The architecture of a PLC is basically the same as that of a personal computer. A personal computer (PC) can be made to operate as a programmable logic controller if you provide some way for the computer to receive information from devices such as pushbuttons or switches. You also need a program to process the inputs and decide the means of turning load devices off and on.
However, PLC is a specially designed computer to operate in an industrial environment, which can operate in wide range of temperature and humidity.
The main difference between computer and PLC are list below on two sections hardware and software.
The PLC comes with its program language built into its memory and has no the permanently attached keyboard CD drive or monitor. While computers are permanently attached to a keyboard and other hardware.
Computers are complex computing machines capable of executing several programs or tasks simultaneously and in any order. Most PLCs, on the other hand, execute a single program in an orderly and sequential fashion from first to last instruction.
PLCs come equipped with terminals for input and output field devices as well as communication ports. PCs have only limited ports and terminals.
PLC control systems have been designed to be easily installed and maintained. Troubleshooting is simplified by the use of fault indicators and messages displayed on the programmer screen.
Input/output modules for connecting the field devices are easily connected and replaced.
PLC software that allows the user to only program and document gives the user the tools to write a PLC program. While a PC has much more options in adding programs.
The PLC support different programming languages such as:
Sequential function chart
Function block diagram
PLC software that allows the user to monitor and control the process is also called a human machine interface (HMI). It enables the user to view a process—or a graphical representation of a process—on a monitor, determine how the system is running, trend values, and receive alarm condition.
Programmable automation controllers (PAC) combine PLC ruggedness with PC functionality. Using PACs, you can build advanced systems incorporating software capabilities such as advanced control, communication, data logging, and signal processing with rugged hardware performing logic, motion, process control, and vision.