PLC

Plc



Theory- Plc

Fully explain the Scanning process and Batch I/O Update

The internal hardware architecture is much the same as other microcontroller based systems with analogue and digital I/O, and RAM and ROM and communications links. The configuration is flexible (modular) so the I/O can be configured to suit the task, by plugging in appropriate modules. This makes it reasonably easy to reconfigure the system as the task changes.

Power line communication (PLC) is a technology that enables data communication using the existing power lines that provide electricity to households and commercial buildings [1,2]. Since power lines have already been installed universally we are able to construct a target network easily and cost-effectively. Recently, much research and industrial efforts have focused on advancing PLC technologies, such as commercializing 200 Mbps PLC devices, constructing backbone networks and access networks using the PLC technology, and developing application services such as automatic meter reading (AMR), home networking, high-speed Internet services, and triple-play services.

The software is what makes them different, as it is organised to be easily programmed for the tasks expected in industrial situations, to do with running machines, monitoring sensors, event processing and timing. This may be called real time control. They can use ladder logic diagrams, but there are many different languages. Some have specialised versions of basic etc. The software is usually written on a PC and downloaded. (Kandray, 2010: 160-174)

A batch process has a start event and an end event. Consider making bread. The operator may enter the quantities for the job, then press a button when ready. The controller could heat the oven and control the temperature, or just turn it on and wait a specific time. It could weigh the materials, fill the hopper, start the mixing, provide the appropriate wait time, then sound an alarm signalling it is ready for the next stage. Whether it could get the dough out and chop it up and put it in the oven depends on whether such machines are available. They could have their own PLCs, so each simply passes the process on to the next task. Alternatively there could be a central processor controlling it all, either a PLC or something with displays and other features not normally found on a PLC.

Homeplug, led by Intellon, is an industry alliance comprised of PLC industry leaders. Its goal is to standardize PLC technologies for interoperability of PLC devices. The Homeplug network is composed of one or more PLC Cells.

Even in basic, there can be a loop that monitors software flags, timers, readings and events. The program branches out to perform tasks as they are detected, and returns to the loop when they are done. It must never spend too long on any task. The design may have a limit of a few seconds or a few milliseconds for any task in the loop, as well as a different time for how long it takes to detect an event. (Laughton, 2009: 235-238)

If things are not fast enough, individual tasks can be passed ...