Best programming practices

[ganutenator]

For the love of sanity -
Don't put multiple contacts before a one-shot

amen

I think the AB really dropped the ball w/ putting too much power in the hands of the clowns w/ that one. Wish they had gone with | P | instruction instead.

 

[ganutenator]

I have many small snippets of code from one of our integrator projects that contains multiple bits called "do_not_forget". I guess he forgot!

lol, I'm looking at a program right now where the comment on the contact is labeled "MUST DEAL WITH THIS LOGIC!!!".

 

[jgreenewv]

lol, I'm looking at a program right now where the comment on the contact is labeled "MUST DEAL WITH THIS LOGIC!!!".

We've got a machine on the floor with a section of code labeled "This needs cleaned up." Not sure if I need to look for optimizations or soap.

 

[JeremyM]

For the love of sanity -
Don't put multiple contacts before a one-shot

Why not?

 

[T Gibbs]

I was told by an AB tech not to BRANCH ahead of a one shot.

 

[ganutenator]

Why not?

one example:

--|  |---|---------|\|------- ons---------(   )

--|  |---|

--|  |---|



versus



--|  |--ons-|---------|\|------- ---------(   )

--|  |--ons-|

--|  |--ons-|

 

[Usireland]

one example:

--|  |---|---------|\|------- ons---------(   )

--|  |---|

--|  |---|



versus



--|  |--ons-|---------|\|------- ---------(   )

--|  |--ons-|

--|  |--ons-|

That example makes sense when you should use multiple one shots, but what about this:

---|  |-----|  |-----[ons]----------------------(   )

It could be a case where you only want to deal with something when the machine is running and a sensor turns on. If the sensor turns on and the machine is already running then this creates an edge, or if the sensor is already on when the machine is running this creates an edge (the may be a desired effect). Why would this be an incorrect use of a ONS?

Regards
Ian

 

[boardmaker]

She's got tags. She knows how to use them.

I got a good chuckle on that one.

 

[ganutenator]

That example makes sense when you should use multiple one shots, but what about this:

---|  |-----|  |-----[ons]----------------------(   )

It could be a case where you only want to deal with something when the machine is running and a sensor turns on. If the sensor turns on and the machine is already running then this creates an edge, or if the sensor is already on when the machine is running this creates an edge (the may be a desired effect). Why would this be an incorrect use of a ONS?

Regards
Ian

Yes, this could be fine. Just remember to think of the off state.
If the sensor is on and the machine stops running and then starts running, then make sure you also want that edge as well.

 

[T Gibbs]

one example:

--|  |---|---------|\|------- ons---------(   )

--|  |---|

--|  |---|



versus



--|  |--ons-|---------|\|------- ---------(   )

--|  |--ons-|

--|  |--ons-|

That's what the AB tech told me NOT to do. Contacts in series ahead of a one shot should be OK.

 

[harryting]

Latch/unlatch - with great power comes great responsibility. Don't use it as as a lazy way of doing state machine or sequence then you end up with a very confused program where one can be in multiple conflicting states. <yes, I'm in the middle of of fixing one>

 

[boneless]

Never download some final changes 5 minutes before you have to leave...

 

[Steve Bailey]

On a related note, the thread below has been going for ten years and still gets the occasional addition.

http://forums.mrplc.com/index.php?/topic/9522-plc-law/

Beware! Don't follow the link unless you have time available.

 

[Lare]

for sequencers use integer number for step state instead of several flipflop bits, it is easier to read and troubleshoot.

 

[JeremyM]

for sequencers use integer number for step state instead of several flipflop bits, it is easier to read and troubleshoot.

Instead of sequencers...