Now let's examine
how you would do an Expression Dataset,
a PI Calculation Dataset. I will select Tools
and Datasets and, again, New
PI Calculation. And what
I would like to do is a CDT158
Temperature, but in Fahrenheit.
So I will type in CDT158
_F,
and I will include a description this time. CDT158
converted to
Fahrenheit.
This time I need to include the entire Expression
as well as the Tag Name. So I will begin
typing left paren, single quote,
CDT158, single quote,
times
9 divided by 5,
and I will add 32 to that.
And, once I do that, it will give me the result
of that calculation. Now, I would like this calculation
to occur at much greater intervals -- or mu... or much smaller
intervals, much greater frequency than
10 minutes. So, I will put in here, 30
seconds. And, what this will do,
is give me the Temperature
in Fahrenheit, every three
seconds. I am going to change this Column Label
to
Degrees_Fahrenheit.
And, we will click OK.
And now, if I use that tag
in a Dynamic Element, that will give me
the result that I am looking for. Let's go and
use the Draw
Value Function, and let's
draw the PI Calculation
Dataset, Degrees Fahrenheit,
for my Tag, and what we will see
is that
my Degrees Fahrenheit for this particular Tag
is 310.011,
and that has a timestamp
of 108.00.
You will notice if we
wait a few seconds and give
this time to recalculate, we should
see the
Temperature change, the reading change,
for this particular Performance Equation.
And we see there that 30 seconds
has gone by and we have a New Value.
So, you can see how an Expression Dataset
can take a tag infro -- take Tag information
and combine it into various
ways and
give you a whole different Value.
In another example, we can
see how you can use multiple tags
to report a given
State of your Process using
the Datasets. I am going to go to Tools and
Datasets and create a New PI Calculation
Dataset once again. And, I am going to call this
my Alarm
Dataset, and in this case, I want to know
if my CDT158 Value
goes over a certain degree
point, and another process
is Inactive. Let's say, maybe my -- I go over a certain
degree and my
Relief Valve is off. So, what I can do
is create an Expression that goes
If 'CDT158' --
I remembered my single quotes - is Greater
Than or Equal To 150,
and
I have a tag here called BA:
Active.1, -- this tag
has values of either Active or Inactive --
I will say if that's Value is
Inactive, then
I want to produce the
Message Warning, and
if it's no... -- if we do not meet that criteria in any
other condition -- I want to report
the Value of
Normal. I am going to
evaluate for this every 15 seconds.
And I am
going to label the Value
CDT -- I am going to label the Value
Tank1. So, it's
my alarm for Tank1.
And I can click OK and close.
And now, what I can do is go and use this
in an Element. I will use this in my Dynamic Value.
I will select PI Calculation
instead of Tag. I will select Alarm and
Tank1, and I will
click OK. And what I will
see here, during Run Mode, is
that as long as my
Values are
met, as long as my Condition's met,
my alarm for Tank1 is going to be Normal.
If I should ever go outside
those Values, if that CDT Tag should
be Greater Than or Equal To 150, and my
Valve is Inactive, then I will set
my Alarm.Tank1 Dataset to
the word "warning." So there's a lot of different ways you can use
Datasets. Remember the Rule, Create the Dataset,
then use it in a Dynamic Element.