Full form of PLC is Programmable Logic Controller.The name
itself gives the idea about PLC.PLC is that device which do
work as a computer.Which senses physical parameter,controls
them by using CPU and gives required output at desired
application.
SCR means Silicon Controlled Rectifier.Like diode SCR also
have anode and cathode but also have gate.Basic difference
between SCR and diode is,SCR gives controlled output by
triggering gate pulse but diode gives uncontrolled outpput