Set and Reset bits - Rant

there are pros and cons for every program method.
the trick is to know what programming method is best suited for the job.

one MUST always remember who our ultimate customer, Maintenance!
writing code that only you can understand will not keep the machine running.
if maintenance can't figure the program out, the machine don't run, production suffers, managers hear about the issue, the plant manager gets involved, calls your boss, who then yells at you.

you in turn spend the next 6 weeks working with maintenance to learn what they can do and rewrite the program.
I have seen 2 programmers get burnt for that.
one was never allowed to write code for that plant again.

james

I understand there are specific time and places for using OTL bits etc... (This was a S7 classic project, still the theroy is the same).

As has already stated, this problem had been going on for over a week with none of their maintenance techs being able to diagnose it.

Result, although they could run, albeit periodically due to it being intermittent, they lost a lot of product and running time.

I wouldn't be surprised if I'm asked to make it more understandable. Now that it's a few year old and components are wearing it's just going to get more unreliable.

I've always found the maintenance team to be worth their weight in gold to win over on a site, I've won jobs previously on the fact my code was cleaner and easier to understand than others.

It isn't the tools folks. It is the programmers and lack of discipline to implement state machines properly.

Keeping track of state through a power outage is hard but back in the mid 1980s I worked for USNR and error recovery from wood jams and power outages were crucial in maintaining Piece count. Again, having a good state machine and retentive memory was critical.

BTW, I really do hate programming PLCs. It is even worse when I have to look/fix at other people's PLC code. I once had to fix some PLC5 code that used one shots every where which would have been OK except they used the same one shot number over and over again. Obviously that didn't work. I sell motion controllers. The motion controllers work well one they are given the right command at the right time. Sometime I think the PLC programmers are out to get me.

BTW, my new love is Python.

James Mcquade said:

one was never allowed to write code for that plant again.

Click to expand...

Didn't see his code, so I'm not trying to defend him... but a lot of times companies want something but fail to specify it. If I have an ST or IL function that does exactly what I want and has been tested and you specify that all code must be in Ladder... then I guess I'll re-write it and charge back. If none of that is specified, I ain't re-writing it.

The key point here is that the guy got hit by something that was left for him to choose and he did. If you want to avoid that, you specify how it must be.