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I think one of the best ways to learn about
Performance Equations Syntax is to use the
PI Point Builder for Performance Equations. Now I
know not all of you may have access to this, but those of you who
are system managers or who have access to the PI System
Management Tools, I suggest you open this up. It's not critical
but it's just a nice tool. So, you'd find that under
All Programs, PI System. This is called the PI
System Management Tools, and under
that we're going to go into the Point Section to the Performance Equations
Builder here. Now, this
Performance Equation Builder allows me to enter
certain Performance Equation
Expressions like the one that you see right here. This
Performance Equation Expression uses a function
and this is a good starting point for our discussion of,
you know, what, what types of functions are available
from within Performance Equations. And that's the
topic of our next section.
There's a whole library of functions within
Performance Equation which we're really very proud of. These are
functions that you would find that are very useful for folks in manufacturing
and these are functions you may not find in other applications.
You certainly don't find them in Excel or Visual Basic or some of the
common Expression Syntaxes. So, for example,
all these functions they, they have some very useful
purposes for people who are looking at Real Time Data. Percent
Good, for example, will return
the percentage of Good Data for
a given period of time. So let me illustrate.
I'll go ahead and bring up our Performance Equation Syntax
again, or Performance Equation Parser here.
Here we see Percent Good. We're looking for
the amount of time, or the percentage of time during
this last day, * minus 1 day to the current time.
It's CDT158 has been Good.
And when we evaluate this, we end up with 100
percent. So, that's just one example of a function
that's, that's fairly useful in looking at Real Time Data.
Some of the other functions are things like
What's the Range of a Process Variable during a
given period of time? What's the Standard Deviation
or the Average, or the Mean, or the Max, the Min or the Totalization
during that same period? And then, in addition to those,
there are many, many other Expression
Functions here. So, if you look at
this list here in our Reference
Manual, you'll find all kinds of very useful functions
as I said, like Percent Good,
functions that are kind of
geared just towards Real Time Data.
Now one of my favorites is, for example, Time Equals.
Give you an example of that. If I would like
to explain, or to derive, how long
a given tag, for example,
this Digital Tag, CDM158.
Let's see how long in the last,
oh, let's say the last Day Shift, Y + 7
hours
to Y + 15
hours. Let's see how long
that's been Equal To the word Auto.
This is going to return that value in seconds. So when I
Evaluate, it tells me for 6600 seconds
this tag, CDM158,
has been Equal To the word Auto, which are the
digital state Auto. So again, that's one very simple
example. We have other functions
available. You'll see all the typical Trig Functions,
Sign, Cosign, etc, plus as I mentioned,
these things that are specific for working with Real Time Data.
We also support an If-Then-Else structure.
So, for example, I can have an Expression like
this: If the Value of
Sinusoid is
Greater Than 50, then, we'll say 1
else Zero. We'll go ahead and
Evaluate this, and apparently the Value of
Sinusoid is currently Greater Than 50.
I have this If-Then-Else, and I can nest these
If-Then-Else's together. So there's no, you know, no artificial
layer of depth that you have to go to for If-Then-Else.
You can do it until you run out of space basically. Now
sometimes when working with an If-Then-Else -- well, you won't really need
that Else portion, you really just want an If-Then. We do have a function
called No Output, which essentially ends up
not changing whatever tag is involved, so it,
there's going to be no Output for that. So that's it on our
discussion of Performance Equation Functions and Syntax.
As I said, there is much more information that you'll find
in the Help File, PE Reference.
You'll find it in this Directory right here.
If you don't have that, there are instructions in your workbook on how to
download that from our Tech Support Website. So as we
work with Performance Equation Syntax in this class,
remember, these are your resources to look up these functions,
to understand how these functions work, etc., and see examples.