- •1.1 TODO LIST
- •2. PROGRAMMABLE LOGIC CONTROLLERS
- •2.1 INTRODUCTION
- •2.1.1 Ladder Logic
- •2.1.2 Programming
- •2.1.3 PLC Connections
- •2.1.4 Ladder Logic Inputs
- •2.1.5 Ladder Logic Outputs
- •2.2 A CASE STUDY
- •2.3 SUMMARY
- •2.4 PRACTICE PROBLEMS
- •2.5 PRACTICE PROBLEM SOLUTIONS
- •2.6 ASSIGNMENT PROBLEMS
- •3. PLC HARDWARE
- •3.1 INTRODUCTION
- •3.2 INPUTS AND OUTPUTS
- •3.2.1 Inputs
- •3.2.2 Output Modules
- •3.3 RELAYS
- •3.4 A CASE STUDY
- •3.5 ELECTRICAL WIRING DIAGRAMS
- •3.5.1 JIC Wiring Symbols
- •3.6 SUMMARY
- •3.7 PRACTICE PROBLEMS
- •3.8 PRACTICE PROBLEM SOLUTIONS
- •3.9 ASSIGNMENT PROBLEMS
- •4. LOGICAL SENSORS
- •4.1 INTRODUCTION
- •4.2 SENSOR WIRING
- •4.2.1 Switches
- •4.2.2 Transistor Transistor Logic (TTL)
- •4.2.3 Sinking/Sourcing
- •4.2.4 Solid State Relays
- •4.3 PRESENCE DETECTION
- •4.3.1 Contact Switches
- •4.3.2 Reed Switches
- •4.3.3 Optical (Photoelectric) Sensors
- •4.3.4 Capacitive Sensors
- •4.3.5 Inductive Sensors
- •4.3.6 Ultrasonic
- •4.3.7 Hall Effect
- •4.3.8 Fluid Flow
- •4.4 SUMMARY
- •4.5 PRACTICE PROBLEMS
- •4.6 PRACTICE PROBLEM SOLUTIONS
- •4.7 ASSIGNMENT PROBLEMS
- •5. LOGICAL ACTUATORS
- •5.1 INTRODUCTION
- •5.2 SOLENOIDS
- •5.3 VALVES
- •5.4 CYLINDERS
- •5.5 HYDRAULICS
- •5.6 PNEUMATICS
- •5.7 MOTORS
- •5.8 COMPUTERS
- •5.9 OTHERS
- •5.10 SUMMARY
- •5.11 PRACTICE PROBLEMS
- •5.12 PRACTICE PROBLEM SOLUTIONS
- •5.13 ASSIGNMENT PROBLEMS
- •6. BOOLEAN LOGIC DESIGN
- •6.1 INTRODUCTION
- •6.2 BOOLEAN ALGEBRA
- •6.3 LOGIC DESIGN
- •6.3.1 Boolean Algebra Techniques
- •6.4 COMMON LOGIC FORMS
- •6.4.1 Complex Gate Forms
- •6.4.2 Multiplexers
- •6.5 SIMPLE DESIGN CASES
- •6.5.1 Basic Logic Functions
- •6.5.2 Car Safety System
- •6.5.3 Motor Forward/Reverse
- •6.5.4 A Burglar Alarm
- •6.6 SUMMARY
- •6.7 PRACTICE PROBLEMS
- •6.8 PRACTICE PROBLEM SOLUTIONS
- •6.9 ASSIGNMENT PROBLEMS
- •7. KARNAUGH MAPS
- •7.1 INTRODUCTION
- •7.2 SUMMARY
- •7.3 PRACTICE PROBLEMS
- •7.4 PRACTICE PROBLEM SOLUTIONS
- •7.5 ASSIGNMENT PROBLEMS
- •8. PLC OPERATION
- •8.1 INTRODUCTION
- •8.2 OPERATION SEQUENCE
- •8.2.1 The Input and Output Scans
- •8.2.2 The Logic Scan
- •8.3 PLC STATUS
- •8.4 MEMORY TYPES
- •8.5 SOFTWARE BASED PLCS
- •8.6 SUMMARY
- •8.7 PRACTICE PROBLEMS
- •8.8 PRACTICE PROBLEM SOLUTIONS
- •8.9 ASSIGNMENT PROBLEMS
- •9. LATCHES, TIMERS, COUNTERS AND MORE
- •9.1 INTRODUCTION
- •9.2 LATCHES
- •9.3 TIMERS
- •9.4 COUNTERS
- •9.5 MASTER CONTROL RELAYS (MCRs)
- •9.6 INTERNAL RELAYS
- •9.7 DESIGN CASES
- •9.7.1 Basic Counters And Timers
plc wiring - 3.15
requires more current than any PLC can handle, but a relay would be relatively easy to purchase and install for that load. All of the input switches are connected to the same supply and to the inputs.
3.5 ELECTRICAL WIRING DIAGRAMS
When a controls cabinet is designed and constructed ladder diagrams are used to document the wiring. A basic wiring diagram is shown in Figure 3.9. In this example the system would be supplied with AC power (120Vac or 220Vac) on the left and right rails.
The lines of these diagrams are numbered, and these numbers are typically used to number wires when building the electrical system. The switch before line 010 is a master disconnect for the power to the entire system. A fuse is used after the disconnect to limit the maximum current drawn by the system. Line 020 of the diagram is used to control power to the outputs of the system. The stop button is normally closed, while the start button is normally open. The branch, and output of the rung are CR1, which is a master control relay. The PLC receives power on line 30 of the diagram.
The inputs to the PLC are all AC, and are shown on lines 040 to 070. Notice that Input I:0/0 is a set of contacts on the MCR CR1. The three other inputs are a normally open push button (line 050), a limit switch (060) and a normally closed push button (070). After line 080 the MCR CR1 can apply power to the outputs. These power the relay outputs of the PLC to control a red indicator light (040), a green indicator light (050), a solenoid (060), and another relay (080). The relay on line 080 switches a relay that turn on another device drill station.
plc wiring - 3.16
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L1 |
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N |
010 |
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stop |
start |
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CR1 |
020 |
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MCR |
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CR1 |
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030 |
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L1 |
PLC |
N |
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CR1 |
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90-1 |
090 |
040 |
I:0/0 |
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O:0/0 |
L1 |
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050 |
PB1 |
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100-1 |
100 |
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G |
060 |
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S1 |
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070 |
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ac com |
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CR1 |
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090 |
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035 |
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100 |
100-1 |
050 |
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110 |
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060 |
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120 |
120-1 |
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CR2 |
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Drill Station |
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130 |
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L1 |
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Figure 3.9 A Ladder Wiring Diagram
plc wiring - 3.17
In the wiring diagram the choice of a normally close stop button and a normally open start button are intentional. Consider line 020 in the wiring diagram. If the stop button is pushed it will open the switch, and power will not be able to flow to the control relay and output power will shut off. If the stop button is damaged, say by a wire falling off, the power will also be lost and the system will shut down - safely. If the stop button used was normally open and this happened the system would continue to operate while the stop button was unable to shut down the power. Now consider the start button. If the button was damaged, say a wire was disconnected, it would be unable to start the system, thus leaving the system unstarted and safe. In summary, all buttons that stop a system should be normally closed, while all buttons that start a system should be normally open.
3.5.1 JIC Wiring Symbols
To standardize electrical schematics, the Joint International Committee (JIC) symbols were developed, these are shown in Figure 3.10, Figure 3.11 and Figure 3.12.
plc wiring - 3.18
disconnect |
circuit interrupter |
(3 phase AC) |
(3 phase AC) |
normally open |
normally closed |
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limit switch |
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limit switch |
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breaker (3 phase AC) |
normally open |
normally closed |
double pole |
mushroom head |
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push-button |
push-button |
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push-button |
push-button |
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vacuum pressure |
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thermal |
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normally closed |
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overload relay |
fuse |
motor (3 phase AC) |
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liquid level |
liquid level |
vacuum pressure |
normally open |
normally closed |
normally open |
Figure 3.10 JIC Schematic Symbols
plc wiring - 3.19
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temperature |
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flow |
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temperature |
flow |
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normally open |
normally closed |
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normally closed |
normally open |
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indicator lamp |
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relay |
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relay coil |
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contact |
relay contact |
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normally open |
normally closed |
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relay time delay on |
relay time delay on |
relay time delay off |
relay time delay off |
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normally closed |
normally closed |
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normally open |
normally open |
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H1 H3 H2 H4
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X1 |
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X2 |
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horn |
buzzer |
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bell |
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2-H |
control transformer |
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solenoid |
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2-position |
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hydraulic solenoid |
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Male connector |
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normally open |
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normally closed |
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Female connector |
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proximity switch |
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proximity switch |
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Figure 3.11 JIC Schematic Symbols
plc wiring - 3.20
Resistor
Rheostat (potentiometer)
Variable Capacitor
Crystal
Shielded Conductor
Common
Tapped Coil
Tapped Resistor |
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Variable Resistor |
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+ |
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Capacitor |
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Polarized Capacitor |
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Capacitor |
Battery |
Thermocouple |
Antenna |
Shielded |
Grounded |
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Coil or Inductor
Coil with magnetic core
Transformer
Transformer magnetic core
Figure 3.12 JIC Schematic Symbols