Ladder diagrams are a type of graphic language used to represent logic systems for industrial control. They resemble a ladder, with two vertical power rails and circuits connected horizontally in rungs. Standard symbols are used to represent components like switches, relays, and outputs. Logic functions like AND, OR, and NOT can be depicted using these symbols. Ladder diagrams are used to program PLCs and show control circuits for machines, depicting inputs, logic functions, and outputs.

1. Chapter 2 FUNDAMENTALS OF PLC PROGRAMMING Industrial Electronics DEK 3113

2. Ladder Diagram Ladder diagrams are specialized schematics commonly used to document industrial control logic systems. It is a language or a method to create a program. The first PLCs were programmed with a technique that was based on relay logic wiring schematics. Basic concept of this diagram is similar to the electrical wiring. However in ladder logic, the symbol has changed and been standardized.

3. Ladder Diagram cont.. Type of graphic language automatic control systems. A drawing program of a switching circuit. Called "ladder" diagrams because they resemble a ladder, with two vertical lines representing the power trails (supply power) and circuits are connected in horizontal lines called rungs. Connection between the element in the rung called link .

4. Ladder Diagram Operational Principle Referring to figure below, between these two rails, a horizontal straight line was drawn with two symbols . These two symbols refer to the input and output devices , which are used in the actual process/system. On the left , we put all kinds of input . While on the right , we place all types of the outputs . Once we complete one line of the program it seems like a ladder. This horizontal line which places the input and output make one rung. Input Interface Output +24V -0V

5. Ladder Diagram Symbols Ladder diagram uses standard symbols to represent the circuit components and functions found in a control system.

6. Example 1: Lamp circuit simple ladder diagram showing a lamp that is controlled by a hand switch

7. Normally Open Schematics (NO)-Input Schematics

8. Normally Closed Schematics (NC)-Input Schematics

9. Output Schematics

10. Logic Function There are 5 logic functions can be developed by combination of switches AND OR NOR NAND EX-OR (XOR)

11. Logic Function…cont AND logic coils is not energized unless both switch A and B closed. Fig. (b) represent for PLC input.

12. Logic Function…cont - AND

13. Logic Function…cont OR logic Coils is not energized until either A or B closed

14. Logic Function…cont - OR DeMorgan's Theorem would predict:

15. Logic Function…cont NOR logic Since there has to be an output when neither A nor B have an input, and when there is an input either A or B.

16. Logic Function…cont - NOR

17. Logic Function…cont NAND logic There is no output when both A and B have an input

18. Logic Function…cont - NAND

19. Logic Function…cont - NOT

20. Logic Function…cont XOR logic There is no output when both input 1 and 2 given.

21. Combination of AND , OR , and inverter (NOT) gates

22. Control Circuit Start stop circuit -PB is pressed, output IR is activated -IR contact will closed -When PB is depressed, the output IR is still activated since current can go through contact IR unless is disturbed by stop button.

23. Vibrating/Jog circuit -When, PB is pressed, output IR is activated. -But after several microsecond, the normally closed IR is open then will stop the output IR. -This applicable to move an object which need to locate at precise location.

24. Overload protection device There are several overload protection device: 1) TOR: Thermal Overload Relay -excess heat 2) CB: Circuit Breaker -excess current 3) Fuse -excess current

25. Control circuit has Overload Protection Device

26. Control circuit in ladder diagram. -When PB is pushed(forward/reverse),motor will move according to the command. -But, when there is an overcurrent,CB will stop the current flow by blow the fuse. -Means, NC of CB will open and stop the current flow to the circuit. -The circuit can be recovered by change the fuse. -If there is thermal overload, TOR will cut the current flow. -Lamp,L3 will turn on and TOR need to be reset.

27. Two wire control -only has one contact for switching device either ON or OFF state. -When ON state, M will energize and activate three phase motor. -Heater will heat if there is over current and open the circuit.

28. Three wire control -the connection almost the same as two wire circuit except has an extra set of contact connected in parallel as the pilot switch. -this extra contact provide extra third wire. -this auxiliary contact keep coil M energize even after start push button release.

29. Two-Wire Control Circuit Used in application of automatic system. Two wire used to provide voltage to load. Applications: pump, heater or compressor. Typically closed a disconnect switch or circuit breaker to energize the circuit. An overload coils is located to protect the circuit against over current.

30. Thank You & Have A Nice Day