What's up with "tags"?

I've worked with slc500 for years and now have a controllogix5000...what's the benefit of "tags". It looks like I can address my contacts or coils without them...can someone explain?

Oh, and first post...w00t!

The only semi-fixed information is that for inputs and outputs. Other than that the 'location' of integers, bits, timers, counter etc is up to the operating system. In the SLC you referred to a specific memory location for these. In the 'ControlLogix' world there is no fixed location. You say, 'I want a timer named Joe' and it sets aside a piece of memory with the structure of a timer and calls it 'Joe'. After that you can refer to Joes.DN or Joe.PRE or JOE.ACC without any worry about where it actually is. If you really wanted to stick to a somewhat SLC'ish naming you could make an array of timers called 'T'. Then you could have T[10].DN, T[10].ACC and T[10].ACC. But what's the fun in that?

The best comes with user-defined-types. Here you can put a whole bunch of different kindes of closely related information together, call that grouping by a name, and then create a new variable (or even an array of variables) with that type. This is much more powerful then ever in the SLC world.

From a process control point of view, tags make it much simpler because you don't have to remember or keep track of all the registers. Take a flow control loop No 101 for example Flowmeter, PID controller and Control valve
You name the I/O point for flow transmitter FT_101
the control valve I/O point FV_101
When you configure your PIC controller (FIC_101) you just call the input and output by the tag.
When you configure the HMI you also call the points up by tag.
This is how DCS systems have been doing it for years.
Once you get used to it you will never look back!
Roy

Can Logix5000 tags be created/modified/deleted during online editing?

Also, the use of tags that are descriptive of the fuctions they are involved in helps lead to self-documenting code.

An instruction with a tag named "Open_Pump1" means a lot more than an instruction with a register labelled "B3.0"

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Sergei Troizky said:

Can Logix5000 tags be created/modified/deleted during online editing?

Click to expand...

During online editing new tags can be created, unreferenced tags can be deleted, and tag names can be edited. However a tag type cannot be changed, eg, you can't convert a DINT to a REAL

Money4Nothing said:

Also, the use of tags that are descriptive of the fuctions they are involved in helps lead to self-documenting code.

An instruction with a tag named "Open_Pump1" means a lot more than an instruction with a register labelled "B3.0"

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Click to expand...

You do not need tags for this.
Device names (symbols) as in Logix500 are enough.

On top of that "Product_at_load_station_PEX" means a whole lot more, and is far more convenient than "I:0.0/1"...

Once again the same comment.
You do not need tags for this.
Device names as in Logix500 are enough.

Try expanding a timer file or integer file or adding a new file online in a SLC 500. Can't do it.

Sergei Troizky said:

Once again the same comment.
You do not need tags for this.
Device names as in Logix500 are enough.

Click to expand...

Maybe it's enough for you, and that's fair. But whether it's enough for others is a matter of opinion. The Logix 5000 method is much more preferrable to me.

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Alaric said:

Try expanding a timer file or integer file or adding a new file online in a SLC 500. Can't do it.

Click to expand...

Inability to change what may be called PLC Settings during online editing is a common property of most PLCs.
No doubt, tag concept adds some capabilities in this aspect.

Money4Nothing said:

Maybe it's enough for you, and that's fair. But whether it's enough for others is a matter of opinion. The Logix 5000 method is much more preferrable to me.
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Click to expand...

I will gladly agree if you specify noticeable difference between names and tags for the mentioned purpose.
I meant enough for what you described, not just enough for me.

Sergei Troizky said:

Can Logix5000 tags be created during online editing?

Click to expand...

Yes

Sergei Troizky said:

Can Logix5000 tags be modified during online editing?

Click to expand...

Yes, sort of, can modify name but not type.

Sergei Troizky said:

Can Logix5000 tags be deleted during online editing?

Click to expand...

Yes, if no longer used.

I'm not interested in trying to convince anyone of anything; I'm merely offering my opinion as an experienced programmer of both Logix500 and CLX5000 that the many advantages that custom-named tags give to a user are significant and helpful. I almost weep whenever I have to go back and work on a 500 platform.

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