network with a coil – Coils are used to terminate a network of logic. – A single network can have several coils, as long as the coils exist on parallel branches of that particular network. Otherwise there can be only one coil per network. – You cannot place more than one coil in a series

Introduction to PLC


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Ladder Programming Rules • Rules about Placing Boxes – You cannot begin a network with a box. – Boxes are used to terminate a network of logic. – If a box has ENO, you can place further instructions after the box. – You can have several boxes with ENO in a series on the same network. – If a box does not have ENO, rules are similar to that of a coil. • There cannot be more than one box in a network. • You cannot place any instructions after it Introduction to PLC


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Ladder Programming Rules

Introduction to PLC


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Ladder Programming Guide Number of contacts for I / Os , timers, counters, etc. is unlimited.

Introduction to PLC


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Ladder Programming Guide Number of contacts to be connected in series or parallel is unlimited.

Introduction to PLC


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Ladder Programming Guide An output coil name can only be assigned once. There cannot be two (or more) coils (or boxes) with same name.

Introduction to PLC


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Ladder Programming Guide A network of the ladder diagram is keyed into PLC from left to right. Programming for counter and other modules having more than one input must be performed in a pre-determined order.

Introduction to PLC


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Ladder Programming Guide Timer & counter data should be entered at the time of programming.

Timer call with a pre-set time of 5.5 seconds

Input/output number, step number, timer/counter values, etc. can be written with only the significant digits.

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Drawing Lines • You can use the horizontal and vertical lines from the Program toolbar, or hold down the CTRL key and press the LEFT, RIGHT, UP, or DOWN ARROW key on your keyboard, to draw lines between the elements of your network and the lefthand power rail when necessary to complete a network.

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Enter Instructions

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Introduction to PLC


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Assigning Addresses • To assign a constant value (such as 100) or an absolute address (such as I0.1), simply type the desired value in the address area of the instruction. (Use the mouse or the ENTER key to select the address area for typing.)

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Compile in LAD • You can compile by using the toolbar buttons or the PLC menu.

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Example: Burglar Alarm • A thin wire has been stretched behind a display window, which breaks if a burglary is attempted. • A closed circuit is interrupted as a result of this and a buzzer is sounded.

Introduction to PLC


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NOT Function +24V

START

Input

Output

0 (Off)

1 (On)

1 (On)

0 (Off)

0V

Truth Table Electrical Circuit Introduction to PLC


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NOT Function



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Press with protective guard • A press stamp 1.0 is to advance only if a push button S1 is actuated and a protective guard is closed. • If one of these conditions is not met, the press tool is to return immediately. • The position of the closed protective guard B1 is monitored by a proximity switch B1. Introduction to PLC


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AND Function +24V

S1

Input 1

Input 2

Output

0

0

0

0

1

0

1

0

0

1

1

1

S2

0V

Truth Table

Electrical Circuit Introduction to PLC


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AND Function



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Bell system • An apartment bell is to ring if bell button S1 at the front door is pressed or bell button S2 at the apartment door.

Introduction to PLC


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OR Function +24V

S1

S2

Input 1

Input 2

Output

0

0

0

0

1

1

1

0

1

1

1

1

0V

Truth Table

Electrical Circuit Introduction to PLC


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OR Function



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Function Block Diagram • There are no contacts and coils, but there are equivalent instructions that appear as box instructions. • The program logic is derived from the connections between these box instructions. • The output from one instruction (such as an AND box) can be used to enable another instruction (such as a timer) to create the necessary control logic. Introduction to PLC


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Introduction to PLC


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Example

Introduction to PLC


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YES Function

Functional Block Diagram Introduction to PLC


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NOT Function



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AND Function



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OR Function



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Statement List • Statement List (STL) editor allows to create control programs by entering the instruction mnemonics. • This text-based concept is very similar to assembly language programming. • The CPU executes each instruction, in the order dictated by the program, from top to bottom, and then restarts at the top.

Introduction to PLC


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Example

Statement List



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YES Function • Statement Logic LD I0.0 = Q0.0

Introduction to PLC


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NOT Function • Statement Logic LDN =

Introduction to PLC

I0.0 Q0.0


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AND Function • Statement Logic LD I0.0 A I0.1 = Q0.0

Introduction to PLC


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AND Function • Statement Logic LD I0.0 LD I0.1 ALD = Q0.0

Introduction to PLC


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OR Function • Statement Logic LD I0.0 O I0.1 = Q0.0

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OR Function • Statement Logic LD I0.0 LD I0.1 OLD = Q0.0

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LD Language • Ladder logic is easy for beginning programmers to use. • Graphical representation is often easy to understand, and is popular around the world. • The LAD editor can be used with both the SIMATIC and IEC 1131-3 instruction sets. • You can always use the STL editor to display a program created with the LAD editor.

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FBD Language • The graphical logic gate style of representation is good for following program flow. • The FBD editor can be used with both the SIMATIC and IEC 1131-3 instruction sets. • You can always use the STL editor to display a program created with the LAD editor. • The expandable AND/OR boxes make it easier to draw complex input combinations.

Introduction to PLC


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STL Language • STL is most appropriate for experienced programmers. • STL sometimes allows you to solve problems that you cannot solve easily with the LAD or FBD editor. • While you can always use the STL editor to view or edit a program that was created with the SIMATIC LAD or FBD editors, the reverse is not always true. • You cannot always use the SIMATIC LAD or FBD editors to display a program that was written with the STL editor.

Introduction to PLC


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PLC Exercises

Introduction to PLC


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Exercise 1: NAND

Introduction to PLC

S1

S2

B1

0

0

1

0

1

1

1

0

1

1

1

0


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Exercise 1: NOR

Introduction to PLC

S1

S2

B1

0

0

1

0

1

0

1

0

0

1

1

0


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Exercise 1: X-OR

Introduction to PLC

S1

S2

B1

0

0

0

0

1

1

1

0

1

1

1

0


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Exercise 2-Logic

Introduction to PLC

Input 1

Input 2

Input 3

Output 1

Output 2

1

1

0

1

0

0

1

1

1

0

1

0

1

0

1

1

1

1

0

1


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Silo control system for two bulk materials

2A 1A

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• A mixing plant permits a selection between two bulk materials per selector switch (S2). • In switch position 1 (S2 = 0 signal), bulk material A reaches a mixing container, if push button S1 is actuated simultaneously. • If selector switch S2 is in position 2 (S2 = 1 signal) and push button S1 is actuated bulk material B is conveyed. • Silo A is opened via cylinder 1A (solenoid 1M1), Silo B via cylinder 2A (solenoid 2M1). Introduction to PLC


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Programming Concept 1. Specification: Description of the task 2. Design: Description of the solution 3. Realisation: Implementation of the solution 4. Integration/commissioning: Incorporating into environment and testing the solution

Introduction to PLC


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Design steps 1. 2. 3. 4. 5.

Sketch the system Identify the sequence Design the power circuits Identify the input signals & Output Signals Design the control circuit according to the control requirement 6. If there are signal overlaps, necessary actions should be taken to overcome signal overlap problems Introduction to PLC


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Introduction to PLC

S2

S1

Y1

Y2

0

0

0

0

0

1

1

0

1

0

0

0

1

1

0

1


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Heavy Work piece feeding

Introduction to PLC


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Exercise 3 A1

1.

Piston moves forward when “Start” button Pressed

2.

Return to initial position when “Reset” button pressed

Y1

Introduction to PLC


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1

+24V

2

3 4

START

5

Nikini

RESET

24V I0 I1 I2 I3 I4 I5 I6 I7

0V Q0 Q1 Q2 Q3 Q4 Q5 Q6 Q7

Y1 0V

Introduction to PLC


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PLC Hardware Components

Introduction to PLC


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Hardware Components of a PLC • A PLC is made up of two basic sections – Input/Output (I/O) Interface – Central Processing Unit (CPU)

• CPU consists of two main parts – Processor – Memory

Introduction to PLC


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Input Modules Input Modules – Interface for input devices. – CPU works in 5V . Input modules convert 24V DC (or higher voltage) to 5V DC. – Isolate Signal given to the CPU. – Input delay to screen input signals.

Introduction to PLC


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Introduction to PLC


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Introduction to PLC


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Types of Input modules

• Sink-type input module interfaced with dry contact switches and PNP sensor Introduction to PLC


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Types of Input modules

• Source-type input module interfaced with dry contact switches and NPN sensor Introduction to PLC


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Output Modules Output Modules – The signals coming from CPU are 0V or 5V. – Amplify and condition the output. – Relay/ Transistor/ Triac Output.

Introduction to PLC


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Introduction to PLC


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Types of output modules

• Transistor Output (Source Type) Introduction to PLC


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• Transistor Output (Sink Type) Introduction to PLC


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• Relay Output Introduction to PLC


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• Triac Type Output Introduction to PLC


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Types of Memory Types of Memory RAM ROM

Random Access Memory

Erasing

Programming

When power is removed, Memory contents are:

Electrical

Electrical

Volatile

Not possible

Using masks in Manufacturing process

Read Only Memory

PROM

Programmable ROM

EPROM

Erasable PROM

Non volatile

With UV light RPROM

Reprogrammable PROM

Electrical

EEPROM Electrically Erasable PROM Electrical EAPROM Electrically Alterable PROM Introduction to PLC


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Basic Memory Areas The Basic memory areas of a PLC : CPU Work Memory (RAM) contains the executable user program (for example logic and data blocks) Load Memory (EEPROM/RAM) Contains the entire User Program

System Memory (RAM) Block stack, Interrupt stack Diagnostic buffer, Local data stack process image input/output tables, bit memory, timers, counters

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PLC Memory • Bit is the abbreviation for binary digit. – The BIT is the smallest binary (bivalent) information unit. – It can accept a signal status of “1” or “0”. 0

• BYTE. – A byte has the size of 8 bits. 0 1 0 1 1 0 0 1

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PLC Memory • WORD – The word length corresponds to the number from 16 binary characters. – A word also has the size of 2 bytes or 16 MSB

LSB

1 0 1 0 0 0 0 1 1 0 1 0 0 1 0 0

• DOUBLE-WORD – A double-word corresponds to the word length of 32 binary characters. MSB

LSB

1 0 1 0 0 1 0 1 1 0 1 0 0 1 0 0 1 0 1 1 0 1 0 1 1 0 1 1 0 1 0 0 Introduction to PLC


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PLC Memory MSB

Bit

20

Byte

27

26

25

24

23

22

21

20

LSB

0 1 0 1 1 0 0 1

MB100

0 MS Byte

Word

MW100 LS Byte

MS Byte

Double Word

MD100

LS Byte Introduction to PLC


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Memory addressing MSB 0

LSB 7

6

5

4

3

2

1

0

I

Bit

1

I 0 . 3

0 M 1 0 V 1 0

Area Identifier Introduction to PLC

Byte Bit of Address Byte

Q 1


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Memory addressing • Byte/ Word/ Double word addressing MB0 MB1 VW10 VD100 Timer and Counter addressing are different

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How the Control Program Works PLC performs the following operations repeatedly:

• Read the states of the input devices. • Copy input status into the Process-Image Input (PII) register. • CPU execute the user program stored in the Load Memory and stores the results of the program logic in various memory areas including ProcessImage Output (PIQ) register. • Transfer status from the PIQ to the field outputs. Introduction to PLC


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Scan Cycle of the PLC One Scan Cycle Reading the inputs

Writing to the outputs Executing the program

Executes the CPU self – test diagnostics

Process any communication requests

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Scan Cycle of the PLC • Reading the inputs: The S7-200 copies the state of the physical inputs to the process-image input register. • Executing the control logic in the program: The S7-200 executes the instructions of the program and stores the values in the various memory areas. • Processing any communication requests: The S7-200 performs any tasks required for point-to-point or network communications. • Executing the CPU self-test diagnostics: The S7-200 ensures that the firmware, the program memory, and any expansion modules are working properly. • Writing to the outputs: The values stored in the process-image output register are written to the physical outputs. Introduction to PLC


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• The execution of the scan cycle is dependent upon whether the S7-200 is in STOP mode or in RUN mode. In RUN mode, your program is executed; in STOP mode, your program is not executed.

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PLC scan cycle time • The time that the processor requires for this execution is called a cycle time. • This time is dependent on the number instructions and types of commands. • Also cycle time is dependent on CPU speed and I/O conversion time delay

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Exercise 4 1B2

1.

Piston moves forward when “Start” button Pressed

2.

Return to initial position automatically when piston moved to 1B2

1M1

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1

+24V

2

3 4

START

5

Nikini

A2

24V I0 I1 I2 I3 I4 I5 I6 I7

0V Q0 Q1 Q2 Q3 Q4 Q5 Q6 Q7

Y1 0V

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Exercise 5 1B1

1B2

1.

Piston moves forward when it reaches to 1B1

2.

Return to initial position automatically when piston moved to 1B2

3.

Continuous cycle starts with “S1” (Start) push button

4.

Continuous cycle stops with “S2” (Stop) push button

1M1

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1

+24V

3 4

START

5

RESET

6

A1

7

Nikini

A2

24V I0 I1 I2 I3 I4 I5 I6 I7

0V Q0 Q1 Q2 Q3 Q4 Q5 Q6 Q7

Y1 0V Introduction to PLC


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Counters

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Counters • Up Counter (CTU) • Down Counter (CTD) • Up-Down Counter (CTUD)

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Up Counter • Counts up from the current value each time the count-up input CU makes the transition from off to on. • When the current value (Cxxx) is greater than or equal to the Preset Value (PV), the counter bit (Cxxx) turns on. • The counter is reset when the Reset (R) input turns on, or when the Reset instruction is executed. • The counter stops counting when it reaches the maximum value (32,767). • Counter ranges:Cxxx=C0 through C255 Introduction to PLC


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Example-LAD

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Example-FBD

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Example-STL

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Down Counter • Counts down from the current value of that counter each time the count down input CD makes the transition from off to on. • When the current value Cxxx is equal to zero, the counter bit (Cxxx) turns on. • The counter resets the counter bit (Cxxx) and loads the current value with the preset value (PV) when the load input (LD) turns on.

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Example-LAD

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Example-FBD

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Example-STL

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Up Down Counter • Counts up each time the count-up input CU makes the transition from off to on. • Counts down each time the count-down input CD makes the transition from off to on. • The current value Cxx of the counter maintains the current count. • The preset value PV is compared to the current value each time the counter instruction is executed. • When the current value Cxx is greater than or equal to the preset value PV, the counter bit Cxx turns on. • Otherwise, the counter bit turns off. • The counter is reset when the Reset (R) input turns on, or when the Reset instruction is executed. The CTUD counter stops counting when it reaches PV.

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Example-LAD

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Example-FBD

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Example-STL

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Timers

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Timer Types • Delay On timer (TON) • Delay OFF timer (TOF) • Retentive On Delay timer (TONR)

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Timer Numbers Timer Type TONR

TON, TOF

Introduction to PLC

Resolution Maximum Time Timer Number 1 ms 10 ms 100 ms

32.767 s 327.67 s 3276.7 s

T0, T64 T1-T4, T65-T68 T5-T31, T69-T95

1 ms 10 ms 100 ms

32.767 s 327.67 s 3276.7 s

T32, T96 T33-T36, T97-T100 T37-T63, T101-T255


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On Delay Timer • Counts time when the enabling input is ON. • When the current value (Txxx) is greater than or equal to the preset time (PT), the timer bit is ON. • Current value is cleared when the enabling input is OFF. • This timer continues counting after the Preset is reached, and it stops counting at the maximum value of 32767.

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Example-LAD

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Introduction to PLC


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Example-FBD

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Example- STL

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Delay Off Timer • Delay turning an output OFF for a fixed period of time after the input turns OFF. • When the enabling input turns ON, the timer bit turns ON immediately, and the current value is set to 0. • When the input turns OFF, the timer counts until the elapsed time reaches the preset time. • When the preset is reached, the timer bit turns OFF and the current value stops counting. Introduction to PLC


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Example-LAD

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Introduction to PLC


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Example-FBD

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Example-STL

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Retentive On Delay Timer • Counts time when the enabling input is ON. • When the current value (Txxx) is greater than or equal to the preset time (PT), the timer bit is ON. • The current value of the Retentive On-Delay timer is maintained when the input is OFF. • A Reset instruction (R) is used to clear the current value of the Retentive On-Delay timer.

Introduction to PLC


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Example-LAD

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Introduction to PLC


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Example-FBD

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Example-STL

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Exercise 6 1B1

1B2

1. Delay 3s at 1B1 and move forward 2. Delay 2s at 1B2 and move backward

1M1

3. Continuous Cycle with S1 (Start) push button 4. Stop when 10 cycles completed 5. Stop with S2 (Reset) push button immediately

Introduction to PLC


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1

+24V

3 4

START

5

RESET

6

A1

7

Nikini

A2

24V I0 I1 I2 I3 I4 I5 I6 I7

0V Q0 Q1 Q2 Q3 Q4 Q5 Q6 Q7

Y1 0V Introduction to PLC


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2A 1A

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Silo control system for two bulk materials • Selector switch “S2” is used to select between material A and B. • When a push button “S1” is pressed, material A should be entered for 10 seconds or material B should be entered for 13 seconds to the mixing bin. • Note: What happens if push button S1 is kept pressed (over 10 or 13 seconds)?

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Areas of System Memory •Input Image Register (I) •Output Image Register (Q) •Bit (M) memory •Variable (V) memory •Special Memory (SM) bits •Timer (T) memory •Counter (C) memory •Analog Inputs (AI) and Outputs (AQ) •Accumulators (AC) •High Speed Counters (HC) •Constant Values: Decimal, Hexadecimal, ASCII Introduction to PLC


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Instruction types • Bit logic • Timer • Counter • Program Control • Logic Operations • Logic Stack • Table • Conversion • High Speed Counter • Interrupt • Real Time Clock • Math, Increment and Decrement • PID • Move, Shift, Rotate and Fill • Communication and Networking

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Organizing the User Program Typical User Program Structure Main Program

Main Program : Executed once per scan MEND

Subroutine : Executed when called from the main program

Interrupt Routine : Executed on each occurrence of the interrupt event

Introduction to PLC


SBR 0 RET SBR 1 RET INT 0 RET INT 1 RET

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Program Flow Main Program

CALL 0

SBR 0

RET

SBR 1 RET CALL 1 Interrupt Event INT 0

MEND

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RET


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SIMATIC S7-200: Freeport communication Option: RS 485 or RS 232 protocol can be used

RS 485

RS 485 modem

PPI cable

Drive (e.g. USS protocol)

Non-Siemens device with RS 485

RS 232

Printer

NonSiemens“ PLC

OP

Modem

PLC Bar code scanner

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SIMATIC S7-200: Fieldbus Communication • • • • • •

Introduction to PLC

PROFIBUS-DP Slave AS-I Master Ethernet IT (TCP-IP) GSM GPRS


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Selecting a PLC •

Understand the process to be controlled 1. list the number and types of inputs and outputs. 2. determine how the process is to be controlled. 3. determine special needs such as distance between parts of the process.

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Selecting a PLC Consideration

Information to record

Notes

1. Proposed system 2. Environmental issues 3. Discrete devices 4. Analog devices 5.Specialty modules or features (application-specific) 6. CPU required 7. I/O locations 8.Communications requirements 9.Programming requirements

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Selecting a PLC • • • • • •

Number & types of Inputs and Outputs Analog Input and Output facility (# and types- V? I?) Expansion facility (Maximum modules, Module types,..) Function modules available (Weighing, Positioning, etc.) Special Functions (HSC, PTO, Real time clock, etc.) Software – Languages available – Monitoring/ Diagnostic facilities – Other facilities (Wizards, HW Configuration) – Ease of Programming • Memory capacity • Speed

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Selecting a PLC • • • • • •

Mathematical Calculations Types of Operator Interface (Operator panels, etc.) Communication facilities with other PLCs and Computers Temperature/ Humidity/ Vibration resistance Ease of Maintenance Spare parts/ After sales service/ Reliability/ Shipping time

• Cost $$

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Selecting a PLC Vendor •

If not already specified, a single vendor should be selected. Factors that might be considered are, 1. 2. 3. 4. 5. 6. 7. 8.

Introduction to PLC

manuals and documentation support while developing programs the range of products available support while troubleshooting shipping times for emergency replacements training the track record for the company business practices (billing, upgrades/obsolete products,etc.) © Nikini Automation Systems (Pvt) Ltd

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Review Introduction to automation technology Introduction to micro PLC systems General Structure of PLC System Installing PLC and configuring hardware CPU memory and data types Basic programming concepts Programming languages Programming instructions Programming of control systems Introduction to PLC


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Questions??

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Introduction to PLC


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Basics • • • • •

Introduction to PLC

Number systems Signal Inputs Signal Outputs PLC memory PLC scan cycle


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Number systems • Decimal 5238 = 5x1000 + 2x100 + 3x 10 + 8x1 5238 = 5x103 + 2x102 + 3x 101 + 8x100

• Binary 101101112= 1x27 + 0x26 + 1x25 + 1x24 + 0x23 + 1x22 + 1x21 + 1x20 = 18310

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Number systems • BCD (Binary Coded Decimal)

Introduction to PLC

Decimal number

BCD number

010

0000BCD

110

0001BCD

210

0010BCD

310

0011BCD

410

0100BCD

510

0101BCD

610

0110BCD

710

0111BCD

810

1000BCD

910

1001BCD © Nikini Automation Systems (Pvt) Ltd

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Number systems • Decimal number 3564 in BCD 0011 0101 0110 0100 BCD

• 16 bits required • BCD coded numbers are often used for seven segment displays and coding switches.

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Number systems • Hexadecimal A =10, B =11, C =12, D =13, E =14, F =15 87BC16 = 8x163 + 7x162 + 11x161 + 12x160 =3474810

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Types of signals

• Binary signal • Binary signals can take the value of 2 possible states. – Signal state “1” = voltage available = e.g. Switch on – Signal state “0” = voltage not available = e.g. Switch off

• In control engineering DC voltage of 24V is used. – + 24 V = “1” for this input. – 0 V = “0” Introduction to PLC


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Types of signals

• Analog signal • Can take many values within a certain range - Examples • Temperature -50 ... +150°C • Current flow 0 ... 200 l/min • Number of revolutions 500 ... 1500 r/min • These measurements are converted to currents or resistances. • analog information are converted to a voltage, current or resistance value. (analog to digital conversion -A/D conversion.) Introduction to PLC


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Input / Output System • Provides the physical connections between the outside world and CPU

Introduction to PLC

Input Devices

Output Devices

•Selector switches

•Alarms

•Push buttons

•Control Relays

•Sensors

•Solenoids

•Circuit breakers

•Lights

•Level sensors

•Horns

•Relay contactors

•Valves

•Motor starter Contacts

•Motor Starters © Nikini Automation Systems (Pvt) Ltd

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PLC Operation

Introduction to PLC


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Introduction to PLC Presentation

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