Micro computer based process control Programmable logic controller

CONTROL EQUIPMENT-Principles Relay based system speed or resistance to electrical noise DIGITAL LOGIC based Computer based complex functions PLC based

DIFFERENCE BETWEEN VARIOUS CONTROL EQUIPMENT Operating speed Physical size Capacity for complicated operations Ease of changing configuration Electrical noise immunity Installation Ease of maintenance Price for function

PLC-history`` 1970-Electro mechanical relays 1968-PLC-General motors company 1977-Microprocessor based plc ALLEN BARDLEY –USA 8080Micro processor 256 Bytes to Mega bytes PID Feed forward etc

Advantages

PLC selection

PLC architecture Selectorswitch proximity, timer contact Pilot light,horn, timer

Architecture details Power supply I/O systems Real time CPU Memory unit Programmer unit Peripheral devices-

Power supply I/O Devices- Bcd,thumblRTD, TC,Flowmeters,strain gauges,pushbuttons,limit switch,electromechanical relay,registers,bcd,thumbwheel etc Output-pilot lights,solenoidvalves,annunciatorwindows,displays,

Programmer units:handheldunits,standalone crt units,pcs, Peripheral devices:pc compatible software Colur graphics,crt,

Basic structure

Plc programming Ladder diagrams:

Ladder translation of plc programming

6 rung Ldder diagram