Programing using a SQO

[somebody]

Hi everybody, I'm new at this and I have a problem. I'm in college trying to learn had to program PLC's and I have to do this lab as follows:
It must be a retentive program with the destination must be the first output address. The Sequence must start automatically after last step. The Sequence must start in the "Home" position and must be 5 seconds between steps.
If the Sequencer is stoped or if a loss of power is experienced, outputs must de-energize and when the power is returned, Sequencer must pick up on the step it was at.

I must use at least the following:
MOV, SQO,Timer, Bit File, Start/Stop, 3 "Real-World" Outputs.

This program has me stund because I really don't understand the SQO.

Can anybody help me with this? I need a ladder logic diagram drawed.
Thank you for your help if you can.

 

[Ron Beaufort]

this thread has helped quite a few people in the past ... if you need more help than this, post again and show us what you've already written ...

 

[widelto]

If you try to do something about your homework and show it here, I know for sure that many people are going to help you.

Do not be afraid to make mistakes, read the plc manual, try to understand how instructions work show your effort and they´ll help you.

 

[msmassey]

I guess if you have to use a SQO, but we had a couple of machines that had those on them and they were virtually impossible to troubleshoot. I eliminated them and we have much better control and performance.

 

[mordred]

They are handy in the right applications. I currently have 5 machines that use them Once you know how to use them I've found they can simplify certain applications the main problem seems to be the hidden bits and masks and setting up the steps Somebody Ron's posting is a good thread on the subject but there has been lots of threads on this subject use the search engine and I'm sure you will get the answers you need in some of those threads there is also some examples

 

[Lancie1]

"It must be a retentive program..."

means that if power to the PLC is lost then recovered, it resumes at the same place as before power was lost. This can be accomplished by using retentive timers and counters to control the SQO.

"...where the destination must be the first output address"

means that one of the parameters in the SQO instruction (the "Destination") has to be set for your first PLC Output address. I assume that the "first output address refers to a specific PLC used in the classroom or lab. Only you would know what this is.

"The Sequence must start automatically after last step"

means that the SQO must be cycled continously. Because the SQO automatically rolls from last position back to position 1, then all you need to do is keep cycling the SQO instruction at long as the Start/Stop switch is ON.

"The Sequence must start in the "Home" position and must be 5 seconds between steps"

is contradictory to the next instuction, because if PLC power is lost, the PLC can restart at same SQO step, or it can be reset to Position 0. Normally this would mean that on the PLC being powered up, you need to reset the SQO to Position 0. That can be done using the First Pass bit, S:1/15 in RSlogix, to set Word 2 of your Control word (probably will be R6:2) to 0. Use a 5-second RTO timer to control the time between steps.

"If the Sequencer is stopped, or if a loss of power is experienced, outputs must de-energize "

means that you can use a RTO (Retentive Timer) instruction to control the SQO. Loss of power must mean not PLC power but circuit power. Otherwise this contradicts the previous instruction. When circuit power is lost, all outputs will normally BE deenergized, so you only have to worry about when SQO is stopped. You could use the required Start/Stop Input bit to set all outputs to 0 (de-energized) when Start is NOT ON.

"and when the power is returned, Sequencer must pick up on the step it was at"

means that if you don't reset it, it will continue working on the same step when power is restored. So use an RTO timer to control the SQO. RTO's do not reset when power is lost. Use a maintained selector switch (Start/Stop switch) to make sure when power is restored that the SQO restarts at the same place.

 

[somebody]

I've tryed to post it here, but I don,t have the RSLogix program on my home computa so I can,t. I've tryed to draw it out and scan it then cut and paste it, but that did not work.

 

[OkiePC]

To add a JPEG to your post, use the "display pictures" button below the text entry window. The picture must meet these requirements:

- Max filesize: 300 KB
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[somebody]

Thanks OkiePC for the infor on displaying pictures.

 

[RichBlunt]

I recently had a job that was all sequencers utilizing the SQO,SQI it was a nice idea, the intention being that no one should ever have to troubleshoot from the plc.
I still think I prefer standard 5 rung maintenance friendly logic.