Example code for Allen Bradley’s MicroLogix 1000

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Thread Starter

Andy

Could you please email to me an example code utilizing Allen Bradley’s MicroLogix 1000
SEQUENCER INSTRUCTIONS.

SEQUENCER COMPARE
SEQUENCER OUTPUT
SEQUENCER LOAD

Simple application:

Imagine the machine has 3 Double Acting Cylinders with proximity on them and single solenoids, one start button and one stop button.

When Start button is pressed first cylinder to actuated, when sensor indicate full extension wait 2 seconds and actuated the second cylinder and retract the first, when sensor indicate full extension wait five seconds and actuated the third cylinder and retract the second. If at any time the stop button is pressed everything stops and all cylinders retracts.

That’s it.

Can you do this?

Thanks

Andy
 
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Joe Jansen/ENGR/HQ/KEMET/US

This could be done with a sequencer, but why? Sequencers are best used in recipe type applications. If the description below is all you are looking to do, it is fairly simple ladder.

The biggest problem with Seq instructions is that they are very difficult to document well.

I will post something on the PLC Archive for you....


www.PLCArchive.com

--Joe Jansen
 
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Joe Jansen/ENGR/HQ/KEMET/US

Actually, rather than post it, I will just send it to you. It is a PDF file, so you will have to open it with Acrobat Reader, but the code is
generic enough to use.

Functionality is only half the problem. The other problem is maintainability. Sequencers are just too hard to propeerly document their
flow. You end up looking at big charts of bits, and cross referencing to the I/O table. Coding small projects like this into a well structured
ladder is much easier to read and maintain. You can probably stay on top of this one without ever needing a printout.

As I said on list, Seq instructions have their place, but it is usually for large recipe and batch processing projects where you are needing to
reprogram the function of the machine for each product produced.

Anyway, Hope that this helps!

--Joe Jansen
Maintainer, PLC Archive
www.plcarchive.com
 
Mr Joe Jansen:

Thank you for taking the time to respond to my questions about sequencer, that was precisely the answer I was looking for and your sample code could not say it better.

Thanks again Mr. Jansen.

Andy
 
M

Michael Griffin

If it is really that good of an example, then it would probably be a good sample for the PLC Archive.

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Michael Griffin
London, Ont. Canada
[email protected]
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