What's the difference between PLC and SCADA?

simply, plc is a programable logic control uses to control the devices such as motors and sensors but scada is a super visor control and data acqustion uses to monitor and control the devices.

PLC - Programmable logic controller. Its a hardware, which is directly in contact with field instruments. it works according to the logic stored in PLC Memory.

SCADA - Supervisory control and data acquisition. Its a software, which shows the output and feedback in Visual manner, that PLC can't do.

well not a very much compareble ideas...better to say like what is difference between RTU and PLC or SCADA system and DCS system.
In general PLC is used more for DCS system and industrial automation system (process control,...) while RTU/SCADA is majorly for remote supervison and control and lees porcess control and automation is expected from this system,

 plc is a programable logic control uses to control the devices  at local area  scada is a super visor control and data acqustion uses to monitor and control the devicesand scada is  used for big area if we can say that plc is the2 th layer of control scada become the next layer after plc

PLC is a Programmable Logic Controller. A programmer written program as per client requirement, which relates to inputs / outputs of PLC. Outputs can activate the field equipment(Motor, Solenoid valve etc.)  and Inputs can sense field equipment ( Limit Switch, Zero Speed Sensor etc.).

SCADA is Supervisory control and data acquisition. A programmer design the animation as per  PLC programming and field equipment position, then make communication between SCADA and PLC. After  successful communication between SCADA and PLC we Can Visualize the operation which is happen in field from Control Room.

plc is used for control on the plant and machine and scada is for monitor and supvising the plant with computer sytem you can use data base and preview historyical data and events plc is apart of scada system

PLC: PLC is a Micro Processor based Electronic Device which is used to control certain process according to predefined programs which are saved in the PLC.
These programs can be change or modified as per the requirement.
SCADA: as its name Implies Supervisory Control and Data acquisition, is used for monitoring and controlling of Processes which displayed graphically.
Through SCADA we can do just small changes during the execution of process ( e.g, we can change only value of variables).
Also it gives feature like storing, and can communicate to other servers.
Here programming is done in Scripting language.

PLC is primarily a Rugged Industrial Computer with Inputs/Outputs for interfacing with field instruments and final control elements.
SCADA is primarily a software that runs in a PC for collecting,logging,displaying,animating of data from PLC

PLC is a programmable Logic controller which is used mainly for interlocking different equipments

SCADA(supervisory control and data acquisition system. It consists of many remote terminals units for collection of data (field),that is being connected with master station through any communication system, having main task of collection of accurate data and controlling of process for smooth operation.

PLC- programmable logic conroller which uses for control the devices on plant, scada- supervisory control and data acquisition it uses for monitoring the plant process and control through PLC.
 

PLC: It is a mini Computer, it should be instructed what to perform.
The PLC knows through a program (which is coded in it) what it has to do.
Actually the PLC is a microprocessor based device.
It has same internal structure to many embedded controllers and computers.
It consists of CPU, Memory and I/O devices.
The main differences between PLCs and other microprocessor based devices are that PLC are rugged design for an industrial setting and are modular allowing easy replacement and addition of units.PLC can be used in any application which needs some sort of electrical control.
SCADA: SCADA (Supervisory Control And Data Acquisition) system for getting remote access to our control system.
DCS( Distributed Control Systems) are properly functional just in a confined area like a building or complex where communication is carried out through local area network(LAN).
So due to these limitations of DCS systems, the SCADA systems are very useful and innovative.
SCADA system consists of one central terminal unit or master terminal unit (MTU) which may be far away from the site and one or more remote sensor terminals or remote terminal units (RTU).
These RTUs send data to the MTU which analyzes and manages this data.
It's types are i) D+R+N (Development + Run + Networking).
ii) R+N (Run + Networking).
iii) Factory Focus.