Programmable Logic Controllers ( Definition according to NEMA standard ICS3-1978) 4/19/2017 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. 19-Apr-17

INTRODUCTION TO PLCS Advantages of PLCs Less wiring. 4/19/2017 INTRODUCTION TO PLCS Advantages of PLCs Less wiring. Wiring between devices and relay contacts are done in the PLC program. Easier and faster to make changes. Trouble shooting aids make programming easier and reduce downtime. Reliable components make these likely to operate for years before failure. 19-Apr-17 2

Solenoids, contactors, alarms Major Components of a Common PLC POWER SUPPLY I M N O P D U U T L E O M U O T D P U U L T E PROCESSOR From SENSORS Pushbuttons, contacts, limit switches, etc. To OUTPUT Solenoids, contactors, alarms etc. PROGRAMMING DEVICE 19-Apr-17

The Microprocessor or CPU Module Is the brain of a PLC system. It consists of the microprocessor, memory integrated circuits, and circuits necessary to store and retrieve information from memory. It also includes communications ports to other peripherals, other PLC's or programming terminals. Today's processors vary widely in their capabilities to control real world devices. Some control as few as 6 inputs and outputs (I/O) and others 40,000 or more. One processor can control more than one process or manufacturing line. Processors are often linked together in order to provided continuity throughout the process. The number of inputs and outputs PLCs can control are limited by the overall capacity of the PLC system hardware and memory capabilities. The job of the processor is to monitor status or state of input devices, scan and solve the logic of a user program, and control on or off state of output devices. 19-Apr-17

In this type of memory, information can be read, but not changed. RAM Random Access Memory is a volatile memory that would lose it's information if power were removed. This is why some processor units incorporate a battery back up. The type of RAM normally used is CMOS or Complementary Metal Oxide Semiconductor. CMOS RAM is used for storage of the user's program (ladder logic diagrams) and storage memory. ROM or Read Only Memory is a non-volatile type of memory. This means you don't need an external power source to keep information. In this type of memory, information can be read, but not changed. For this reason the manufacture sometimes calls this firmware. It is placed there for the internal use and operation of processor units. EEPROM or Electrically Erasable Programmable Read Only Memory Is usually an add-on memory module that is used to back up the main program in CMOS RAM of the processor. In many cases, the processor can be programmed to load the EEPROM's program to RAM if RAM is lost or corrupted. 19-Apr-17

Input Module There are many types of input modules to choose from. 4/19/2017 There are many types of input modules to choose from. The type of input module used is dependent upon what real world input to the PLC is desired. Some examples of inputs are limit switches, electric eyes, and pushbuttons. DC inputs, such as thumbwheel switches, can be used to enter integer values to be manipulated by the PLC. DC input cards are used for this application. Since most industrial power systems are inherently noisy, electrical isolation is provided between the input and the processor. Electromagnetic interference (EMI) and Radio Frequency Interference (RFI) can cause severe problems in most solid state control systems. The component used most often to provide electrical isolation within I/O cards is called an optical isolator or Opto-coupler. The wiring of an input is not complex. The object is to get a voltage at a particular point on the card. Typically there are 8 to 32 input points on any one input module. Each point will be assigned a unique address by the processor. Analog input modules are special input cards that use analog to digital conversion (A to D) to sense variables such as temperature, speed, pressure, and position. The external device normally is connected to a controller (transducer) producing an electrical signal the analog input card can interpret. This signal is usually (4 to 20) mA or a (0 to 10) volt signal. 19-Apr-17

Output Module Output modules: can be used for ac or dc devices such as solenoids, relays, contractors, pilot lamps, and LED readouts. Output cards usually have from 6 to 32 output points on a single module. The output device within the card provides the connection from the user power supply to the load. Usually silicon controlled rectifiers (SCR), triac, or dry contact relays are use for this purpose. Individual outputs are rated most often at 2 to 3 Amperes. Output cards, like input cards have electrical isolation between the load being connected and the PLC. Analog output cards are a special type of output modules that use digital to analog conversion (D to A). The analog output module can take a value stored in a 12 bit file and convert it to an analog signal. Normally this signal is (0 -10) volts dc or (4 to 20) m A. This analog signal is often used in equipment such as motor operated valves and pneumatic position control devices. 19-Apr-17

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NAND Gate 19-Apr-17

In the rung above, it can be seen that if input A is be true (1), NOT OPERATION C A Rung In the rung above, it can be seen that if input A is be true (1), then the output C is true (0) or when A is (0), output C is 1. 19-Apr-17 13

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These are the physical connections from the real world to the PLC. INPUTS These are the physical connections from the real world to the PLC. They can be limit switches, push buttons, sensors, anything that can "switch" a signal on or off. The voltage of these devices are usually, but not always,  24 Volt DC. PLC Manufacturers make inputs that can accept a wide range of voltages both ac and dc. It should be remembered that an input will be ON, "status 1", when the voltage is present at the input connection and OFF, "status 0", when the voltage is no longer present at the input connection. 19-Apr-17

OUTPUTS These are the connections from the PLC to the real world. They are used to switch solenoids, lamps, contactors, etc. ON and OFF. Again they are usually 24 Volt DC, either relay or transistor, but can also be 115/220 Volt AC. 19-Apr-17

I/O Module The I/O interface section of a PLC connects it to external field devices. The main purpose of the I/O interface is to condition the various signals received from or sent to the external input and output devices. Input modules converts signals from discrete or analog input devices to logic levels acceptable to PLC’s processor. Output modules converts signal from the processor to levels capable of driving the connected discrete or analog output devices. 19-Apr-17 18

Common Industrial Hardware Representing the Binary Concept 19-Apr-17

I/O Module DC INPUT MODULE IS NEEDED TO: OPTO- ISOLATOR IS NEEDED TO: Prevent voltage transients from damaging the processor. Helps reduce the effects of electrical noise Current Limiting Resistor FROM INPUT DEVICE USE TO DROP THE VOLTAGE TO LOGIC LEVEL Buffer, Filter, hysteresis Circuits TO PROCESSOR 19-Apr-17 20

I/O Module AC INPUT MODULE IS NEEDED TO: OPTO- ISOLATOR IS NEEDED TO: Prevent voltage transients from damaging the processor. Helps reduce the effects of electrical noise Rectifier, Resistor Network FROM INPUT DEVICE CONVERTS THE AC INPUT TO DC AND DROPS THE VOLTAGE TO LOGIC LEVEL Buffer, Filter, Hysteresis Circuits TO PROCESSOR 19-Apr-17 21

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OUTPUTS INPUTS MOTOR CONTACTOR LAMP PUSHBUTTONS PLC 19-Apr-17 24

Allen-Bradley 1746-1A16 I= Input L2 L1 I:2 LADDER PROGRAM INPUT MODULE slot # in rack I:2 P. B SWITCH Module Terminal # Address I:2.0/0 LADDER PROGRAM INPUT MODULE WIRING DIAGRAM 19-Apr-17 25

Discrete Input A discrete input also referred as digital input is an input that is either ON or OFF are connected to the PLC digital input. In the ON condition it is referred to as logic 1 or a logic high and in the OFF condition maybe referred to as logic o or logic low. Normally Open Pushbutton Normally Closed Pushbutton Normally Open switch Normally Closed switch Normally Open contact Normally closed contact 19-Apr-17 26

An analog output is an output signal that has a continuous signal. Typical outputs may vary from 0 to 20mA, 4 to 20mA or 0 to10V. Electric to pneumatic transducer OUT E Supply air PLC Analog Output Module 0 to 10V P Pneumatic control valve 19-Apr-17 27

PLC Operation Basic Function of a Typical PLC Read all field input devices via the input interfaces, execute the user program stored in application memory, then, based on whatever control scheme has been programmed by the user, turn the field output devices on or off, or perform whatever control is necessary for the process application. This process of sequentially reading the inputs, executing the program in memory, and updating the outputs is known as scanning. 19-Apr-17 28

While the PLC is running, the scanning process includes the following four phases, which are repeated continuously as individual cycles of operation: PHASE 1 Read Inputs Scan PHASE 2 Program Execution PHASE 3 Diagnostics/ Comm PHASE 4 Output Scan 19-Apr-17 29

PHASE 1 – Input Status scan A PLC scan cycle begins with the CPU reading the status of its inputs. PHASE 2– Logic Solve/Program Execution The application program is executed using the status of the inputs PHASE 3– Logic Solve/Program Execution Once the program is executed, the CPU performs diagnostics and communication tasks 19-Apr-17 30

PHASE 4 - Output Status Scan An output status scan is then performed, whereby the stored output values are sent to actuators and other field output devices. The cycle ends by updating the outputs. 19-Apr-17 31

Selecting a PLC Criteria • Number of logical inputs and outputs. • Memory • Number of special I/O modules • Scan Time • Communications • Software 19-Apr-17

A Detailed Design Process 1. Understand the process 2. Hardware/software selection 3. Develop ladder logic 4. Determine scan times and memory requirements 19-Apr-17

Specifications OUTPUT-PORT POWER RATINGS Each output port should be capable of supplying sufficient voltage and current to drive the output peripheral connected to it. SCAN TIME This is the speed at which the controller executes the relay-ladder logic program. This variable is usually specified as the scan time per 1000 logic nodes and typically ranges from 1 to 200 milliseconds. 19-Apr-17 34

PLC Status Indicators Power On Run Mode Programming Mode Fault 4/19/2017 PLC Status Indicators Power On Run Mode Programming Mode Fault 19-Apr-17

Examples of PLC Programming Software: 1. Allen-Bradley – Rockwell Software RSLogix500 2. Modicon - Modsoft 3. Omron - Syswin 4. GE-Fanuc Series 6 – LogicMaster6 5. Square D- PowerLogic 6. Texas Instruments – Simatic 6. Telemecanique – Modicon TSX Micro 19-Apr-17

A special computer for logic controls using ladder logic programming. What is a PLC? A special computer for logic controls using ladder logic programming. 19-Apr-17

PLC a Real World Relay Replacement Real world Parts: Switch Bell Relay Switch controlling AC circuit or bell Relay 19-Apr-17

Example of a Motor Control START STOP EQUIVALENT DIAGRAMS output START STOP output Normally Open Contact Normally Closed Contact 19-Apr-17

How to program PLCs? Using a specialized Ladder Logic Software Allen-Bradley uses RsLogix 500 software to program SLC, Micrologix and so on Omron uses Cx Programmer software for its SYSMAC PLCs Other manufacturers has their own software 19-Apr-17

Ladder Logic Ladder logic is a method of drawing electrical logic schematics A graphical language popular for PLCs Controllers Invented to describe logic made from relays Language resemble ladders, with two vertical "rails" and a series of horizontal "rungs" between them Rule-based language, rather than a procedural language Executed sequentially by software, in a loop 19-Apr-17

Examples Relay Logic Ladder Logic 19-Apr-17

Binary Data Representation We communicate to others using groups of letters arranged into words. The PLC uses groups of bits called words. Different bit patterns represent different information. 19-Apr-17

PLC Words One measure of a computer’s capabilities is the length of the data words on which it can operate. Current PLCs use 16-bit words. Newer PLCs use 32-bit words. SLC 500 family PLCs are 16-bit computers. 19-Apr-17

Information Represented as Combinations of Bits 19-Apr-17

Parts of a 16-Bit Word 19-Apr-17

Bytes, Nibbles, and Bits 19-Apr-17

16-Point Module’s I/O Points Represented in a Word 19-Apr-17

Physical Input Conditions and the Corresponding Input Data Word 19-Apr-17

8-Point Input Module Represented in a Word 19-Apr-17

24-Point I/O Module Represented in Two Words 19-Apr-17

Two Words Representing Inputs for a 32-Bit Module 19-Apr-17

Data Table Format Words are 16 bits. First word or bit is always 0. Bits 0 through bit 15 First word or bit is always 0. SLC 500 data tables can contain up to 256 words (0 to 255). 19-Apr-17

Words Arranged in a Data Table 19-Apr-17

Input Data File (1 of 2) Each input screw terminal has one memory location to store on or off status. Input data is stored in the input data file. Also called the input status file Input status file holds input status information, which is used to solve ladder program. 19-Apr-17

Input Data File (2 of 2) Identified as an I-type data file Only one input status file allowed per project Only has words created for actual modules in system 19-Apr-17

Output Data File (1 of 3) Each output screw terminal has one memory location to store on or off status. Output data is stored in the output data file, also called the output status file. 19-Apr-17

Output Data File (2 of 3) Output status file holds output status information to update outputs Is the result of solving the ladder program. Output data sent to modules during output update portion of scan 19-Apr-17

Output Data File (3 of 3) Identified as an O-type data file Only one output status file allowed per project Only has words created for actual modules in system 19-Apr-17