Basics of PLC Programming EE 100 Intro to

Basics of PLC Programming EE 100 – Intro to EE Fall 2004 Dr. Stephen Williams, P. E.

Overview ® How did we get where we are today? ® How does a project at GM in 1968 relate to the work of Henry Leland in the late 1800 s?

Vocabulary ® Programmable Logic Controllers ® Definite-purpose computers design to control industrial processes and machines ® Drives ® Solid-state devices designed to control motors ® Sensors ® Transducers used to obtain information

First Programmable Controller ® General Motors Corporation ® Hydromatic Division ® Replaced relay-controlled system ® PDP-8 minicomputers? ® MODICON 084 ® Modular Digital Controller

Information Flow

Genesis of Automation ® Operation ® May sheets date back to the 1830 s ® Listing of: ® All machining operations ® The machine tools employed ® Tools, jigs, fixtures, and gauges ® Organization and flow of work

Industrial Revolution ® High-volume production ® Interchangeable parts ® Transportation system ® Inexpensive energy (coal) ® Frederick W. Taylor ® Scientific ® Henry management Ford

Purpose of Automation ® Increase productivity ® Standardize components or processes ® Free workers from repetitive, and sometime dangerous, tasks

Early Automation Applications 1869 – Refineries in Pennsylvania automatically covert crude oil to kerosene ® 1937 – Pictured is the loading and unloading of stators via an overhead conveyor for dipping in continuous process oven ®

The Case Against Automation ® Las Vegas Sun, August 2, 1961 ® Jimmy Hoffa saw a new industrial revolution forming with automation being a threat to his giant union more menacing than the Justice Department, Attorney General Bobby Kennedy and the president himself. ® He felt he could cope with the Senate committees, the FBI, and all the new legislation being written, which he thinks is aimed at unionism. It is with automation that all his talents, energy and ability must be directed.

Forces Driving Automation ® Lower costs ® Faster production ® Better quality control ® How have they remained relevant today?

Engineering Resources ® Why do you need all of these engineers running around to make all of this stuff work?

Breakthroughs and Plateaus ® Where have we seen breakthroughs, and then plateaus of technology? ® Microprocessors ® Graphical User Interfaces ® Power Electronics ® Software Systems

Brief Review of Technology ® Traditional (ancient? ) devices ® Still used in many plants ® If it ain’t broke … ® Where are we going?

Traditional Relay Logic ® Used since … ® Control via a series of relay contacts ® On and off inputs ® Race conditions on the outputs ® Very expensive ® Hard to design and construct ® Difficult to maintain

Traditional Devices ® Relays ® Contactors ® Motor Starters ® Manually operated switches ® Mechanically operated switches ® Electrically operated switches

Relays ® Original control elements ® Now used as auxiliary devices ® The PLC is not designed to switch high currents or voltages

Contactors ® Used for heavy-duty switching ® Provides isolation from high voltages and large currents ® Usefully for large inductive currents, such as motor starting

Motor Starters ® Contactors + Overload Relay ® Overload relays were usually heaters and bimetal strips ® The ® Next bimetal strip separates when heated steps: ® PLCs and motor starters ® Electronic overloads ® Intelligent starters

Manually Operated Switches ® Pushbuttons ® Normally open ® Normally closed ® Break-then-make ® Make-then-break ® Selector switches ® Maintained or spring return

Mechanically Operated Switches ® Limit Switches ® Temperature Switches ® Pressure Switches ® Level Switches

Electrically Operated Switches ® Photoelectric Switches ® Proximity Switches

What's ahead? ® Solid state devices to replace motor starters ® Distributed smart sensors ® Micro- and nanomachines ® Adaptive control ® Smart maintenance

Summary ®A very brief history of industrial automation ® Overview of some of the older technologies ® Some thoughts on the future

PLC Systems ® CPU ® Processor ® Memory ® ® One Module Power Supply ® Part of the chassis or a separate module ® Programming/ Monitoring Device ® I/0 Modules

Small Logic Controllers

Input and Output ® Input Modules ® Convert ® 24 V, 120 V, Analog, etc. ® Output Modules ® Convert ® “real world” signal to PLC input PLC signal to “real world” output 24 V, 120 V, Analog, etc. ® Limiting ® PLC values power supply

Configurations ® Fixed I/O ® Limited expandability ® Rack ® Many modules, with the possibility of chaining many racks together ® SLC 500 is a fixed I/O device ® SLC 5/02 uses a rack configuration

Chassis Versus Rack ® One “Rack” is 128 inputs/outputs ® A chassis is the outer shell of the PLC ® Chassis ≠ Rack ® SLC 5/02’s in S-340 have a ten-slot chassis ® Slots are numbered from 0 to 9

SLC Image Tables ® Hex numbering ® Addressing ® I 1: 2. 0/01 ®I is for the file type ® 1 is the file number ® 2 is the element number ®. 0 is the sub-element number (>16) ® /01 is the bit number

“Real World” Address ® I 1: 3. 0/01 ®I is the module type ® 1 is redundant ® 3 is the slot number ®. 0 is for terminals above 15 ® /01 is the terminal number

Remote Racks ® I/O racks located close to the equipment being monitored ® Simplifies wiring ® Communication modules Similar to LAN ® Fiber Optic ® Coaxial cable ®

Discrete I/O Modules ® Either “on” or “off” ® Bit oriented ® Various ratings ® 24 V ® 120 V ® TTL ® 4 – 20 m. A

Special I/O Modules ® Analog ® High speed counter ® Thumb-wheel ® TTL ® Encoder ® PID ® Servo

Memory Organization ® Not the same on all manufactures ® Allen Bradley uses two main types ® Memory Maps ® Data table ® User program ® Internal registers ® Memory variable allocation could be fixed or

SLC Program File Structure Program File Number 0 Use System Functions 1 Reserved 2 Main Program 3 -255 Subroutines

RSLogix 500 Screen ® Define controller attributes Model ® Memory ® Communication ® ® Program files Main program ® Subprograms ®

SLC Data File Structure Data File Number 0 Use Output Image Table 1 Input Image Table 2 Status Table 3 Bit Table

SLC Data File Structure Data File Number 4 Use Timer Table 5 Counter Table 6 Control Table 7 Integer Table

SLC Data File Structure Data File Number 8 9 10 -255 Use Reserved (Floating Point Value Table) Network Table Any combination of Bit, Timer, Counter, Control, or Integer Tables

RSLogix 500 Screen ® Access to input and output tables ® Access to timer and control files

Address Format ® What type of device or module ® Where is it located physically or in memory ® For example, T 4: 0/DN is the done bit for timer 0 in file 4 ® I: 2. 0 is an input module in slot 2 ® Word versus bit addresses ® I: 3. 0 is a word, I: 3. 0/04 is a bit

Multiword Elements ® Timers, counters, and control elements ® Three words used ® Control word to store status ® Preset word to store desired value ® Accumulated word to store present value ® Control file store a length and position value (on functions other than counters and timers)

Counter Element Example Name Address Example Control Word C 5: 0/DN Preset Word C 5: 0. PRE 5000 Accumulated Word C 5: 0. ACC 1240

RSLogix 500 Screen ® Counter C 5: 0

Program Scan ® Each cycle through the program and I/O process is called a scan ® Scan times vary with the length of the program and the speed of the processor

Programming Environments ® Languages available ® Ladder logic ® Boolean ® Function chart ® Ladder logic is the most common ® Function chart is the future ® C, BASIC, etc. , are also possible

Transducers ® Converts energy from one form to another ® Input transducers ® Real world into the PLC ® Output ® PLC transducers to real world

Sensors ® Sensors are transducers used to measure or detect ® Convert mechanical, magnetic, thermal, or optical variations into electrical quantities ® Sensor input is the basis for most of the decisions made in a large system

Proximity Sensors ® Detect the presence of a object (target) without physically touching the object ® Solid-state devices ® Completely encapsulated ® Used when: ® Detecting small objects ® Rapid response is required

Inductive Proximity Sensors ® Senses a metallic object ® A change in the magnetic field occurs when a metallic object enters into range ® This type of sensor can “see” through cardboard boxes and other enclosures ® Current-sourcing or current-sinking output

Manually Operated Switches ® Pushbuttons ® Normally open ® Normally closed ® Break-then-make ® Make-then-break ® Selector switches ® Maintained or spring return

Counter Instructions ® Count Up or Down ® Similar to timers, but without an internal source ® Two methods used: block and coil ® SLC 5/02 s use the coil format ® PREset and ACCumlated values ® RESet similar to RTO

How Counters Work ® Increment or decrement on a false to true input transition ® They are retentive ® The accumulated value remains when the rung goes false ® PREset ® Move can be changed by the program a new value into C 5: 0. PRE

Control Bits 15 14 13 12 11 10 CU CD DN OV UN UA ® CU = Count Up ® CD = Count Down ® DN = Done ® OV = Overflow, UN = Underflow

Integer Limits ® PREset and ACCumulator values must be integers ® Integers on the SLC 5/02 range from 32, 767 to -32, 768 ® Cascade counters to go beyond these limits

Cascading Example

Down Counters ® The SLC 5/02 does not have a true down counter ® The counter does not start at a value and become true when the ACCumulator is zero ® The SLC 5/02 CTD works with another counter with the same address

Down Counter Example

Types of Data Instructions ® Math Functions ® Add, ® Data subtract, multiply, etc. Conversion and Comparison ® Integer ® Logical to BCD, Less than, Equal, etc. Operations

Bits, Words, and Files ®A bit is the smallest unit of information ® T 4: 0/DN ®A is a bit “word” is another name for a register ® T 4: 0. PRE ®A is a word “file” is a block of words, also known as a table ® T 4 is a file

Data Transfer – Move ® The move instruction takes a value from a register, or a constant value, and places it in another register

BCD Move Into a Register ® Moves an integer value into a BCD device. ® In lab, the LED Display

BCD Move From a Register ® Moves an BCD value into an integer register. ® In lab, the thumb-wheel inputs

Comparisons ® Greater than, less than, equals, etc. ® When true, output is true

Today’s Task ® Use what you have learned to “break the code” ® Each bench has a PLC program ® The first bench to turn on all five lamps wins!