Compare PLC and Relay

Advantages of PLCs over electromagnetic relays

• Ability to interface / communicate with computers but not with reley
• Simple programming is possible using ladder logic but not with relay
• Plc have High reliability
• High controllability due to the use of timers and counters.
• Easy maintenance
• Rugged construction - can operate in extremely harsh conditions
• Small size
• Easy expandability
• Economical in long term

Limitation of Relay

• It suffer from contact wear and reliability problems
• Unsuitable for designing complex control circuit
• Relay occupies large space
• Relay takes large time to actuate