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DIFFERENCE BETWEEN RELAY PANEL & PLC.
Relay Panel – It is an operating on analog system.
PLC – It is an operating on digital system.
Relay Panel –The maximum time any change in input is reflected in any output is t1.
PLC – The maximum time any change in input is reflected in any output is t1+t2+…+ Tn.
Relay Panel –Since this is made from analogue components. It is possible to replace. A logic section without stopping execution of other logic sections if wired correctly.
PLC – This is made with a digital micro-controller. The micro-controller must be halted to replace a logic section. All other logic sections will stop operation.
Relay Panel –Since parallel execution of logic sections, all outputs are a function of one set of inputs.
PLC – Since serial execution of logic sections, all outputs may not be a function of one set of inputs.
Example: input I2 may change as the micro-controller is processing Logic section. Therefore Q1 and Q2 are based on different inputs.
 PLC is the much less complex than large relay based system.
 PLC is the very flexible due to network architecture compare to relay panel.
 PLC is the virtually self-documenting compare to relay panel.
 PLC is the very space efficient and less manpower required to install compare to relay panel.
 PLC is the upfront material costs are similar, but savings on installation, maintenance, and troubleshooting increase rapidly as system size increases compare to relay panel.
 PLC`s reliability in industry and lab experience demonstrate PLCs comparable to relay system.
 PLCs huge knowledge base in industry compares to relay panel
 PLCs training and operating is very easy to handle its hardware and programming is also easy to learning.
 Its ability to monitor every sensor speeds debug and repair.
 In the PLC have no complicated wiring compare to relay panel.