University of Technology Control and System Engineering Department Computer and Mechatronics Engineering Branches

Transcription

1 University of Technology Control and System Engineering Department Computer and Mechatronics Engineering Branches Programmable Logic Controllers Third year Class 1 st Semester 2017 / 2018 Lecture 1

2 Programmable Logic Controller

3 Programmable Logic Controller PLC Definition(according to NEMA * standard ICS3-1978): A digitally operating electronic apparatus which uses a programming memory for the internal storage of instructions for implementing specific functions such as logic, sequencing, timing, counting and arithmetic to control through digital or analog modules, various types of machines or process. * NEMA: National Electrical Manufacturers Association

4 Historical Background 1-In 1968 GM Hydra-Matic (the automatic transmission division of General Motors) issued a request for proposals for an electronic replacement for hard-wired relay systems based on a white paper written by engineer Edward R. Clark. The winning proposal came from Bedford Associates of Bedford, Massachusetts. The first PLC, designated the 084 because it was Bedford Associates' eighty-fourth project, was the result. 2-Bedford Associates started a new company dedicated to developing, manufacturing, selling, and servicing this new product: Modicon, which stood for MOdular DIgital CONtroller. One of the people who worked on that project was Dick Morley, who is considered to be the "father" of the PLC. 3-The Modicon brand was sold in 1977 to Gould Electronics, later acquired by German Company AEG, and then by French Schneider Electric, the current owner.

5 PLC Dick Morley And MODICON 084

6 Development achieved During the past four decades, enormous progress was made in the development of micro electronics has greatly influenced PLCs design and programming methods. The range of functions and application fields have grown considerably. Analogue processing, and the use of a PLC in distributed control systems (DCS) networks is common in PLC systems. Visualisation, which is the representation of machine statuses such as the control program being executed, via display or monitor with capability to enter commands and variables can now be integrated into many PLC systems.

7 Subsequent development resulted in a system featuring: The simple connection of binary signals The requirements as to how these signals were to be connected was specified in the control program With the new systems it became possible for the first time to plot signals on a screen and to store these in electronic memories

8 Leading PLC manufacturers list AMERICAN 1. Allen Bradley 2. Gould Modicon 3. Texas Instruments 4. General Electric 5. Westinghouse 6. Cutter Hammer 7. Square D EUROPEAN JAPANESE 1. Siemens 2. Klockner & Mouller 3. Festo 4. Telemechanique 1. Toshiba 2. Omron 3. Fanuc 4. Mitsubishi

9 PLC Advantages Flexibility In the past, each different electronically controlled production machine required its own controller; 15 machines might require 15 different controllers. Now it is possible to use just one model of a PLC to run any one of the 15 machines. Each of the 15 machines under PLC control would have its own distinct program (or a portion of one running program). Implementing Changes and Correcting Errors With a wired relay-type panel, any program alterations require time for rewiring of panels and devices. When a PLC program circuit or sequence design change is made, the PLC program can be changed from a keyboard of a program loader in a matter of minutes. No rewiring is required for a PLC-controlled system. Also, if a programming error has to be corrected in a PLC control program, a change can be typed in quickly. Large Quantities of Contacts The PLC has a large number of contacts for each coil available in its programming. Suppose that a panel-wired relay has four contacts and all are in use when a design change requiring three more contacts is made, time would have to be taken to procure and install a new relay or relay contact block. Using a PLC, however, only three more contacts would be typed in. Contacts are now a software component

10 PLC Advantages (Continued) Lower Cost Increased technology makes it possible to condense more functions into smaller and less expensive packages. Now a PLC can be purchased with numerous relays, timers, and counters, a sequencer, and other functions for a few hundred dollars. Pilot Running A PLC programmed circuit can be evaluated in the lab. The program can be typed in, tested, observed, and modified if needed, saving valuable factory time. Visual Observation A PLC circuit's operation can be seen during operation directly on a screen. The operation or mis-operation of a circuit can be observed as it happens. Logic paths light up on the screen as they are energized. Troubleshooting can be done more quickly during visual observation. Reliability and Maintainability Solid-state devices are more reliable, in general, than mechanical systems or relays and timers. Consequently, the control system maintenance costs are low and downtime is minimal. Documentation An immediate printout of the true PLC circuit is available in minutes, if required. There is no need to look for the blueprint of the circuit in remote files. The PLC prints out the actual circuit in operation at a given moment. Often, the file prints for relay panels are not properly kept up to date. A PLC printout is the circuit at the present time; no wire tracing is needed for verification.

11 PLC Disadvantages Fixed Program Applications Some applications are single-function applications. It does not pay to use a PLC that includes multiple programming capabilities if they are not needed. Their operational sequence is seldom or never changed, so the reprogramming available with the PLC would not be necessary. Fail-Safe Operation In relay systems, the stop button electrically disconnects the circuit; if the power fails, the system stops. This, of course, can be programmed into the PLC; however, in some PLC programs, you may have to apply an input voltage to cause a device to stop. These systems may not be fail-safe.

12 Characteristics of a PLC System There are seven distinct characteristics in a PLC system, these are: 1. It is field programmable by the user. This characteristic allows the user to write and change programs in the field without rewiring or sending the unit back to the manufacturer for this purpose. 2.It contains preprogrammed functions. PLCs contain at least logic, timing, counting, and memory functions that the user can access through some type of control-oriented programming language. 3.It scans memory and inputs and outputs (I/O) in a deterministic manner. This critical feature allows the control engineer to determine precisely how the machine or process will respond to the program. 4.It provides error checking and diagnostics. A PLC will periodically run internal tests of its memory, processor, and I/O systems to ensure that what it is doing to the machine or process is what it was programmed to do. 5.It can be monitored. A PLC will provide some form of monitoring capability, either through indicating lights that show the status of inputs and outputs, or by an external device that can display program execution status. 6.It is packaged appropriately. PLCs are designed to withstand the temperature, humidity, vibration, and noise found in most factory environments. 7.It has general-purpose suitability. Generally a PLC is not designed for a specific application, but it can handle a wide variety of control tasks effectively.

13 Types of PLC Construction: Compact PLC - it covers units with up to 128 I/O s and memories up to 2 Kbytes. - Capable of providing simple to advance levels or machine controls Modular PLC -The most sophisticated units of the PLC family. They have up to 8192 I/O and memories up to 750 Kbytes. - Can control individual production processes or entire plant.

14 Basic Elements of a PLC Power Supply Processor (CPU) Memories Input/output modules Programming Port PLC Bus Expansion Models

15 Power Supply The basic function of the power supply is to convert the field power into a form more suitable for Use electronic devices that comprise the PLC In large PLC systems, this power supply does not normally supply power to the field devices. In small and micro PLC systems, the power supply is also used to power field devices.

16 Power Supply Features and Specifications It is typically non-redundant. Hence a failure of the PLC power supply can cause the entire control system to fail. It will typically contain high-voltage components. Hence an isolation failure can create the potential for serious injury or fire. Useful guidelines when considering the power supply of a PLC include the following: 1. The power supply should be packaged properly so that the heat generated by the power supply can be removed in order to prevent overheating. This will increase reliability. If the power supply cabinet is hot to the touch at room temperature in an office environment, it will be hotter still when locked in a control panel or located on the factory floor. Care, of course, must always be taken to avoid touching any exposed power terminals. 2. The power supply should be tested by a certification agency, such as Underwriters Laboratories ( ) or the Canadian Standards Association ( ). These agencies perform temperature testing and electrical isolation testing on power supply components. A UL or CSA mark on the PLC power supply will indicate that the power supply was tested to comply with some basic minimum standards. 3. The power supply should meet at least one reputable standard for noise immunity. Two of these standards are NEMA ICS (a showering arc noise test) and IEEE Std. 472 (a high-voltage impulse test). Some noise testing may also be performed by certification agencies, such as UL and CSA. The power supply should also be capable of withstanding line-voltage variations such as dropouts, brownouts, and surges, which are common to industrial facilities.

17 Processor Module This module is the prime essence of a PLC system It consists of a microprocessor which is sometimes specially designed for the purpose of being implemented in a PLC system design for implementing the logic, and controlling the communications among the modules. The processor module accepts input data from various sensing devices via Input modules, executes the stored user program, and sends appropriate output commands to control devices via output modules. Processor Module

18 Processor Module Details A detailed block diagram of the processor section of a PLC is shown in Figure below. This section consists of four major elements: (1) power supply, (2) memory, (3) central processing unit (CPU), and (4) I/O interface.

19 Memories The program memory receives and holds the downloaded program instructions from the programming device -This memory is usually an EEPROM (electrically erasable programmable ROM) or a battery-backup RAM, both of which are capable of retaining data Data memory is RAM memory used as a scratch pad by the processor to temporarily store internal and external programgenerated data For example, it would store the present status of all switches connected to the input terminals and the value of internal counters and timers.

20 Memory Designs VOLATILE. A volatile memory is one that loses its stored information when power is removed. Even momentary losses of power will erase any information stored or programmed on a volatile memory chip. Common Type of Volatile Memory RAM. Random Access Memory(Read/Write) Read/write indicates that the information stored in the memory can be retrieved or read, while write indicates that the user can program or write information into the memory.

21 Memory Designs Several Types of RAM Memory: 1.MOS 2.HMOS 3.CMOS The CMOS-RAM (Complimentary Metal Oxide Semiconductor) is probably one of the most popular. CMOS-RAM is popular because it has a very low current drain when not being accessed (15microamps.), and the information stored in memory can be retained by as little as 2Vdc.

22 Memory Designs NON VOLATILE. A non volatile memory is one that does not lose its stored information when power is removed. EPROM, Erasable Programmable Read Only Memory Ideally suited when program storage is to be semi-permanent or additional security is needed to prevent unauthorized program changes. The EPROM chip has a quartz window over a silicon material that contains the electronic integrated circuits. This window normally is covered by an opaque material, but when the opaque material is removed and the circuitry exposed to ultra violet light, the memory content can be erased. The EPROM chip is also referred to as UVPROM.

23 Memory Designs NON VOLATILE EEPROM, Electrically Erasable Programmable Read Only Memory Also referred to as E 2 PROM, is a chip that can be programmed using a standard programming device and can be erased by the proper signal being applied to the erase pin. EEPROM is used primarily as a non-volatile backup for the normal RAM memory. If the program in RAM is lost or erased, a copy of the program stored on an EEPROM chip can be down loaded into the RAM. Battery backed CMOS RAM can also be classified as non-volatile

24 I/O Section Consists of input modules and output modules. Input module connects to : Field sensors: switches, flow, level, pressure, temp. transmitters, etc. Output modules connect to: Field output devices: motors, valves, solenoids, lamps, or audible devices

25 I/O Section Input Module Forms the interface by which input field devices are connected to the controller. The terms field and real world are used to distinguish actual external devices that exist and must be physically wired into the system.

26 I/O Section Output Module Forms the interface by which output field devices are connected to the controller. PLCs employ a relay or an optical isolator which uses light to electrically isolate the internal components from the input and output terminals.

27 Programming Device PC with appropriate software The computer monitor is used to display the logic on the screen. The personal computer communicates with the PLC processor via a serial or parallel data communications link. A personal computer (PC) is the most commonly used programming device. The software allows users to create, edit, document, store and troubleshoot programs. If the programming unit is not in use, it may be unplugged and removed. Removing the programming unit will not affect the operation of the user program.

28 Programming Device Hand-held unit with display They are compact, inexpensive, and easy to use, but are not able to display as much logic on screen as a computer monitor. Hand-held programming devices are sometimes used to program small PLCs. Hand-held units are often used on the factory floor for troubleshooting, modifying programs, and transferring programs to multiple machines.

29 PLCs Versus Personal Computers Same basic architecture PLC -operates in the industrial environment -is programmed in relay ladder logic -has no keyboard, CD drive, monitor, or disk drive -has communications ports, and terminals for input and output devices PC -capable of executing several programs simultaneously, in any order -some manufacturers have software and interface cards available so that a PC can do the work of a PLC

30 PLC Size Classification Criteria - number of inputs and outputs (I/O count) - cost - physical size Allen-Bradley PLC-5 Family - handles several thousand I/O points Allen-Bradley SLC-500 Family - handles up to 960 I/O points Micro PLC - handles up to 32 I/O points Nano PLC - smallest sized PLC - handles up to 16 I/O points

31 Areas of Application Manufacturing / Machining Food / Beverage Metals Power Mining Petrochemical / Chemical

32 End of Lecture 1

33 University of Technology Control and System Engineering Department Computer and Mechatronics Engineering Branches Programmable Logic Controllers Third year Class 1 st Semester 2017 / 2018 Lecture 2

34 PLC Programming

35 Devices Connecting to PLC I/O Modules Devices connecting to PLC input modules - Pushbuttons momentary contact: Toggle switches: Throw - number of states Pole - number of connecting moving parts (number of individual circuits). S - single, D - double - There are special purpose input modules that can be connected directly to special sensing devices like shaft encoders and analogue sensors like thermocouples *IEC: International Electrotechnical Commission

36 - Other types of switches: Devices Connecting to PLC I/O Modules continued Limit switch Liquid level (float) switch Pressure switch Temperature actuated switch

37 Devices Connecting to PLC I/O Modules -Proximity switches / sensors: continued Reed switch Inductive proximity switch / sensors For ferrous and ferromagnetic objects

38 Devices Connecting to PLC I/O Modules -Proximity switches / sensors: continued Optical proximity switch / sensors Through beam Reflective Retro-reflective Reflective scan

39 Devices Connecting to PLC I/O Modules continued Devices connecting to PLC output modules -There are Several output devices that ca be controlled through the output modules of the PLC system, the symbols of these devices are shown next to this text. In general these can be categorized as follows: Indicators and Alarm. Relays and contactors. Solenoids and solenoid valves. Motors. heaters. -There are special output modules that can drive special output devices like stepper motors and analogue metering devices.

40 Devices Connecting to PLC I/O Modules continued Solenoid: construction and operation. Solenoid valve: construction and operation. Relay: construction

41 Devices Connecting to PLC I/O Modules continued Relay: Operation and symbol Contactor: Construction and symbol

42 PLC Programming Languages

43 PLC- Programming languages - IL IL: Instruction List Fastest possible logic execution. Low level language Similar to assembly language

44 PLC- Programming languages - ST ST: Structured Text High level language Equations, table manipulation Complex algorithms (If/Then)

45 PLC- Programming languages - LD Traditional ladder logic is an easy-to-use graphical programming language that implements relay-equivalent symbol. Intuitive. LD in old PLCs had limited functionalities. LD Functionality has been greatly improved in modern PLCs

46 PLC- Programming languages - FBD FBD : Function Block Diagram Easy way of programming Easy way of debugging Limited for complex algorithms

47 PLC- Programming languages - SFC SFC : Sequential Function Chart A graphical method of representing a sequential control system (stepper).

48 PLC- Programming software tools Siemens : Simatic Step7 v5.5 Modular Wide range of functionalities Diagnostic tools Network configuration LSis/GLOFA: GMWIN for GM4 and GM6 v4.18 Supports the international language (IEC ) IL, LD, SFC Simulation Program test and debugging without PLC Editing, monitoring, debugging using symbol and variable name Automatic memory allocation support Compiler sets a variable location automatically Optimization (PLC code) by compiler method User-defined function/function block support

49 PLC Programming Process Creating a new LD project using GMWIN package. Defining the labels to be in an LD program. Creating an LD program for GLOFA GM6 PLC. Converting the created LD program into an executable sequence program (Compiling). Correcting the program if any error occurs in execution.

50 Programming PLC Using LD (Ladder Diagram) Language The ladder diagram consists of two vertical lines representing the power rails. Circuits are connected as horizontal lines, i.e., the rungs of the ladder, between these two verticals LD language convention: 1. The vertical lines of the diagram represent the power rails between which circuits are connected. The power flow is taken to be from the left-hand vertical across a rung. 2. Each rung on the ladder defines one operation in the control process. 3. A ladder diagram is read from left to right and from top to bottom, the figure on the right shows the scanning motion employed by the PLC. The top rung is read from left to right. Then the second rung down is read from left to right and so on.

51 LD language convention: Continued 4. When the PLC is in its run mode, it goes through the entire ladder program to the end, the end rung of the program being clearly denoted, and then promptly resumes at the start. This procedure of going through all the rungs of the program is termed a cycle. The end rung might be indicated by a block with the word END or RET for return, since the program promptly returns to its beginning. 5. Each rung must start with an input or inputs and must end with at least one output. The term input is used for a control action, such as closing the contacts of a switch, used as an input to the PLC. The term output is used for a device connected to the output of a PLC, e.g., a motor. 6. Electrical devices are shown in their normal condition. Thus a switch, which is normally open until some object closes it, is shown as open on the ladder diagram. A switch that is normally closed is shown closed. 7. A particular device can appear in more than one rung of a ladder. For example, a relay that switches on might be used on one or more devices. The same letters and/or numbers are used to label the device in each situation. 8. The inputs and outputs are all identified by their addresses, the notation used depending on the PLC manufacturer. This is the address of the input or output in the memory of the PLC.

52 Types of PLC Control Action Temporal -- control based in time State -- control based in state level Hybrid both temporal and state Functions of PLC Systems 1) on-off control, 2) sequential control, 3) feedback control, and 4) motion control

53 Basic symbols of LD Language

54 PLC Programming Using GMWIN Software in LD Language General form of an LD Rung. GLOFA GMWIN form of an LD Rung.

55 LADDER DIAGRAM A ladder diagram (also called contact symbology) is a means of graphically representing the logic required in a relay logic system. Rail start PB1 emergency stop PB2 R1 Rung R1 R1 A

56 PLC Instructions 1) Relay, 2) Timer and counter, 3) Program control, 4) Arithmetic, 5) Data manipulation, 6) Data transfer, and 7) Others, such as sequencers.

57 Relay A Relay consists of two parts, the coil and the contact(s). Contacts: a. Normally open - - b. Normally closed - / - Coil: a. Energize Coil -( )- b. De-energize -(/)- c. Latch -(L)- d. Unlatch -(U)- ( )

58 Logic States ON : TRUE, contact closure, energize, etc. OFF: FALSE, contact open, de-energize, etc. The internal relay and program should not be confused with the external switch and relay. Internal symbols are used for programming. External devices provide actual interface.

59 AND and OR LOGIC AND OR

60 Combined AND & OR R1 = PB1.OR. (PB2.AND. PB3)

61 Logic for Ladder Solution

62 An Example of a Sequential Task The sequential task is as follows: 1. Start button is pressed. 2. Table motor is started. 3. Package moves to the position of the limit switch and automatically stops Relay wiring diagram PLC with I/O wiring

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64 End of Lecture 2

65 University of Technology Control and System Engineering Department Computer and Mechatronics Engineering Branches Programmable Logic Controllers Third year Class 1 st Semester 2017 / 2018 Lecture 3

66 Examples on PLC Programming Using Ladder Language to Solve Automation Problems

67 Writing a Ladder Logic Program Directly from a Narrative Description In most cases, it is possible to prepare a ladder logic program directly from the narrative description of a control process. Some of the steps in planning a program are as follows: Define the process to be controlled. Draw a sketch of the process, including all sensors and manual controls needed to carry out the control sequence. List the sequence of operational steps in as much detail as possible. Write the ladder logic program to be used as a basis for the PLC program. Consider different scenarios where the process sequence may go astray and make adjustments as needed. Consider the safety of operating personnel and make adjustments as needed. The following are examples of ladder logic programs derived from narrative descriptions of control processes.

68 Experiment 1 The figure to the left shows the sketch of a drilling process that requires the drill press to turn on only if there is apart present and the operator has one hand on each of the start switches. This precaution will ensure that the operator s hands are not in the way of the drill. The sequence of operation requires that switches 1 and 2 and the part sensor all be activated to make the drill motor operate. The next figure shows the ladder logic program required for the process implemented using a GLOFA GM6 PLC.

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70 Experiment 2 A motorized overhead garage door is to be operated automatically to preset open and closed positions. The field devices include one of each of the following: Reversing motor contactor for the up and down directions. Normally open down limit switch to sense when the door is fully closed. Normally open-held closed up limit switch to sense when the door is fully opened. Normally open door up button for the up direction. Normally open door down button for the down direction. Normally closed door stop button for stopping the door. Red door ajar light to signal when the door is partially open. Green door open light to signal when the door is fully open. Yellow door closed light to signal when the door is fully closed. The sequence of operation requires that: When the up button is pushed, the up motor contactor energizes and the door travels upward until the up limit switch is actuated. When the down button is pushed, the down motor contactor energizes and the door travels down until the down limit switch is actuated. When the stop button is pushed, the motor stops. The motor must be stopped before it can change direction. The figure below shows the ladder logic program required for the operation implemented using a GLOFA GM6 PLC.

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72 EXPERIMENT 3 The figure below shows the sketch of a continuous filling operation. This process requires that boxes moving on a conveyor be automatically positioned and filled. The sequence of operation for the continuous filling operation is as follows: Start the conveyor when the start button is momentarily pressed. Stop the conveyor when the stop button is momentarily pressed. Energize the run status light when the process is operating. Energize the standby status light when the process is stopped. Stop the conveyor when the right edge of the box is first sensed by the photo-sensor. With the box in position and the conveyor stopped, open the solenoid valve and allow the box to fill. Filling should stop when the level sensor goes true. Energize the full light when the box is full. The full light should remain energized until the box is moved clear of the photo-sensor. The figure after shows the ladder logic program required for the operation.

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75 End of Lecture