1. Ladder Concept

2. LADDER DIAGRAM
A ladder diagram is a means of graphically representing the logic required in a relay logic system.
Rail
Rung

4. Coils
Coils represent relays that are energized when power flows to them. When a coil is energized it causes a corresponding output to turn on by changing the state of the status bit controlling the output to 1. That same output status bit maybe used to control normally open or normally closed contact anywhere in the program. 4

5. Boxes represent various instructions or functions that are
Executed when power flows to the box. Some of these
Functions are timers, counters and math operations. 5

7. Electrical Ladder

8. PLC Implementation

9. I/O Module Connection

11. Relay Ladder

12. PLC Implementation

16. Simple Ladder Diagram

17. Symbols

18. Symbols

20. Multiple Contacts

21. Multiple Contacts

22. Output Used as Internal coil

23. Is this legitimate?

24. No. Do not repeat output coil

25. Reverse Power Flow is not allowed

26. Corrected version

28. Solution

29. Question

30. Solution

31. PLC Ladder Diagram INSTRUCTIONS
1) Relay,
2) Timer and counter,
3) Program control,
4) Arithmetic,
5) Data manipulation,
6) Data transfer, and
7) Others, such as sequencers.

32. Each rung or network on a ladder program represents
AND OPERATION B C A
Rung
Each rung or network on a ladder program represents
a logic operation. In the rung above, both inputs A and B
must be true (1) in order for the output C to be true (1). 32

33. In the rung above, it can be seen that either input A or B
OR OPERATION C A
Rung B
In the rung above, it can be seen that either input A or B
is be true (1), or both are true, then the output C is true (1). 33

34. NOT OPERATION C A
Rung
In the rung above, it can be seen that if input A is be true (1),
then the output C is false (0) or when A is (0), output C is 1.

35. AND and OR LOGIC AND OR PB1 PB2 R1 R1 = PB1.AND.PB2 PB3 PB4 R2
R1 = PB1 .OR. PB2 OR
PB2

36. COMBINED AND & OR
R1 = PB1 .OR. (PB2 .AND. PB3)
PB1 R1
PB3
PB2

37. PROGRAMMING EXAMPLE 1

38. Operation id description state explanation
MSI microswitch 1 part arrive
R1 output to bar code reader 1 scan the part
C1 input from bar code reader 1 right part
R2 output robot 1 loading cycle
R3 output robot 1 unloading cycle
C2 input from robot 1 robot busy
R4 output to stopper 1 stopper up
C3 input from machine 1 machine busy
C4 input from machine 1 task complete

39. PLC WIRING DIAGRAM

40. Operation
Rung 1. If part arrives and no part is stopped, trigger the bar code reader.
Rung 2. If it is a right part, activate the stopper.
Rung 3. If the stopper is up, the machine is not busy and the robot is not busy, load the part onto the machine.
Rung 4. If the task is completed and the robot is not busy, unload the part from the machine.

41. PLC Ladder

42. A Detailed Design Process
1. Understand the process
2. Hardware/software selection
3. Develop ladder logic
4. Determine scan times and memory requirements

43. PLC Status Indicators
Power On
Run Mode
Programming Mode
Fault

44. Troubleshooting
1. Look at the process 2. PLC status lights HALT - something has stopped the CPU RUN - the PLC thinks it is OK (and probably is) ERROR - a physical problem has occurred with the PLC 3. Indicator lights on I/O cards and sensors 4. Consult the manuals, or use software if available. 5. Use programming terminal / laptop.

45. List of items required when working with PLCs:
1. Programming Terminal - laptop or desktop PC.
2. PLC Software. PLC manufacturers have
their own specific software and license key.
3. Communication cable for connection from Laptop
to PLC.
4. Backup copy of the ladder program (on diskette, CDROM, hard disk, flash memory). If none, upload it from the PLC.
5. Documentation- (PLC manual, Software manual, drawings, ladder program printout, and Seq. of Operations manual.)

46. SWITCHES DPST SPDT N o n - l o c k i n g L o c k i n g N o r m a l l y1 P 2 M u l t i p l e T h r o w M u l t i p l e P o l e B r e a k - b e f o r e - m a k e M a k e - b e f o r e - b r e a k

47. TERMS Throw - number of states
Pole - number of connecting moving parts (number of individual circuits).
SPDT
A serial switch box (A-B box) has
two 25 pin serial ports to switch from. A B
Output
Input
DPST
Knob
How is this switch classified?

48. TYPES OF SWITCHES Selector switches Pushbutton switches
Photoelectric switches
Limit Switches
Proximity switches
Level switches
Thumbwheel switches
Slide switches
RATING:
24 Volts AC/DC
48 Volts AC/DC
120 Volts AC/DC
230 Volts AC/DC
TTL level
(Transistor-to-transistor
±5V)
Isolated Input

49. Switches

50. What is this?

51. Cylinder Pneumatic
Also called Actuator

52. ElectroPneumatic Valve
Directional Control Valve which acts as a ‘switch’ to direct compressed air to each side of pneumatic actuator.

53. 5-Port 2 Way Valve
Also called Double Acting Pneumatic Actuator and 5/2 way solenoid operated directional control valve.
Two ports to allow air in, one for outstroke (extend) and one for in-stroke (retract). 

54. Cylinder & Valve Assembly

55. TIMER

56. TIMER
A timer consists of an internal clock, a count value register, and an accumulator. It is used for or some timing purpose.
Time 5 seconds.

57. ON-DELAY TIMER (TON)
For this example the timer has been set for 5 seconds. When S1 is closed, TR1 begins timing. When 5 seconds have elapsed, TR1 will close its associated normally open TR1 contacts, illuminating pilot light PL1. When S1 is open, de-energizing TR1,
the TR1 contacts open, immediately extinguishing PL1. This type of timer is referred to as ON delay..

58. TON Example
When the switch is closed input 4 becomes a logic 1, which is loaded into timer T37. T37 has a time base of 100 ms (.100 seconds). The preset time (PT) value has been set to 150. This is equivalent to 15 seconds (.100 x 150 ). The light will turn on 15 seconds after the input switch is closed.

59. Retentive On-Delay (TONR)
The Retentive On-Delay timer (TONR) functions in a similar manner to the On-Delay timer (TON). There is one difference. The Retentive On-Delay timer times as long as the enabling
input is on, but does not reset when the input goes off. The timer must be reset with a RESET (R) instruction.

60. TONR Example

61. TONR Example Cont.
The same example used with the On-Delay timer will be used with the Retentive On-Delay timer. When the switch is closed at input I0.3, timer T5 (Retentive timer) begins timing. If, for example, after 10 seconds input I0.3 is opened the timer
stops. When input I0.3 is closed the timer will begin timing at 10 seconds. A RESET (R) instruction can be added. Here a pushbutton is connected to input I0.2. If after 10 seconds input I0.3 were opened, T5 can be reset by momentarily closing input I0.2. T5 will be reset to 0 and begin timing from 0 when input I0.3 is closed again.

62. OFF-DELAY (TOFF)
The Off-Delay timer is used to delay an output off for a fixed period of time after the input turns off. When the enabling bit turns on the timer bit turns on immediately and the value is set to 0. When the input turns off, the timer counts until the preset time has elapsed before the timer bit turns off.

63. TIMER MAX VALUES

64. TIMER EXAMPLE
Start PB Pressed >> Pump1 ON (5 sec) >> Pump2 ON (3 sec) >> Mixer ON (60 sec) >> Drain Valve ON >> Pump 3 (8 sec)

65. Counter

66. COUNTER
Digital counters output in the form of a relay contact when a pre-assigned count value is reached. 5

67. CTU, CTD, and CTUD

68. UP COUNTER (CTU)

69. Down Counter (CTD)

70. UP/DOWN COUNTER (CTUD)

71. COUNTER EXAMPLE

72. Example

73. Example (cont.)