SLC500 Sequencer Instruction

I am new to AB (not to PLC's) and have a current application that I am programming for a SCL500 1747-L511 processer. One part of the machine has a indexing rack that feeds Master Cases down the line. There are 5 possible cases or some may be missing. Position 1 is the place where an empty case is put into the machine, position 2 stages an empty case, position 3 is filling the case, position 4 closes the top flaps and position 5 is the exit into the taping machine.

Would the sequencer instructions be the best choice to monitor the presence or absence of cases?

Are there any more examples of the sequencer instruction besides the SLC Instuction Set Manual?

Does anyone have any tips or tricks for using this set of instructions?

Thanks
John

sequencer

Sequencers serve the purpose for machines that have mostly the same movements or sequences. For parts of the circuit that you would like to disable during the steps, use the mask words for your monitoring.

You could use a shift register.

Register's input is loaded by a sensor at initial position. This way each process attached to following positions can monitor if a case is present for it before running. Usefull for non sequential processes, because it breaks all relationships in programs between initial position and following processes (each one runs independently).

Regards

If you are just trying to monitor the prescence/abscense of cases, I dont think that a sequencer (SQO?) is what you need. If you just want a 1 for present and a 0 for absent, then a bit shift would be more appropriate (BSR, BSL). This is an easy to do part tracking through stations in a machine. An AB SQO instruction does not monitor bits, but it turns them on/off in a predetermined sequence.

Since you only have 5 positions and at least three of them(steps 1, 3, and 4), I would guess, already have a part present sensor of some sort, It might be easier to use "simple" logic to determine part present status per station. With so few steps in this process, I dont really think using one of the more complicated instructions (sequencer or bit shift) is going to save you any code or scan time.

There is another AB sequencer example here: http://www.mrplc.com/cgi-bin/code/filedisplay.cgi?category=machab its about halfway down the page and its called PicknPlaceSequencer

Hi jthornton,

Are you asking if it is best to use the sequencer instruction to track the position of the box?? OR do you intend to use the sequencer to to control the sequence of events in moving the box down the line depending on input siganls?? If you are just monitoring status to indicate where the box is, or doing ,just use limit switches.

If you are wanting to control a sequence of events depending on limit switches or on a timed event basis, a sequence will do the job.

Give us some more information and we can help further.

You could search this site for more examples on how to use the sequencer instruction (I'm sure there are lots!!) or you could also try http://www.thelearningpit.com/ or http://www.mrplc.com/

Hope this helps..

Andrew Evenson

The other part of the machine collates product boxes with either 3, 4, 5, or 6 rows. Would the sequencer be the way to do that part or is it better to just code it in using normal ladder?

Thanks
John

John, here is how I see it. There are numerous ways to do what you are asking, shift register, sequence using mask as monitor, indexing, etc etc. What is right is what works for you, if you havent done some of this then this may be the time to try it. Use one or all of these to determine if it makes it easier to do and understand. You can always go back to what you call normal ladder.

TO help you understand a little about sequencing, originally drum sequencers were used when a machine had constant repetitions. The drum sequencer couldnt stop in the middle for another operation to happen.

The PLC(AB) sequencer is a little different, during the sequence you can monitor the word value/bits so can make determinations in the sequence whether ready to move to next position.

Like some mentioned before dont forget about Shift registers, indexing maybe...doesnt matter really. Try one or all and see if it works cleaner, takes too much time...whatever. Its tools to use, any time is a good time to attempt to use just to learn the tool.

Thanks for all the input

John