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Old August 24th, 2012, 09:18 AM   #1
mcdaniel@kconline.co
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Step Sequencer in RSLogix 5000

I have a control process that needs to sequence through a number of steps using the same input. Hitting the same pushbutton should "step" the program through the steps. I can program this in simple ladder logic but it takes up a lot of space to accomplish. Is there an easier way to get the same results?
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Old August 24th, 2012, 10:13 AM   #2
robw53
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how about using an ADD instruction to increment through a sequence then EQU conditioning the rungs for each step?

what do you have at present?

any more info would be great, how many sequences you need etc
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Old August 24th, 2012, 11:13 AM   #3
James Mcquade
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I am not the 5000 guy to answer your question, but if you are referring to sequencer output type program, please consider the following:

is maintenance well versed in sequencers on all shifts?
are they willing to learn them and put forth the effort
to trouble shoot the program?

if yes, then discuss the program with them and get their thoughts.
if not, you will be getting a lot of calls to fix the machine.

regards,
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Old August 27th, 2012, 06:55 AM   #4
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For 30 or less steps, create a dint tag called "seq_step" or whatever. Load a "1" into it to reset it to the first step and then add it to itself at each step. The 1's in the tag will step along as the value doubles. Just one rung, plus a "mov 1" at the last step to reset it.
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Old August 27th, 2012, 08:06 AM   #5
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Quote:
Originally Posted by James Mcquade View Post
I am not the 5000 guy to answer your question, but if you are referring to sequencer output type program, please consider the following:

is maintenance well versed in sequencers on all shifts?
are they willing to learn them and put forth the effort
to trouble shoot the program?

if yes, then discuss the program with them and get their thoughts.
if not, you will be getting a lot of calls to fix the machine.

regards,
james
James

The OP may be wanting to use sequence based logic where you move a 1 into a rgister and that enables the sequence 1 logic and when it is complete you move a 2 into that register by a auto fashion or by a manual fashion like a push button and that enbles the logic for sequence step 2 and so on.

This is very organized and easy to troubleshoot. Have your sequence register viewable at the top of the program and using rung comments and subroutines break up the sequence steps as the fit the application. When the machine has a unplanned stop you can look at the sequence register and see exactly where you are and what is holding you out without searching all over a large program.

I hate programs that use the built in sequencer instructions such as SQO and SQL and SQC and I think those were what you were making reference to also. Programs like that do make things difficult for maintenance techs and trades.
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Old August 27th, 2012, 06:45 PM   #6
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Quote:
Originally Posted by The Plc Kid View Post
I hate programs that use the built in sequencer instructions such as SQO and SQL and SQC and I think those were what you were making reference to also. Programs like that do make things difficult for maintenance techs and trades.
These instructions exist to replicate the Cam or Drum timers that were used extensively to sequence a pre-defined set of actions.

No different than a pianola roll, and just think of the enjoyment that gave.

They are the very best instructions to use, in the right places, just like any other instruction.

And the SQO, SQL, etc. have been in A-B PLCs for more years than I care to remember, is it really too hard on the maint tech's to have taken them on board by now ???
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Old August 27th, 2012, 07:34 PM   #7
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I have done them both ways Daba but in my opinion it is still easier to troubleshoot my own rolled sequencer logic than to use these instructions but it depends a lot on the situation and the equipment you are using them on. We have some pretty intricate and involved sequences and you would have to use a lot of the base sequencer instructions to do the stuff that I do.

Referencing all the bit pattern tables when troubleshooting and makinmg changes is more of a headache than it's worth IMHO at least on the stuff I do.
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Old August 27th, 2012, 07:40 PM   #8
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SQI and SQO -- Run AWAY!

Do not use SQI and SQO.
You and everyone else after the fact will be held at bay.

I agree with above posts, build your own sequencer by incrementing an integer (or DINT).

But... do not increment by one... inctement by 5 or 10, this allows easy insertion of futures steps without modifying all logic.
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Old August 27th, 2012, 09:02 PM   #9
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It is a good practice to increment by 5 to allow later steps to be added with minimal programming changes later, the first place i saw this was in reliance Automax where you could give each line its own number when you created the logic, so that later on when you went back to make additions you did not have to re-sequence the program.
Remember this software was DOS based so did not have all the bells and whistle's that modern windows software has that we now take for granted, but in its time was very powerful.

Alan
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Old August 27th, 2012, 09:27 PM   #10
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My steps typically increment by 100. I'll start at 1000 and use go up to the next 1000 for every sub sequence. I'll have typical step ranges for certain modes such as tooling return or recovery.

With a DINT being over 4 billion there is no reason not to utlize ranges more to add an extra level of organization.

Up in the top rung I will have an extended comment that serves as the "index" for the ranges.

If it is a really long sequence and depending on the controller/software, I will break them up into separate subroutines just to cut down on the scrolling. Depending on how they are displayed I may have to modify my naming convention such that they show up in the sequence that they execute as opposed to alphabetically.
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Old August 28th, 2012, 03:04 PM   #11
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Quote:
Originally Posted by DamianInRochester View Post
With a DINT being over 4 billion .....
Ewww ! Are you using negative numbers in your sequencer steps ?

The maximum positive DINT is 2,147,483,647
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Old August 31st, 2012, 09:02 AM   #12
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Quote:
Originally Posted by daba View Post
Ewww ! Are you using negative numbers in your sequencer steps ?
No, that would be silly.




Quote:
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The maximum positive DINT is 2,147,483,647
....... in RSLogix 5000 snd for LONG in 500 since AB does not recognize unsigned data types.
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