- •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 timers - 9.19
9.6 INTERNAL RELAYS
Inputs are used to set outputs in simple programs. More complex programs also use internal memory locations that are not inputs or outputs. These are sometimes referred to as ’internal relays’ or ’control relays’. Knowledgeable programmers will often refer to these as ’bit memory’. In the Allen Bradley PLCs these addresses begin with ’B3’ by default. The first bit in memory is ’B3:0/0’, where the first zero represents the first 16 bit word, and the second zero represents the first bit in the word. The sequence of bits is shown in Figure 9.19. The programmer is free to use these memory locations however they see fit.
|
bit |
memory |
bit |
memory |
|
|
number |
location |
number |
location |
|
|
|
|
|
|
|
0 |
B3:0/0 |
18 |
B3:1/2 |
||
1 |
B3:0/1 |
19 |
B3:1/3 |
||
2 |
B3:0/2 |
20 |
B3:1/4 |
||
3 |
B3:0/3 |
21 |
B3:1/5 |
||
4 |
B3:0/4 |
22 |
B3:1/6 |
||
5 |
B3:0/5 |
23 |
B3:1/7 |
||
6 |
B3:0/6 |
24 |
B3:1/8 |
||
7 |
B3:0/7 |
25 |
B3:1/9 |
||
8 |
B3:0/8 |
26 |
B3:1/10 |
||
9 |
B3:0/9 |
27 |
B3:1/11 |
||
10 |
B3:0/10 |
28 |
B3:1/12 |
||
11 |
B3:0/11 |
29 |
B3:1/13 |
||
12 |
B3:0/12 |
30 |
B3:1/14 |
||
13 |
B3:0/13 |
31 |
B3:1/15 |
||
14 |
B3:0/14 |
32 |
B3:2/0 |
||
15 |
B3:0/15 |
33 |
B3:2/1 |
||
16 |
B3:1/0 |
34 |
B3:2/2 |
||
17 |
B3:1/1 |
etc... |
etc... |
||
Figure 9.19 |
Bit memory |
|
|
An example of bit memory usage is shown in Figure 9.20. The first ladder logic rung will turn on the internal memory bit ’B3:0/0’ when input ’hand_A’ is activated, and input ’clear’ is off. (Notice that the B3 memory is being used as both an input and output.) The second line of ladder logic similar. In this case when both inputs have been activated, the output ’press on’ is active.