Hello forum participants,

I keep on seeing references to ''tags'' in different discusions here, like in statements
of the kind ''...access to the tag from HMI...''
or ''...alarm on tag...'' etc. What is actually
meant by the word ''tag'' in these cases?
Is it just plain value of some device or something more ?

Happy New Year

Yours sincerely
Ariel Burbaickij

 

In short the name of a control element (controller, analog/digital input etc).

Longer:
In the old instrumentation days separate instruments (controllers, valves...) had a small label ("tag")attached to the instrument with the name of the instrument seen in the diagrams - for instance FIC2100(flow controller).

Today, with the digital control systems the various measurments or loops have names similar to the old "tags", which are still called "tag names" despite the fact that all these names does not always have phisical instrumet or real tag attached to an instrument. Today the tag name FIC2100 could be the name of the software control algorithm performed in a digital control system - virtual "instrument".
The name "tag" is now interchangable with "variable" or "point" - > control tags = control points.
"Alarm on a tag FI2100" means "Alarm on instrument (or measurment) FI2100"

Hope this helps.

B.Baharov

 

Tags are similar to variables in a programming language.These are connected to a particular addressin a PLC. It can be either an input, output or dataword,counter or a timer

 

Essentially, yes. A SCADA tag is equivalent to PLC point (coil or register).

The main difference is that it often has associated properties with it, like units, range or human name, which in a PLC are usually relegated to the programmer's documentation.

Depending on the SCADA, parts of the program might be notionally associated with the tag (for instance alarms, display, etc), rather than being gathered together in a main program. If the SCADA does that a lot, it's called "Object-Oriented".

Jiri
--
Jiri Baum <[email protected]> http://www.csse.monash.edu.au/~jirib
MAT LinuxPLC project --- http://mat.sf.net --- Machine Automation Tools

 

> What is actually meant by the word ''tag'' in these cases?

"Tag" is short for "tagname", and refers to a named value. Most SCADA software systems use some form of database in which process values (I/O
points, configuration variables, etc) exist as named records. "Tag" can refer to the record, to its name, or to the "current value" of the
point/record.

Regards,

Greg Goodman
Chiron Consulting

 

Hello Ariel
Tag is a substitute name for refering to an device in industrial.For example in instrument refer to tranmeters,valves,I/P,junction box,cable,cabinet,controler,.....
Tag uses for refering to an above element and is a name for one element.Like these:
2-FIT-335 ------->FLOW TRANSMETER NO. 335
2-FIT-336 ------->FLOW TRANSMETER NO. 336
3-PIC-023 ------->PRESSURE CONTROLER NO.023
5-JB-001 ------->JUNCTION BOX NO.001

and Etc.
Best regards

 

As I see it, a 'tag' as used in HMI systems is a name associated with some value, which might be representive of a register in a PLC or some
derived value in the HMI itself. I first encountered it in the Wonderware Intouch HMI system, in which the 'tagname database' is a key component. It's a symbolic identifier, synonomous with 'variable' in many programming languages.

--
Ken Irving <[email protected]>

 

A tag is a unique, alphanumeric identifier for a device or a measurement point. Often the identifier is constructed according to a scheme which allows an experienced person in the plant to
identify immediately which part of the plant, which machine, what type of measurement etc. Tags often appear on mill diagrams which allows you to pinpoint where in the process the measurement was made, and are also used as a unique key to reference the measurement in DCSs and data archiving systems.

Diana Bouchard
Pulp and Paper
Research Institute of Canada (Paprican), Pointe Claire QC Canada
dbouchard(AT)paprican.ca

 

Hi, Ariel,

I first heard the term in connection with Wonderware licensing (1500 tag license, 5000 tag license...). It fundamentally refers to some atom of information stored in some device, be it a PC, a PLC, or a HMI. It could be a discrete boolean bit, like "MOTOR ON", or an integer or floating point value, such as "OVEN TEMPERATURE". Many HMI applications use the term
internally, although its usage seems less common in PLC's, but on this forum, I would just read it as "a boolean or analog variable in some device,
or the value of that variable".

 

A tag in an HMI program is similar to a variable or maybe a struct in a "normal" programming language. Of course, they must confuse the issue and not call it a variable because then it would imply "programming" The HMI vendors like to advertise that "no programming is required", so they must create new terminology to separate themselves from the C++, Java, VB... crowds.

Bill Sturm

 

On Mon, 30 Dec 2002, Steve Myres wrote: [...]
> Many HMI applications use the term internally, although its
> usage seems less common in PLC's, but on this forum, I would
> just read it as "a boolean or analog variable in some device,
> or the value of that variable".

Pretty good modern description.

A long, long time ago the "tags" were metal tags affixed to the field devices by the suppliers as specified on the PO. The process went something like this. An engineering firm lays out the control scheme, and assigns a unique identifier to each control device, i.e. TCV1 was a temperature control valve somewhere, PR12 was some pressure regulator somewhere, etc. For a big plant these "tagnames" would also include a system designator like FW-PR1 would be a pressure regulator in a fresh water system.

Once all the drawings were complete and signed off, then a purchaser would go the the various vendors and place orders for all the parts. Obviously, for a big electric generating plant or pulp wood plant with thousands of instruments getting delivered some way was required to keep track of what valve was supposed to go where. So part of the purchase agreement was that the instruments vendors would supply the parts with a tag embossed with the identifier. This tagname then became the device's name forever.

As HMI software came along it became natural to keep the names of the devices as the identifier inside the software, too. By now, however, the concept of a tag in the HMI software has expanded to include all kinds of stuff like memory variables, status bits, and who knows what not that have nothing to do with a field device.

But, such is the nature of language.

MB
--
Michael R. Batchelor - Industrial Informatics, Inc.
Contribute to society: http://www.distributed.net/ogr/

 

Hello List,

To be short "tag" is a value that identifies type of a data (e.g., 0 - to identify integer, 1 - for float, 2 - for boolean, etc.)... or (as a jargon word) it is used to point the data (that is identified by the tag indeed).

or

"Computer Science.
a.A label assigned to identify data in memory.
b.A sequence of characters in a markup language used to provide information, such as formatting specifications, about a document."


or

http://dictionary.reference.com/search?q=tag


--
Best regards.
Vladimir E. Zyubin mailto:[email protected]
Saturday, January 04, 2003, 7:19:38 PM

 

Many systems support tags where the main tagname for an object has many subtags, so for example the Set Point of TC124 can be addressed as TC124.SP

Some (the more modern object orientish ones) support more 'hierachical' tags such as R123.TC01.SP where R123 is a reactor unit and TC01 is the first temperature in the unit. Or even longer tags like Area1.R123.TC01.SP
This is particularly true with DCS systems, although some SCADA and even PLC languages support this to a degree.
IMHO, tagging schemes are hugely important, for making software production efficient and for operation.
Unfortunately a lot of the tag numbering schemes I come across are not as logical as they could be, and this costs.

If the tags in all similar units are the same then the same software modules should be able handle them all.
If not then these lists have to be produced and documented and possibly each similar unit coded individually.

Francis
www.controldraw.com

 

A "tag" or "point" used to be one simple field instrument such as transmitter, valve, switch or solenoid. That was back one devices were dumb and you only got one variable to/from each devices. Back then a plant with 5000 field devices needed a system for 5000 points/tags. These days even transmitters use communication networks and you can now get hundreds of variables of each in the case of FOUNDATION(tm) Fieldbus. Since systems today are so information intensive it no longer makes sense to count individual variables. We (Smar) count function blocks instead, where each block (object) may group together a few up to hundreds of related pieces of information and has some additional attributes. Even the simplest system can have thousands of parameters (tags) so preferably your HMI should be licensed in such a way that you only pay for as much as you would use simultaneously at any one time, not for all that exist in the system since 99.9% are idle.

Jonas Berge
==================
[email protected]
www.smar.com

 

Good observation Jonas;

I've recently created a system using Wizcon with 10,000 tags, only 2,000 of which where actual I/O.

They only charge for the tags that are communicating with external devices and not ones used to for internal manipulation.

Good development environment.

Mark Hill