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Thread: Do you use Alias Tags? Automation Talk for March 22, 2019

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    Administrator Shawn Tierney's Avatar
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    Do you use Alias Tags? Automation Talk for March 22, 2019


    One limitation of legacy programmable controllers like the PLC-5, SLC-500, and MicroLogix, was the inability to save "address names" known...

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    Member Paul Warning's Avatar
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    I advocate for IO Mapping, and I advocate using alias tags. However my interpretations of pros and cons seems to be a bit different than most.

    IO Mapping allows me to continue with software development before electrical design is completed. On larger projects it's inevitable the electrical design will change as the project evolves. As long as I have a current list of devices the control system will use I can write a functional program. Once we are ready to commission and I have the electrical "as-built" drawing set I can quickly generate IO mapping ladder logic (Excel is very powerful). This also ensures my development environment isn't limited in testing. I can move the program to a different type of controller for testing, and avoid any conflicts which might be introduced should physical IO references be present in the program but missing from the hardware tree.

    Alias tags are great for program replication, or for providing a readable reference to an element in an array.

    An extremely simple example is a program to control tanks within a tank farm (don't let the simple example equate to an AOI, keep a program reference in mind). I might have a program for tank control, which would essentially be the same across all tanks. Alias tags allow for extremely quick replication.

    Code:
    Tank #1
    -------------------
    InletValve - V101
    OutletValve - V102
    Agitator - M102
    Level - LT110
    
    Tank #2
    -------------------
    InletValve - V201
    OutletValve - V202
    Agitator - M202
    Level - LT210
    InletValve, OutletValve, Agitator, and Level are all PROGRAM scoped tags, aliased to CONTROLLER scoped tags.

    The alias allows the program logic to be identical between Tank 1 and Tank 2 programs, but provides for control of the different devices associated with each tank. You can make logic changes in one program, and copy them to another program without changing any tag references. If you need to add an additional tank, you can duplicate the program and simply update the program alias references to the new devices.

  3. The Following User Says Thank You to Paul Warning For This Useful Post:

    Shawn Tierney (03-25-2019)

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    Member tspisak's Avatar
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    I always use Alias tags for everything. Luckily I developed that habit of using symbols in SLCs & PLC5s and I have encouraged every new controls engineer to do the same. Online editing of tags has always been a pain. If I can't take the processor offline then I often rename the bad tag with a "zzz_" prefix and re-create the correct/new tag. So if you ever are in my programs - delete all of the zzz tags.

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    Shawn Tierney (03-25-2019)

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    Administrator Shawn Tierney's Avatar
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    Good afternoon @Paul Warning,

    Thanks for sharing your example - it's excellent! Very much appreciated!

    Shawn Tierney,
    Instructor at The Automation School
    Looking for affordable automation training? If you are, check out my courses at TheAutomationSchool.com!

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    Administrator Shawn Tierney's Avatar
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    Good afternoon @tspisak,

    Yeah, I've definitely used that strategy too! Thanks for commenting!

    Shawn Tierney,
    Instructor at The Automation School
    Looking for affordable automation training? If you are, check out my courses at TheAutomationSchool.com!

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