add some relays, debug and do it all over again. A single PLC can be programmed to replace thousands of relays. Software revision replaced the re-wiring of hard-wired control panels when production models changed.
modification Enabled future growth Were highly reliable Reduced Downtime Occupied very little space Increased capability data collection and communications became easy Overall costs dropped
Output Process PLC being a dedicated controller processes one program over and over again. It involves reading inputs from the other modules, executing the logic based on the inputs and then updated outputs accordingly.
of configuration, alarm reporting, etc. Most modern PLCs can communicate over a network to RTUs (Remote Terminal Unit) or some other system, such as a computer running a SCADA (Supervisory Control And Data Acquisition) system .
for harsh environments. Ease of Use Connections are easy thereby interfacing. Connecting I/O to the PC is not always as easy. Flexibility Easy to add modules. Designed for modularity and expansion. Limited by the number of cards slots and not easily expandable. Speed Executes only a single program in sequential order. Easy to handle real time tasks. Meant to handle simultaneous tasks. They have difficulty handling real time events. Reliability A PLC never crashes over long periods of time. Freezes up and crashing is frequent. Programming languages Languages are typically fixed to ladder logic. Very flexible and powerful in what to use for programming. Data management Limited memory cant store a lot of data. Long term data storage possible. Cost Just too hard to compare