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Drum Not Activating Outputs

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I am using a Samba 4.3 to control a portland cement grout batch plant. My original program just used analog input information and contact/coil logic to perform the batching operation. I am new to the ladder logic realm and I researched the Drum Sequencer as a better method to perform my operation. I have the drum configuration and scan in a sub routine for one of the batches that I produce and the subroutine kicks on when the operator selects the automatic batch on the HMI. When my analog input values change the drum index MI changes correctly, but the outputs for different valves/material handlers never come on. If the drum scan is powered by the rail, shouldn't the outputs change as the step index progresses?

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  • MVP 2023

Joe is correct.  Both must be in the Main routine as shown.

But I'll also add that if you have controlled the outputs later in your ladder, then these controls over-ride previous decisions made by the logic. 

Given that you say you are new to ladder logic, this is a critical thing to understand.  All your outputs should actually only have one ladder rung referencing each of them, and ideally this rung is active all the time.   ie there is only one appearance of a physical output in the entire program.   If you need to have multiple references to the same output, you do this in a variety of ways, the simplest being a number of MBs configured in that one rung so that when any of them are on, the output is on. 

Be careful calling outputs with subroutines, you can have situations where your output won't change state as you might think when you turn a subroutine on or off.

In some ways you need to treat PLCs like the dumbest of dumb.  You have to tell them everything, and in the correct sequence, to get them to work as you want.

A bit like descriptive text.  "Make toast and spread jam on it."  A tiny bit of this translates into:

1 Open bread box

2 Locate bread in bag

3 Find the end with the closure

4 Remove closure  blah blah blah   etc etc

And don't forget that all 4 of these actually involve far more bits of logic and actions to achieve.....I have simplified it a little to illustrate the point.  (And try to make you laugh!)  The entirely simple thing to make toast and spread jam would be an instruction set with many hundreds of individual instructions/references, all of them critical to achieving what you want.



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Thank you very much everyone! I was calling the configuration block continually. I set it up off of the power up bit and it works just fine now... after I figured out how to use a positive transition contact. I had the human Flash's musical drum for a minute calling a next step operation continuously.

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