Hi
In this we going to see detail about the basic things of PLC Ladder logic Program. After reading this you can understand about what is ladder logic and how it is working.
ELEMENTS OF LADDER LOGIC
INPUTS
1. OPEN CONTACT
2. CLOSE CONTACT
3. OPEN BRANCH
4. CLOSE BRANCH
The inputs in above can be used as inputs from Push Button,Emergency Button,Limit Switch..etc
OUTPUTS
1. COIL
2. APPLICATION INSTRUCTION
3. SET ELEMENT
4. RESET ELEMENT
The Output in above can be used as outputs to Lamp,Motor,Hooter..etc
What is PLC Ladder Programming ?
The electrical wiring diagram show the circuit wiring and the associated devices ( push buttons,Relay,Counters etc.)with their relative physical location.To simplify understanding of how the circuit work,a ladder diagram is used.
A simplified ladder diagram of the wiring diagram is shown below. It does not contain the
power portion of the circuit and shows only the control circuit.
The ladder diagram is to be read left to right, then top to bottom.
The two vertical lines L1 and N represent the potential of the circuit.
The stop button is shown as ‘closed’ because it is its normal condition.
All the contacts shown above change position when the devices associated with them change position.
The PLC ladder diagram is same as that of the one shown above, with similar vertical lines. Also, the
devices having N/O contacts are represented by the symbol –| |– and N/C contacts by –|/|– .
The contactor or relays coils are represented by the symbol –( )–.These symbols are associated with
predetermined OP (operation) codes which instruct the CPU to take specific action while executing
the ladder.
The ladder is a combination of the above symbols interconnected with each other in a sequence
with a predetermined syntax. One branch of such a ladder is known as a ‘rung’. The above symbols
are called as the relay type of instructions and are discussed below
Relay type instructions
1. –| |– This is a single Normally Open (NO) contact in series with the previous instruction.
2. –| /|– This is a single Normally Closed (NC) contact in series with the previous instruction.
3. –( )– This represents the coil of output, flag etc. It becomes ON if the result of ladder programmed
prior to it is 1 (true).Relay type instructions
A simple example -
The above circuit is represented by a PLC ladder as
In this we going to see detail about the basic things of PLC Ladder logic Program. After reading this you can understand about what is ladder logic and how it is working.
ELEMENTS OF LADDER LOGIC
INPUTS
1. OPEN CONTACT
2. CLOSE CONTACT
3. OPEN BRANCH
4. CLOSE BRANCH
The inputs in above can be used as inputs from Push Button,Emergency Button,Limit Switch..etc
OUTPUTS
1. COIL
2. APPLICATION INSTRUCTION
3. SET ELEMENT
4. RESET ELEMENT
The Output in above can be used as outputs to Lamp,Motor,Hooter..etc
What is PLC Ladder Programming ?
The electrical wiring diagram show the circuit wiring and the associated devices ( push buttons,Relay,Counters etc.)with their relative physical location.To simplify understanding of how the circuit work,a ladder diagram is used.
A simplified ladder diagram of the wiring diagram is shown below. It does not contain the
power portion of the circuit and shows only the control circuit.
The ladder diagram is to be read left to right, then top to bottom.
The two vertical lines L1 and N represent the potential of the circuit.
The stop button is shown as ‘closed’ because it is its normal condition.
All the contacts shown above change position when the devices associated with them change position.
The PLC ladder diagram is same as that of the one shown above, with similar vertical lines. Also, the
devices having N/O contacts are represented by the symbol –| |– and N/C contacts by –|/|– .
The contactor or relays coils are represented by the symbol –( )–.These symbols are associated with
predetermined OP (operation) codes which instruct the CPU to take specific action while executing
the ladder.
The ladder is a combination of the above symbols interconnected with each other in a sequence
with a predetermined syntax. One branch of such a ladder is known as a ‘rung’. The above symbols
are called as the relay type of instructions and are discussed below
Relay type instructions
1. –| |– This is a single Normally Open (NO) contact in series with the previous instruction.
2. –| /|– This is a single Normally Closed (NC) contact in series with the previous instruction.
3. –( )– This represents the coil of output, flag etc. It becomes ON if the result of ladder programmed
prior to it is 1 (true).Relay type instructions
A simple example -
EXAMPLE LADDER PROGRAMS :
Please feel free to ask questions if any
CONTENT EXPLAINED ABOUT PLC IS GOOD
ReplyDeletecovered Basic Details nice.. Thank you
ReplyDeletesir,please explain how to interface in scada system.
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