Programmable Logic Controllers

1
Chapter 17

• Programmable Logic Controllers

2
Objectives

• Read and analyze electrical controls ladder
  diagrams.
• Identify various electrical controls and
  schematic symbols.
• State and describe various parts of a PLC.
• Describe how a PLC operates when it executes a
  program.
• Write simple ladder logic programs for a PLC.
• Design and draw simple PLC-to-machine wiring
  diagrams.

3
17-1 Introduction
4
17-2 Introduction to Machine Controls
5
17-3 Machine Control Components

• Reference Designators
• Wire Numbering
• Control Transformer
• Fuses
• Switches
• Lamps
• Relays
• Time-Delay Relays
• Delay-On
• Delay-Off

6
Wire number marker.
7
Control transformer symbol.
8
Fuse symbol.
9
Control transformer with fuse blocks.
10
Pushbutton switch symbols, (a) normally open, (b)
normally closed, (c) both.
11
Selector switch symbols.
12
Limit switch.
13
Limit switch symbols, (a) normally open, (b)
normally closed.
14
Lamp.
15
Relay cross section, (a) de-energized and (b)
energized.
16
Relay symbols, (a) normally open contact, (b)
normally closed contact, (c) coil.
17
Delay-on time-delay relay, (a) timing diagram,
(b) schematic symbols.
18
Delay-off time-delay relay, (a) timing diagram,
(b) schematic symbols.
19
17-4 Ladder Diagrams
20
Top of an electrical controls diagram.
21
Control circuit with one rung.
22
Control circuit with two rungs.
23
Control circuit with three rungs.
24
17-5 Latch Circuit
25
Latch circuit.
26
17-6 PLC Types

• Open Frame
• Shoe Box
• Modular

27
17-7 PLC Configuration

• CPU
• Power Supply
• Input
• Output
• Programming Unit

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17-8 PLC Operation

• Perform I/O Update
• Solve the Program

29
17-9 Fundamental PLC Programming
30
Simple PLC program.
31
Series contact arrangement.
32
Parallel contact arrangement.
33
Series contact arrangement with one normally
closed contact.
34
Latch program.
35
Example 17-1 solution.
36
Example 17-2 solution.
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Example 17-3 solution.
38
Program with three inputs and three outputs.
39
Simpler program with three inputs and three
outputs.
40
17-10 PLC Programs with Timers
41
Timer symbols.
42
Solution for example 17-4.
43
Solution for example 17-5.
44
17-11 Advanced PLC Features

• Counters
• Sequencers
• Mathematics

45
17-12 PLC Wiring

• Power Connections
• Discrete Inputs
• Discrete Outputs

46
PLC dc input circuit.
47
PLC ac input circuit.
48
Connection of input devices to a four-point PLC
input.
49
Various PLC relay output configurations.
50
Four-point form A relay output.
51
Four-point NPN solid-state output with various
loads.
52
Four-point PNP solid-state output with various
loads.
53
Triac output connected to a lamp load.