42 Fundamental Laws of PLC Programming

42 Fundamental Laws of PLC Programming 

Dear friends cant stop sharing this with you. The 42 fundamental laws of PLC ,a programmer must know this .
Courtesy of the Members of MRPLC.COM

42 Fundamental Laws of PLC Programming
42 Fundamental Laws of PLC Programming

PLC LAW 1 – don’t over complicate the simple. 

PLC LAW 2 – make sure you plug the cable in before you try to figure out why you can’t go online. 
PLC LAW 3 – during startup, always verify i/o before testing the program 
PLC LAW 4 – when connecting your laptop to the plc, don’t tighten the screws on the serial cable at the laptop side. 
PLC LAW 5 – read the manual before trying to install/commission an unfamiliar piece of hardware. 
PLC LAW 6 – always have all possible backup files (plus read from plc etc.) Before starting any changes… 
PLC LAW 7 – always double check you have the right cables for your CPU type and backup install software with you before you step on the plane. 
PLC LAW 7.1 – when working in a lan or wan environment always triple check processor id’s before erasing and downloading new code. 
PLC LAW 8 – each vendor has their own programming software, so plan accordingly.
PLC LAW 8.1 – some vendors software may not play well with others… See rslinx…
PLC LAW 8.2 – order the correct software from your vendor instead of asking for it on mrplc
PLC LAW 9 – when powering up a plc the first time, make sure that the power supply voltage switch is set to the right
PLC LAW 10 – try to stage and test as much as possible before making big changes. 
PLC LAW 11 – spares should not sit of the shelf. They should be used for training and testing.
PLC LAW 11.1 – there must be spares for critical parts! 
PLC LAW 12 – programs should have many rungs of diagnostic ladder that can be enabled or disabled quickly. This
includes timers for timeouts. These determine when input devices are not working properly. Fifos are good for logging real time events. Counters that count errors are handy too. 
PLC LAW 13 – the best plc programs are able to recover from error conditions quickly. This can make a big difference
to overall production. 
PLC LAW 14 – all programs should be well documented 
PLC LAW 15 – make sure you actually understand the question in the dialog box before hitting “ok” 
PLC LAW 16 – remember to put a paper copy of the latest plc ladder in the electrical cabinet. 
Plc law 17 – when all else FAILS, ADD A TIMER, AND A ONESHOT TOO JUST IN CASE.
PLC LAW 18 – when a non plcite tells you that a machine is not working because of “programming errors”, ask
for proof before changing your masterpiece. 
 PLC LAW 18.1 – when the machine is down, the blame will be assigned to whichever component the person assigning the blame understands the least.
PLC LAW 18.2 – american money says “in god we trust” – with plc’s all others bring relevant data. 
PLC LAW 19- make sure that your plc and or process will run without the hmi (if using one).
PLC LAW 20 – a good programmer will never believe the guy who says nothing has changed since it worked. 
PLC LAW 21 – make sure that the default settings doesn’t cause the plc to fail from starting to operate properly after
a blackout. 
PLC LAW 22 – plc logic can not change by itself. 
PLC LAW 23 – never under any circumstances leave forces in a processor. They should only be used for
temporary testing which means remove them before going offline 
PLC LAW 24 – always be sure that the rung / ladder / block you are troubleshooting is being scanned before you make major changes or spend 6 hours troubleshooting it!!!
PLC LAW 25 – when teaching points on a robot, or programming a vision system that interfaces with a machine designed with a dial indexer, make sure your index table is on station… 
PLC LAW 26 – the controls people can always count on being the last to leave and the first to return to solve
problems on any plc job. Even when the problem is not plc related.  
PLC LAW 27 – share your updated work..  
                       PLC LAW 27.1 – after changes make sure they work 
PLC LAW 28 – machines with intermittent faults always seem to work okay for hours when the programmer is at the
location. When the programmer leaves, they may start failing within five minutes…
PLC LAW 29 – problems with controls and automated systems at plants happen every day. But it is only the day after you visited all problems must have a connection with your visit.
PLC LAW 29.1 – some specific faults in  controls and automated systems are there for years already, and the operators
know exactly how to deal with it. Until the plant supervisor notices…. Then all of a sudden it is a matter of life and death. 
PLC LAW #30 – any problem which goes away by itself will return by itself (but at the least convenient time.) 
PLC LAW 31 – check for proper equipment grounding before power up.
PLC LAW 32 – don’t have to many backups it will lead to confusion, have your backup in organized way in proper place. 
PLC LAW 33 – the program never fails. 
PLC LAW 34 – the cheapest price is not always the best option. The best option is the lowest price for quality
PLC LAW 34.1 – the lowest bid may simply represent the biggest mistake in estimating.
PLC LAW 34.2 – the lowest bid may simply represent a few more mistakes in your Machine. 
PLC LAW 35 – if the program already works properly, don’t touch it
PLC LAW 35.1 – “broke ” or “ok” is in the eye of the beholder. 
PLC LAW 36 – idiots, stupidity and other people problems defy common sense most of the time.
PLC LAW 36.1 – “there’s no such thing as idiot proof, only idiot resistant.”
PLC LAW 36.2 – “artificial intelligence never overcomes natural stupidity”
PLC LAW 36.3 – if you write a program to help make a machine “idiot proof” the hr department will just hire
better idiots
PLC LAW 36.4 – ozz variant – “you can make things idiot proof but not operator proof.”
PLC LAW 37 – the machine will always run when your watching, then suddenly stops running or jams up when the boss
watches or when your customer comes for the sign off. 
PLC LAW 38 – when all else fails…….pdpu………..(power down power up) 
PLC LAW 39 – create a pm for replacing plc batterys or an alarm for low battery. 
PLC LAW 40 – if you change addressing, update the backup program. 
PLC LAW 41 – in a system where a plc and a windows computer (pc) exchange data, the plc usually isn’t the one that
stops the data exchange. 
PLC LAW 42 – service agreements will never meet the needs of all parties {engineers, maintenance, production and
Thankful to Members of MRPLC.COM

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