Microcomputer Control of Thermal and Mechanical

Systems

W. F. Stoecker University of Illinois at Urbana-Champaign

P. A. Stoecker Hewlett-Packard Company

ШЕ VAN NOSTRAND REINHOLD New York

Contents 1 Microcomputer Control 1

1-1 The Penetration of Microprocessors into Engineering Fields 1 1-2 The Path by which Microcomputer Control Has Grown . . . 2 1-3 Chemical and Process Industries 3 1-4 Environmental Control of Buildings 4 1-5 Automobiles о 1-6 Home Appliances 6 1-7 Computer Control in Manufacturing 7 1-8 Electric Power Generation and Regulation 7 1-9 Agricultural Applications of Computer Control 8 1-10 What the Engineer Who Applies Computers Needs to Know 8 References 9

2 DC Circuits and Power Supplies 11 2-1 Understanding Circuits 11 2-2 Kirchhoff's Laws 11 2-3 Thevenin Equivalent 12 2-4 Norton Equivalent 14 2-5 RC Circuits 16 2-6 Resistors 18 2-7 Diodes 20 2-8 Rectifying Circuit 22 2-9 Voltage Ripple 23 2-10 Commercial Power Supplies 24 2-11 Voltage Regulators 24 Problems 25

3 Operational Amplifiers 29 3-1 Application of Operational Amplifiers 29 3-2 Basic Characteristic of the Op Amp 30 3-3 Comparator 30 3-4 Inverting Amplifier 30 3-5 Choice of Resistances 32 3-6 Non-inverting Op Amp 32 3-7 Buffer or Follower Amp 33 3-8 Signal Conditioning 33

ix

x Contents

3-9 Summing and Multiplying Amplifier 34 3-10 Generalized Circuit for an Op Amp 36 3-11 Integrator 37 3-12 Pin Diagram of 741 Op Amp 39 3-13 Limitations and Ratings of the Op Amp 40 General References 41 Problems 41

4 Transistors 45 4-1 Impact of the Transistor 45 4-2 Symbols and Terminology 45 4-3 Current Characteristics 47 4-4 Bipolar-Junction and Field-Effect Transistors 49 4-5 Voltages at the Transistor Terminals 49 4-6 Voltage Amplifier 49 4-7 Transistor as a Switch, and Saturating the Transistor . . . . 51 4-8 Common Emitter and Common Collector Circuits 52 4-9 Zener Diode 53 4-10 Constant-Current Source 54 4-11 Designing a Constant-Current Source 55 4-12 Operating Limits of a Transistor 56 4-13 Transistor Packages 57 References 58 Problems 58

5 Transducers 61 5-1 Importance of Good Instrumentation 61 5-2 Thermocouples 62 5-3 Thermocouple Reference Junction 63 5-4 Metal and Thermistor Resistance-Temperature Devices . . . 63 5-5 Series Circuit 64 5-6 Bridge Circuits 67 5-7 Amplification of a Bridge Output 69 5-8 RTD Circuits Supplied with Constant Current 70 5-9 Temperature-Dependent Integrated Circuits 71 5-10 Application of Sensors—Liquid Temperature 71 5-11 Application of Sensors—Temperature of Air and Other Gases 75 5-12 An Overview of Temperature Sensors and Transducers . . . 77 5-13 Flow Rate and Velocity Measurement 78 5-14 Venturi Tubes Liquid Flow Measurement 79 5-15 Orifice Liquid Flow Measurement 81

Contents xi

5-16 Flow Measurement of a Compressible Fluid in a Venturi or Orifice 83

5-17 Pitot Tubes 85 5-18 Hot-Wire Anemometer 85 5-19 Turbine Flow Meter 86 5-20 Ultrasonic Flow Meters 86 5-21 Vortex-Shedding Flow Meters 87 5-22 Evaluation of Flow-Measuring Devices 89 5-23 Pressure Transducers 90 5-24 Evaluation of Types of Pressure Transducers 90 5-25 Force 91 5-26 Torque 91 5-27 Electric Current 91 5-28 Humidity Sensors 92 5-29 Chemical Composition 92 5-30 Liquid Level 93 5-31 Position and Motion Sensors 94 5-32 Rotative Speed 97 5-33 How to Choose Transducers 97 References 98 General References 99 Problems 99

6 Actuators 105 6-1 Actuators for Computer Control Systems 105 6-2 Two-Position DC Electric Switch 106 6-3 Silicon-Controlled Rectifier (SCR) for DC Switching 107 6-4 Triac Alternating Current Switching 108 6-5 Optically Isolated Switch 110 6-6 Solid-State Relays 110 6-7 Electric-Motor Actuators 112 6-8 Magnetic Operator 113 6-9 Hydraulic Actuator 114 6-10 Pneumatic Valve and Damper Operators 114 6-11 Electric-to-Pneumatic Transducer 115 6-12 Stepping Motors 115 6-13 Performance of Stepping Motors 118 References 121 Problems 121

xii Contents

7 Binary Numbers and Digital Electronics 123 7-1 Transition to Digital Electronics 123 7-2 Binary Numbers 124 7-3 Conversion between Binary and Decimal Numbers 125 7-4 Addition of Binary Numbers 126 7-5 Basic Logic Operations 126 7-6 OR Gate 127 7-7 AND Gate 127 7-8 Inverter 128 7-9 NOT-OR (NOR) Gate 128 7-10 NOT-AND (NAND) Gate 129 7-11 Exclusive-OR (XOR) Gate 129 7-12 Combining and Cascading Gates 129 7-13 De Morgan's Laws 130 7-14 Gate Chips 131 7-15 Ladder Diagrams for Conditional and Sequential Control . . 131 7-16 Ladder Diagram Using Gates 135 7-17 Sequential Logic Circuits 137 7-18 Binary Addition with Gates 137 7-19 Pull-Up Resistor 138 7-20 Three Classes of Outputs Found on Inverters and Buffer

Gates 139 7-21 Debounced Switch 141 7-22 Clocks and Oscillators 142 7-23 Flip-Flops 143 7-24 Divide-By Counters 144 7-25 Schmitt Trigger 145 7-26 Monostable Multivibrator 148 7-27 Low-Frequency Pulses 148 7-28 Latches 149 7-29 Comparators 150 7-30 Analog Switches Field-Effect Transistors 150 7-31 Binary-Coded Decimal (BCD) 151 7-32 Seven-Segment LEDs 151 7-33 Summary 153 General References 153 Problems 154

8 Conversion Between Digital and Analog 159 8-1 Elements of a Microcomputer Controller 159 8-2 A Simple DAC 160 8-3 DAC Using R-2R Ladder Circuit 162

Contents xiii

8-4 The 1408 DAC 163 8-5 Applying the 1408 DAC 165 8-6 Multiplexers 167 8-7 Fidelity of Voltage Transmission Through a MUX 169 8-8 Sample-and-Hold Circuits 170 8-9 Operating Sequence with Multichannel Control 172 8-10 Where Analog-to-Digital Conversion Is Needed 173 8-11 Internal Functions of One Class of ADCs 174 8-12 More Complete Description of the Internal Functions of an

ADC 175 8-13 Staircase and Successive Approximation Search Routines

and Dual-Slope Integration 176 8-14 Pin Diagram of an 8-Bit ADC 177 8-15 Characteristics of the ADC 0800 178 8-16 Analog-to-Digital Conversion Using a DAC in Combination

with Software 180 8-17 Choosing the ADC 180 Problems 182

9 Memories 185 9-1 Function and Types of Memories 185 9-2 ROMs 186 9-3 EPROMs 187 9-4 RAMs 187 9-5 The MCM6810 RAM 189 9-6 Four-Bit RAMs the MCM2114 190 9-7 Dynamic RAMs 192 9-8 EEPROMs 192 9-9 Memories on the Microcomputer 192 General References 193 Problems 193

10 Binary Arithmetic 195 10-1 The Eight-Bit Microcomputer 195 10-2 Two's Complement Arithmetic—Subtraction 195 10-3 Multiplication 196 10-4 Hexadecimal System 197 10-5 Labeling Conventions 197 10-6 Signed and Unsigned Numbers 198 10-7 Unsigned Numbers The Carry Flag 200 10-8 Signed Numbers—Two's Complement Overflow 204 10-9 Status Registers on Microprocessors 206

xiv Contents

References 207 Problems 208

11 Programming a Microprocessor 209 11-1 A Generic Microprocessor 209 11-2 Data and Address Buses in a Generic Microcomputer . . . . 209 11-3 The Accumulator with its Arithmetic, Logic, and Transfer

Operations 210 11-4 The Fetch-Decode-Execute Sequence 211 11-5 Preliminary Instruction Set 212 11-6 Program Counter 214 11-7 Status Register and Jumps 214 11-8 Another Accumulator Incrementing and Decrementing . . 217 11-9 Additional Addressing Modes 218 11-10 The Index Register and the Use of Register Addressing . . . 219 11-11 Subroutines and the Stack 221 11-12 The Intel 8080/8085 Microprocessor 222 11-13 Loading Into and Storing From the Accumulator 228 11-14 Forms of Addressing on the 8080/8085 228 11-15 Flag Register 229 11-16 Subroutines 231 11-17 The 8080/8085 Programming Guide 232 11-18 The Motorola 6800 Family 232 11-19 Registers in the 6800 Microprocessor 232 11-20 The Instruction Set of the 6800 234 11-21 Condition Codes 237 11-22 Forms of Addressing 238 11-23 Branches—Relative Addressing 238 11-24 Index Register—Indexed Addressing 240 11-25 Loops 240 11-26 Stack Pointer 242 11-27 Subroutines 243 11-28 The 6800 Microprocessor Programming Guide 243 11-29 Summary 244 References 246 Problems 246

12 Assembly Language Programming 249 12-1 Machine Language; and Assembly Language 249 12-2 An Overview of the Assembly Process 249 12-3 Major Components of the Program 250 12-4 Assembly Language Statements 251

Contents xv

12-5 Assembler Directives 253 12-6 The Location Counter 254 12-7 Using Assembler Labels and Symbols 255 12-8 Relocating Assemblers and Loaders 257 12-9 The Operation of an Assembler 258 References 259 Problems 259

13 The Structure of an Elementary Microcomputer 261 13-1 Definition of an Elementary Microcomputer 261 13-2 The Bus Structure 262 13-3 Flow of Information on the Buses During Execution of a

Program 263 13-4 The Intel 8080 Microprocessor 264 13-5 Structure of the SDK-85 System Design Kit 266 13-6 Memory Map of the SDK-85 266 13-7 The Motorola 6802 Microprocessor 268 13-8 Structure of the MEK6802D5 Evaluation Kit 269 13-9 Memory Map of the D5 Evaluation Kit 270 13-10 Common Features of an Elementary Microcomputer 271 References 272 Problems 272

14 Parallel Input/Output and Interrupts 273 14-1 Parallel Input/Output 273 14-2 A Generic Parallel I/O Chip 274 14-3 Processing Interrupts 275 14-4 The Motorola Peripheral Interface Adapter (PIA) 276 14-5 Registers in the PIA 277 14-6 Preparing the PIA to Send and Receive Data 278 14-7 Interrupt from a Peripheral—An Overview 279 14-8 The Control Register and the Control Lines 281 14-9 Setting the Microprocessor to Receive an Interrupt 283 14-10 Structure of an Interruptible Program 283 14-11 User I/O Socket 285 14-12 Intel 8155/8156 RAM with I/O 286 14-13 Intel 8212 I/O Chip 286 14-14 Rudimentary Control Capability Now Available 287 Problems 288

xvi Contents

15 Serial Input/Output and Modems 289 15-1 Serial Data Transmission 289 15-2 Mark, Space, and Baud Rate 290 15-3 Synchronous and Asynchronous Communication 291 15-4 Parity 292 15-5 Shift Register 292 15-6 A Generic Universal Asynchronous Receiver/ Transmitter

(UART) 293 15-7 The MC6850 Asynchronous Receiver/Transmitter (ACIA) . 297 15-8 Registers in the ACIA 297 15-9 The Control Register 299 15-10 The Status Register 300 15-11 Transmitting and Receiving with the ACIA 301 15-12 The Intel 8251A Programmable Communication Interface . 302 15-13 The Control and Status Register on the 8251A 303 15-14 Communicating Using RS-232-C and Modems 305 15-15 RS-232-C Interface 306 15-16 Level Conversion Between RS-232-C and TTL 308 15-17 Communicating Between Two Elementary Microcomputers

Using RS-232-C 310 15-18 Transmission over Telephone Lines Using Modems 310 15-19 Dial-Up Modems 313 15-20 ASCII Characters 313 15-21 One-on-One Communication 313 References 315 Problems 315

16 Dynamic Behavior of Systems 317 16-1 Returning to the Thermal and Mechanical System 317 16-2 On/Off Controls 318 16-3 Make/Break Sensor with On/Off Actuator 319 16-4 Analog Sensor with On/Off Actuator 320 16-5 Modulating Control Strategies 321 16-6 Proportional Control 322 16-7 Proportional-Integral Control 324 16-8 Proportional-Integral-Derivative (PID) Control 327 16-9 Dynamic Analysis 327 16-10 Laplace Transforms 327 16-11 Inverting a Transform 328 16-12 Transforms of Derivatives 330 16-13 Solving Differential Equations by Means of Laplace

Transforms 330

Contents xvii

16-14 Transfer Functions 332 16-15 Feedback Loops 333 16-16 Stability Criteria for a Feedback Control Loop 334 16-17 A Proportional Controller Regulating the Pressure in an

Air-Supply System 336 16-18 Response of a Proportional Air-Pressuro Controller to a

Disturbance in Air-Flow Rate 339 16-19 The Integral Mode of Control 344 16-20 The Proportional-Integral (PI) Mode of Control 350 References 354 Problems 354

17 The Computer and Its Sampling Processes 357 17-1 Unique Features of Computer Control 357 17-2 Numerical Simulation 358 17-3 Sampled Data 362 17-4 Responses to Sampled Values 365 17-5 The z-Transform 370 17-6 Response to a Series of Impulses 376 17-7 The Zero-Order Hold (ZOH) 378 17-8 Inverting a z-Transform 380 17-9 Cascading z-Transforms and Transforms of a Feedback Loop 382 17-10 How a z-Transform Can Indicate Stability of a Control Loop 386 17-11 Proportional Control 390 17-12 Proportional-Integral Control 397 17-13 Forms of Actuator Signals 399 17-14 Non-linearities- Dead Time 400 17-15 Non-linearities Hysteresis 401 17-16 Summary 401 References 402 Problems 402

18 Field Application of Microcomputer Controllers 409 18-1 Applying Microcomputer Controllers to Field Processes . . . 409 18-2 Practical Control Algorithms 410 18-3 Incremental PI Control Algorithm 411 18-4 Position PI Control Algorithm 412 18-5 Criteria for Tuning 414 18-6 Manual Control Test 418 18-7 Trial-and-Error Tuning 419 18-8 Closed-Loop Tuning 422 18-9 Open-Loop Tuning 423

xviii Contents

18-10 Hysteresis Compensation 426 18-11 Summary 427 References 428 Problems 429