I am using Control Logix version 15, most of the programming that I am familiar with uses step counters to step the machine thru the process. I am wanting to use sequencers, (SQI), (SQL), (SQO), in my program, I have created a User defined data type with all the information that I need but I am having trouble understanding how sequencers work, the items needed to make them work, such as array, mask, source, control(this one in particular), length, position. Any help would be useful, I have been to Rockwells Literature site but they do not have examples that are useful to me.
Sequencers
- Thread starter mrjig
- Start date
Alan Case
Lifetime Supporting Member
Please dont do that. Stepping through with a dint is so much easier to follow for everyone on else who ever has to work on your machine.
Regards Alan
Regards Alan
TConnolly
Lifetime Supporting Member
Ditch the SQL and SQI. Use the SQO and condition the input rung to advance for each step.
I gave a really basic description of the SQO in this thread:
http://www.plctalk.net/qanda/showthread.php?t=17323&highlight=SQO
While I wouldn't normally use a sequencer to solve that particular problem, the original poster asked and it was a simple example for the explanation.
I gave a really basic description of the SQO in this thread:
http://www.plctalk.net/qanda/showthread.php?t=17323&highlight=SQO
While I wouldn't normally use a sequencer to solve that particular problem, the original poster asked and it was a simple example for the explanation.
Last edited:
mellis
Member
I have to agree with Alan here. Just because a PLC has a sequencer instruction in no way means that it is the best way to control a sequence. Your questions are some of the best reasons NOT to use one. I just spent the last two weeks troubleshooting a program someone else wrote with SQO instructions.
In my opinion, the use of an SQO is intentional obfuscation.
In my opinion, the use of an SQO is intentional obfuscation.
Mickey
Lifetime Supporting Member
I had to look it up.
Obfuscation refers to the concept of concealing the meaning of communication by making it more confusing and harder to interpret.
Obfuscation may be used for other purposes. Doctors have been accused of using jargon to conceal unpleasant facts from a patient. Author and doctor Michael Crichton has claimed that medical writing is a "highly skilled, calculated attempt to confuse the reader". [1]. Similarly text-based language, like gyaru-moji and some forms of leet are obfuscated to make them incomprehensible to outsiders.
Retrieved from "http://en.wikipedia.org/wiki/Obfuscation"
Obfuscation refers to the concept of concealing the meaning of communication by making it more confusing and harder to interpret.
Obfuscation may be used for other purposes. Doctors have been accused of using jargon to conceal unpleasant facts from a patient. Author and doctor Michael Crichton has claimed that medical writing is a "highly skilled, calculated attempt to confuse the reader". [1]. Similarly text-based language, like gyaru-moji and some forms of leet are obfuscated to make them incomprehensible to outsiders.
Retrieved from "http://en.wikipedia.org/wiki/Obfuscation"
Right on target, guys. That's what any Sequencer instruction is good for: confusing the problem.
In my opinion, the sequencer instructions were included back in the old days to make the PLC resemble the old mechanical drum switches. Drum switch = no flexibility, fixed inputs, fixed outputs. Why would you want to limit your PLC program in its flexibility?
In my opinion, the sequencer instructions were included back in the old days to make the PLC resemble the old mechanical drum switches. Drum switch = no flexibility, fixed inputs, fixed outputs. Why would you want to limit your PLC program in its flexibility?
jstolaruk
Lifetime Supporting Member
Slightly O/T, there is a GM facility near me that has only two requirements in their programming specifications: no use of sequencers and real I/O is not to be mapped to an intermediate bit.
Eric Nelson
Lifetime Supporting Member + Moderator
I actually used one of these drum sequencer instructions in the very first program I ever wrote (early '80s). It was written on an Omron S6 PLC used to replace, amazingly enough, an old Camco mechanical drum sequencer... 
I have never used any 'canned' sequencer instruction since...
-Eric
I have never used any 'canned' sequencer instruction since...
-Eric
I'm automating a pick & place overhead crane system, and the SQO has worked very well for automated P2P movements. Could I do it another way? Yep. Is the SQO a quick, dirty, easy way to call up nessecary already debugged subroutines? You bet. Even gives a nice Status indicator for quick refrence.
CaseyK
Member
When I first was learning GE Fanuc 9030's, I had about 100 PLC's running drum programs, and another 150-200 with mechanical drums. I thought it was pretty dumb, then I saw the original schematic for using relays. WOW.
Drum logic has it's place, and in a way, is another form of some Block Logic programs.
I don't use Drums much any mmore, but will if it is the most logical for the job.
Very handy when the operator must make a lot of set up changes, such as for building 20-30 different sized tires on one machine.
regards.....casey
Drum logic has it's place, and in a way, is another form of some Block Logic programs.
I don't use Drums much any mmore, but will if it is the most logical for the job.
Very handy when the operator must make a lot of set up changes, such as for building 20-30 different sized tires on one machine.
regards.....casey
rdrast
Lifetime Supporting Member
/Agree with almost all of the above. Sequencers, unless directly translating a mechanical drum to a PLC in a hurry, are a true pain to actually work with and debug.
SInce you are using Logix5000 anyway, you might consider using an SFC routine for your sequenced logic, as it is much clearer what is going on when someone looks at it. Of course, many people aren't familiar with SFC either
And, for those into TRUE obfuscation, I give you:
http://www0.us.ioccc.org/main.html
SInce you are using Logix5000 anyway, you might consider using an SFC routine for your sequenced logic, as it is much clearer what is going on when someone looks at it. Of course, many people aren't familiar with SFC either
And, for those into TRUE obfuscation, I give you:
http://www0.us.ioccc.org/main.html
jstolaruk
Lifetime Supporting Member
I always felt C/C++ was naturally confusing without any extra effort.
leitmotif
Member
I think you have to learn sequncers first and understand how they work to choose when and where they are appropriate to your application.
I grant they are kind of a pain to set up
takes a couple of data sets
and you gotta keep all them numbers in the "right box".
TO LEARN
start with a simple traffic lite for a 4 way intersection.
littlemore advanced a home washer.
When you can get these to operate correctly you will now know enough to choose a sequencer for your operation or do something different.
Dan Bentler
I grant they are kind of a pain to set up
takes a couple of data sets
and you gotta keep all them numbers in the "right box".
TO LEARN
start with a simple traffic lite for a 4 way intersection.
littlemore advanced a home washer.
When you can get these to operate correctly you will now know enough to choose a sequencer for your operation or do something different.
Dan Bentler
Rod
Member
Am I stupid here? (probably)
I am ONLY familiar with the 'drum' on an AD06 and it only took me 30 minutes to code 4 drums, each triggering the next drum and then retrigger the first drum with 4 timers between them.
What am I missing?
Please educate this old man.
Rod (The CNC dude)
I am ONLY familiar with the 'drum' on an AD06 and it only took me 30 minutes to code 4 drums, each triggering the next drum and then retrigger the first drum with 4 timers between them.
What am I missing?
Please educate this old man.
Rod (The CNC dude)
Alan Case
Lifetime Supporting Member
The sequencer instructions are a fair bit harder to follow on an AB compared to an AD.
Regards Alan Case
Regards Alan Case
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