the importance of electrical ladder diagram...
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THE IMPORTANCE OF ELECTRICAL LADDER
DIAGRAM in PLC PROGRAMMING AND
APPLICATIONS Gamaliel F. Itao, PEE
Programmable Logic Controller
• Defined as the first digital computer used for automation of industrial processes, such as control of machines in factory assembly lines.
• It is the basic building block of Industrial Automation and is the heart of the control system.
PLC Composition
• Progmmable Logic Controller is like typical PCs, it has two components, namely hardware and software.
• The hardware consists of the CPU, memory, input and output communication modules.
PLC SOFTWARE
• The software is composed of the languages or programs that run the hardware and perform certain functions.
• To name some languages , they are the ff: 1. Basic statement list
2. Mnemonic
3. Function block
4. Structured text
5. Ladder Diagram
Ladder Diagram
• Is the most common language and popular and which is even considered as the standard language of the PLC.
• It is similar to the hardwired Electrical Relay Ladder Diagram. The Control Logic is portrayed in the simple logic circuits of series, parallel and its combination series –parallel and the parallel –series connection.
Relay Ladder Diagram
• Is the foundation of the Programmable Ladder diagramming which can easily be traced by plant electricians and maintenance personnel.
PLC Ladder
• For this reason, PLCs are still dominant in the automated manufacturing control systems because of the existence of PLC software Ladder Diagram.
• Plant electricians are used to electrical relay ladder as it can easily be learned compared to the scripted languages of non PLCs.
Control Engineering Magazine
• Published in the USA reported that PLCs now control 95% of plant manufacturing and equipment as well as process operation control systems in the US.
• Only 5 % goes to non PLC and dedicated control operations such as Robotics and Process automation controllers(PACs).
PLC APPLICATIONS
Conventional Control Panel (Waste Water Pumping Station)
Old Panel Indicators
Conventional Control System
Industrial Controls Corporation Phone: (632) 687-4814 Fax: (632) 687-2443
www.IndustrialControlsCorp.com
Industrial Controls Corporation Phone: (632) 687-4814 Fax: (632) 687-2443
www.IndustrialControlsCorp.com
Equipment
Equipment
PLC – Scada Based System
SCADA BASED PC MONITOR/CONTROL
Panel Wirings for a
5MW Generator (Rehab)
PLC Based Purifier System
PLC / HMI
PLC – HMI Based Process Monitoring System
SUB CONTROL SYSTEM PRIMARY CRUSHER
INSTRUMENTATION AND CONTOL SYSTEMS ARCHITECTURE
PRIMARY CRUSHER AND AUXILLARIES
HMI-OPERATORS WORK STATIONS
DISTRIBUTED I/O GYRATORY CRUSHER & AUXILLARIES
DISTRIBUTED I/O PAN FEEDER & WEARING CONVEYOR
DISTRIBUTED I/O CONVEYOR NO. 1
LINK TO STC CONTROL SYSTEM
SUB CONTROL SYSTEM SEC & TER CRUSHERS
INSTRUMENTATION AND CONTOL SYSTEMS ARCHITECTURE
STC-SCREENING-COS-CONVEYING-FOB
HMI-OPERATORS WORK STATIONS
HMI-OPERATORS WORK STATIONS
HMI-ENGINEERING WORK STATIONS
SUB CONTROL SYSTEM PRIMARY SCREEN
SUB CONTROL SYSTEM SCREENING PLANT
SUB CONTROL SYSTEM CONVEYING
SUB CONTROL SYSTEM FOB
DISTRIBUTED I/O PRIMARY SCREEN
DISTRIBUTED I/O SCREENING PLANT
DISTRIBUTED I/O CONVEYING
DISTRIBUTED I/O FOB
DISTRIBUTED I/O SEC & TEC CRUSHER
CONTROL SYSTEM
Control System
I. Open Loop System
INPUT LOGIC OUTPUT
-Pushbuttons
-Limit Switches
-Level Switches
-Flow Switches
-Relays
-Timers
-Counters
-Motors
-Solenoid valves
-Lamps
PLC
A typical Control System (electromechanical)
CONTROLLER
CNT
ELECTRONIC CARDS
RESET
COUNTER
CLOCK
TIMER COIL
LATCHING COIL
COIL
RELAY
8 8 8
INPUT DEVICES
PUSHBUTTON
LIMIT SWITCH
THUMB
WHEEL
SWITCH
LEVEL SWITCH
FLOW SWITCH
OUTPUT DEVICES
HEATER
8 8
MOTOR
SOLENOID
LED
DISPLAY
HEATER
LAMP
II. Closed Loop (Feedback) System
Control Unit Final Control Element
Process Variable
Measuring Element
Set Point
Error
Measured Variable
Primary Element / Transducer
Pressure
Level
Temperature
Flow
Control System
_ +
1. Process Variables - a quantity that can be measured in an industrial process. This maybe regulated or simply measured. Example: Pressure, Level, Temperature, Flow 2. Measuring Element – the element which converts a measurable variable into a form or signal that the controller can understand. Example: Transmitter - A transmitter sense the actual value of a system
and transforms the value to a standardized signal - 4-20 mA is common for analog signals - as input for the control system.
Controller
3 Final Control Element – the final device which actually control the process flows in response to controller output. Example: 1. Control Valves 2. Inverter 3. I/P Converter 4. Heater
PLC Based Process Control Unit: Typical Configuration
INSTRUMENTATION LOOP
UNDERSTANDING ELECTRICAL
CONTROL CIRCUITS: (RELAY LADDER )
WHAT IS A RELAY? A relay is an
electrically operated
switch.
The Functions of a Relay
1. Conversion
2. Multiplication
3. Memory
4. Amplification
R
L
1. Conversion
3. Memory Latching Circuit
L1
R
L2
2. Multiplication
L1
R1 R1
(+) (-) 3. Amplification
M
L1 L2
OFF ON
R1
R1
R1
R1
R1
R1
PB PB
ON OFF
220 V
Types of Control Logic Circuits
I. Series
End to end connection of contacts
Used in interlocks
Processing logic action is AND (.)
L1 (+) L2 (-)
S3 S1 S2
Out 1
Logic Statement
S1 . S2. S3 = Out1
II. Parallel
Both ends of contacts are connected
Used in different location or multiple contacts provide some signal
Process action is OR (+)
S1
S2
S3
Out 1
Logic Statement
S1 + S2 + S3 = Out1
III. Series-Parallel Circuit
Contacts in series and connected parallel
S1 S2
S3 S4
Logic Statement
(S1 . S2) + (S3 . S4) = Out1
Out 1
IV. Parallel-Series Circuit
S1 S2
S4 S3
Out 1
Logic Statement
(S1 + S3) . (S2 + S4) = Out1
Exercise:
Simplify the circuit. What is the type of circuit?
S1 S2
S5 S3
S4
Out 1
Answer:
Simplifying using KISS (Keep It Simple and Safe) concept. The flow of circuit in the
1) Circuit is from left to right (Line 1 to Line 2) (Pattern 1-2)
2) Circuit is from top to bottom and bottom to top. (Pattern 3-4)
S1 S2
S5 S3
S4
Out 1
L1 L2
L1 L2
Out 1
S1 S2
S3 S4
S5 S4 S1
S3 S4 S2
What type of circuit is it now?
Input = Output
2 TYPES OF SEQUENTIAL CIRCUIT DESIGN TECHNIQUES
1. ELECTROMECHANICAL SEQUENTIAL CIRCUIT USING RELAYS
2. PLC BASED DESIGN TECHNIQUE
1. VECTOR REPRESENTATION
CYLINDER FORWARD OR
CYLINDER RETRACT OR
2. CYLINDER FORWARD (+)
CYLINDER REVERSE (-)
A+B+A-B-
REPRESENTATION OFMOTION SEQUENCE OF MECHATRONICS OUTPUT DEVICE
A
B
1 2 3 4 5
MOTION STEP DIAGRAM
Graphical Representation
EXERCISE 2 ELECTRO-PNEUMATIC
DOUBLE ACTING CYLINDER
DOUBLE ACTING CYLINDER
4/2 WAY DIRECTIONAL CONTROL VALVE.
DOUBLE SOLENOID VALVE
A+ A-
A+ A-
A a0 a1
BASIC PNEUMATIC/HYDRAULIC CYLINDER CIRCUIT
RIGHT TRAVELLING
LOWERING
(DOWN)
B
A-POINT B-POINT
A
C
LEFT TRAVELLING
(UP)
RAISING
BASIC PICK AND PLACE ROBOT EXAMPLE
WORK
UNCLAMP
CLAMP
MOVE
B
A-POINT B-POINT
A
C
BASIC PICK AND PLACE ROBOT EXAMPLE C+
BACK
A+
B
A-POINT B-POINT
A
C
BASIC PICK AND PLACE ROBOT EXAMPLE A-
BACK A+C+
B
A-POINT B-POINT
A
C
BASIC PICK AND PLACE ROBOT EXAMPLE B+
BACK A+C+A-
A
C
B
A-POINT B-POINT
BASIC PICK AND PLACE ROBOT EXAMPLE A+
BACK A+C+A-B+
A B
A-POINT
BASIC PICK AND PLACE ROBOT EXAMPLE C-
C
B-POINT
BACK
A+C+A-B+A+
28
A B
A-POINT
BASIC PICK AND PLACE ROBOT EXAMPLE A-
C
B-POINT
BACK
A+C+A-B+A+C-
A B
A-POINT
BASIC PICK AND PLACE ROBOT EXAMPLE B-
C
B-POINT
BACK
A+C+A-B+A+C-A-
B
A-POINT B-POINT
A
C
BASIC PICK AND PLACE ROBOT EXAMPLE BACK
A+C+A-B+A+C-A-B-
Design Technique 1
STEPS USING SIMPLIFIED ELECTRICAL DESIGN
TECHNIQUE
1. Analyze work process and come up with its abbreviated notation for the representation of motion sequence.
Example 1: Bending A+ A- B+ B-A- 2. Divide the sequence into minimum number of groups
according to basic rules, (like:no letter must appear more than once in any group)
Example 2: A+ / A- B+ / B-
CYL A CYL B
SOL 1 SOL 2 SOL 3 SOL 4
CYL B
CYL A
A+A-B+B- a0 a1 b0 b1
EX.2 ELECTROMECHANICAL
3. Appropriate signals involved
Appropriate Input
a1 b1
Ex.3: A+/ A- B+/ B-
start a0 b0
GRP R1 GRP R2
NO. OF RELAYS = NO. OF GROUPS+ 1 AUXILIARY RELAY
= 3 +1
= 4
NO CONTACT
OF OWN GROUP
RELAY
Rx Ry
Rx
LAST LS OF
PREVIOUS
GROUP
NC CONTACT
OF NEXT GP
RELAY
GROUP
RELAY
LATCH CIRCUIT
(GROUP RELAY CIRCUIT)
4. Appropriate a group relay for each group (a latch circuit)> (Rx=(Ls+Rx) RY) which is turned on by change over limit switch (last limit switch of previous group) and turned off by opening of the NC contact of control relay on the next group.
EX. 4
R1
R2
R3
R4
SOL 1
SOL 2
SOL 3
SOL 4
R2
R3
R1
R1
R2
R2
R4
R3
R3
R3
start stop
a1
a0
b0
b1
A+/A- B+/B- START
a1
a0
b1
B0
NO. OF RELAYS = NO. OF GROUPS+ 1 AUXILIARY RELAY
= 3 +1 = 4
A+
A-
B+
B-
8 8 8
INPUT DEVICES
PUSHBUTTON
LIMIT SWITCH
THUMB
WHEEL
SWITCH
LEVEL
SWITCH
FLOW
SWITCH
OUTPUT DEVICES
HEATER
8 8
MOTOR
SOLENOID
LED
DISPLAY
HEATER
LAMP
SOFTWARE CIRCUIT
PROGRAMMABLE CONTROLLER
DESIGN TECHNIQUE
PLC BASED:
6 DESIGN STEPS IN PLC BASED SYSTEM
STEP I. SCHEMATIC OR POWER DIAGRAM
Exercise 1 FORWARD/ REVERSE SCHEMATIC DIGRAM OF 3-PHASE MOTOR
M
STEP II.CONTROL DIAGRAM (RELAY DIAGRAM) OF EXERCISE 1
PB FORWARD
PB STOP
REV
FWD
FWD
REV
FWD
REV
100 01
100 02
STEP IV. PLC DIGRAM
1 3 10002
10001 10001
10002
3 2
STEP III. INPUT/OUTPUT ASSIGNMENT OF EXERCISE 1
PB FWD –1 FWD-10001
PB REV - 2 REV-10002
PB STOP- 3
STEP V. (BOOLEAN/MNEMONIC STATEMENTS) OF EXERCISE
(Optional : Automatic View : Lad <>Mnemonic
ADDRESS/STEP INSTRUCTION DATA 0 LD 1
1 OR 10001
2 ANDN 3
3 ANDN 10002
4 OUT 10001
5 LD 2
6 OR 10002
7 ANDN 3
8 ANDN 10001
9 OUT 10002
10 END
STEP VI. PLC LAY-OUT
CENTRAL PROCESSING UNIT
1 2 3
FWD
REV
INPUT MODULE OUTPUT MODULE
PS
+ -
Com(-)
220 Vac / 24 Vdc
OUT 1
OUT 2
Com L1 L2
FREE TRAININGS: PLCs, MECHATRONICS NC II
and INSTRUMENTATION NC II
Thru TESDA
Training for Work Scholarship Program ( TWSP)
MECHATRONICS TECHNOLOGIES CORP. ( MTC )
Tel. 9283307 and 9286297
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