RsLogix 500 - Sequencing Machine Steps Part 7 - Sequencer Instructions

In this lesson you will dive deep into how the LAD 8 SEQUENCER routine of the previous RsLogix 500 - Sequencing Machine Steps uses sequencer instructions to sequence through steps.

If you are looking for the text book answer your instructor wants then here you go, but if there is one method that industry frowns upon then this one is it.

The advantages of this method are few, aside from the fact that this instruction is designed specifically to sequence through events.

The disadvantage of this method is not accepted by industry. I always like to share the example of when I was an young eager programmer using this method and the veteran maintenance manager asked “What's that?” I thought I was about to teach that old man something and went through my spill about how it worked and how easy it was to adjust machine operation. He looked me dead in the eye and said “If you ever put that on one of my machines again then you won't be allowed back in my plant”. He went on to explain while this method was clean to program, it is very tough to troubleshoot. Also while most PLCs have some type of sequencer instruction, they vary significantly from brand to brand so in a plant that has a variety of PLCs, it is very difficult to train maintenance personnel to troubleshoot them where as an input, output, timer, counter, etc instruction is fairly universal from brand to brand.

1.  Download the CougarTurnSignalSequencer.RSS file.  This is a simplified version of the RSS file you used in the Sequencing Machine Steps lesson, only including the sequencer instruction sequence programming.

2.  Open the RSS file in RsLogix 500, download it to your PLC, switch the PLC to Run Mode, and Go Online.

3.  Open up the LAD 8 SEQUENCER routine.

4.  Turn on I:0/0.  It should still be wired to the Green button from the previous lesson.

5.  Your screen should be sequencing through rungs 1-3 similarly to the video below.  You may have to right click the image below and open and new tab depending on your browser.

sequencerturnsignal.gif

 

 

This programming example is here mainly to acknowledge that this method exist however since we don't recommend it, we are not going to get into the details of how it works.  RsLogix 500's help file has some very detailed information on the SQL Sequencer Load and SQC Sequencer Compare instructions. 

Continue to the next lesson, RsLogix 500 - STI Selectable Timed Interrupt for Precise Timing.

Next Steps

Go to the Allen Bradley RsLogix 500 PLC Training PLC Training Getting Started Lesson series to select your next lesson.  There are also many other Lesson Series on PLC Programming and Industrial Automation.

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