What is a difference of scad and plc system?

PLC means Programmable Logic Controller. It is a hardware which is used to reduce the manual power. A solid state device that controls output devices based on input states and a user developed program.

SCADA  means Supervisiory Control And Data Acquistion

Supervisory - Monitoring the process

Control- Controlling the process output . To change the set value, but cnt change the process.

Data Acquisition - Collection of data from the field