1. PROGRAMMABLE LOGIC CONTROLLER (PLC) MUNIRA MOHAMED NAZARI PPK BIOPROSES UniMAP

2.  Introduction  PLC Size and Application  Basic PLC Programming

3. PLC in Agricultural Industry PLC omponents Advantages PLC Vs Computer

4.  A Programmable Logic Controller (PLC) is a solid- state device designed to perform logic functions previously accomplished by electromechanical relays.

5.  A Programmable Logic Controller (PLC) is an industrial computer control system that continuously monitors the state of input devices and makes decisions based upon a custom program, to control the state of devices connected as outputs.

6.  Almost any production line, machine function or process can be automated using a PLC.  It is capable not only performing relay switching tasks, but also counting, calculating, comparing and the processing the analogue signals.  The speed and accuracy of the operation can be greatly enhanced using this type of control system.  But the biggest benefit in using a PLC is the ability to change and replicate the operation or process while collecting and communicating vital information.

7. Basic PLC Operation

8. PRINCIPLES OF OPERATION Example: A mixer motor is to be used to automatically stir a vat when the temperature and pressure reach preset values. Direct manual operation of the motor is provided by means of a separate pushbutton station. The process is monitored with temperature and pressure sensor switches that close their respective contacts when conditions reach their preset values.

9.  The use of PLCs and similar devices in the agricultural industry is widespread and growing.  Example ◦ food processing ◦ building environmental control ◦ grain drying ◦ aquaculture production ◦ tractor and machinery systems

10.  A PLC consists of following main parts:

11. A PLC can be divided into parts: the central processing unit (CPU), the input/output (I/O) section, the power supply and the programming device.

12.  The power supply supplies dc power to other modules that plug in rack and other field devices.  The processor (CPU) is the ‘brain’ of the PLC. It consists of a microprocessor for implementing the logic and controlling the communications among the modules.  Required memory for storing the results of the logical operation performed by the microprocessor.  The CPU is designed so that the user can enter the desired circuit in ladder logic.  The programming devices are used to enter the desired program into the memory of the processor.  This program is entered using relay ladder logic. The program determines the sequence of operation and ultimate control of the equipment or machinery.

13. There are two ways in which I/O is incorporated into PLC: 1)Fixed I/O: It’s small PLCs that come in one package with no separate, removable units. The processor and I/O are packed together and the I/O terminals are available but cannot be changed. Advantage: Lower cost, the number of available I/O points is varies and usually can be expanded by buying additional units of fixed I/O. Disadvantage: Lack of flexibility, limited with the quantities and type of packaging. If any part in the unit fails, the whole unit must be replaced. There are two ways in which I/O is incorporated into PLC: 1)Fixed I/O: It’s small PLCs that come in one package with no separate, removable units. The processor and I/O are packed together and the I/O terminals are available but cannot be changed. Advantage: Lower cost, the number of available I/O points is varies and usually can be expanded by buying additional units of fixed I/O. Disadvantage: Lack of flexibility, limited with the quantities and type of packaging. If any part in the unit fails, the whole unit must be replaced.

14. 2) Modular I/O:  It’s divided by compartment into separate modules can be plugged.  Thus, increases the options and the unit’s flexibility. The modules available can be chose from manufacturer and mix them as desired.  It’s consisting of a rack, power supply, processor module (CPU), input/output (I/O modules) and operator interface for programming and monitoring. 2) Modular I/O:  It’s divided by compartment into separate modules can be plugged.  Thus, increases the options and the unit’s flexibility. The modules available can be chose from manufacturer and mix them as desired.  It’s consisting of a rack, power supply, processor module (CPU), input/output (I/O modules) and operator interface for programming and monitoring.

16.  Offer several advantages over a conventional relay:

17. Using the relay method for motor control PLC ladder logic diagram

18. PLCRelay method

19. Some important characteristics distinguish PLCs from general-purpose computers.  Unlike computers, the PLC is designed to operate in the industrial environment with the wide range of ambient temperature and humidity. A well designed PLC is not affected by the electrical noise inherent in most industrial locations.  Hardware and software of PLCs are designed for easy use by plant electricians and technicians. Unlike the computer, the PLC is programmed in relay ladder logic or other easily learned languages. The PLC comes with its program language built into permanent memory, whereas a personal computer requires a disk operating system (DOS). PLC is limited by the language it comes with, unless it is a modular type that enables to plug in a language module.

20.  PCs have large user memory (several megabytes), which enables you to load and use software stored on disk. Any language capabilities can be made via this software. PLCs are not design with this kind of flexibility but are meant to be specialized computers for control, interfacing and control with external devices.  Computers are complex computing machines capable of executing several programs or task simultaneously and in any order. Most PLC executes a single program in an orderly and sequential fashion from first to last instruction.  PLCs have been designed for installation and maintenance by plant electricians who are not required to be highly skilled computer technicians. PLC has been designed for simplified trouble shooting because they include indicators and written fault information. Easily connected and replaced for modular interfaces with the field devices.

21. Major Size Categories Types of PLC The I/O Section

22.  PLCs are divided into three major size categories:  Small: ◦ It covers units up to 128 I/Os and memories up to 2K bytes. It capable of providing simple to advanced levels of machine control.  Medium: ◦ It have up to 2048 I/Os and memories up to 32K bytes. Special I/Os modules make medium PLCs adaptable to temperature, pressure, flow, weight, position and any type of analog function encountered in process control applications.  Large: ◦ The most sophisticated units of PLCs family. They have up to 16,000 I/Os and memories up to 2M bytes. It has almost unlimited applications and can control individual production processes or entire plants.

23.  Single-ended: ◦ It involves one PLC controlling one process. This would be a stand-alone unit and would not be used for communicating with other computers or PLCs.  Multitask: ◦ It usually calls for a medium size PLC and involves one PLC controlling several processes. It can be a subsystem for larger processes and communicating with a central PLC.  Control management: ◦ It involves one PLC controlling several others. It requires a large PLC processor designed to communicate with other PLCs and possibly with a computer. The control management PLC supervises several PLCs by downloading programs that tell the other PLCs what has to be done.

24.  The memory size of PLC ranges from 1K to 2M. The amount of memory required depends on the application.  Factors affecting the memory size are include:  Number of I/O points used  Size of control program  Data-collecting requirements  Future expansion

25.  The input and output interface modules provide the equivalents of eyes, ears and tongue to the brain of PLC/CPU.  The I/O section consists of an I/O rack and individual I/O modules  Input interface modules accept signals from the machine or process devices and convert them into signals that can be used by the controller.  Output interface modules convert controller signals into external signals used to control the machine or process  A slot in the PLC can hold any type of I/O module.

26.  The I/O system provides an interface between the hardwire components in the field and the CPU.  A chassis is a physical hardware assembly that houses devices such as I/O modules, processor modules and power supplies.  Chassis come in different sizes according to the number of slots they contain. In general, they can have 4,8,12, or 16 slots.

27.  There are two type of rack:  1) Logical rack: ◦ It is an addressable unit consisting of 128 input points and 128 output points. ◦ A rack uses 8 words in the input image table and 8 words in the output image table. ◦ An I/O group is a word in the output image tables that corresponding to the word in the input image file. ◦ A rack can contain a maximum of 8 I/O groups, numbered from 0 through 7  There are two type of rack:  1) Logical rack: ◦ It is an addressable unit consisting of 128 input points and 128 output points. ◦ A rack uses 8 words in the input image table and 8 words in the output image table. ◦ An I/O group is a word in the output image tables that corresponding to the word in the input image file. ◦ A rack can contain a maximum of 8 I/O groups, numbered from 0 through 7

28.  There are two type of rack:  2) Remote I/O rack: ◦ One benefit of a PLC system is the ability to locate the I/O modules near the field devices to minimize the amount of wiring required. ◦ It located away from the processor module. To communicate with the processor, the remote rack uses a special communications network. ◦ The remote racks are linked to the local rack through communication module using fibre optic and coaxial cable.  There are two type of rack:  2) Remote I/O rack: ◦ One benefit of a PLC system is the ability to locate the I/O modules near the field devices to minimize the amount of wiring required. ◦ It located away from the processor module. To communicate with the processor, the remote rack uses a special communications network. ◦ The remote racks are linked to the local rack through communication module using fibre optic and coaxial cable.

29.  The location of a module within a rack and the terminal number of a module to which an input or output device is connected will determine the device’s address.  This address is used by the processor to identify where the device is located to monitor or control it.

30.  Basic addressing elements include:  1.Type: ◦ The type determines if an input or output is being address.  2.Slot: ◦ The slot number is the physical location of the I/O module. This maybe a combination of the rack number and the slot number when using expansion racks.  3.Word and Bit: ◦ The word and bit are used to identify the actual terminal connection in a particular I/O module.

31. Ladder Logic and Coil Ladder Diagram Branching Program Scan PLC Programming Language

32.  PLCs are primarily programmed in ladder logic, which is really just a symbolic representation of an electrical circuit whose symbols were chosen to be similar to schematic symbols of electrical devices.  The main function of PLC program is to control outputs based on the condition of inputs.  The symbols used in ladder logic programming can be divided into two broad categories: Contacts (inputs) and Coils (outputs)

33.  Most inputs to a PLC are simple devices that are either on (true) or off (false). These inputs are sensors and switches that detect part presence, empty or full status, and so on.  Contacts can be thought of as switches. The two basic kinds of switches are normally open and normally closed.  A normally open switch does not pass current until it closed.  A normally closed switch allows current flow until it closed.

34.  Coils are output symbols. There are many types of real-world output devices: motors, lights, pumps, counters, timers and relays.  The PLC examines the contacts (inputs) in the ladder and turns the coils (outputs) on or off, depending on the condition of the inputs.

35.  The basic ladder diagram looks similar to a ladder. It has two uprights and the rungs that make up the PLC ladder.  The left and right uprights represent power. If we connect the left and right uprights through a load, power can flow through the rung from the left upright to the right upright.  The PLC then runs the ladder and monitors the input continually and controls output. This called scanning.

36.  The amount of time it takes for the PLC to go through the ladder logic each time is called the scan time.  Scan time varies from PLC to PLC. Even a low PLC scan time is in milliseconds. The longer the ladder logic is, the longer the scan time is. Conceptual view of a PLC system. The real-world inputs are attached to an input module (left side of the figure). Outputs are attached to an output module (right side of the figure). The centre of the figure shows the logic that the CPU must evaluate by looking at the inputs and then turning on outputs based on the logic. In this case, if input 0 (a normally open switch) is closed, output 0 (the doorbell) turns on.

37.  Each time the PLC scans the doorbell ladder, it checks the state of the input switch before it enters the ladder (time 1).  While in the ladder, the PLC then decides whether it needs to change the state of any outputs (evaluation during time 2).  After the PLC finishes evaluating the logic (time 2), it turns on or off any outputs based on the evaluation (time 3).  The PLC then returns to the top of ladder, checks the inputs again, and repeats the entire process. The total of three stages makes up scan time.

38.  Normally Closed Contacts ◦ The normally closed will pass power until it is activated. A normally closed contact in a ladder diagram passes power while the real-world input associated with it is off. ◦ A home security system is an example of the use of normally closed logic. Assume that the security system was intended to monitor the two entrance doors to a house. ◦ One way to wire the house would be to wire one normally open switch from each door to the alarm, just like a doorbell switch. ◦ Then if a door opened, the system closes the switch and sounds the alarm.  Normally Closed Contacts ◦ The normally closed will pass power until it is activated. A normally closed contact in a ladder diagram passes power while the real-world input associated with it is off. ◦ A home security system is an example of the use of normally closed logic. Assume that the security system was intended to monitor the two entrance doors to a house. ◦ One way to wire the house would be to wire one normally open switch from each door to the alarm, just like a doorbell switch. ◦ Then if a door opened, the system closes the switch and sounds the alarm.

39.  Often it is desirable to turn on an output for more than one condition.  For example, in house, the doorbell should sound under two conditions: the front button in pushed or the rear door is pushed. The ladder, called branch  Two paths (or conditions) can turn on the doorbell. (this can also be called a parallel condition or logical OR condition)

40.  Two type of basic scan pattern: ◦ Horizontal scan: Processor examines input and output instructions from the first command, top left in the program, horizontally, rung by rung. ◦ Vertical scan: Processor examines input and output instructions from the top left command entered in the ladder program, vertically, column by column and page by page.

41. Scan process and scan cycle

42. Horizontal and vertical scanning

43.  Refers to the method by which user communicates information to the PLC.  There are three most common languages: ◦ Ladder diagram language: the most common used by PLC language. ◦ Boolean language: The statements refers to the basic AND, OR and NOT logic gate function. ◦ Function chart system: It is a method of programming a control system that uses a more structured approach.

44.  Function chart programming used function blocks (steps and transition units).  It is a pictorial representation or a special type of flow chart of a sequential control process.  Allow the description of the process to become the actual control program and aids in understanding the system and localizing problems.  A block of logic can be programmed as a module and transition logic ensures that only appropriate software modules will operate at any given time.  Function chart programming used function blocks (steps and transition units).  It is a pictorial representation or a special type of flow chart of a sequential control process.  Allow the description of the process to become the actual control program and aids in understanding the system and localizing problems.  A block of logic can be programmed as a module and transition logic ensures that only appropriate software modules will operate at any given time.

45.  Simpler programming, faster scan time, enhanced maintainability and ease of future enhancements.  The overall program may be fairly complex but individually simple, divide the program into several steps or stages instead of creating long ladder program.  Processors understand which parts of the program are active and scan only the active steps, thus reducing scan time.  Reducing interlocks programming time, the processor does not even scan those parts of the program that are inactive, makes control much easier.

47.  The form of programming commonly used with PLCs.  Involves each program task being specified as through a rung of a ladder.  Involves writing a program in a similar manner to drawing a switching circuit. Figure 1: (a), (b) Alternative ways of drawing an electric circuit, (c) comparable rung in a ladder program

48.  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. Figure 2: Ladder program

49.  The sequence followed by a PLC when carrying out a program can be summarized as: ◦ Scan the inputs associated with one rung of the ladder program. ◦ Solve the logic operation involving those input. ◦ Set/reset the outputs for that rung. ◦ Move on to the next rung and repeat operations 1,2,3. ◦ And so on until the end of the program with each rung of the ladder program scanned in turn. The PLC then goes back to the beginning of the program and start again.

50.  Obtained by combinations of switches. ANDOR

51. NORNAND EXCLUSIVE-OR (XOR)

52.  Truth table. InputsABCOutput 0000 0010 0100 0110 1000 1011 1101 1111 OR logic situation

53. Shop open switch Customer approaching sensor Solenoid output Off OnOff OnOff On Shop Door System AND logic situation

54. Example PLC is used to controlling lubricating oil being dispensed from a tank. This is possible by using two sensors, one near the bottom (low level) and one near the top (high level), as shown in the picture below. Both of our inputs will be normally open fiber-optic level sensors. When they are NOT immersed in liquid they will be ON. When they are immersed in liquid they will be OFF.