PROGRAMMABLE LOGIC CONTROLLER Control Systems Types Programmable Logic

PROGRAMMABLE LOGIC CONTROLLER

Control Systems Types Ø Ø Ø Programmable Logic Controllers Distributed Control System PC- Based Controls

Introduction Ø The PLC is an assembly of solid state digital logic elements design to make logical decisions and provide outputs.

Programmable Logic Controllers Ø Ø Ø Sequential logic solver PID Calculations. Advanced Subroutines BIT Operations. Data Transfer. Text Handling.

Programmable Logic Controllers Applications : Ø Machine controls, Packaging, Palletizing, Material handling, similar Sequential task as well as Process control Advantages of PLC : Ø Ø They are fast and designed for the rugged industrial environment. They are attractive on Cost-Per-Point Basis. These Devices are less Proprietary ( E. g. . Using Open Bus Interface. ) These Systems are upgraded to add more Intelligence and Capabilities with dedicated PID and Ethernet Modules. Disadvantages of PLC : Ø Ø PLC were Designed for Relay Logic Ladder and have Difficulty with some Smart Devices. To maximize PLC performance and Flexibility, a number of Optional Modules must be added

Programmable Logic Controllers PLC Types Ø Ø Ø Nano (Small) Micro (Medium) Large Basic criteria for PLC Types Ø Ø Ø Memory Capacity I/O Range Packaging and Cost per Point

P L C Components Ø Ø Ø Central Processing Unit (CPU) Input Output Modules Power Supply Bus system Programming Device IN CPU OUT MODULE PROGRAM DEVICE m

P L C : Central Processing Unit Ø Ø It is a micro-controller based circuitary. The CPU consists of following blocks : Arithmatic Logic Unit (ALU), Program memory Process image memory (Internal memory of CPU) Internal timers and counters Flags CPU performs the task necessary to fulfill the PLC funtions. These tasks include Scanning, I/O bus traffic control, Program execution, Peripheral and External device communication, special functions or data handling execution and self diagnistics.

PLC : Input module Ø Ø Ø These modules act as interface between real-time status of process variable and the CPU. Analog input module : Typical input to these modules is 4 -20 m. A, 0 -10 V Ex : Pressure, Flow, Level Tx, RTD (Ohm), Thermocouple (m. V) Digital input module : Typical input to these modules is 24 V DC, 115 V AC, 230 V AC Ex. : Switches, Pushbuttons, Relays, pump valve on off status

PLC : Input module L 1 120 V ac PB input field device L 2 L 1 1 2 3 4 L 2 Input module terminal board Input status indicator

PLC : Output module Ø Ø Ø These modules act as link between the CPU and the output devices in the field. Analog output module : Typical output from these modules is 420 m. A, 0 -10 V Ex : Control Valve, Speed, Vibration Digital output module : Typical output from these modules is 24 V DC, 115 V AC, 230 V AC Ex. : Solenoid Valves, lamps, Actuators, dampers, Pump valve on off control

PLC : Output module L 1 120 V ac L 1 L 2 Output status indicator 1 2 3 Output field device 4 L 2 Output module Module blown Fuse indicator

I/O SPECIFICATION Ø Ø Ø Ø Ø INPUT VOLTAGE – Magnitude and type of voltage ON-STATE INPUT VOLTAGE RANGE – voltage at which signal is recognized Nominal current per input – Min. current to operate input circuit AMBIENT TEMP RATING – Max temp of surrounding the I/O module INPUT DELAY – Time duration for input signal to be on before known as valid input. ( 9 -ms to 25 ms) NOMINAL OUTPUT VOLTAGE – It is min and max o/p operating voltage. e. g. Rated 120 v ac o/p ckt. Works in 92 to 138 v range. MAX O/P CURRENT RATING – Max current a single o/p or module can safely carry under load OFF –STATELEAK CURRENT PER O/P – Max value of leak current flows through the o/p in OFF position ELECTRICAL ISOLATION – Max volts between I/o and logic ckt.

P L C : Power Supply Ø Ø Ø The power supply gives the voltage required for electronics module (I/O Logic signals, CPU, memory unit and peripheral devices) of the PLC from the line supply. The power supply provides isolation necessary to protect the solid state devices from most high voltage line spikes. As I/O is expanded, some PLC may require additional power supplies in order to maintain proper power levels.

P L C : Bus System Ø Ø It is path for the transmission of the signal. Bu system is responsible for the signal exchange between processor and I/O modules The bus system comprise of several single line ie wires / tracks

Relay Connection L 1 L 2 L 3 M M M T 1 T 2 T 3 M CR CL 1 2 CR M 3 4 L 2 M MOTOR

Advantage of PLC Over Relay Style RELAY 1 -Hard wiring PLC 1 -Less wiring 2 -Changes difficult 2 -Easy modification 3 -More power 3 -Low power 4 -More maintenance 4 -Solid state reliability 5 -Difficult to expand -Ease of expansion

PLC Cycle Ø Ø Ø Sense the Input Process the Logic Give Output Programmable controller Inputs Outputs Machine or Process

PLC Signal Flow Input Module Processor Memory Output Modules Data Output Input Image Table I: 0/6 O: 0/7 I: 1/4 O: 1/5 Input Devices Output Devices Ladder Program I: 1/4 I: 0/6 O: 0/7 I: 1/4 O: 1/5 Programming Terminal O: 1/5

PLC Architecture Evolution u Mid - 1970 s : Discrete Machine Control Programming Terminal Connection is Point to Point PLC Programming Language : Connection is Point to Point I/O - Relay ladder logic - Flexibility in altering Control system operation

PLC Architecture Evolution u Early - to - Mid 1980 : Discrete and Process Control MS - DOS Reasonable Computer Running PLC Programming Software PLC Programming Language : I/O - Ladder Program - PID - Data Storage

PLC Architecture Evolution u Late 1980’s to early 1990’s : Discrete and Process Control Windows PC running PLC Programming Software Connection in networked allowing Multiple PLC I/O PLC became a part of the developing enterprise resource system

PLC Architecture Evolution Today : Distributed I/O Modules PLC Distributed I/O scanner Data Communication Bus Distributed I/O modules

PLC Architecture Evolution Today : Hot Redundant System TAPS SPLITTERS Remote I/O Network FIBER OPTIC LINK Remote I/O

PLC Architecture Evolution Today : Ethernet Technology in PLCs Workstation Switched Hub Controller

PLC Architecture Evolution Today : Wireless communication PLC Wireless Modem Remote Platform Wireless Modem PLC HMI Display PC

PLC Systems of various vendors Siemens Ø Ø S 5 -110 U, 115 U, 135 U S 7 - 200, 300, 400 Allen Bradley Ø Ø Ø Micrologix 1000, 1200, 1500 SLC 5/01, 5/02, 5/03 PLC 5/10, 5/25 and 5/40 Modicon Ø Nano Ø Ø Ø Micro Premium Quantum

Configuration of PLC : Modicon Built in display for I/O (in-rack, AS-i) and Diag Programming Terminal PC Connection 8 Analog Inputs 1 Analog Output I/O Modules Up/Down Fast Counter Up Counter Unitelway Port for connection of up to 5 Slaves TSX 37 -22 PCMCIA communications port PCMCIA memory expansion port

Configuration of PLC : Siemens CPU I/O Modules External Power Supply

Configuration of PLC : Allen Bradley CPU I/O Modules Power Supply

Configuration of PLC : GE FANUC I/O Modules CPU Back plane

PLC Programming Standards The open, manufacturer-independent programming standard for automation is IEC 61131 -3. You can thus choose what configuration interface you wish to use when writing your application : Ø Ø Ø Ladder Diagram Statement List Instruction List Function Block Diagram Sequential Function Chart Structured Text

Scan Rate Ø The completion of one cycle of the sequence is called- SCAN Ø Time required for one cycle is called SCAN TIME

PLC DCS Selection Criteria Ø Ø Ø Cost of hardware, software, Integration Engineering, Design, Installation, Start-up and Commissioning, Validation documentation and Execution, Training, Spare parts, Maintenance, System service contract and system life cycle. Reliability, Flexibility, Scalability and Validatability. Ease of Database configuration, Graphics development, Interlocks and Batch processing. Integration of High-level Application. Control Philosophy for Centralized versus Remote Operator Console or both. Compliance with an Industry batch standard such as ISA SP 88 and new Communication Protocol.

Memory Types Ø Ø Ø ROM (Read Only Memory) RAM (Random Access Memory) PROM (Programmable ROM) EPROM (Erasable PROM) EAROM- Electrically alterable ROM EEPROM-Electrically erasable PROM

Binary System u u u BIT – Each digit of a binary number BYTE – Group of 8 bit WORD – Group of one or more byte LSB – Least significant bit or smallest value MSB – Most significant bit or largest value 7 6 5 4 3 2 1 0 8 BIT WORD MSB LSB BYTE 18 BIT WORD

PLC : Terminology u INPUT is referred by – Ixxyy u OUTPUT is referred by – Qxxyy u TIMER is referred by – T xyyzzzz u FLAGS are referred by – M xxxx u COUNTERS are referred by – C xxxx