This is a basic question fresh automation personnel, who first introduced to PLC may ask about.
The important difference between PLC & PC is the environment they deal with. The PLC had to deal with hard environmental conditions while PC don’t need.
· PLCs are designed to operate under a wide range of ambient temperature, vibration and humidity conditions in an industrial environment. The electrical noise in the industrial environment does not work.
· In computers, the inputs are floppy drives and CD Roms and the output is a printer, but in PLC the inputs are signals from control elements such as push-buttons, limit switches, temperature switches, pressure switches and transducer etc. installed on the machines to be controlled. The output also includes final control elements such as contractors, solenoids, valves for positioning, indication lights, etc.
· The PLC includes ROM memory operating systems and application programs. The operating system, as it is already in ROM, does not have to load an application program. Differentiating between PLCs, ‘ BIOS, ‘ OS, and application program is difficult.
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Programming language: PLC is not programmed in one of the high language used for
programming a computer.
Since PLC is designed for plant engineers and maintenance personnel with limited computer knowledge, it is designed for programming using RELAY LADDER LOGIC
There are some PLCs that can be programmed using FORTRAN and BASIC, but the most popular is relay ladder programming. Some PLCs are also programmed using the languages Boolean Algebra, Statement Lists and Control System Flow Chart.
· The PLC is not a PC-like disk based system. There is a continuous check of what to do next with a disk-based system. There is no consultation with a PLC inherent in the answer of what to do next. The PLC program is stored in RAM or EPROM supported by the battery.
· Another major difference is that in most PLCs troubleshooting is simplified because it includes fault indicators, blown-fuse indicators, input and output status indicators and written error information that can be displayed on the programmer.