PLC Advantages

PLCs have been gaining popularity on the factory floor and will probably remain predominant for some time to come.  Most of this is because of the advantages they offer which are :

(a)           Flexibility: In the past, each different electronically controlled production machine required its own type of controller.  But now one model of a PLC can serve as the controller for any of the machines.

(b)           Implementing Changes and Correcting Errors: With a wired relay-type panel, any program alterations require time for rewiring of panels and devices. When a PLC program circuit or sequence design is made, the PLC program can be change from a keyboard sequence in a matter of minutes.  No rewiring is required for a PLC-controlled system.

(c)           Lower Cost – Increased technology makes it possible to condense more functions into smaller and less expensive packages.  Now, you can purchase a PLC with numerous relays, timers, counters and other function for a few hundred dollars.

(d)           Large Qualities of Contacts: The PLC has a large quantity of contacts for each coil available in its programming.  Time will be taken to procure and install a new relay or relay contact block when a design change is made requiring more contacts.

(e)           Pilot Running: A PLC programmed circuit can be prerun and evaluated in the officer or lab.

(f)            Visual Observation: A PLC circuit’s operation can be seen during operation directly on a CRT screen. The operation or misoperation of a circuit can be observed as it happens.  Logic paths light up on the screen as they are energized.  Troubleshooting can be done more quickly during visual observation.

(g)           Speed of Operation – Relays can take an unacceptable amount of time to actuate.  The operational speed for the PLC logic operation is determined by the scan time, which is a matter of milliseconds.

(h)           Ladder or Boolean Programming Method: The PLC programming can be accomplished in the ladder mode by an electrician or technician.  Alternately, a PLC programmer who works in digital or Boolean control systems can also easily perform PLC programming.

(i)            Reliability and Maintainability: Solid-state devices are more reliable in general than mechanical system or relays and timers.  The PLC is made of solid-state components with very high reliability rates.  Consequently, the control system maintenance cost are lower and downtime is minimal.

(j)            Documentation: An immediate print out of the true PLC circuit is available in minutes if required.

(k)           Security: A PLC program change cannot be made unless the PLC is properly unlocked and programmed. Relay panels tend to undergo document changes.

(l)            Ease of Changes by Reprogramming: Since the PLC can be reprogrammed quickly, mixed production processing can be accomplished. For example, if part B comes down the assembly line while part A is still being processed, a program for part B’s processing can be reprogrammed into the production machinery in a matter of seconds.

(m)         Simplicity of Ordering Control System Components: When the PLC arrives, all the counters, relays and other components arrive as one delivery.  With the PLC, one more relay is available – provided you ordered a PLC with enough computing power.