What is the difference between PLC and embedded systems?

An embedded system is typically made to do one set of task or similar sets of tasks. An internet router uses an embedded system and so does an MP3 player. There are usually some options as to how the task are carried out, such as choosing to set a passWord for your router or choose a song on the MP3 player.

PLC's on the other hand, operate using IF-THEN instructions. If the water gets too high, THEN open the valve to release some. IF the water gets too low, THEN turn on the pump. A PLC can be used to operate a whole process, like brewing beer or refining fuel. Most PLC's connect to many different types of sensors for inputs. Some examples of these sensors are: flow, pressure, temperature, and level, but there are many more. Outputs usually are connected to relays to control power to electrical devices that require more current than the PLC can put out.

A PLC may also interface with an embedded system. There are some cases where either will do. One commonly used appliance that would work with either is an automatic coffee maker. Also, clothes washing machines used to use simple PLC's while many of the new ones use embedded systems.