We are about to start learning more about the individual tag attributes.
If you recall, the attributes
are just those things about a tag that define how the tag behaves.
Just to give you a kind of a preview of what's coming up with tag management, let
me take you
into the PI SMT utility,
or the tag configurator.
The tag configurator allows you to manage tags and their attributes from within
a spreadsheet.
So, for example, I can import
all of the attributes for my server,
for these tags.
Each tag,
represented by each row, has columns and columns of attributes.
This is the bulk tool for managing these tags.
If you are the one managing it, you don't have to do it one at a
time.
Let's start looking
at the individual attributes.
We'll start by looking at the name of the tag.
Now the name of the tag is basically a unique
name that's usually following some kind of local
naming convention.
We see naming conventions that
try to abbreviate things
to make it easier for people to find and understand what they're looking at.
To be honest though sometimes the tag names themselves can be pretty obscure.
For example, try to guess what this means.
I’ll give you a second. Pause this if you need to
and write your answer down on the line there.
OK. So what we're looking at here is
Motor #3,
Enclosure #1, Panel #2.
The name of that is Motor Drive 1202
and the
value we're looking at is the Run Status.
So taking this all together,
what we're looking at here is
a very obscure
local naming convention for showing us
exactly what it is we're looking at: the Run Status of a motor that’s located in
Enclosure #1, Panel #2.
That's typical of the name or what we call the tag.
In addition
there is a Descriptor.
Now the Descriptor is going to be something that’s usually a lot more user-friendly
or human readable as opposed to the machine readable one that we just saw. It's used a lot
in search criteria.
You can
search for tags by their Descriptor.
This is
what we would call the full name
and this would be more like the jargon that the instrument technicians
use for their naming convention or
just the short cut that everybody in the plant uses.
The Descriptor is typically the full name.
I should point out also sometimes
we see the Tag Name
equivalent to the name as it appears on the data source and the Descriptor
appears in a more
human friendly format.
Next is Engineering Units.
Engineering Units is an open field.
You will notice
that you can put in gallons/minute
or gallons per minute or gal/m
or gpm.
It's actually is something that is completely open. It's your choice. That can lead to
a lot of
inconsistency
from one
person who creates tags to another.
We do have, for purposes of
calculations in AF,
Engineering Unit
conversions
where the Engineering Unit you specify actually do you mean something.
But in the case of the
the regular PI point database,
the Engineering Units it is simply an open field that you can use.
Next we see the Point Type.
The Point Type is the
type of tag that we’re actually storing.
We've gone over all the different points types earlier: string, int32, real, float32, etc,.
The Point Type is something that's very useful when it comes to searching for things.
Most of the fields you see here are things you can search for in a tag search.
Point Type ends up being useful for that.
When it comes to Zero and Span,
all you have to remember is that the
Span is added to the Zero to get the overall range.
For example, if your Zero
is 0 and your
Span is 100,
then you’ve effectively got a range of 0 – 100.
Compare that to
the case where your Zero is 50
and your Span is also 100.
This is your range - 50 to 150.
The last of the fields we’ll look at
right now
that are common is the Point Source field.
The Point Source is used
to indicate what the source of the data is.
Typically it's a
character string of one or more characters that simply identifies
the source as in “H” for Honeywell control system, or
“B” for Allen Bradley
programmable logic controller, etc.
You'll find this used in tag searches.
If you know what the source of the data is, the Point Source will help you find
specific points.
All of these common
the PI attributes
are useful, as I mentioned that earlier, in the tag search. For example, I’ve switched
over now.
Within my tag search I can search for things
using specific Point Sources. For example
I just want to see those whose Point Source is “R” and
whose tag mask begins with the letters “CD”.
It shows me just that subset.
Compare that to, for example, when I look for all tags that use
that Point Source “R”.
Now what I'm finding is all tags the use the Random interface.
I can switch this to a different Point Source. For example,
Point Source of 9
stands for the Ramp Soak interface. I’ll find just those tags that are associated with
that interface.
Each of these,
the Point Type, the
Descriptor, are all searchable within the tag search.