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Explain how a Programmable Logic Controller (PLC) is different from an ordinary personal computer. Also write the advantages and disadvantages of PLC.

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1 It has embedded processor with limited computing power
It has a CPU with high computing power 
2 Design of PLC is for reliable operation in industrial environment with nois
Design of PC is suitable for indoor or office use or mid range industrial environment
3 Start up time is negligible
Longer startup time
4 PLC has high reliability
PC is less reliable as comp to PLC
5 Software of PLC is mainly for real time 
Software of PC is designed for information processing
6 PLCs are available in compact sizes
Size of PLC is larger than PLC
7 Modularity is design of PLC makes it very
Addition of I/O module to PC is hardware dependent and


1) Flexibility. 

2) Implementing changes & correcting errors. 

3) Speed of operation. 

4) Reliability & maintainability. 

5) PLCS are smaller in size & can operate Number of devices at a time. 

6) Logic change can be very easily done by just adjusting the ladder logic. 

7) Operation of PLC can be displayed on CRT or LCD screen. 

8) Error occurred in operation can be very easily observed. 

9) PLC can keep records of status of Input & Output signals.

10) PLC can provide security for ladder programming. 


1) PLC code is not portable. 

2) Cost of PLCs with analog I/O is very high as comp to digital i/o PLC 

3) Use of PLCs may be restricted in some high heat, vibration environment not suitable for electronic circuit

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