SIX WEEK TRAINING PRESENTATION ON:

PROGRAMMABLE LOGIC CONTROLLER

SUBMITTED BY:

PARAMPREET SINGH

AUTOMATION

AUTOMATION OR AUTOMATIC CONTROL, IS THE USE OF VARIOUS CONTROL SYSTEMS FOR OPERATING EQUIPMENT SUCH AS MACHINERY, PROCESSES IN FACTORIES, BOILERS AND HEAT TREATING OVENS, SWITCHING IN TELEPHONE NETWORKS, AND AIRCRAFT AND OTHER APPLICATIONS WITH MINIMAL OR REDUCED HUMAN EFFORT. SOME PROCESSES HAVE BEEN COMPLETELY AUTOMATED.

RELAYA RELAY IS AN ELECTRICALLY OPERATED SWITCH. MANY RELAYS USE AN ELECTROMAGNET TO MECHANICALLY OPERATE A SWITCH, BUT OTHER OPERATING PRINCIPLES ARE ALSO USED, SUCH AS SOLID-STATE RELAYS. RELAYS ARE USED WHERE IT IS NECESSARY TO CONTROL A CIRCUIT BY A LOW-POWER SIGNAL (WITH COMPLETE ELECTRICAL ISOLATION BETWEEN CONTROL AND CONTROLLED CIRCUITS), OR WHERE SEVERAL CIRCUITS MUST BE CONTROLLED BY ONE SIGNAL.

COMMON TYPES OF RELAY

SPST:–THESE HAVE TWO TERMINALS WHICH CAN BE CONNECTED OR DISCONNECTED. INCLUDING TWO FOR THE COIL, SUCH A RELAY HAS FOUR TERMINALS IN TOTAL..SPDT:– A COMMON TERMINAL CONNECTS TO EITHER OF TWO OTHERS. INCLUDING TWO FOR THE COIL.DPST:– THESE HAVE TWO PAIRS OF TERMINALS. EQUIVALENT TO TWO SPST SWITCHES OR RELAYS ACTUATED BY A SINGLE COILDPDT:- THESE HAVE TWO ROWS OF CHANGE-OVER TERMINALS. EQUIVALENT TO TWO SPDT SWITCHES OR RELAYS ACTUATED BY A SINGLE COIL.

FUNCTIONING OF RELAY RELAYS ARE SWITCHES THAT OPEN AND CLOSE

CIRCUITS ELECTROMECHANICALLY OR ELECTRONICALLY. RELAYS CONTROL ONE ELECTRICAL CIRCUIT BY OPENING AND CLOSING CONTACTS IN ANOTHER CIRCUIT. AS RELAY DIAGRAMS SHOW, WHEN A RELAY CONTACT IS NORMALLY OPEN (NO), THERE IS AN OPEN CONTACT WHEN THE RELAY IS NOT ENERGIZED. WHEN A RELAY CONTACT IS NORMALLY CLOSED (NC), THERE IS A CLOSED CONTACT WHEN THE RELAY IS NOT ENERGIZED. IN EITHER CASE, APPLYING ELECTRICAL CURRENT TO THE CONTACTS WILL CHANGE THEIR STATE.

RELAYS ARE GENERALLY USED TO SWITCH SMALLER CURRENTS IN A CONTROL CIRCUIT AND DO NOT USUALLY CONTROL POWER CONSUMING DEVICES EXCEPT FOR SMALL MOTORS AND SOLENOIDS THAT DRAW LOW AMPS. NONETHELESS, RELAYS CAN "CONTROL" LARGER VOLTAGES AND AMPERES BY HAVING AN AMPLIFYING EFFECT BECAUSE A SMALL VOLTAGE APPLIED TO A RELAYS COIL CAN RESULT IN A LARGE VOLTAGE BEING SWITCHED BY THE CONTACTS.

ADVANTAGES OF RELAY Electromagnetic relays have fast operation

and fast reset They can be used for both ac and dc

systems for protection of ac and dc equipments

Electromagnetic relays operating speeds which has the ability to operate in milliseconds are also can be possible

They have the properties such as simple, robust, compact and most reliable

These relays are almost instantaneous. Though instantaneous the operating time of the relay varies with the current.

PLC (PROGRAMMABLE LOGIC CONTROLLER) A 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, OR LIGHT FIXTURES. PLCS ARE USED IN MANY INDUSTRIES AND MACHINES. PLCS ARE DESIGNED FOR MULTIPLE ANALOGUE AND DIGITAL INPUTS AND OUTPUT ARRANGEMENTS, EXTENDED TEMPERATURE RANGES, IMMUNITY TO ELECTRICAL NOISE, AND RESISTANCE TO VIBRATION AND IMPACT. PROGRAMS TO CONTROL MACHINE OPERATION ARE TYPICALLY STORED IN BATTERY-BACKED-UP OR NON-VOLATILE MEMORY. A PLC IS AN EXAMPLE OF A HARD REAL-TIME SYSTEM SINCE OUTPUT RESULTS MUST BE PRODUCED IN RESPONSE TO INPUT CONDITIONS WITHIN A LIMITED TIME. IT IS A MULTIPURPOSE, CLOCK DRIVEN, MEMORY BASED DEVICE WHICH DEALS WITH THE DIFFERENT LEVEL OF COMPLEXITY AND CONTROL SYSTEM.

ARCHITECTURE OF PLC

PLC ADVANTAGES AND BENEFITS

HIGHER RELIABILITY:ONCE THE PROGRAM WRITTEN AND TESTED IT CAN BE EASILY DOWNLOADED INTO OTHER PLC'S MEMORY.

MORE FLEXIBILITY:IT IS EASIER TO CREATE A NEW PROGRAM MODULE OR CHANGE AN EXISTING PROGRAM IN PLC COMPARED TO HARD WIRED CIRCUITRY SYSTEM.

LOWER COST:PLCS WERE ORIGINALLY DESIGNED TO REPLACE RELAY

CONTROL LOGIC WHICH IS NOT ECONOMICAL AND COMPLEX ESPECIALLY FOR LARGE CONTROL CIRCUITS.

COMMUNICATION CAPABILITY:COMMUNICATION CAPABILITY OF PLC WITH THE OTHER CONTROLLERS AND COMPUTERS IN THE SYSTEM IS ONE OF THE MAIN ADVANTAGES COMPARED TO RELAY CONTROL CIRCUIT.

FASTER RESPONSE:PLCS ARE DESIGNED FOR HIGH SPEED AND FOR THE REAL TIME APPLICATIONS.RESPONSE TIME FOR PLCS ARE MUCH SMALLER COMPARED TO RELAY LOGIC CIRCUITS.

EASY TO TROUBLESHOOT:PLCS HAVE INBUILT DIAGNOSTICS AND OVERRIDE FUNCTIONS THAT HELPS THE USER TO EASILY TRANCE THE SOFTWARE AND HARDWARE ERRORS.

COMPONENTS OF PLC

PROCESSOR: IT IS THE CENTRAL PROCESSING UNIT (CPU) OF THE PROGRAMMABLE CONTROLLER, IT EXECUTES THE VARIOUS LOGIC AND SEQUENCING FUNCTIONS BY OPERATING ON THE PLC INPUTS TO DETERMINE THE APPROPRIATE OUTPUT SIGNALS.

THE PROCESSOR ACCEPTS THE INPUT DATA FROM VARIOUS SENSING DEVICES, EXECUTES THE STORED USER PROGRAM AND SENDS APPROPRIATE OUTPUT COMMANDS TO CONTROL DEVICES

MEMORY : MEMORY UNIT IS CONNECTED TO THE CPU, WHICH CONTAINS THE PROGRAMS OF LOGIC, SEQUENCING AND I/O OPERATIONS .

IT ALSO HOLDS DATA FILES ASSOCIATED WITH THESE PROGRAMS, INCLUDING I/O STATIONS BITS, COUNTER AND TIMER CONSTANTS, AND OTHER VARIABLE AND PARAMETER VALUES.

THIS MEMORY UNIT IS REFERRED TO AS THE USER OR APPLICATION MEMORY BECAUSE ITS CONTENTS ARE ENTERED BY THE USER AND ALSO DIRECTS THE EXECUTION OF CONTROL PROGRAM AND COORDINATES I/O OPERATIONS WITH THE AID OF SYSTEM MEMORY.

POWER SUPPLY:

A POWER SUPPLY OF 240V ALTERNATING CURRENT(AC) IS TYPICALLY USED TO DRIVE THE PLC (SOME UNITS OPERATE ON 120 V AC).

THE POWER SUPPLY CONVERTS THE 240V AC INTO DIRECT CURRENT (DC) VOLTAGES OF ±5V.

THESE LOW VOLTAGES ARE USED TO OPERATE EQUIPMENT THAT MANY HAVE MUCH HIGHER VOLTAGE AND POWER RATINGS THAN THE PLC ITSELF.

THE POWER SUPPLY OFTEN INCLUDES A BATTERY BACKUP THAT SWITCHES IN AUTOMATICALLY IN THE EVENT OF AN EXTERNAL POWER SOURCE FAILURE.

I/O MODULUS:

THE INPUT/OUTPUT MODULE PROVIDES THE CONNECTIONS TO THE INDUSTRIAL EQUIPMENT OR PROCESS THAT IS NOT TO BE CONTROLLED.

INPUTS TO THE CONTROLLER ARE SIGNALS FROM LIMIT-SWITCHES , PUSH-BUTTONS, SENSORS , AND OTHER ON/OFF DEVICES.

OUTPUTS FROM THE CONTROLLER ARE ON/OFF SIGNALS TO OPERATE MOTORS, VALVES, AND OTHER DEVICES REQUIRED TO ACTUATE THE PROCESS.

MANY PLCS ARE CAPABLE OF ACCEPTING CONTINUOUS SIGNALS FROM ANALOG SENSORS AD GENERATING SIGNALS SUITABLE FOR ANALOG ACTUATORS.

INPUT ADJUSTMENT INTERFACE

LANGUAGE USED

THE LANGUAGE USED FOR PLC PROGRAMMING IS LADDER LOGIC.

LADDER LOGIC IS A PROGRAMMING LANGUAGE THAT REPRESENTS A PROGRAM BY A GRAPHICAL DIAGRAM BASED ON THE CIRCUIT DIAGRAMS OF RELAY LOGIC HARDWARE.

LADDER LANGUAGE

TIMER

• TIMERS ARE USED TO PERFORM THE TIMING OPERATIONS.

• TIME BASE IS THE MINIMUM VALUE OF TIME IN SECOND THAT CAN BE TAKEN BY THE TIMER.

• PRESET VALUE IS THE TOTAL NUMBER OF THE SECONDS FOR WHICH THE TIMING OPERATION HAS TO BE DONE

• ACCUMULATOR STARTS INCREASING THE TIME IN SECONDS UP TO THE PRESET VALUE.

• UP TO THE PRESET VALUE OF THE ACCUMULATOR THE ENABLE BIT OF TIMER IS HIGH & THE TIMER RUNS.

• WHEN ACCUMULATOR REACHES THE PRESET VALUE THEN THE TIMER STOPS AND THE DONE BIT OF THE TIMER BECOMES HIGH.

COUNTER

•COUNTERS ARE USED TO COUNT THE NUMBER OF OPERATIONS.

•ITS FUNCTION IS SAME AS THE TIMER EXCEPTS THAT THE TIMER COUNTS THE NUMBER OF SECONDS AND THE COUNTER COUNTS THE NUMBER OF OPERATIONS OR PULSES.

•AT EACH OPERATION THE VALUE OF THE ACCUMULATOR INCREASES AND WHEN THE VALUE OF THE ACCUMULATOR COMES TO THE PRESET VALUE OF THE COUNTER THEN THE COUNTER STOPS

COMPARE FUNCTION

COMPARE FUNCTIONS ARE INPUT INSTRUCTIONS. PREVIOUS FUNCTION BLOCKS WERE OUTPUTS, THESE REPLACE INPUT CONTACTS.

List of compare function: EQU NEQ LES LEQ GRT GEQ LIM

Thank you