Programming of PLC PDF

Basuwaqi, A. M 1 PROGRAMMING OF PLC Types of PLC Programming Language a. Structured text programming (ST) - A high level language that has some similarities to Pascal. Statements can be used to assign values to variables. b. Logic diagram (LD) – A graphical language, and most widely used....

Basuwaqi, A. M 1 PROGRAMMING OF PLC Types of PLC Programming Language a. Structured text programming (ST) - A high level language that has some similarities to Pascal. Statements can be used to assign values to variables. b. Logic diagram (LD) – A graphical language, and most widely used. Use Boolean mnemonics to represent the process, before converting into logic diagram. c. Functional Block Diagram Programming (FBD) – A graphical language. Used in applications involving the flow of signals between control blocks. d. Instruction List (IL) - A low level programming language, much like assembly language programming. e. Sequential Function Chart (SFC) - A graphical programming method. Very useful for describing sequential type processes. Basuwaqi, A. M 2 PROGRAMMING OF PLC Instruction lists (IL) A programming method, which can be considered to be the entering of a ladder program using text, is instruction lists (IL). Instruction list gives programs which consist of a series of instructions. Each instruction being on a new line. An instruction consists of an operator followed by one of more operands. Mnemonic codes are used, each code corresponding to an operator/ladder element. The codes used differ to some extent from manufacturer to manufacturer Basuwaqi, A. M 3 PROGRAMMING OF PLC IL Language Instruction code mnemonics Basuwaqi, A. M 4 PROGRAMMING OF PLC Instruction lists (IL) Consider the following example instructions Operands Comments Basuwaqi, A. M 5 PROGRAMMING OF PLC Instruction lists (IL) with there being the instruction earlier in the program to jump to PUMP_OK if a particular condition is realized. an N after it is used to negate its value. Thus the ANDN operator inverts the value of ladder contacts and ANDs the result Basuwaqi, A. M 6 PROGRAMMING OF PLC Ladder programs and instruction lists 1. whenever a rung is started, it must use a ‘start a rung code’. This might be LD, or perhaps A or L, to indicate the rung is starting with open contacts. 2. LDI, or perhaps LDN or LD NOT or AN or LN, to indicate it is starting with closed contacts. 3. All rungs must end with an output or store result code. This might be OUT or = or ST Basuwaqi, A. M 7 PROGRAMMING OF PLC Ladder programs and instruction lists MITSUBISHI SIEMENS Basuwaqi, A. M 8 PROGRAMMING OF PLC Ladder programs and instruction lists Basuwaqi, A. M 9 PROGRAMMING OF PLC Ladder programs and instruction lists Basuwaqi, A. M 10 PROGRAMMING OF PLC Ladder programs and instruction lists Basuwaqi, A. M 11 PROGRAMMING OF PLC Ladder programs and instruction lists Branch codes ORB (OR branches/blocks together) Basuwaqi, A. M 12 PROGRAMMING OF PLC Ladder programs and instruction lists Basuwaqi, A. M 13 PROGRAMMING OF PLC Ladder programs and instruction lists More than one rung Basuwaqi, A. M 14 PROGRAMMING OF PLC Ladder programs and instruction lists Example 1: A B C Basuwaqi, A. M 15 PROGRAMMING OF PLC Ladder programs and instruction lists Answer Example1 A B C Basuwaqi, A. M 16 PROGRAMMING OF PLC Sequential function charts (SFC) The term sequential function chart (SFC) is used for a pictorial representation of a system’s operation to show the sequence of the events involved in its operation SFC charts have the following elements Basuwaqi, A. M 17 PROGRAMMING OF PLC Sequential function charts (SFC) Part of an SFC and its equivalent ladder program Basuwaqi, A. M 18 PROGRAMMING OF PLC Structured text Structured text is a programming language that strongly resembles the programming language PASCAL. Programs are written as a series of statements separated by semicolons (;). Assignment statements are used to indicate how the value of a variable it to be changed, Light := SwitchA; Consider: Basuwaqi, A. M 19 PROGRAMMING OF PLC Structured text Conditional statements IF... THEN... ELSE is used when selected statements are to be executed when certain conditions occur. For example: Basuwaqi, A. M 20 PROGRAMMING OF PLC Structured text Examples: Programs have first to define the data types required to represent data Basuwaqi, A. M 21 PROGRAMMING OF PLC Structured text signals from sensors and output signals to be used in a program, Basuwaqi, A. M 22 PLC WIRING DIAGRAMS Electromagnetic Control Relays The PLC’s original purpose was the replacement of electromagnetic relays with a solid-state switching system that could be programmed. The programmable controller is designed to replace the physically small control relays that make logic decisions but are not designed to handle heavy current or high voltage. Basuwaqi, A. M 23 PLC WIRING DIAGRAMS Electromagnetic Control Relays Operation Basuwaqi, A. M 24 PLC WIRING DIAGRAMS Contactors A contactor is a special type of relay designed to handle heavy power loads that are beyond the capability of control relays. Unlike relays, contactors are designed to make and break higher powered circuits without being damaged. Three-pole magnetic contactor Basuwaqi, A. M 25 PLC WIRING DIAGRAMS Contactors PLC used in conjunction with a contactor to switch power on and off to a pump Contactor used in conjunction with a PLC output Basuwaqi, A. M 26 PLC WIRING DIAGRAMS Motor Starters A motor starter is designed to provide power to motors. The motor starter is made up of a contactor with an overload relay attached physically and electrically to it. Overload relays are designed to meet the special protective needs of motor control circuits. They allow harmless temporary overloads that occur when a motor starts. The overload relay will trip and disconnect power to the motor if an overload condition persists. Overload relays can be reset after the overload condition has been corrected Basuwaqi, A. M 27 PLC WIRING DIAGRAMS Motor Starters Three-phase magnetic motor starter Basuwaqi, A. M 28 PLC WIRING DIAGRAMS Motor Starters PLC control of a motor Basuwaqi, A. M 29 PLC WIRING DIAGRAMS Manually Operated Switches Manually operated switches are controlled by hand. These include toggle switches, pushbutton switches, knife switches, and selector switches. Pushbutton switches are the most common form of manual control Commonly used types of pushbutton switches Basuwaqi, A. M 30 PLC WIRING DIAGRAMS Manually Operated Switches Three-position selector switch Dual in-line package (DIP) switches Basuwaqi, A. M 31 PLC WIRING DIAGRAMS Mechanically Operated Switches A mechanically operated switch is controlled automatically by factors such as pressure, position, or temperature Mechanically operated limit switch Basuwaqi, A. M 32 PLC WIRING DIAGRAMS Mechanically Operated Switches Temperature switch Basuwaqi, A. M Pressure switch 33 PLC WIRING DIAGRAMS Sensors Sensors are used for detecting, and often measuring, the magnitude of something. They convert mechanical, magnetic, thermal, optical, and chemical variations into electric voltages and currents Proximity sensor: that detect the presence of an object (usually called the target) without physical contact Basuwaqi, A. M 34 PLC WIRING DIAGRAMS Sensors Capacitive proximity sensors Basuwaqi, A. M 35 PLC WIRING DIAGRAMS Sensors: Light Sensors Through-beam scan Basuwaqi, A. M 36 PLC WIRING DIAGRAMS Sensors: Ultrasonic Sensors An ultrasonic sensor operates by sending high-frequency sound waves toward the target and measuring the time it takes for the pulses to bounce back Basuwaqi, A. M 37 PLC WIRING DIAGRAMS Output Device Control Solenoid Basuwaqi, A. M 38 Basuwaqi, A. M 39