SQC's, SQO's, and timers

[dkep96]

Hey guys,

My name is David and I began teaching myself the art of PLC programming using RSLogix 500 last summer. I am currently working on converting a sequential program I found in an old Control Technologies 2021 Controller to RSLogix form. I feel I have a pretty fair grasp on the funtion and programming of sequencers and timers, but my problem arises when I try to step through my SQO with both the SQC and the timers. If you have any advice on how iI could simultaneously use timers and SQC's, I would be very grateful to your help; or if I am completely wrong I would appreciate being pointed in the right direction.
Thanks again,
David Kepper

 

[OkiePC]

Hey guys,

My name is David and I began teaching myself the art of PLC programming using RSLogix 500 last summer. I am currently working on converting a sequential program I found in an old Control Technologies 2021 Controller to RSLogix form. I feel I have a pretty fair grasp on the funtion and programming of sequencers and timers, but my problem arises when I try to step through my SQO with both the SQC and the timers. If you have any advice on how iI could simultaneously use timers and SQC's, I would be very grateful to your help; or if I am completely wrong I would appreciate being pointed in the right direction.
Thanks again,
David Kepper

I am not sure I understand what you are doing.

The SQC is just a MEQ with indexed addressing and a built in counter.

If you want to allow it to control the step number AND you want to be able to have timers affect the step number as well, then there are several options.

Personally, I prefer to use MEQ instead of SQC so that I can be more flexible in how I manipulate the step number. Maybe I want a "step backward" push button or I want a timer to advance the sequence in some steps, or fault the system in other steps.

In those cases, I use my own logic to drive the step value on separate rungs from the MEQ where the inputs are masked and compared.

Tell us more about how you want the sequence to behave with regard to the timer(s)...

Paul

 

[dkep96]

I am not too familiar with MEQ. Please elaborate.

Well I guess what I am trying to say is at certain points in my sequence, I want to advance the SQO with a T4:?/dn bit and others I would like to advance with the control found bit. Does that make any sense?

 

[dkep96]

I figure I could program them in parallel, but then the problem is that a few of my timers are to be activated by certain input conditions that are true in other, untimely places in the program. I'm trying to figure out how to integrate these.

its a 22 input, 16 output bag-in-a-box filler

 

[OkiePC]

General sequencer advice:

Start with a chart. Two columns: Column A = Description of actions. Column B = conditions for completion.

Then make a copy of it. Copy 1 becomes the output sequencer, Copy 2 becomes the input definitions. Insert a multiple of 16 columns between A and B in each copy and begin the work of populating the input and output definitions across a row inserted at the top, but don't use real I/O for the sequencer inputs or outputs.

Give each input names that makes sense for the application, and don't worry about how to put it into ladder logic at this point.

Make your input definitions generic enough that you can define your input bits as needed.

Make your output bits much the same way. Example: Input Bit 3 = "Main turret is in position", Output Bit 7 = "Step Time Limit Active"

When your chart is done, and all the appropriate conditions are checked off, then you can go about putting that into ladder logic.


I can't say for sure how to construct the logic without more knowledge of the details. It might be simplest to CLR the mask when the timer is done, which would let the regular SQC go true, but then you have to put the mask back to its normal state (or work with a copy in the actual SQC).

It might be best to use a single timer, and load its preset with a value from an indirect address based on the step number.

Maybe you need a unique input bit to the sequencer for those specific steps, called "Step x Done", "Step y Done" and you can define them however you want.

Hope this helps...

Paul

 

[dkep96]

-"don't use real I/O for the sequencer inputs or outputs."

what do you mean by that?

"It might be best to use a single timer, and load its preset with a value from an indirect address based on the step number."

how would that be set up?

I'm going right now to upload what I have done so far so you can see along what lines i was thinking.

 

[dkep96]

um, how do I upload a .RSS file?

 

[OkiePC]

By "don't use real I/O" I mean use internal addresses in the sequencer instrucions. You can "map" them from/to the real I/O separately with very simple ladder logic. Often, the mapping is the proper place to do interlocking and debounce timing. There are many advantages to doing this, and no disadvantages worth noting.

By loading a single timer with a preset that changes with each step, I mean sometihng like:

MOV N10:[step_number] T4:100.PRE

So, N10:1 is the preset for step one, N10:2 is for step 2 and so on.

Then in your sequencer inputs, you can "map" T4:100/DN to an input you use for steps in which you want to ensure that this timer is done.

Only bother with this if you need a different timer preset in a bunch of different steps.

If it is only a couple of different steps, then skip the above method, and just use multiple sequencer input bits and multiple timers for simplicity's sake.

When you attach the file, you must zip it first, or simply change the .rss to .zip, but let us know which method you perform, so we can open the file.

 

[dkep96]

I simply changed it to .zip, although it didn't appear on the pst preview...

My shot at using sequencers is in ladder four, ladder three is simply a push button cycled sequencer, and the main ladder was my initial attempt to program without sequencers. I quickly realized that RSLogix doesn't cyle through step by step haha

 

[dkep96]

It didn't work, did it?

 

[OkiePC]

No attached file yet. After you browse to select it, are you hitting the upload button?

 

[dkep96]

yup, and it pauses for a few seconds, then the file name disappears from the browse window.

 

[OkiePC]

It is probably too big. Look for a messge in the upload dialog box after the pause...If it is too big, delete the stuff from it that you don't require and try again...OR, actually compress it to a zip and see what that does for the filesize.

 

[dkep96]

let's hope it works this time...

 

[dkep96]

here's the original program