PLC Introduction What does PLC stand for n

PLC - Introduction What does PLC stand for? n n PLC - programmable logic controller PLC implements logic control functions by means of a program PLC introduction 1

PLC - Introduction Features PLC introduction 2

PLC - Introduction Features PLC introduction 3

PLC - Introduction An application example 1: Gate Control n n PLC can sense a vehicle at the entrance or exit, and open and close the gate automatically The current vehicle count is easily determined by programming a simple counter PLC introduction 4

PLC - Introduction An application example 2: Conveyor System n n PLC can be used to start/stop latching logic for motor control Counters can be used for monitoring product amounts PLC introduction 5

PLC - Introduction Comparing traditional and programmable control systems - 1 PLC introduction 6

PLC - Introduction Comparing traditional and programmable control systems - 2 n n In traditional control, the switches S 1, S 2 and S 3 must close for K 1 to be turned on - the wiring makes the rule In PLC systems, the program is written to perform the logic “when S 1 is closed AND S 2 is closed AND S 3 is closed, THEN turn on K 1” - the program makes the rule It is much simpler to change program than wiring! PLC introduction 7

PLC - Introduction How does a PLC differ from a computer? n A computer is optimized for calculation and display tasks n A computer is programmed by specialists n A PLC is designed for (logic) control and regulation tasks n A PLC is programmed by non-specialists n A PLC is well adapted to industrial environment PLC introduction 8

PLC - Introduction Why are PLCs so common? n They are cost-effective n They are flexible, reliable and compact n They have significant advantages over traditional control systems based on relay or pneumatics PLC introduction 9

PLC - Introduction Where are PLCs used? n In every industry where automation is involved, from individual machines to whole processes PLC introduction 10

PLC - Introduction What tasks do PLCs perform? n n The logic control tasks such as interlocking, sequencing, timing and counting (previously undertaken with relays or pneumatics) In addition, PLCs can perform a variety of calculation, communication and monitoring tasks PLC introduction 11

PLC - Introduction Communication Ports (RS-485) Outputs & Power Supply Inputs PLC introduction 12

PLC - Introduction Structure of a PLC introduction 13

PLC - Introduction The PLC processor PLC introduction 14

PLC - Introduction PLC Input/Output Devices PLC introduction 15

PLC - Introduction PLC Input Devices n Push buttons n Switches (limit switches, level switches, etc. ) n Sensors n . . . PLC introduction 16

PLC - Introduction PLC Output Devices n Relay contacts n Solenoid valves n Signal devices (such as lamps, alarms, etc. ) n Motors n . . . PLC introduction 17

PLC - Introduction Programming terminal PLC introduction 18

PLC - Introduction n Programming is done through programming terminal n Programming terminal translates engineering language (logic control) to machine language (binary code) PLC introduction 19

PLC - Introduction Programming through standard computer n Most PLC manufacturers offer software packages that allow a standard computer to be used as a programming terminal State diagram PLC introduction 20

PLC - Introduction Programming through standard computer PLC introduction 21

PLC - Introduction Relating the program to inputs and outputs n The CPU reads the data from the inputs n The program in the CPU uses the inputs to evaluate the control logic. As the program runs, the CPU updates the data n The CPU writes the data to the output PLC introduction 22

PLC - Introduction Relating the program to inputs and outputs PLC introduction 23

PLC - Introduction Data Flow in the PLC introduction 24

PLC - Introduction n One of the advantages of PLC is that it can be programmed by non-specialists n Program can be written either in the form of a statement list: a set of mnemonic instructions representing a function of the CPU or a ladder diagram: a graphical language resembling the electrical relay diagrams PLC introduction 25

PLC - Introduction statement list PLC introduction 26

PLC - Introduction Ladder diagram PLC introduction 27

Example Pump 28

SLLD PLC diagram or code Pump-valve-tank system X 1: pump; X 2: valve 29