A PI Tag -- it's basically
a unique storage place in the PI Server
for a specific stream of data.
In fact, you will hear, sometimes used interchangeably with the term
Data Stream. But, in fact, a PI,
a PI Tag is where we would store, for example, the
flow rate from a flow meter, or if
you have got a, a controller, the mode of the controller
is stored as a Digital String. Then that would be
stored in a PI Tag. Other
examples of Tags: for example, the, the batch number
that's associated with a product when you are doing Event
Tracking using our Batch System. If you have got some
operator comments that you'd like to store in a --
store on the Pi Server, we do that through a Text Tag.
The results of a calculation. Those are all things
that would be considered PI Tags. Let's take
a look at a Tag. Here's graphically
what a tag would look like. I am looking at
three tags here, and I -- if
I zoom in I can see this represents real-time process
data. So this, the fundamental unit
of PI, is known as a tag.
Sometimes you will hear it called a point as well.
Now, if you chose
that you would like to create the Default PI Points, then you will notice
there's a series of tags with, with
unique names like Sinusoid and
CDT158, and this
CDM158. There's a whole series of about 10 or 11
tags that you will find you kind of get by
default, and those are great tags to keep around
for testing purposes. As I have mentioned before, you know,
if you are having, for example, problems with your OPC Interface,
and you think it might be an
archive problem and not an interface problem,
simply check to see if the values of these tags
are changing. If the values of these tags are changing,
then you know what you have is
probably some kind of an interface problem and not a problem
with the archive, since the test tags are working.
Every PI Tag belongs
to a Point Class. Now, Point Class is going to identify
how many Attributes that particular Point
supports. So, all PI Tags support the
Base Attribute Set. The Base Attribute Set's a series
of these 39 Attributes, and they are very simplistic things like
the Name of a Tag, the Zero,
the Span, the Engineering Units, things like that.
Now, in addition to those Attributes, we
al... also have other Attributes that are required for
different purposes. For example, if you are
getting your data in real-time like from a Control System like the
vast majority of PI Tags are, then there are
going to be some additional Attributes, what we call Classic
Attributes. Now, I am going to go ahead and retrieve
the Classic -- a set of Classic Attribute Tags.
I am going to use the PI System Management Tools to do this.
So, let me to into PI SMT.
That's used to import Tags. We will be going over
this later on. And so, for the Point
Source, I think what I will do is I will look at all Point
Sources, and I will look for all the PI Tags
that begins, that begin with the letter CD.
It's going to bring in all Attributes for this.
Now we are going to look just at a Point Class called Classic.
And these are the different Types of Points you could have.
I am just choosing Classic.
And, as you can see, this has
brought in a small number of Tags, three Tags,
and each of those Tags has
a series of Attributes. So these are, you know,
some of these are Base Class Attributes, some of these are Classic Attributes,
but these are the Types of Attributes that you are going
to see when you start
building PI Tags --
you know, things like the, the
Span and the Zero that's
associated with a Tag. Now those are the Attributes.
And, as I mentioned, every PI Tag
has all these 39 Base Attributes.
Now, beyond the 39 Attributes, it really depends on
what the purpose of that tag is.
As I mentioned, for gathering real-time data, we have Classic Attributes.
And, we will look at those one at a time. We also have
specialized tags such as Totalizers, SQC Alarm
Tags, Regular Alarm Tags, and these have the
Base Attributes plus a variety of other Attributes. In this case,
18 for the Totalizer,
26 for SQC, and Alarm
has another 22 Attributes.
So, at this point, I am going to go through a series of the
Attributes and just describe the Attributes briefly.
Now, first of all, every PIPoint has a
Tag Attribute. Tag is simply the name of the Point.
So it does have certain constraints. As we see
here, first character must be a letter or number.
They must be unique on the Server. And, we do not allow any
control characters. These characters that you see right here
-- those characters are not allowed. So any
of those characters, it's just going to object to that.
Also, we do suggest you avoid the Underscore. The Underscore,
not a good idea because if you are making use
of any of our SQL Query Tools like the ODBC
Support or OLE DB Support, you will notice the Underscores
may run into problems when passed to those
types of Applications.
Another Attribute is the
Descriptor, and a third is the Engineering Units.
Fairly self-explanatory, these are
obviously spelled exactly as shown.
So, one of the most common mistakes people make
when working with, you know, these types of things,
is they may, they may misspell something.
For sos... for example, we are looking here
at the Attribute named Descriptor. If you
misspell that description, for example, you try to edit
this, then that's going to give you an error.
Now, next up in our List of Attributes,
is PointType. And for PointType --
well, let's take a look at a couple of the slides
in. This is the variety of PointTypes that we support.
By default, all PI Tags are Float32s.
That's a Single-Precision Real.
Now, we do support higher resolution, but that does come
at a cost. It's going to be twice as large
on the -- the number
component's going to be twice as large on disc. We also
support something out of Float16. But, that's mainly
to maintain incompatibilities of older versions of
PI. We support Integers.
And we also support Digitals. Digitals
would be discreet values like On-Off,
Open-Close, etc. Let's take a look at
a Digital Tag. I am going to switch
over to a copy of Excel. And here's a PI Tag
called CDM185. As you can see, it's
got different values that are -- they look
like Strings but, in fact, we are storing them internally as Integers
that are mapped to a Digital State Table.
So, you know, compare that to,
for example, a Real Tag, a, a, Real
Float, Float32. That would be
showing us as a Single-Precision Real.
So, the comparison here is, of course, this is going to
be a finite number of String entries.
And that's what we have for support for Digitals.
And in, in addition to those,
we also support String Tags themselves f
or Operator Comments, for example,
we do support something called Blobs, Binary Large Objects. Not very
big at this point, only 976 bytes,
but we do, you know, plan on supporting
being able to associate large files
like multi-media files, like pictures or WAVE files
or something with PI Tags. And then, finally,
we have Timestamps. You can, itself --
or store a timestamp itself that will have a timestamp
that represents the time at which you stored that timestamp.
So, these are the different Types of Points that
you, that you can create in PI.
The Zero and Span are used to specify the overall
range of the PI Tag, and that does have
implications in a couple of applications. Now, for example, with
a Zero of 50, that means the
bottom of the range is going to be 50. The Span
of 100 means effectively we go from 50
to 150. Now, for
Float32 Tags, there's really no
implication in the archive for this. For Float16 Tags,
this actually will limit the
Values that can be stored in the archive. About the only thing that
this affects for other types of Tags is
the, the displays that you will see in ProcessBook. So, for
example, if you take a look at this display in ProcessBook,
if you notice the -- this particular
Tag, CDT158 -- we are currently looking at this
using an Auto-Scaling Function. Look at
Auto Range is turned on. So, we span from
whatever the Current Values are for the Y
Axis. If we switch over, make this database,
then you will notice we are simply going to pick up that Zero and Span.
There we go -- we are picking up the 50
to 250. We are picking up that Zero and Span
from the PI Tag. If we were to look at the Attributes
of this Tag, you will notice the Zero is 50 and the
Span is 200. And,
perhaps the easiest way to demonstrate that is to just
go ahead and select this Trend, and use the lee --
use this little binoculars here to indicate we are going to look at
the Tag Attributes.
And, if we look at the Zero and Span,
you will see the Zero is 50, the Span
is 200. Now, this affects
a variety of different things within our Client
Applications. Of course, in RtWebParts, the visualization
tool for Win... or for the Thin Client
on a web, we have that same effect.
And one, perhaps
more subtle is that if you were to take
this object right here and make it into a
Multi-state, and make
use of that Tag, CDT158, notice
that the number of states
that you choose are going to be split
among the numbers in
the Range. So, if you look, this goes from
50 at the bottom, all the way to 250. Now, that is
something that will definitely be limited if you
do not set your Zero and Span properly. Occasionally we find
folks who leave the default of Zero
to 100 since the PI System
will store something beyond the top of the Range. Well, when they
go to use Multi-state Symbols, they are disappointed because
they cannot go beyond the Range that's specified
in the database. So, be careful of that.