On 8/13/2012 1:45 PM, EBo wrote: > On Mon, 13 Aug 2012 10:39:03 -0400, Dave wrote: > >> ... >> >> On many hardware PLCs you can make programming changes on the fly >> without pausing the controller which means that you don't need to >> stop >> the machine >> to make program changes. Very important when it takes an hour or >> more >> to restart the machine after a shutdown. >> > a restart takes an hour or more after shutdown? Out of curiosity, what > machine might that be, and why so long? > > ------------------------------------------------------------------------------ > Live Security Virtual Conference > Exclusive live event will cover all the ways today's security and > threat landscape has changed and how IT managers can respond. Discussions > will include endpoint security, mobile security and the latest in malware > threats. http://www.accelacomm.com/jaw/sfrnl04242012/114/50122263/ > _______________________________________________ > Emc-developers mailing list > Emc-developers@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/emc-developers > >
That is common with a lot of process related equipment. Large extruder/molding systems, web processing machines are not usually as long but they can take a long time to restart, with a lot of people running around to get things going again. When the web is running a couple hundred feet per minutes in coordination with a number of other axes which are running applicators, cut offs, feeders,etc, you really don't want to shut it down to make a minor change. The machine cell I was working on two weeks ago took about 30 minutes to fully load with all of the parts in the queue - 5 machines with a robot in the center, and about 15 minutes to unload. If we had to shut down the system controller for each change, we would have to start all over again as machine and system state information would be lost Instead we made changes on the fly as much as possible to speed the debug process. Last year I was working on the controls for a refrigeration system for a plant that processed food. When we shut down the compressor system to make a change we would have to coordinate the shutdown with the rest of the plant so they would not require refrigeration for the duration of the process, it was a huge deal for the process people as the food has to be chilled at a certain rate during the process and the plant was large and was cooking multiple batches of food at various times. So all possible changes were made on the fly (very carefully). Once, when I had to shut it down for a couple of minutes (literally) to download a change that had to do with the controller hardware, they had 10+ people standing around with radios through out the plant all coordinated to tell me when I could put the controller in stop mode, download the change, and then put it back into run mode. That was not a fun situation. Part of that was a system design problem. The process engineer put all of the refrigerant compressors on one controller. :-( So while the change only took a couple of minutes, it took a while to restart all of the compressors and bring the system back up to pressure. When that plant loses power they throw out a lot of food. Power plant boiler controls are the same way. They take hours to shutdown and start up. Any company that runs a machine 24x7 usually has the same problem. Usually the reason they run it 24x7 is that the startup and shutdown process takes hours. Dave ------------------------------------------------------------------------------ Live Security Virtual Conference Exclusive live event will cover all the ways today's security and threat landscape has changed and how IT managers can respond. Discussions will include endpoint security, mobile security and the latest in malware threats. http://www.accelacomm.com/jaw/sfrnl04242012/114/50122263/ _______________________________________________ Emc-developers mailing list Emc-developers@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-developers
