Chapter 2 – PLC Hardware Components 1/18/2019

Recap Programmable logic controllers (PLCs) are specialized industrial computers. It is used to execute specific functions such as sequence control, on/off control, arithmatic operations, and other functions. PLCs were originally made to replace hard-wired relay control systems. Advantages of using PLCs: Eliminates the hard wiring More reliability Lower cost Flexibility Communication capability Easy troubleshooting Faster response time 1/18/2019

PLC Architecture & Components (1) The central Processing Unit contains the microprocessor and the memory Central Processing Unit (CPU) Input/Output Memory Microrpocessor Question: What microprocessors are usually used by Siemens PLCs? Siemens PLCs usually use Intel mircoprocessors Question: What microprocessors are usually used by Allen Bradley PLCs? Allen Bradley PLCs usually use Motorolla mircoprocessors 1/18/2019

The I/O Section The section to which all field devices are connected and provides the interface between them and the CPU. 1/18/2019

The I/O Section The hardware assembly that houses I/O modules, processor modules, and power supplies is referred to as the chassis. A logical rack is an addressable unit consisting of 128 input points and 128 output points. 1/18/2019

The I/O Section Addressing 1/18/2019

The I/O Section Addressing 1/18/2019

Addressing The I/O Section The smallest unit is the bit 1 byte = 8 bits 1 word = 2 bytes 1 Double Word = 4 bytes = 32 bits 1/18/2019

Addressing The I/O Section Type – Input/Output Slot – Physical location of I/O Module Word and Bit – Identifies the terminal connection EX: I0.5 1/18/2019

Inputs : The I/O Section Limit Switch Reed Sensors Pushbuttons Ultrasonic sensors 1/18/2019

Outputs : The I/O Section Motor Starter Relay Signal Column Cylinder 1/18/2019

Types of Memory RAM: Random Access Memory. Fastest but volatile ROM: Read Only Memory PROM: Programmable ROM, this memory is non erasable once porgrammed. EPROM: Erasable PROM, this memory is erasable using a strong UV radiation dose. EEPROM: Electrically Erasable PROM, can be erased while in the circuit. Flash memory: non-volatile high capacity memory Note: Other forms of memory storage include Non-stationary (rotating) disks such as Hard Disk Drive, Floppy Disk, and Compact Disk (CD). These forms are normally not used in PLC systems. 1/18/2019

Memory Usage Load Memory: A flash type of memory, this part of memory contains the user program and the hardware configuration. In Siemens PLCs built after 2002, this memory is implemented in the memory card. Work Memory: A Random Access Memory (RAM) that is used to temporarily store portions of the program code to execute them. After that portion of the program code is executed, it is erased from the work memory System Memory: A Random Access Memory (RAM) that is used to store variables when running and executing the program such as variables of timers, counters, memory bits,..etc. 1/18/2019

Human Machine Interface (HMI) connected to communicate with a PLC and to replace pushbuttons, selector switches, pilot lights, thumbwheels, and other operator control panel devices 1/18/2019

PLC Architecture & Components (2) Siemens PLCs have all or some of the following components: Power Supply Central Processing Unit: contains the following - Microprocessor - EEPROM/ RAM memory storage - MicroSD card Slot (after 2002 - Lithium battery (in models before 2002) - MPI connection: for MPI interface - DP connection: for Profibus interface (Not always provided) - Ethernet connection : for Profinet connection (not in S300) - Status indicators: SF, Run, Stop, … - Mode selector: Stop, Run, MRES Input/Output Modules: can be fixed (such as on the S314 stations) or mudular (such as in the S315 station in the lab). Other modules: such as the interface and communication modules 1/18/2019

Real Time Definition: A system operates in real time when it reacts to an event that occurs on the field within a time constraint. Examples: 1. The airbag system: must respond to a collision in real time so that airbags are deployed in the right time. 2. Real-Time surveillance and tracking in UAVs (Drones): cameras are connected to a network (“online“) for processing to respond to events that take place. 3. Non-real time ( “offline“) surveillance of the Sonar underwater drones: sonar scans are recorded to be processed after submarine emerges from water. 1/18/2019

a) It responds before the time it is supposed to Example: A mechatronic system does not respond in Real Time, what could be a possible discription of this system? a) It responds before the time it is supposed to b) It responds in a time after it is supposed to c) It records data to be processed later by another system component. d) All of the above are possible 1/18/2019

Background Why binary? Easier to have 2 states On or OFF, thence simpler electronics The smallest unit is the bit 1 byte = 8 bits 1 word = 2 bytes 1 Double Word = 4 bytes = 32 bits 1/18/2019

Review: Decimal Vs. Binary How many bytes are there in 1 KByte? Solution: 1KB = 210 Bytes = 1024 Bytes Decimal Binary 1 kilo = 1000 1 Kilo = 210=1024 1 mega = 1000,000 1 Mega = 220=1,048,576 How many bits are there in 2 KBytes? Solution: 2×1024×8 = 16,384 bits 1/18/2019

Decimal and Binary numbers Decimal numbers have a base of 10 Binary numbers have a base of 2 Decimal Binary Base 10 0, 1, 2, 3, 4…. 8, 9 2 0, 1 kilo 103 = 1000 Use small “k” 210 = 1024 Use capital “K” Mega 106 = 1000,000 220 = 1,048,576 Gega 109 = 1000,000,000 230 1/18/2019

Decimal and Binary Numbers Example 1: Fill in the blank: 1 µm = ______ meter 1 Kg = _______ grams 6 MHz = __________Hz 6 MB = __________ Bytes 1 Nibble = ______ bits 1 Byte = _______ bits 1 word = ________ bytes = ______ bits 10 -6 1000 6,000, 000 6,291,456 4 8 2 16 1/18/2019

Example 2: How many bytes are there in 16 KB? 16 KB = 16 * 1024 = 16,384 Bytes How many bytes are there in 1 MB? 1 MB = 220 = 1,048,576 How many bits are there in 24 KB? number of bytes = 24 * 1024 = 24,576 but there are 8 bits in a byte thus, number of bits = 24,576 * 8 = 196,608 bits 1/18/2019

Introduction to computer programming Compiler Assembler 4th generation 3rd generation LabView, SPSS, Simulink 2nd generation C++, C, Java, Visual basic Ladder Logic, Matlab, Basic, Pascal,..etc 1st generation Assembly Language Machine Code Punch cards 1/18/2019

What type of memory is volatile and therefore only used of storing variables? Only one answer ROM FLASH RAM EPROM PROM 1/18/2019