Title of presentation
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PLC BASIC CONCEPTS
CPU/ RAM/ Hard disk
Key board, Mouse, Remote station (LAN) CPU/Memory Inputs Monitor, Printer, Projector Etc., Outputs Power Supply OS: Windows XP / SW: MS Office Software 220V AC, 1 Ph. PLC Computer
CPU/ RAM/ Flash Card
Push Button, Selector, Limit Switch, PxS, Bus Interface
Solenoids, Relays, Lamps, Motors, HMI
OS: Firmware / SW: Machine Logic 220V AC / 24V DC
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Inputs
Outputs Controller
Machine
Relays, Solenoids, Power contactors
Actuators: Motors, Cylinders, Heaters, Lamps etc., Push Buttons,
Selector Switches
Limit Switch, Proximity, Reed Switch etc.,
Command Signals Status Signals
HMI
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Power Contactor
Over Load Relay
Aux. Contactor
Relays
Cylinders Servo Motor
Manifold Block
9 Before the PLC, control, sequencing, and safety interlock logic for manufacturing automobiles was accomplished using hundreds or thousands of relays, cam timers, and drum sequencers and dedicated closed‐loop controllers. The process for updating such facilities for the yearly model change‐over was very time consuming and expensive, as electricians needed to individually rewire each and every relay. History of PLC
The PLC is an industrial computer.
It is capable of storing instructions to implement control functions such as sequencing, timing, counting, arithmetic, data manipulation and communication.
The I/O interfaces provide the connection between the PLC and the
information providers (inputs like pushbuttons, sensors,…) and the controllable devices (outputs like valves, relays, lamps,…).
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The PLC controls industrial machines and processes. In different areas of the industry PLC are being applied, e.g.: materials handling, packaging, palletizing,
milling, boring, grinding, filling, sorting, weighing,...etc.
In the past the movements of industrial machines were controlled by relay circuits. These relay-controlled systems were replaced by PLC.
The primary function of the PLC was to perform the sequential operations that were previously implemented with relays.
Before we can talk about the working method of an PLC, we must understand the function of relay circuits.
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A relay is an electrical switch. It contains:
a iron core
a coil a switch
and a iron bar connected to
the switch What is a Relay ?
When a current goes through the coil...
I How does a Relay work ?
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… a magnetic field is produced in the coil and the iron core in the coil becomes magnetic.
I How does a Relay work ?
The electromagnetic force pulls in the switch and...
I How does a Relay work ?
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…a current can go through the switch.
I I
The answer to this question shall be shown with the following example circuits, A, B, C, and D. L1 S1 24V K1 K1 technical symbol of a relay coil electro magn. connection internal switch
A).
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The answer of this question shall be shown with a little example circuit.
K1 L1
S1 24V
0V
Function of the electrical circuit:
When the user presses button S1, the relay K1 pulls in its internal switch and the lamp L1 turns on.
The answer of this question shall be shown with a little example circuit. S1 24V 24V S1
PLC
Input Output Power PowerC).
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The answer of this question shall be shown with a little example circuit.
K1 L1 S1 24V 0V S1 24V 0V L1 PLC logic
D).
S1 24V
SPS logic
The PLC logic is not a mechanical part of the controller. The PLC logic is a software program, which runs on the
processor in the PLC. This program has to be created with a special programming tool on a PC. After downloading the
the program into the PLC, the control automatically starts the program.
23 START PB STOP PB PC PC TMR1 TMR1 Ph. 220V AC SUPPLY N LADDER PROGRAM I1 I2 Q1 Q1 M1 TMR1 En M1 Trig Time Q T#5s Q1
Communication module
Power supply Input modules Output modules RAM E-EPROM network power cord Programming tool CPU
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Communication module
Power supply Input modules Output modules RAM E-EPROM network power cord Machine Programming tool CPU Central processing unit PLC
Communication module
Power supply Input modules Output modules RAM E-EPROM network power cord Programming tool CPU
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Communication module
Power supply Input modules Output modules RAM E-EPROM network power cord Machine Programming tool CPU Program editor and monitoring PLC
Communication module
Power supply Input modules Output modules RAM E-EPROM network power cord Programming tool CPU PLC
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Communication module
Power supply Input modules Output modules RAM E-EPROM network power cord Machine Programming tool CPU Actuator command output PLC
Communication module
Power supply Input modules Output modules RAM E-EPROM network power cord Programming tool CPU PLC
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Read input signals, store in table
Determine new output state of output module
Write output commands in table
Set output values on output module Read user program & Copy to RAM
Start PLC from E-EPROM
Schematic: Starting position: vac. off, slide right, up; swivel not used (front position) Sequence of movements: 1) slide left 5) move down 2) move down & switch on vacuum 6) switch off vacuum 3) move up 7) move up 4) slide right pick place shuttle cylinder swivel device up/down cylinder suction pad
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Sequence of movements:
slide left
move down & vacuum on move up
slide right move down vacuum off move up
