PI Performance Equations
John Daniels, Technical Instructor
Show Me How Webinar Series
© Copyright 2009, OSIsoft Inc. All rights Reserved.
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PI Performance Equations Subsystem
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Executes real time calculations
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May use multiple tags
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Stores calculation results in a PI tag
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Contains a rich library of built-in functions
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Performance Equations Scheduler
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Start up file: \pi\bin\pipeschd.bat
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/f : Scan class period and phase. The period is the
amount of time between scans. The phase is the time to
start the first scan as an offset from midnight.
Example: /f=08:00:00,07:00:00
This example will execute the calculation every 8 hours
starting at 07:00:00
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Scan Classes - Offsets
Ten seconds scan class with
no offset
(/f = 00:00:10)
Ten seconds scan class with a five
seconds offset (/f = 00:00:10,
00:00:05)
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Calculation Dependencies
Tag
Scan class
A
/f=08:00:00,07:00:00
B
/f=08:00:00,07:00:00
C
/f=08:00:00,07:00:00
Tag
Scan class
A
/f=08:00:00,07:00:00
B
/f=08:00:00,07:00:00
C
/f=08:00:00,07:00:01
If all tags have the same Scan Class and
Tag C relies on data from Tags A and B,
calculations could be done out of order.
If Tag C has a later Scan Class, a
Calculation Dependency will be set and
the data will be correct.
Note: An easier way would be to make Tag C an Event Triggered tag based
on Tag B.
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DEMO: Bat file and ICU

Go configure the BAT file and the ICU

D:\PI\bin

Change host name
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Add scan classes
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Import in ICU
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PI PE Expression Syntax

Numbers
 0, 0.125, 34.56

Tag names in single quotes
 'sinusoid' , 'trc4226.pv'

Timestamps in single quotes
 '*' , '14-dec-02', 't-8h'

Strings in double quotes
 "This is a string"
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PI PE Expression Syntax
Relational, Logical and Mathematical Operators

A PE expression can use the following relational
operators:
 >, <, >=, <=, =, <>

A PE expression can use the following logical operators:
 And, Or, Not, In .., In ()

A PE expression can use the following mathematical
operators:
 +, - , *, /, ^, Mod
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PI PE Expression Syntax
If-Then-Else Operator

A PE expression can use If-Then-Else operators
 IF expr0 THEN expr1 ELSE expr2
Ex.: IF ‘Tag1’ < 50 THEN “under limit” ELSE “good”
 You must include the IF, the THEN, and the ELSE
 Nested operations are supported

Possibility to use the NoOutput() function, which does not
send anything to PI
 Ex.: IF TagAvg(‘sinusoid’, ‘*-1h’, ‘*’) > 80 THEN “Alarm” ELSE
NoOutput()
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PI PE Expression Syntax
Built-In Functions

A PE expression can use built-in functions







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Mathematical functions (Abs, Sin, Cos, Sqr, …)
Aggregate functions (Avg, Max, Min, …)
Archive retrieval (NextEvent, PrevVal, TagVal, …)
Archive search (FindEQ, FindGT, TimeLT, …)
Archive statistics (TagAvg, Range, EventCount, …)
Point attributes (TagSpan, TagType, TagDesc, …)
Time functions (Bod, Bom, Hour, Minute, …)
String functions (Len, Trim, Concat, …)
Functions can be nested and combined in expressions
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DEMO: View the help file

Use the PEReference.chm help file to view the
available functions
 On the PI server in the \pipc\help folder
 On the training web site (http://training.osisoft.com)
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Built-In Functions
Archive Search Example

TimeEQ or TimeNE: returns the number of seconds
that a tag was equal or not equal to a specified value

TimeLT or TimeLE: returns the number of seconds
that a tag was less than or equal to a specified value

TimeGT or TimeGE: returns the number of seconds
that a tag was greater than or equal to a specified
value
Time??(tag, start time, end time, value)
Ex: TimeGT(‘trc322.pv’, ‘y’, ‘t’,10)
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Conversion Factors

It is important to supply the correct conversion factor
when calculating TOTALS with PI because PI assumes
the engineering units of the rate tag are units per day.
Rate tag
engineering units
Units/day
Units/hour
Units/minute
Units/second
Assumption of
the PI Server
Units/day
Units/day
Units/day
Units/day
Conversion
Factor
1
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1440
86400
Example: For a flow measured in gpm, a conversion factor of 1440 must
be supplied to convert between the engineering units of the rate tag and
the units/day assumption of PI.
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What is a Conversion Factor?

A multiplier used to change a number from one unit of
measure to another
 Ex: 1000 g/kg, 2.54 cm/inch, 24 hours/day, 1440 minutes/day

When using the tagtot function in a PE expression, it is
used to correct PI’s assumption that the data is in units
per day
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Computing Totals
Flow 7
(gpm)
5
PI assumes this
measurement to be
units/day
3
1
0
0
1
2
3
4
5
6
7
8
9
10
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Time (m)
Normal total = (3 gpm x 3m) + (5 gpm x 2m) + (1 gpm x 3m) = 22 gallons
PI total = ((3 gallons per day x 3m x 1day/1440m) + (5 gallons per day
x 2m x 1day/1440m) + (1 gallon per day x 3m x 1day/1440m)) *
1440m/1d = 22 gallons
The total computed by PI must be multiplied by a factor of 1440
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DEMO: Build Tags in SMT and Excel

Use the Performance Equations PI SMT plug-in to
create, set scheduling and validate an equation’s
syntax before putting it online
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DEMO: PI Performance Equations
Tag Configuration

PointType: Digital, Float64, Float32, Int32, Int16, String

PointSource: often C, as set in the interface start up file
(pipeschd.bat)

Configuration parameters for scan based calculations
 ExDesc: PE Expression
Ex: tagavg(‘sinusoid’, ‘*-1h’, ‘*’)
 Location3: 0
 Location4: scan class number
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DEMO: PI Performance Equations
Tag Configuration

Configuration parameters for event triggered calculations
 ExDesc: event=Trigger_Tag_Name, PE_Expression
Ex: event=sinusoid, tagavg(‘sinusoid’, ‘*-1h’, ‘*’)
 Location4: 0
 Location3: determines the timestamp of the result
0: sets the timestamp to the time when the
expression is evaluated
1: sets the timestamp to the time of the triggering
event
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DEMO: PI Performance Equations
Tag Configuration

It is appropriate to turn off data compression for
calculated tags since each event is significant in itself
 ExcDev: 0
 ExcMax: 0
 Compressing: 0 (off)

The step attribute can be used to ensure no interpolated
data is returned to end users
 Step: 1 (on)
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DEMO: PB Trend with PE tag
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YesterdayComp vs BA:Conc.1
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DEMO: PIPETEST
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D:\PI\ADM
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Can load text files
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Gives error location
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Installed on Server
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PI PE’s versus PI ACE
Performance Equations
PI ACE
Installed with each PI Server
Comes with Enterprise Server
Professional or separately
Simple deployment
More complex deployment
Accesses data from a single PI Server
Can access multiple PI Servers
Built in library of functions
Anything in VB or coded
Simple logic (4096 character limit)
Logic limited only by coding ability
Note: For more information about PI ACE, please see our PI ACE course
offering or our webinar Building Calculations in ACE to Support Plant
Performance Monitoring
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For Further Information

PEReference.chm
 In \PIPC\Help
 On OSIsoft website

PI Server Applications User Guide

www.techsupport.osisoft.com

Previous webinar: Recalculating Performance Equation
and ACE Calculation Results
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Questions
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