I
NTRODUCTION TO
P
ROGRAMMABLE
L
OGIC
C
ONTROLLERS
S
TUDENT
G
UIDE
For Review Only,
Table of Contents
INTRODUCTION ... 1
OBJECTIVES ... 1
NUMBER THEORY ... 2
Identifying the Base of a Number ... 2
Positional Notation and the Decimal Numbering System ... 3
The Binary Number System ... 4
Binary System Positional Notation ... 5
How to Convert a Number from Binary to Decimal ... 5
How to Convert a Number from Decimal to Binary ... 6
The Octal Number System ... 7
Octal System Positional Notation ... 7
How to Convert a Number from Octal to Decimal ... 8
How to Convert a Number from Decimal to Octal ... 8
Conversions between Octal and Binary ... 9
How to Convert a Number from Octal to Binary... 9
How to Convert a Number from Binary to Octal ... 10
The Hexadecimal System ... 11
Conversions between Hexadecimal and Binary ... 12
How to Convert a Number from Hexadecimal to Binary ... 12
How to Convert a Number from Binary to Hexadecimal ... 13
INTRODUCTION TO THE PLC-5... 14
PLC-5 Hardware ... 14
Equipment Chassis ... 15
Power Supply Module ... 16
Processor Module ... 17
Key Switch ... 20
Front Panel LEDs ... 20
Battery ... 22
Processor Module DIP Switches ... 22
Memory Modules ... 24
Input Modules, Output Modules, and Field Wiring ... 24
For Review Only,
RSLOGIX 5 INTRODUCTION ... 40
Screen Layout and Organization ... 41
Ladder Window ... 42
Project Window ... 44
Controller Folder ... 45
Program Files Folder ... 46
Data Files Folder ... 47
Results Window ... 53 Windows Toolbar ... 55 Standard Toolbar ... 56 Instruction Toolbar ... 57 On-Line Toolbar ... 58 Finding Help ... 59
FILES, MEMORY AREAS, AND ADDRESSING ... 61
Memory Areas... 61
Program Memory Area ... 62
How to Create a New Program File ... 63
Data Memory Area ... 68
How to Create a New Data File ... 70
Addressing ... 75
Logical Addressing ... 75
Indexed Addressing ... 77
Indirect Addressing ... 78
Symbolic Addressing ... 81
How to Create or Edit a Symbolic Name for an Address ... 82
I/O Image Addressing ... 85
Chassis, Slots, I/O Racks, and Groups ... 86
Slot Addressing for I/O Transfer ... 88
Examples of I/O Image Addressing ... 92
USING RSLOGIX 5 ... 93
Going On-Line with a Controller ... 93
How to Go On-Line with a Controller ... 93
Uploading a Project from a PLC-5 ... 98
How to Upload a Project ... 98
Saving a Project ... 101
How to Save a Project ... 101
How to Change the Default Path where Projects are Saved ... 104
Downloading a Project to a PLC-5 ... 106
How to Download a Project ... 106
Editing Ladder Logic ... 112
Edit Zone Markers ... 112
Online Editing ... 113
Online Editing Restrictions ... 114
For Review Only,
Offline Editing ... 125
How to Verify a Single Rung ... 125
How to Verify a File or Project ... 127
UNDO and REDO ... 127
Inserting and Appending Rungs of Ladder Logic ... 128
How to Insert a Rung ... 128
How to Append a Rung ... 130
Branching ... 132
How to Insert a Branch ... 132
PROGRAMMING WITH BIT INSTRUCTIONS ... 135
Selected Bit Instructions ... 135
Examine IF CLOSED (XIC) ... 136
Examine IF OPEN (XIO) ... 139
Output Enable Instruction (OTE) ... 140
Output Latch (OTL) ... 141
Output Unlatch (OTU) ... 141
Using Bit Instructions ... 142
How to Insert Bit Instructions into a Program ... 143
How to Assign a Logical Address Directly at the Instruction ... 148
How to Drag and Drop a Logical Address from a Data File ... 153
How to Search for Unused Logical Addresses ... 156
PROGRAMMING WITH TIMERS ... 159
Timer Operation ... 159
Timer Type ... 159
Timer On-Delay (TON) ... 160
Timer Off-Delay (TOF) ... 161
Retentive Timer On-Delay (RTO) ... 161
Timer Address ... 162
Timer Preset Value ... 162
Timer Accumulator Value ... 162
Timer Status Bits ... 163
Time Base ... 163
Reset Timer/Counter Instruction (RES) ... 164
Using Timer Instructions ... 164
How to Insert a New Timer into a Program ... 164
For Review Only,
Count Up Counter (CTU) ... 185
Count Down Counter (CTD) ... 185
Counter Address ... 186
Counter Preset Value ... 186
Counter Accumulator Value ... 186
Counter Status Bits ... 186
Using Counter Instructions ... 187
How to Insert a New Counter into a Program ... 187
How to Assign or Modify a Counter Address ... 190
How to Assign or Modify a Preset Value at the Instruction ... 193
How to Assign or Modify a Preset Value using the C5 Data File ... 195
How to Create an Up/Down Counter ... 198
TROUBLESHOOTING ... 199
Systematic Troubleshooting ... 199
Clearing Processor Memory ... 200
How to Clear Processor Memory ... 201
Forcing I/O Bits ... 204
How to Determine the Status of Forces in a Project ... 206
How to Install and Remove a Force Using Popup Menus ... 208
How to Install and Remove a Force Using the Force Tables ... 214
Cross Referencing Instructions ... 221
How to Open the Cross Reference Report ... 222
From the Ladder Window ... 222
From the Project Window ... 224
Data Table Monitoring ... 227
How to Open a Data Table ... 228
From the Ladder Window ... 228
From the Project Window ... 230
How to Change Values Using a Data Table ... 232
Searching ... 234
How to Search using Popup Menus at an Instruction ... 234
How to Search using Drop Down Menus from the Windows Toolbar ... 237
Find ... 238
Replace ... 240
Go To ... 241
How to Search Using the Standard Toolbar ... 244
Histograms ... 248
How to Create a Histogram ... 249
For Review Only,
List of Figures
Figure 1: Equipment Chassis ... 15
Figure 2: Power Supply Module ... 16
Figure 3: PLC 5/15 Processor Module ... 19
Figure 4: Processor Module Switches ... 23
Figure 5: 1771-IAD AC Input Module ... 26
Figure 6: 1771-OAD AC Output Module ... 29
Figure 7: Remote I/O Adapter Module ... 31
Figure 8: Hypothetical Circuit ... 33
Figure 9: Hypothetical Circuit Controlled by PLC System ... 34
Figure 10: Vat Control System ... 36
Figure 11 Hardwired Vat Control System ... 36
Figure 12: PLC Vat Control System ... 37
Figure 13: Hardwired System Changes ... 37
Figure 14: PLC System Changes ... 38
Figure 15: RSLogix 5 Main Window ... 41
Figure 16: Ladder Window ... 42
Figure 17: Ladder Window with Multiple Open Programs ... 43
Figure 18: Renaming a Program ... 43
Figure 19: Project Window ... 44
Figure 20: Controller Properties Popup Window ... 45
Figure 21: Expanded Program Files Folder ... 46
Figure 22: Expanded Data Files Folder ... 47
Figure 23: Cross Reference Report Popup Window ... 48
Figure 24: Output Image Data File Popup Window ... 49
Figure 25: Usage Popup Window ... 50
Figure 26: Input Image Data File Popup Window ... 51
Figure 27: Timer Data File Popup Window ... 52
Figure 28: Search Results Window ... 53
Figure 29: Results Window Moved in Display ... 54
Figure 30: Windows Toolbar ... 55
Figure 31: Standard Toolbar ... 56
Figure 32: Tool Tip ... 56
Figure 33: Instruction Toolbar ... 57
For Review Only,
Figure 43: New File in Program Files Folder ... 66
Figure 44: LAD 50 – SUBR-1 File Open for Editing in Ladder Window ... 67
Figure 45: Data Area File Assignments ... 68
Figure 46: Popup Window for New Data File ... 70
Figure 47: Create Data File Popup Window ... 71
Figure 48: Data File Type Selection ... 72
Figure 49: Completed Create Data File Popup Window ... 73
Figure 50: New Integer Data File Created ... 74
Figure 51: File N100 – TEST Popup Window ... 75
Figure 52: Status Register S:24 ... 77
Figure 53: Integer Register N7 ... 78
Figure 54: Integer Data Register N7 and Indirect Addressing ... 79
Figure 55: User-Defined N100 Data File ... 80
Figure 56: N100 Data File ... 81
Figure 57: Popup Window for Symbolic Name Entry... 82
Figure 58: Symbolic Name Entry ... 83
Figure 59: Symbolic Name Entry Completed ... 83
Figure 60: Symbolic Name and Description in Ladder Logic ... 84
Figure 61: I/O Address in Ladder Logic ... 85
Figure 62: Data Files Folder ... 87
Figure 63: 1-Slot Addressing ... 89
Figure 64: 2-Slot Addressing ... 90
Figure 65: 1/2-Slot Addressing ... 91
Figure 66: Sixteen Point I/O Modules ... 92
Figure 67: Starting RSLogix 5 ... 94
Figure 68: Comms Drop Down Menu/WHO ACTIVE GO ONLINE Selection ... 95
Figure 69: Communications Popup Window ... 96
Figure 70: RSLogix On-Line with a Controller ... 97
Figure 71: Starting RSLogix 5 ... 98
Figure 72: Comms Drop Down Menu/UPLOAD Selection ... 99
Figure 73: Going to Online Programming State Popup Window ... 100
Figure 74: Floppy Disk Icon from Standard Toolbar ... 101
Figure 75: File Drop Down Menu/SAVE Selection ... 102
Figure 76: Revision Note Popup Window ... 103
Figure 77: Tools Drop Down Menu... 104
Figure 78: System Options Popup Window ... 105
Figure 79: Set Directory Popup Window ... 106
Figure 80: Starting RSLogix 5 ... 107
Figure 81: Open Folder Icon ... 107
Figure 82: Open/Import PLC5 Program Popup Window ... 108
Figure 83: Open Project in RSLogix Display ... 109
Figure 84: Comms Drop Down Menu ... 110
Figure 85: RSLogix 5 Popup Window ... 111
Figure 86: Original Ladder Logic for Online Editing Example ... 114
For Review Only,
Figure 88: New Rung for Editing (Offline) ... 116
Figure 89: OTE Logical Address Changed ... 117
Figure 90: Popup Menu for Verifying Rung Edits ... 118
Figure 91: Rung Verified ... 119
Figure 92: Popup Menu for Accepting Rung Edits ... 120
Figure 93: Rung Edits Accepted ... 121
Figure 94: TEST EDITS Button from Online Editing Toolbar ... 122
Figure 95: Test Edits Confirmation Popup Window ... 122
Figure 96: Test Edits Online Indication ... 123
Figure 97: Edits Assembled ... 124
Figure 98: Popup Window to Verify a Single Rung of Ladder Logic ... 125
Figure 99: Results Window ... 126
Figure 100: Verify File and Verify Project Icons ... 127
Figure 101: UNDO Button (Left Arrow) and REDO Button (Right Arrow) ... 127
Figure 102: Popup Menu with Mouse Pointer over Rung Number ... 128
Figure 103: New Rung Inserted ... 129
Figure 104: Popup Window with Mouse Pointer Over Rung Number ... 130
Figure 105: New Rung Appended ... 131
Figure 106: Location for New Branch ... 132
Figure 107: Rung Icon Under USER Tab of Instruction Toolbar ... 132
Figure 108: Insertion Points for the New Branch ... 133
Figure 109: New Branch Inserted ... 133
Figure 110: Dragging the Branch to the Termination Point ... 134
Figure 111: New Branch Terminated ... 134
Figure 112: XIC Instructions ... 136
Figure 113: XIC Instruction and the Input Image Data Table ... 137
Figure 114: XIC Instruction and the Bit Data Table ... 138
Figure 115: XIO Instructions ... 139
Figure 116: Comparison of XIC and XIO ... 140
Figure 117: OTE Instruction ... 140
Figure 118: OTL Instruction ... 141
Figure 119: OTU Instruction ... 141
Figure 120: Arrangement of Latch And Unlatch Instructions ... 142
Figure 121: Bit Instruction Icons under BIT Tab of Instruction Toolbar ... 143
Figure 122: Insertion Points for XIC Instruction ... 144
Figure 123: XIC Instruction Inserted into Ladder Logic ... 145
For Review Only,
Figure 133: Logical Address Targets... 154
Figure 134: Logical Address Assigned to OTE Instruction ... 155
Figure 135: I1 Input Image Data Table File ... 156
Figure 136: Logical Address Usage ... 157
Figure 137: XIC Logical Address Changed from B3:0/0 to I:010/0 ... 158
Figure 138: Timer On-Delay (TON) Instruction ... 160
Figure 139: Timer Off-Delay (TOF) Instruction ... 161
Figure 140: Retentive Timer On-Delay (RTO) Instruction ... 161
Figure 141: Reset Timer/Counter (RES) Instruction ... 164
Figure 142: Timer Instruction Icons under TIMER/COUNTER Tab of Instruction Toolbar ... 164
Figure 143: Insertion Point for RTO Instruction ... 165
Figure 144: RTO Instruction Inserted into Ladder Logic ... 166
Figure 145: T4 Data File Popup Window ... 167
Figure 146: Timer Usage ... 168
Figure 147: Unused Timer T4:61 ... 169
Figure 148: “Timer” Field in RTO Instruction as the Logical Address Target ... 170
Figure 149: Completed Logical Address Assignment ... 171
Figure 150: Time Base Drop Down Menu ... 172
Figure 151: New Time Base Selected ... 173
Figure 152: New Time Base Entered ... 173
Figure 153: New Value Typed into “Preset” Field ... 174
Figure 154: New Preset Entered ... 174
Figure 155: XIC Instruction Inserted into Ladder Logic ... 175
Figure 156: T4 Data File Popup Window ... 176
Figure 157: Timer Address Located in Data File Popup Window ... 177
Figure 158: XIC Instruction as the Logical Address Target ... 178
Figure 159: Logical Address Assignment Complete ... 179
Figure 160: Timer Instruction Icons under TIMER/COUNTER Tab of Instruction Toolbar ... 179
Figure 161: Insertion Point for RES Instruction ... 180
Figure 162: RES Instruction Inserted into Ladder Logic ... 181
Figure 163: Dialog Box for Logical Address Entry ... 181
Figure 164: Logical Address for the RES Instruction ... 182
Figure 165: Symbolic Name/Comment Popup Window ... 182
Figure 166: Comment and Symbolic Name Information ... 183
Figure 167: Logical Address, Symbolic Address, and Comment ... 183
Figure 168: CTU Instruction ... 185
Figure 169: CTD Instruction ... 185
Figure 170: Counter Instruction Icons under TIMER/COUNTER Tab of Instruction Toolbar ... 187
Figure 171: Insertion Point for CTU Instruction ... 188
Figure 172: CTU Instruction Inserted into Ladder Logic ... 189
Figure 173: C5 Data File Popup Window ... 190
For Review Only,
Figure 175: Dialog Box for Logical Address Entry ... 191
Figure 176: Instruction Type Popup Menu ... 192
Figure 177: Logical Address Popup Menu ... 192
Figure 178: Completed Logical Address Assignment ... 193
Figure 179: “Preset” Field Open for Editing ... 193
Figure 180: New Value Typed into “Preset” Field ... 194
Figure 181: New Preset Entered ... 194
Figure 182: C5 Data File Popup Window ... 195
Figure 183: Preset Field Open for Editing ... 196
Figure 184: New Preset Value Entered ... 197
Figure 185: Count Up/Count Down Ladder Logic ... 198
Figure 186: On-Line Drop Down Menu ... 201
Figure 187: Change Mode Confirmation Popup Window ... 201
Figure 188: Processor in Program Mode ... 202
Figure 189: Comms Drop Down Menu ... 202
Figure 190: Clear Memory Confirmation Popup Window ... 203
Figure 191: Force Table Positioning Diagram ... 205
Figure 192: Force Status Indications ... 206
Figure 193: Forces Installed but Not Enabled ... 207
Figure 194: Forces Installed and Enabled ... 207
Figure 195: Popup Menu with Install Force Selections... 208
Figure 196: Inputs Forced ON ... 209
Figure 197: Drop Down Menu with Enable Force Selection ... 209
Figure 198: Enable Forces Confirmation Popup Window ... 210
Figure 199: Forces Enabled ... 210
Figure 200: Multiple Forces in Project ... 211
Figure 201: Popup Menu with Remove Force Selections ... 212
Figure 202: Selected Force Removed ... 213
Figure 203: Force Files in Project Window ... 214
Figure 204: O0 (Output Force File) Popup Window ... 215
Figure 205: Output Address to Force ... 216
Figure 206: Force Installed ... 217
Figure 207: Enable Forces Confirmation Popup Window ... 217
Figure 208: Force Enabled ... 218
Figure 209: Popup Menu with Remove Force Selections ... 219
Figure 210: Force Removed ... 220
For Review Only,
Figure 220: Data Files Folder Open in Project Window ... 230
Figure 221: Data Table Open ... 231
Figure 222: N10 Data Table for Address N10:22 ... 232
Figure 223: New Value in Data Table ... 233
Figure 224: Value Changed through Data Table ... 233
Figure 225: Find All Popup Menu ... 234
Figure 226: Search Results Window for O:011/16 ... 235
Figure 227: Going to an Instruction in the Ladder Logic from a Search Result ... 236
Figure 228: Search Drop Down Menu ... 237
Figure 229: Find Popup Window ... 238
Figure 230: FIND ALL Search Results ... 239
Figure 231: Replace Popup Window ... 240
Figure 232: Go To Popup Window ... 241
Figure 233: Go To Example ... 241
Figure 234: Address/Symbol Editor Popup Window ... 242
Figure 235: Additional Options Available through Popup Menu ... 242
Figure 236: Search Results from Address/Symbol Editor ... 243
Figure 237: Search Entry Box and FIND Buttons ... 244
Figure 238: Searching for TON Instruction ... 245
Figure 239: Result of FIND NEXT for TON Instruction ... 246
Figure 240: Result of FIND ALL for TON Instruction ... 247
Figure 241: Histogram ... 248
Figure 242: Comms Drop Down Menu ... 249
Figure 243: Histogram Popup Window ... 250
Figure 244: Entering Target Address ... 251
Figure 245: Histogram Popup Menu ... 252
Figure 246: Histogram Properties Popup Window ... 253
Figure 247: Creating Histogram Trends ... 254
For Review Only,
List of Tables
Table 1: Number System Bases ... 2
Table 2: Decimal and Binary Equivalents ... 4
Table 3: Decimal to Binary Conversion ... 6
Table 4: Decimal, Binary, and Octal Equivalents ... 7
Table 5: Decimal to Binary Conversion ... 8
Table 6: Binary and Octal Equivalents ... 9
Table 7: Octal to Binary Example ... 9
Table 8: Binary to Octal Example ... 10
Table 9: Decimal, Binary, and Octal Equivalents ... 11
Table 10: Hexadecimal to Binary Example ... 12
Table 11: Binary to Hexadecimal Example ... 13
Table 12: Power Supply Ratings ... 17
Table 13: PLC-5 Processors ... 18
Table 14: AC and DC Input Modules ... 25
Table 15: AC and DC Output Modules ... 28
Table 16: Data Files ... 47
Table 17: PLC-5 Default Data Files ... 69
Table 18: PLC-5 User Defined Data File Types ... 69
Table 19: Logical Address Format ... 76
Table 20: I/O Image Address Format ... 85
Table 21: Data File Type Abbreviations ... 231
For Review Only,
PLC Basics
INTRODUCTION
This course provides information on PLC concepts, hardware, software, ladder logic functions (relay contacts, timers, counters). There are hands-on exercises for configuration and programming.
OBJECTIVES
Upon completion of this course, you will be able to perform the following: 1. Convert a number from one base to another.
2. Describe the major components of the PLC-5. 3. Explain the basic operation of a PLC-5 system.
4. Identify the major components of the RSLogix 5 main window. 5. Access the RSLogix 5 on-line help files.
6. Describe the organization of processor memory. 7. Describe hardware and software addressing. 8. Establish a communication link to the PLC. 9. Save, restore, and create program files. 10. Edit existing rungs of ladder logic. 11. Explain the operation of bit instructions 12. Use bit instructions in a program.
13. Explain the operation of timer instructions. 14. Use timer instructions in a program.
15. Explain the operation of counter instructions. 16. Use counter instructions in a program.
17. Clear processor memory. 18. Monitor the data tables.
19. Force bit instructions on and off. 20. Describe the operation of histograms.
21. Describe a basic systematic troubleshooting process.
For Review Only,
NUMBER THEORY
The section introduces four commonly used systems for numbering: decimal, binary, octal, and hexadecimal. You are probably most familiar with the decimal system, as this the system of numbers we use every day. Programmable logic controllers (PLCs), however, do not understand the decimal system. PLCs, along with every other computer in the world, are based on two stable states. These two states are represented most effectively using the binary number system. The octal and hexadecimal systems, which are easily derived from the binary system, are convenient for representing strings of binary numbers. Octal numbering is especially important with Allen-Bradley products as much of the technical PLC documentation is based on this system.
I
DENTIFYING THEB
ASE OF AN
UMBERA number is a symbol that represents a quantity. The base, or radix, of a number system identifies the number of unique symbols in that particular system. The base of the decimal system is ten because we use ten unique symbols (0, 1, 2, 3, 4, 5, 6, 7, 8, 9) to represent all of the numbers. A number system using three symbols (0, 1, and 2) would be base three. Remember to count zero as a symbol when determining the base of a number system.
The base of a number system is indicated by a subscript at the end of the number. Table 1 illustrates some examples of different number system bases.
Table 1: Number System Bases
Number Base
125710 Ten (decimal)
100100012 Two (binary)
23458 Eight (octal)
12FA416 Sixteen (hexadecimal)
For Review Only,
You should also note that the highest value symbol used in a number system is always one less than the base of the system. In base ten, the symbol with the largest value is 9; in base 5, it is 4; and in base 2, it is 1. Base 16 (hexadecimal) is a little different. Base 16 uses 16 unique symbols to represent all of the numbers. Since we run out of unique number symbols after 9, the letters A through F are used to make up the rest of the symbols.
P
OSITIONALN
OTATION AND THED
ECIMALN
UMBERINGS
YSTEMPositional notation is a system that describes the value of a number by the position of the symbol within the number. Each position is assigned a weight. The number in the right-most position has the lowest weighted value. Weighted values increase as you move from right to left. In the decimal system, the weighted values are 1, 10, 100, 1000, and so on. Numerical quantities are determined by multiplying the digit in a particular position by the weighted value of the position, then summing the results. Positional notation is best described through an example.
The number 687 (in base 10) is made up of three digits - 6, 8, and 7. The least significant digit (LSD) is 7, and its value is 7. The next significant digit is 8 and has a value of 80 (8 x 10). The 6 is the most significant digit (MSD) and has a value of 600 (6 x 100). The 7 occupies the ones position; the 8 occupies the 10’s position; and the 6 is in the 100’s position. Using scientific notation, the number 687 is written:
(6 x 102) + (8 x 101) + (7 x 100) Which is equivalent to:
(6 x 100) + (8 x 10) + (7 x 1) = 600 + 80 + 7
= 687
What about a number like 67.832? We interpret this as: (6 x 101)+(7 x 100)+(8 x 10-1)+(3 x 10-2)+(2 x 10-3) Which is equivalent to:
(6 x 10)+(7 x 1)+(8 x 1/10)+(3 x 1/100)+(2 x 1/1000) = 60 + 7 + 0.8 + 0.03 + 0.002
= 67.832
For Review Only,
T
HEB
INARYN
UMBERS
YSTEMThe binary system of numbering is based on two digits, 0 and 1. Therefore, the binary number system has a base of 2. The binary numbering system is ideal for use with all digital devices, which includes PLCs and computers. All digital devices operate using two different states: off and on. The binary numbers 0 and 1 correspond nicely to these states. Normally, 0 represents the “off” state of the digital device, and 1 represents the “on” state.
Counting in binary is performed the same way as counting in decimal. Binary numbers, however, can be quite lengthy because there are so few symbols available to represent all of the numbers. Table 2 compares the first 16 decimal numbers to their binary equivalents.
Table 2: Decimal and Binary Equivalents
Decimal Binary 0 0000 1 0001 2 0010 3 0011 4 0100 5 0101 6 0110 7 0111 8 1000 9 1001 10 1010 11 1011
For Review Only,
Binary System Positional Notation
The decimal system uses powers of 10 as weighted values of particular positions within a number. The binary system, however, uses powers of 2. The following illustrates binary system positional notation:
24 23 22 20 2-1 2-2 2-3 2-4 Where: 24 = 2 x 2 x 2 x 2 = 1610 23 = 2 x 2 x 2 = 810 22 = 2 x 2 = 410 21 = 2 = 210 20 = 110 2-1 = 1/2 = 0.510 2-2 = 1/(2 x 2)= 0.2510 2-3 = 1/(2 x 2 x 2)= 0.12510 2-4 = 1/(2 x 2 x 2 x 2)= 0.062510
How to Convert a Number from Binary to Decimal
Converting from base 2 (binary) to base 10 (decimal) is relatively easy. Just sum the weighted values of all positions where a 1 is present in the binary number.
Example: Convert the binary number 1100112 to its decimal equivalent.
1100112
= (1 x 25) + (1 x 24) + (0 x 23) + (0 x 22) + (1 x 21) + (1 x 20) = (1 x 32) + (1 x 16) + 0 + 0 + (1 x 2) + (1 x 1)
= 5110
Example: Convert the binary number 0.01012 to its decimal equivalent.
0.01012
= (0 x 20) + (0 x 2-1) + (1 x 2-2) + (0 x 2-3) + (1 x 2-4) = 0 + 1/4 + 0 + 1/16
= 0.312510
For Review Only,
How to Convert a Number from Decimal to Binary
Decimals are converted to another base by successively dividing the decimal by the desired base. You begin by dividing the decimal number by the base. The remainder of this step becomes the least significant (right-most) digit in the converted number. All of the remainders from the successive divisions, when placed together, become the converted number.
Example: Convert 15110 to its binary equivalent.
Begin by dividing 151 by 2, and then successively divide the result of each step by 2. The remainders, when taken together, are the converted number. The steps of each successive division are shown in Table 3.
Table 3: Decimal to Binary Conversion
Division Result Remainder
151 / 2 75 1 75 / 2 37 1 37 / 2 18 1 18 / 2 9 0 9 / 2 4 1 4 / 2 2 0 2 / 2 1 0 1 / 2 0 1
We are finished with the successive divisions when we get 0 as the result. The remainders now become the converted decimal. The remainder from the first division is the least significant digit of the base 2 conversion. So:
15110 = 100101112
You can check your result by converting the binary number back to its decimal equivalent.
For Review Only,
T
HEO
CTALN
UMBERS
YSTEMThe octal, or base 8 system of numbering is based on eight digits: 0, 1, 2, 3, 4, 5, 6, and 7. Allen-Bradley uses the octal number system extensively with all models of PLC. Table 4 compares a decimal number to its binary and octal equivalents.
Table 4: Decimal, Binary, and Octal Equivalents
Decimal Binary Octal
0 0000 0 1 0001 1 2 0010 2 3 0011 3 4 0100 4 5 0101 5 6 0110 6 7 0111 7 8 1000 10 9 1001 11 10 1010 12 11 1011 13 12 1100 14 13 1101 15 14 1110 16 15 1111 17
Octal System Positional Notation
The octal system uses powers of 8 as the positional notation weighted values. The following illustrates the octal system positional notation:
84 83 82 80 8-1 8-2 8-3 8-4 Where: 84 = 8 x 8 x 8 x 8 = 409610 83 = 8 x 8 x 8 = 51210 82 = 8 x 8 = 6410 81 = 8 = 810 80 = 110 8-1 = 1/8 = 0.12510 8-2 = 1/(8 x 8)= 0.01562510 8-3 = 1/(8 x 8 x 8)= 0.00195310 8-4 = 1/(8 x 8 x 8 x 8)= 0.00024410
For Review Only,
How to Convert a Number from Octal to Decimal
The same principles are used to convert octal to decimal as were used to convert binary to decimal. The only difference is that octal uses 8 for the base instead of the 2 used in binary. You must also multiply the weighted value of the position by the number occupying the position.
Example: Convert the binary number 1428 to its decimal equivalent.
1428
=(1 x 82) + (4 x 81) + (2 x 80) = (1 x 64) + (4 x 8) + (2 x 1) = 9810
How to Convert a Number from Decimal to Octal
Decimals are converted to octal by successively dividing a decimal number by eight. The method is the same as was used to convert decimal to binary.
Example: Convert 14910 to its octal equivalent.
Table 5: Decimal to Binary Conversion
Division Result Remainder
149 / 8 18 5
18 / 8 2 2
2 / 8 0 2
We are finished with the successive divisions when get 0 as the result. The remainders now become the converted decimal. The remainder from the first division is the least significant digit of the base 8 conversion. So:
14910 = 2258
For Review Only,
Conversions between Octal and Binary
Octal numbers can be represented using three binary digits. Table 6 illustrates octal numbers and their binary equivalents.
Table 6: Binary and Octal Equivalents
Octal Binary 0 000 1 001 2 010 3 011 4 100 5 101 6 110 7 111
How to Convert a Number from Octal to Binary
Using the information in Table 6, locate the octal number in the table then read across to the binary equivalent. Write down the binary equivalent below the octal digit being converted. Convert each octal digit using the table. The binary equivalent then becomes the string of ones and zeros that were written down for each octal digit.
Example: Convert 236538 to binary.
Use Table 6 and write the binary equivalent below each octal digit. This is illustrated in Table 7.
Table 7: Octal to Binary Example
Octal 2 3 6 5 3
Binary 0 1 0 0 1 1 1 1 0 1 0 1 0 1 1
The binary equivalent of 236528 is 0101001101010112.
For Review Only,
How to Convert a Number from Binary to Octal
You can use Table 6 to convert from binary to octal, but you have to separate the binary number into groups of three digits starting on the right side of the number. You then read the octal equivalent from the table for each group of three binary digits.
Example: Convert 111001002 to octal.
Separate the binary number into groups of three digits beginning from the right side. Use Table 6 and write the octal equivalent below each group of three binary digits. This is illustrated in Table 8. Add leading zeros to the last group, as in this example, to complete a group having one or two digits.
Table 8: Binary to Octal Example
Binary 0 1 1 1 0 0 1 0 0
Octal 3 4 4
The octal equivalent of 111001002 is 3448.
For Review Only,
T
HEH
EXADECIMALS
YSTEMThe hexadecimal, or base 16 system of numbering is based on sixteen digits. Since we run out of unique numbers after 9, the letters A through F are used to represent the remaining numbers in the base. Table 9 compares a decimal number to its binary, octal, and hexadecimal equivalents.
Table 9: Decimal, Binary, and Octal Equivalents
Decimal Binary Octal Hex
0 0000 0 0 1 0001 1 1 2 0010 2 2 3 0011 3 3 4 0100 4 4 5 0101 5 5 6 0110 6 6 7 0111 7 7 8 1000 10 8 9 1001 11 9 10 1010 12 A 11 1011 13 B 12 1100 14 C 13 1101 15 D 14 1110 16 E 15 1111 17 F
For Review Only,
Conversions between Hexadecimal and Binary
Conversions between hexadecimal and binary are similar to octal/binary conversions in that you can use a table of equivalent values to perform the conversion. The only difference is that you need four binary digits to represent a hexadecimal digit instead of the three used with octal. The most difficult part of hexadecimal conversions is remembering that a letter represents a number.
How to Convert a Number from Hexadecimal to Binary
Using the information in Table 9, locate the hexadecimal number in the table then read across to the binary equivalent. Write down the binary equivalent below the hexadecimal digit being converted. Convert each hexadecimal digit using the table. The binary equivalent then becomes the string of ones and zeros that were written down for each hexadecimal digit.
Example: Convert A5F16 to binary.
Use Table 9 and write the binary equivalent below each hexadecimal digit. This is illustrated in Table 10.
Table 10: Hexadecimal to Binary Example
Hexadecimal A 5 F
Binary 1 0 1 0 0 1 0 1 1 1 1 1
The binary equivalent of A5F16 is 1010010111112.
For Review Only,
How to Convert a Number from Binary to Hexadecimal
You can use Table 9 to convert from binary to hexadecimal, but you have to separate the binary number into groups of four digits starting on the right side of the number. You then read the hexadecimal equivalent from the table for each group of four binary digits.
Example: Convert 111001002 to hexadecimal.
Separate the binary number into groups of four digits beginning from the right side. Use Table 9 and write the hexadecimal equivalent below each group of four binary digits. This is illustrated in Table 11. Add leading zeros to the last group, if necessary, to complete a group of four digits.
Table 11: Binary to Hexadecimal Example
Binary 1 1 1 0 0 1 0 0
Hexadecimal E 4
The hexadecimal equivalent of 111001002 is E416
.
For Review Only,
INTRODUCTION TO THE PLC-5
This section introduces the basic operation and organization of the PLC-5 programmable logic controller. Although this training specifically discusses the PLC-5, the concepts introduced in this text are applicable to most programmable logic controllers.
PLC-5
H
ARDWAREA programmable logic controller (PLC) is a specialized type of computer designed for industrial automation and process control. The complexity of the operating environment defines the number of PLCs in the system. Simple applications may use only one PLC. However, multiple PLCs may be connected together via a common communication network in order to provide sophisticated control over complex operating environments. The PLC-5 is a family of PLCs manufactured by Allen-Bradley. The PLC-5 is a modular system, which provides flexibility in order to meet a wide range of possible applications. A basic PLC system consists of the following components:
• Equipment chassis • Power supply • Processor module
• I/O modules with field wiring • Remote I/O adapter module
For Review Only,
Equipment Chassis
The equipment chassis is a single, compact enclosure that holds the programmable controller module, power supply, and I/O or specialty modules that make up the system. Modules are inserted into the chassis on plastic slots and plug into the back plane connections. Four different size chassis are available: 4-slot, 8-slot, 12-slot, and 16-slot. This design provides for easy system expansion and module replacement. The left-most slot of the chassis accepts the controller module (or the remote I/O adapter if the chassis is being used as a remote I/O rack). An example of an equipment chassis is shown in Figure 1.
Figure 1: Equipment Chassis
The power supply jumper is used to set up the system for either an internal (in the same rack) power supply, or an external power supply. The configuration plug is moved to the left side when an internal power supply is used, and to the right side for an external power supply.
For Review Only,
The back plane switch assembly consists of eight rocker switches that determine the chassis output operation in the event of a fault, the addressing mode of the chassis, and the operation of memory modules.
Power Supply Module
The purpose of the power supply is to supply and regulate the power to the modules in the PLC-5 equipment chassis. The power supply module can be installed in any slot in the chassis (except the processor slot on the left side of the chassis). A variety of power supply modules are available, each with different ratings for input and output voltages. An example of a power supply module is shown in Figure 2.
For Review Only,
The 1771-P4 power supply is a two slot module. It accepts 120 VAC, 60 Hz input and delivers 8A, 5VDC output to the chassis back plane. This power supply contains output over-voltage, under-voltage, and over-current protection to the I/O chassis and its modules. If one of these faults occur, the power supply will shutdown. You must turn the power supply off for 15 seconds to reset it. The power supply will also shutdown if the processor line voltage drops below 92 VAC and will restart the processor when line voltage increases to 97 VAC. This prevents the processor from operating when voltage is too low, and any resulting errors.
The operation, protection features, and external wiring connectors of the power supplies are essentially the same. Table 12 lists the ratings of the various slot power supplies commonly used with the PLC-5.
Table 12: Power Supply Ratings
Power Supply Model Input Power Output Power
1771-P3S 120VAC/60Hz 3A/5VDC/38W 1771-P4 120VAC/60Hz 8A/5VDC/79W 1771 -P4S 120VAC/60Hz 8A/5VDC/60W 1771-P4S1 100VAC/60Hz 8A/5VDC/60W 1771-P5 24VDC 8A/5VDC/72W 1771-P6S 220VAC/60HZ 8A/5VDC/60W 1771-P6S1 200VAC/60Hz 8A/5VDC/60W Processor Module
The processor module is a small, rack-mounted computer. The processor module does not have a keyboard, so you must connect some type of programming interface in order to monitor or direct the operation of the device. The programming interface is usually a laptop computer, although it can be a desktop computer connected over some distance to the controller through a communication network. In either case, the programming interface runs the RSLogix 5 software. The RSLogix 5 software allows you to create the programs (application software) that tell the controller module what to do.
The application software resides in the processor’s memory. Although there are different types of application software that you can write for the PLC-5, the most common type is known as ladder logic. The ladder logic ultimately controls the machines and processes associated with the PLC. If the ladder logic does not operate correctly, then the machine or process being controlled by the PLC will not operate properly.
For Review Only,
There are many types of processor modules in the Allen-Bradley PLC-5 family of controllers. Differences between the types of processors generally relate to I/O capacity, remote rack capability, memory, and scan time. Table 13 summarizes the capabilities of the several models of processors.
Table 13: PLC-5 Processors Processor Model Memory (Words) I/O Points I/O Racks (Maximum) Rack Configuration Communication Mode 5/10 6,000 256 4 4 local None 5/12 6,000 256 4 4 local Adapter 5/15 6,000 512 4 4 local/3 remote Scanner/Adapter 5/25 13,000 1024 8 4 local/7 remote Scanner/Adapter 5/40 48,000 2048 16 4 local/15 remote Scanner/Adapter 5/60 64,000 3072 24 4 local/23 remote Scanner/Adapter
For Review Only,
The processor module always occupies the left-most slot in the chassis. The processor requires 2.5 Amperes of current for operation and draws this power from the chassis back plane. All processor modules have essentially the same physical appearance and operate the same internally. Figure 3 illustrates the PLC 5/15 processor module as an example.
Figure 3: PLC 5/15 Processor Module
For Review Only,
A 9-pin, D-shell connector labeled PEER COMM INTFC is the communication port between the processor and the programming device. This connection lets the programming device communicate with any device on the link. Once you connect the programming device to one processor, the device can communicate with each processor on the network.
There are two communication ports on the processor module located directly below the D-shell connection. The upper connector, labeled PEER COMM INTFC, is for the peer communications link (Data Highway Plus). The lower terminal labeled REM I/O is the remote I/O connector.
Key Switch
The front-panel key switch has three positions for controlling the mode of processor operation. They are RUN, PROGRAM, and REMOTE. In the RUN mode, you can run the loaded program, force I/O, and save programs to a disk drive. In this mode you cannot:
• Create or delete ladder or data files. • Program on-line.
• Modify the size of a data file.
• Change mode of operation through the programming device.
In the PROGRAM mode, you can enter a program, modify ladder files, down load to an EEPROM module, and save or restore programs. In this mode, outputs are disabled, inputs are not updated, and the processor does not scan the program.
In the REMOTE mode, you can change between remote program, remote test, and remote run modes through the programming device. Be aware that the outputs are disabled in Remote Test mode, even though the ladder logic executes. Note that you cannot create or delete ladder logic or data files while in the Remote Test mode.
Front Panel LEDs
The processor module has six LED status indicators. These are:
For Review Only,
COM (Communication Active) LED
The COM LED indicates the operation of the PLC-5 processor within the Peer Communication Link, and provides indication of communication faults. The Peer Communication Link allows the PLC-5 processor to communicate with other PLC-5 processors and with the industrial terminal. The maximum number of stations you can connect to the Peer Communications Link is 64. The status indications of the COM LED are as follows:
• Blinking Green: Processor transmitting/receiving on the communication link • Steady Bright Red: Watchdog timer time out
• Steady Dull Red: Duplicate station address selected • Off: No communication
REM I/O (Remote I/O Active) LED
The REM I/O LED light indicates the operation of the remote I/O rack and provides indication of a remote I/O fault. The status indications of the REM I/O LED are as follows:
• Steady Green: Active remote I/O link • Steady Red: Remote I/O link fault
• Blinking Green/Red: Partial remote I/O link fault • Off: No remote I/O selected
ADPT (Adapter) LED
The ADPT (adapter) LED indicates the mode of operation of the PLC-5 processor. The processor may operate in Adapter Mode or Scanner Mode.
When in the Adapter Mode, the PLC-5 processor communicates with a supervisory processor capable of remote I/O and it controls the I/O in its local chassis. In the Scanner Mode, the processor communicates with I/O in up to three remote I/O chassis and with its local I/O. The ADPT LED will be on when in adapter mode and off in scanner mode. The ADPT LED status indications are as follows:
• Steady Green: Active remote I/O link
• Steady Red: Duplicate station address selected
• Blinking Green: No communication with host processor • Sporadic Green: Bad communication with host processor • Off: Not in Adapter mode.
For Review Only,
BATT (Battery) LED
The BATT LED indicates the status of the battery. The LED is off if the battery is good and on if the battery is low.
PROC (Processor) LED
The PROC LED indicates the condition and program mode of operation within the processor. The PROC LED status indications are as follows:
• Steady Green: Run Mode. The program is running. • Steady Red: Major Fault
• Off: Program Mode, Test Mode, or the processor is not receiving power. The program is not running.
FORCE LED
The FORCE LED is amber. It indicates that a force exists within the processor. The FORCE LED is on steady when forces are installed and enabled, blinks when forces are installed but not enabled, and off when no forces are installed.
Battery
The processor houses one AA lithium battery. If power is not applied to the processor module, the battery retains the processor memory for up to one year. The battery is held beneath a cover on the front of the processor module. The date the battery was installed should be written on the front of the module.
Processor Module DIP Switches
The processor module is configured for operation through three groups of DIP switches. These switches, labeled SW1, SW2, and SW3, are located inside the processor module as illustrated in Figure 4.
For Review Only,
Figure 4: Processor Module Switches
Switch assembly SW1 is an eight-switch assembly. It is used to determine the station number of the processor module when it is configured in a peer communications link (data highway plus). This switch assembly also configures the processor for scanner or adapter operation.
Switch assembly SW2 is also an eight-switch assembly. It sets the number of words exchanged between the host processor and the PLC-5 processor when the PLC-5 processor is in adapter mode. The PLC 5/15 can transfer eight words between the host PLC-5 and the adapter module per scan. This switch assembly also establishes the beginning I/O group number assigned to the PLC-5 processor, and the I/O rack number of the processor module when it is in adapter mode.
Switch assembly SW3 is a four-switch assembly that connects a terminator across the line when the processor module is the last device in a peer communications link remote I/O link. The specific switch settings for this module are found in the processor technical bulletin.
For Review Only,
Memory Modules
Each processor module contains a base memory. This is usually an adequate level for most applications. However, due to system expansion and increased needs, additional memory may be required. These memory modules are installed into the memory-module slot on the bottom of the processor memory-module. There are three memory memory-modules that may be added to the processor:
• EEPROM Module (1785-MJ) - Provides up to 6K words of nonvolatile memory backup.
• CMOS RAM Module (1785-MR) - Provides 4K words of RAM memory in addition to the processor’s base memory.
• CMOS RAM Module (1785-MS) - Provides 8K words of RAM memory in addition to the processor’s base memory.
The EEPROM module may be used in any processor. The two CMOS RAMs are only available for use with the PLC 5/15 and 5/25 processors.
Input Modules, Output Modules, and Field Wiring
Input modules accept input signals from field devices and condition them to meet the power requirements of the processor. Output modules accept the control signals from the processor and energize the designated output module point. Field wiring connects the modules to signaling or control devices in the facility.
Input Modules
An input is any signal that supplies information to the programmable controller. The interface between all physical inputs and the controller is the input module. The input module receives the signal from the input device, transforms the signal to a format that is recognizable by the ladder logic, and then passes the information on to the controller through common connection in the equipment rack. Common types of input devices are push buttons, limit and proximity switches, control relays, sensors, and operator controls.
For Review Only,
There are several types of input modules. Input modules are available in 8-point (8 input signal terminals), 16-point, and 32-point designs and accept AC or DC input signals. The type of input module selected for a particular application depends on the type of input signal. This includes analog inputs, digital inputs, and specialty modules for inputs from thermocouples, resistance-temperature devices, and encoders. Table 14 summarizes the rating characteristics of the various AC and DC input modules commonly used with the PLC-5.
Table 14: AC and DC Input Modules
Model Number Input Voltage Rating Number of Input Points 1771-IA 92-138 VAC/VDC 8 1771-IAD 77-138 VAC 16 1771-IA2 92-138 VAC 8 1771-IB 10-27 VDC 8 1771-IBD 10-30 VDC 16 1771-IBN 10-30 VDC 32 1771-IC 42-56 VDC 8 1771-ICD 20-60 VDC 16 1771-IH 24-50 VDC 8 1771-IM 184-276 VAC/VDC 8 1771-IMD 184-250 VAC 16 1771-IN 12-28 VAC 8 1771-IND 10-30 VAC 16 1771-IQ 5-30 VDC 8 1771-IT 10-27 VDC 8 1771-IVN 10-30 VDC 32
A typical input module is the 1771-IAD. This number provides descriptive information about the module. The “1771” identifies the PLC-5 family and indicates that the module fits into a 1771-series universal chassis. The “I” indicates an input module, the “A” indicates an AC module, and the “D” indicates high density. A high-density module is a module with 16 or more points.
This module converts sixteen individual 120VAC inputs to a logic level compatible with the processor. Typical field device inputs to this module are proximity switches, limit switches, and push buttons. The input signals are filtered within the module to limit the effects of voltage transients caused by contact bounce and electrical noise. This prevents false data input to the processor. The input circuits within the input module are optically isolated from the back plane of the chassis.
For Review Only,
The power used to operate the logic circuitry within the input module is drawn from the chassis back plane. Each input module requires approximately 0.25 Amperes of current. Figure 5 illustrates the 1771-IAD module.
Figure 5: 1771-IAD AC Input Module
For Review Only,
The 1771-IAD module occupies one slot in the universal chassis and can be placed in any location within the universal chassis except for the very first slot to the left, which is reserved for the processor. To install the module, slide it into the slotted track located within the chassis. To remove the module, pull outward on the tab located on the top of the module.
The field devices are wired to the terminal block on the front of the module. This terminal block is hinged on the bottom and connected to the universal chassis. This eases the removal and replacement of a module. Note that the first four terminals (A, B, C, D) are not used on input modules. The next sixteen terminals are numbered 00 through 17 (octal). The last terminal (E) is for the common ground connection. A hinged plastic cover protects the terminals.
The input status indicators are located on the front of the module above the terminal strip. The status indicators show the condition of the module and its inputs. The green ACTIVE LED when the module is powered and the opto-isolator data paths are functioning properly. The remaining sixteen LEDs (00 to 17) illuminate red when the associated input has power present on the terminal.
The input module fault mode selection configuration plug is located on the top of the module. The purpose of this plug is to determine the status of the inputs to the processor during a module failure. The plug has two positions: “state” and “reset.” In the last-state position, the inputs to the processor from the module remain in the last known valid state when a failure is detected. In the reset position, the inputs are reset to the off position when a module failure occurs.
For Review Only,
Output Modules
An output from the programmable controller causes an external event to occur. The interface between the controller and a physical output is the output module. The output interface module interprets the control signals controller from the controller then outputs the signals that actually change the position of equipment or modify processes. Typical output devices include relays, solenoids, lamps, and system displays or monitors. There are several types of output modules. As with the input module, the type of output module depends on the application. Types of output modules include those for analog and digital signals, and linear position transducers. Table 15 summarizes the rating characteristics of the various AC and DC output modules commonly used with PLC-5.
Table 15: AC and DC Output Modules
Model Number Output Voltage Rating Number of
Output Points 1771-OA 92-138 VAC 8 1771-OAD 10-138 VAC 16 1771-OB 10-27 VDC 8 1771-OBD 10-60 VDC 16 1771-OBN 10-30 VDC 32 1771-OC 42-53 VDC 8 1771-OM 184-276 VAC 8 1771-OMD 184-250 VAC 16 1771-ON 20-30 VAC 8 1771-OQ 24 VDC 8 1771-OVN 10-30 VDC 32 1771-OW 24-138 VAC 8 1771-OYL 0-24 VAC/VDC 8
A typical output module is the 1771-OAD. This number provides descriptive information about the module. The “1771” identifies the PLC-5 family and indicates that the module fits into a 1771-series universal chassis. The “O” indicates an output module, the “A” indicates AC module, and the “D” indicates high density. A high-density module is a module with 16 or more points.
For Review Only,
The power used to operate the logic circuitry within the output module is drawn from the chassis back plane. Each output module requires approximately 0.7 Ampere of current. Figure 6 illustrates the 1771-OAD module.
Figure 6: 1771-OAD AC Output Module
For Review Only,
The 1771-OAD module occupies one slot and can be placed in any location within the chassis except for the very first slot to the left, which is reserved for the processor. The module is installed and removed in the same manner as its corresponding input module. The field devices are wired to the terminal block on the front of the module. This terminal block is hinged on the bottom to allow easy module removal without removing the field device wiring. A hinged plastic cover protects the terminals. AC power is supplied to this module through the four terminals labeled L1. These four terminals should be jumpered together to prevent overstressing any single point. Power is supplied to all four points to protect from exceeding the total surge rating of the module. Field devices are connected to terminals 00 to 17 (octal). The connection paths are from the module to the field device to ground. The last terminal (L2) may or may not be used as a common ground with the field device. If it is not used, no connection to this point is necessary.
The output status indicators operate in a manner similar to the input module. The ACTIVE LED indicates power to the output module and opto-isolation data path operation. The red output LEDs (00-17) indicate that the processor has commanded an output on. They do not indicate the presence of power on a given terminal. One additional indicator is present on the status panel. It is the FUSE indicator. When illuminated, it indicates that the output fuse has blown.
The output module fault mode selection configuration plug is located on the bottom of the module. This plug determines the state of the outputs following a module failure. The possible plug positions are “last state” and “reset.” In the last-state position, the outputs will remain in the last known current state should a module failure occur. In the reset position, the outputs will reset to off following a module failure.
The module configuration plug operates independently of the last-state switch on the I/O chassis back plane. The module plug position takes precedence when a module fault occurs. The I/O chassis back plane plug takes precedent if a rack fault occurs.
Field Wiring
All inputs and outputs are connected to the programmable controller by field wiring. Field wiring is all wiring, junction boxes, and connectors used to connect the programmable controller to external devices. Field wiring completes the PLC-5
For Review Only,
Remote I/O Adapter Module
The 1771-ASB Remote I/O Adapter module is an interface between remote racks and the processor module. Essentially, the remote I/O adapter takes the place of the processor module in the remote racks. The adapter communicates with the other I/O modules in the remote rack, and the processor module communicates with the adapter. The adapter occupies one slot in the universal chassis and must be placed in the left-most slot, just as with the processor module. The power to operate the module is drawn from the chassis back plane. The module requires 1.2 Amperes of current. Figure 7 illustrates the Remote I/O Adapter module.
Figure 7: Remote I/O Adapter Module
For Review Only,
The terminal block on the front of the module is used for connection of external I/O communication cables and an optional chassis restart button. The module has built-in fault detection capabilities. If a fault should occur in a remote I/O chassis containing inputs, the inputs to the processor will remain in their last pre-fault state. As a result, when a fault occurs, the outputs in an un-faulted local or remote rack will remain in the last state ordered prior to the fault.
Two switch assemblies are located inside the 1771-ASB Remote I/O adapter module. These switches are labeled SW-1 and SW-2. They are used to set group numbers and rack numbers in both a complimentary and non-complimentary I/O configuration. The positioning procedures for these switches are contained in the equipment technical bulletin.
The module has three status indicators. The ACTIVE indicator is green. When on, it indicates: that there is active communication between the processor and the adapter module, that DC power is on and supplying the entire I/O rack, and that the I/O adapter module is actively controlling the modules. When it is OFF it indicates there is no communication between the processor and the adapter module. When flashing it indicates that a communication link is established between the processor and the remote I/O adapter module, the processor is in the program or test mode, and the remote I/O adapter module is not actively controlling the I/O modules.
The ADAPTER FAULT indicator is red. When on it indicates that the module is not operating properly, there is a fault, and that the I/O rack response is in the manner denoted by the last state switch (switch number one of the I/O chassis back plane switch assembly). When it is flashing, it shows that the processor restart lockout switch on the I/O chassis back plane switch assembly is on. Depress the I/O rack restart push button (if installed) to clear the restart lockout.
The I/O RACK FAULT indicator is red. When on, it indicates that a fault has been detected at the remote I/O adapter module on the logic side of the I/O modules.
For Review Only,
PLC-5
S
YSTEMO
PERATIONThe major components of a PLC are the equipment chassis, processor module, input module, output module, and power supply. A programming terminal is used to program the processor, but it is not considered a major component because once the processor is programmed, the terminal may be disconnected. The operation of these major components is best illustrated by developing a hypothetical hardwired circuit, then implementing the same circuit using the major PLC components.
Figure 8 illustrates the hypothetical circuit for this example. This circuit controls two different lamps. Switch 1 and Switch 2 are normally open push button switches. Lamp 1 illuminates when switch 1 is closed, and lamp 2 illuminates when switch 2 is closed.
Figure 8: Hypothetical Circuit
For Review Only,
Figure 9 shows the same switches and lamps under the control of a PLC system. The push button switches connect to an input module in the PLC system instead of directly to the lamps. The lamps are connected to the output module. Notice also that the input module is indirectly connected to the output module via the processor.
Figure 9: Hypothetical Circuit Controlled by PLC System
The processor is programmed to connect Switch 1 to Lamp 1, and Switch 2 to Lamp 2 through software. This software is also known as ladder logic since it appears similar to a standard electrical ladder diagram. The processor is programmed using a terminal (laptop) connected to a communication port on the processor. The operation of the hardwired lamp system and the PLC-controlled system appear identical. When Switch 1 is closed, Lamp 1 lights, and when Switch 2 closes, Lamp 2 lights. The major differences between the two models relate to the signal flow paths.
For Review Only,
Signal Flow Paths
When a push button is pressed in the hardwired system, power moves from the voltage source through the switch to the lamp, and then to ground. Electrical power simply follows the wire conductors to the lamp. When the switch is opened, power is interrupted and the light goes out.
In the PLC controlled system, power moves from the voltage source, through the switch, into the input module. The input module senses the presence of this voltage and in turn, sends a small signal voltage into the processor through the back plane connections to the equipment chassis. The voltage from the switch is isolated from the voltage signal that the module sends into the processor. This isolation is necessary since the fragile processor chip operates at very low voltage and current levels.
The signal received by the processor is analyzed and interpreted by the ladder logic. The ladder logic generates a low-voltage output signal from the processor to the output module. This output signal not only contains the ON signal to the lamp, but also tells the output module to which terminal the lamp is connected to on the module. This allows the output module to discriminate between Lamp 1 and Lamp 2. An observer of both hardwired and PLC controlled systems would not notice any difference in the system operation. In both systems, Switch 1 controls Lamp 1, and Switch 2 controls Lamp 2.
The greatest advantage of a programmable logic controller becomes evident when a change is needed in the circuits previously discussed. For example, if you needed to change the circuits of a hardwired system to have Switch 1 control Lamp 2, and Switch 2 control Lamp 1, it would take several minutes to rewire them, and would involve exchanging the wires at the switches or the lamps. With a PLC, a simple editing operation can make these changes internal to the program. This eliminates the need for rewiring and this process takes only a fraction of the time required to change a
hardwired system
For Review Only,
Ladder Logic and I/O Control
A practical application demonstrating the flexibility of a PLC ladder program is illustrated in the next example. Figure 10 shows a vat containing a liquid. In this system, a motor is energized to rotate the stirrer and mix the contents of the vat when certain conditions of temperature and pressure are met.
Figure 10: Vat Control System
Figure 11 illustrates the hardwired method for vat control. In this example, a pressure switch and a temperature switch are hardwired in series. This means both switches must be energized at the same time before the motor will start. A manual override push button is also installed in order to bypass the temperature and pressure switches and start the motor on demand.
For Review Only,
Figure 12 illustrates the vat control circuit implemented in PLC ladder logic. Notice that the three different inputs (pressure switch, temperature switch, and manual override) are represented by the contacts 000, 001, and 002, respectively. The actual pressure switch and the temperature switch would be hardwired to two different terminals on an input module. The manual override push button would be hardwired to a third input terminal. The motor, represented by the coil labeled 110, would be hardwired to a terminal on an output module.
Figure 12: PLC Vat Control System
It now becomes quite easy to change the operating logic in the PLC without physically moving a wire connection. Figure 13 shows how a traditional circuit would be reconnected in order to make temperature a critical path for the motor to work. As you can see, the wiring of the switch must be physically changed, which could involve extensive work depending on its location.
Figure 13: Hardwired System Changes
For Review Only,
Figure 14 shows how the PLC ladder logic is reprogrammed to implement the same changes without ever touching a wire.
Figure 14: PLC System Changes
Remote I/O
Complex operating environments may require more input and output terminals than a single, fully populated equipment chassis can provide. When this is the case, additional racks of I/O modules may be connected to the processor. These additional racks are known as remote I/O because they are located remotely from the equipment chassis that contains the processor module. Note that any I/O modules that reside in the same chassis as the processor are known as resident I/O.
A remote I/O chassis consists of various input and output modules, a power supply, and an interface adapter. There is no processor module in the remote I/O rack. The interface adapter, which is installed in the left-most slot of the chassis in place of the processor, provides a serial communication link from the remote racks to the processor.
For Review Only,
Individual racks are normally connected to the processor using a daisy chain or star configuration via one or two twisted-pair conductors or a single coaxial cable. The distance a remote rack can be placed away from the processor varies between manufacturers, but can be as much as two miles. Remote I/O offers tremendous savings on wiring materials and labor costs for large systems in which the field devices are in clusters at various spread-out locations. With the processor in a central area, only the communication link is brought back to the processor, instead of hundreds of field wires. Distributed I/O also offers the advantage of allowing subsystems to be installed and started up independently, as well as allowing maintenance on individual subsystems while others continue to operate.
Linking Multiple Processors
Data Highway Plus (DH+) is a communications network used to transfer information between multiple processors in a network. Each processor on the highway is assigned a unique address, which identifies the station on the network. Up to sixty-four (64) stations are allowed on a single data highway plus network, with station number assignments ranging from 08-778. Multiple processors may be connected in a daisy
chain or, in a trunkline/dropline architecture.
For Review Only,
RSLOGIX 5 INTRODUCTION
This section introduces the RSLogix 5 software. RSLogix 5 operates using a Windows-based environment. This section discusses the major components found in the main operating window of the software, and introduces several basic software functions.
