PLC-2, Sequencers and bad programming

[(8{)} ( .)]

OK Guys...

The process in question had 4 sequencer output and 4 sequencer input instructions to control 12 silos and the delivery piping to and from the silos. The sequencer instructions didn't perform a sequence, they were there for the masking capabilities.

The sequencers did the following tasks
Sequencer 1 - Silos 1-6 inlet valves
Sequencer 2 - Silos 7-12 inlet valves
Sequencer 3 - Silos 7-12 outlet valves
Sequencer 4 - Silos 1-6 outlet valves

The support logic for these things was ridiculous - align all of the inputs and outputs so that we can use the same data for both
the SQI and SQO in addition to the logic required to have the sequencer jump to the right step.

Basically, garbage...

I used no sequencers for the valve programming and grew my own for the startup and shutdown stages (since these stages were different depending on the material path).

End results:
* Smaller Code
* Servicable Code
* REALLY happy customer
* Lots of posts on PLCS.NET

Cheers,

(8{)} .)

(Yosi)

 

[jstolaruk]

Almost all of the customers my employer deals with (Big 3 Auto and their suppliers) state in their specifications that sequencer instructions are NOT to be used. And with damn good reason in my book. Yes, I'm sure there are good examples of their use but mostly they are misused and just about impossible for the service people or the customer's support staff to reverse engineer and understand. Sequencer, MCR, Jumps/Gotos can really make things more complicated than they need to be.
-Jeff