Sequencer SQL

OK so I have figuerd out how to use the SQO, and the SQC functions of the RsLogix500, with the help of this site. Very nice explanations by the way. By using the SQC and the SQO, I can do my sequencing. But now I am left with a curios question, Where does the SQL come in to the picture, and why would I use it?

I've never seen it used, but the SQL (sequencer load) is intended to provide you with the means to program a "teach" facility in your system so that it can learn a new sequence without reprogramming.

Greetings Allan,



my distinguished colleague Gerry is absolutely correct ... and I’ve never seen it used either ... but here’s the basic “what’s it for?” idea in a nutshell ...



suppose that the machine’s sequence needs to be changed from time-to-time ... maybe a new product is being produced ...



now the machine operator might know exactly how the machine is required to step through the steps of its new cycle ... but the operator has a problem ... specifically, he doesn’t know anything about programming a PLC and he doesn’t have access to the programming software ...



but suppose that the machine’s original programmer has inserted an SQL (Sequencer Load) instruction into the program and made sure that the operator knows how to turn it on and trigger it ...



now the operator (without the programmer’s help) can manually lead the machine’s actuators, etc. through the various stages of operation and then press the SQL’s “store” button once each step in the sequence has been reached ... in effect the operator is now “reprogramming” the machine without having to understand, or have access to, the PLC’s programming software ... as Gerry said, he’s “teaching” the machine the new sequence of operation ...

Wow,


Guys, thanks for that explanation. I love sequencers and have used a few, but have never seen that instruction used. Nor did I ever really try to figure out what it did. That is a powerful tool, if used properly.


David

Well I am not sure I would give an operator that kind of power. While I have found some operators are awsome, far to many would use this to get another smoke break or some thing. I am certaintly glad I asked, but I can not see my self using this if that is the case.

The big problem with using SQL is knowing which inputs to mask out for each step. I think that's the main reason it's very rarely used. I've never seen it used either.

Well I am not sure I would give an operator that kind of power

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that's a good point ... but one solution might be to make the SQL's "enable" switch a physical keyswitch ... only the operator's foreman/supervisor would have a key ...

the main idea is that without the SQL you're forced to call in a PLC programmer for each change to the sequence ... $$$ ... for some small applications that would not be acceptable ...

I wouldn't put much faith in most supervisors either. I can see its uses but the error checks would have to be carefully thought out.

I wouldn't put much faith in most supervisors either.

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then only the CEO/president has a key ... come on guys ... you've got to trust SOMEBODY ...

just joking ... just joking ... just joking ... this would be a good place for a big friendly smilie face ... but for some reason i just can't make myself use those things ...

anyway the SQL is just a tool ... if Allen-Bradley had left it out, then someone would complain that they needed one ...

I trust they will screw up does that count?????