Ron Beaufort
Lifetime Supporting Member
from drbitboy:
BINGO! ... that in a nutshell is the viewpoint of the hapless Maintenance Manager who can't keep the plant's machinery running ... it's usually NOT that the PLC code is fragile ... it's the fact that back in the "good old days" there was a physical WIRE connecting something that wouldn't RUN (example: a pump) back to the something that told it WHEN to run (example: a proximity switch) ... even a trained monkey could eventually track down the problem by following the physical wire from one end to the other ...
but ...
nowadays – there is no PHYSICAL wiring between the "innies" and the "outies" ... the connection is made through the logic/code of the PLC ...
let's just assume (gosh I hate that word) that the necessary software is loaded on the maintenance technician's laptop computer ... (how many forum threads and posts have been sacrificed to THAT simple assumption?) ...
and let's just assume that it's possible to have the laptop go online and communicate with the processor ... (yet another plethora of threads and posts sacrificed toward accomplishing what should be a fairly simple connection) ...
but let's just say that now the technician is online – and ready to track down WHICH prox switch is keeping the Bo$$ from making money tonight ... if he's lucky (I prefer to say "blessed") then maybe the "green on the screen" (or rather the lack thereof) will help him nail down the problem – just like the tech was taught in the PLC training classes that he attended ...
oops! ...
turns out that this code wasn't written in Ladder Logic ... so how about Structured Text, Function Block Diagrams, Sequential Function Charts, Equipment Phases, Add-On Instructions, and so on and on – ad infinitum ...
throw in a "loop – a whirl – and a vertical climb" or two – and now we're back to James Mcquade's statement ...
sounds like a good objective to me ... (the old saying: "money talks" comes to mind) ...
I know from personal experience that most Maintenance Managers are NOT interested in their technicians troubleshooting the PLC's code ... they just want their crews to be able to "track down" the NON-PHYSICAL connection between the money-making outputs – and something like a malfunctioning input - which might be keeping the system from working ...
[my emphasis added] ...the line went down, probably a rare failed prox, and Joe my maintenance tech went into your code but could make neither heads nor tails of it to aid in diagnosing WHICH prox
BINGO! ... that in a nutshell is the viewpoint of the hapless Maintenance Manager who can't keep the plant's machinery running ... it's usually NOT that the PLC code is fragile ... it's the fact that back in the "good old days" there was a physical WIRE connecting something that wouldn't RUN (example: a pump) back to the something that told it WHEN to run (example: a proximity switch) ... even a trained monkey could eventually track down the problem by following the physical wire from one end to the other ...
but ...
nowadays – there is no PHYSICAL wiring between the "innies" and the "outies" ... the connection is made through the logic/code of the PLC ...
let's just assume (gosh I hate that word) that the necessary software is loaded on the maintenance technician's laptop computer ... (how many forum threads and posts have been sacrificed to THAT simple assumption?) ...
and let's just assume that it's possible to have the laptop go online and communicate with the processor ... (yet another plethora of threads and posts sacrificed toward accomplishing what should be a fairly simple connection) ...
but let's just say that now the technician is online – and ready to track down WHICH prox switch is keeping the Bo$$ from making money tonight ... if he's lucky (I prefer to say "blessed") then maybe the "green on the screen" (or rather the lack thereof) will help him nail down the problem – just like the tech was taught in the PLC training classes that he attended ...
oops! ...
turns out that this code wasn't written in Ladder Logic ... so how about Structured Text, Function Block Diagrams, Sequential Function Charts, Equipment Phases, Add-On Instructions, and so on and on – ad infinitum ...
throw in a "loop – a whirl – and a vertical climb" or two – and now we're back to James Mcquade's statement ...
I would write the code so maintenance can trouble shoot it and keep the system running.
sounds like a good objective to me ... (the old saying: "money talks" comes to mind) ...
I know from personal experience that most Maintenance Managers are NOT interested in their technicians troubleshooting the PLC's code ... they just want their crews to be able to "track down" the NON-PHYSICAL connection between the money-making outputs – and something like a malfunctioning input - which might be keeping the system from working ...
Last edited: