FactoryTalk direct referencing vs HMI Tag DB

Hi. I would like to know experienced opinions about what's the point of making an HMI tag addressed to a device tag if you could just direct reference it through RSLinx Enterprise? If the choice is there it must be because of something. You could even use offline files if the PLC is offline so I don't know why would you take the time to create a device HMI tag alias if you could just browse to it directly. I've heard some people despise direct referencing. What are the pros and cons of both methods? Thanks for your answer.

Mi Vale:
I´m suppose your talking about FT View SE, and I would say that in the past they were used only for alarm purposes. But nowadays with ALMA and ALMD, I don´t see the reason to use them. But if you´re talking about FT View ME then HMI tags is the only way to set up alarms.

widelto said:

if you´re talking about FT View ME then HMI tags is the only way to set up alarms.

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Yes I'm using ME, I'll find out down the road when I get to the part of setting alarms up, thanks for the tip. So other than that what's the benetfit of using application tag DB instead of direct referencing?

This is an excellent question! I also want to hear what others think is the answer.

I have been using View ME since version 3.00 and I've always made a tag database for my projects. Now that we are on version 5.10 I have encountered a couple of jobs where I had to follow someone that used direct references. This means there was not a tag database, they just input the direct tag.

I also know of a situation where another engineer here had to use a MicroLogix 1100 with a serial connection (sounds strange to you too?) to a Panelview Plus and the tags would not work at all so he had to use direct referencing.

The irony about the View ME software is the tag database is pointless as far as I can see. There is no cross-reference. If you change a tag name in the database it does not "fix" the program where you used the tag. It's not really a tag, then - is it?

So back to the OP's question: What's the point of making an HMI tag addressed to a device tag if you could just direct reference it through RSLinx Enterprise?

Alarms can be direct reference or HMI. Not an issue.

I like the "idea" of direct reference tags, but tend to prefer HMI tags. My biggest reasons are:

• I can define properties like Min and Max once for an HMI tag. With direct reference you must specify your min and max values for each animation occurrence.
• If an address changes in the PLC you must replace every direct reference. HMI tag only needs to be updated in the database once.

HMI tags are more work up front and are probably slower at updating, but I do prefer them.

OG

Looking at it from a programming point of view; With the shift in programming paradigms to portability, re-usability, and object orientation it makes sense to use HMI tags.

You can rapidly deploy your screens on different architectures without having to change object properties.

This is all IMO, pretty much no industry experience here.

HMI tags all the way. I actually use the Logix Tag Import utility for most of the grunt work, even though it is 'not quite finished'. Then I go and edit things in Excel, and import them into FTView ME/SE.

Direct reference tags might be okay for some small, one-off projects, but I tend to find them annoying to work with. Just some simple reasons, they don't have description fields (handy for displaying them on a trend), they can't be scaled, and due primarily to the incredible lack of tag/display/code cross-referencing, if you have to re-assign a tag, it's much easier to change it once in the tag database.

Properly structured, it is simple to reuse displays and such for similar projects. Export to Excel, change the topic name, re-import.

Here's my 2c, I have only done one project with FT ME, there were 2x 10" screens, plus a 6" developed by another company that I had to modify.

I started off with a tag database, but then found during startup that the memory was getting low reasonably often, and coming up with an annoying windoze error message.
Then, it became a task to update the application due to low memory issues. Cycling power was the way to overcome this.

I then looked at direct referencing, and found that not only did they update faster than the tags that were in the database, it also helped to reduce the tag database size, therefore overcoming the issues I mentioned above.

I do still have a certain no of tags, for the purposes mentioned above, such as trending & Setpoint limit entry etc, and also for some descriptions, but that is it. The reduction in file size was a huge benefit, as was the faster update. I do agree about the portability & single point of modification etc, but in this instance I had to look at an alternative option.

We have since upgraded the terminal CF & Ram to a larger model, so the tag database size may of not been as much of an issue now, but I am sticking with direct referencing on this project, & if we do another one, would probably do it again.

Operaghost said:

If an address changes in the PLC you must replace every direct reference. HMI tag only needs to be updated in the database once.

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Good point.

You can change the address by deleting the tag and then creating another one with the same name, assigning the new address at creation.

Paul B said:

Good point.

You can change the address by deleting the tag and then creating another one with the same name, assigning the new address at creation.

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True, but correct structure (IMOHO anyway ), should negate the need for having to do this, a tag is a tag. Its connection to the real world is all that should be changed.

95% of our projects these days follow this method, that way the HMI/SCADA can be developed without the actual IO allocations, this can be fitted in at any time.

This goes for all types of PLC's, whether they be tag based or address based.

My comment was tounge in cheek...

With most any other hmi programming software you can rename a tag, change the address the tag points to, etc. With View Me renaming the tag breaks it, references to the old tag have to be manually corrected. And isn't it silly the only way to change the address is to delete the tag and re-create it?

When I first started I used to transfer PLC tags to HMI tags until I learned the direct method. If it is 1 on 1 I chose this method. Then I got into tag replacement to reduce pages and work load. HMI tags are needed to do this. So I vote both.

Paul B said:

My comment was tounge in cheek...

With most any other hmi programming software you can rename a tag, change the address the tag points to, etc. With View Me renaming the tag breaks it, references to the old tag have to be manually corrected. And isn't it silly the only way to change the address is to delete the tag and re-create it?

Click to expand...

Not sure I follow you there. You CAN change the underlying PLC address/tag name tied to the HMI tag without deleting anything. I do it all the time.

What you cannot do is rename the HMI tag once it has been created. You must duplicate it and assign a new name to the new tag and then if required, delete the original. Clumsy, but not all that unusual.

OG

I understand this is an old thread, but I just wanted to insert an idea here that has not been mentioned. Whenever I get to build the HMI & PLC programs from scratch, I always create dedicated arrays in the PLC for transferring data to/from the HMI. So they will be named something like To_HMI and From_HMI. Maybe event a UDT to handle all forms of data, but sometimes a DINT and a Real to cover everything. So the value for water flow, for instance, will be moved to array tag To_HMI[5] or such. If in the future this needs to be changed in the PLC, just change the value being moved to To_HMI[5] and you are set. If you start off this way and make your arrays versatile enough, you won't ever have to do massive changes in the HMI project.