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Equations

142

2005 ACR Systems Inc.

7.9 APPENDIX B Compound Line Equations

Compound Line

Equation

7.9.1 Compound Line Equation Language

Compound line equations in

TrendReader Standard 2

use the VB.Net language. Therefore,

any code in an equation must be compliant with the syntax of VB.Net. Although the equation

script is VB.Net compliant, you cannot use all VB.Net methods and functions because some

method related references may not be added to the equation project. Currently, all equation

projects have

Microsoft.VisualBasic

and

System

references imported, so any functionality

and definitions under these two references can be implemented. For detailed information

please refer to VB.Net documentation.

The code for compound line equations and regular equations is very similar. See

APPENDIX A Equation Language

for more details on regular equations. The main difference

between the two is the use of public variables and objects.

The public variables available in compound line equations are: SOURCE0, ..., SOURCE9, and

ANSWER0, ..., ANSWER9. Whereas the SOURCE variables represent properties such as

sample rate, calibration values, and compensation values for regular equations, in compound

line equations they are used to input data into the equation. For example, to calculate watts,

you need voltage, current, and power factor correction. In your equation, you could use

SOURCE0 to represent voltage, SOURCE1 for current, and SOURCE2 for power factor

correction. When you add the compound line equation in your graph, you would be asked to

enter values for SOURCE0, SOURCE1, and SOURCE2. You would select which logger

channel corresponds to SOURCE0 and SOURCE1 and possibly enter a constant for

SOURCE2. You can associate a logger channel or a constant to a SOURCE variable.

ANSWER0 is used the same as for regular equations: to store the result of the equation. The

variables ANSWER1 to ANSWER9 are channel level variables you can use that are persistent

during the whole life cycle of the logger, such as for time accumulation type equations.

An object is a software entity which can be used in equations. An object includes properties

and methods which can be invoked by equations. For compound line equations, you only

have access to the Logger object, which is a software representation of the physical logger.

The only property associated with the Logger available for compound line equations is the

sample rate, stored as type Double, Logger.SampleRate (in seconds).

An example of a compound line to calculate total Watt Hours is shown below:

Sub

Equation()

Dim

Watts

Double

Dim

Hours

Double

'SOURCE0=voltage, SOURCE1=current, SOURCE2=power factor correction

Watts=SOURCE0*SOURCE1*SOURCE2

Hours=Logger.SampleRate/(60*60)

ANSWER1=Watts*Hours + ANSWER1

'Accumulate Watt Hours over time

ANSWER0=ANSWER1

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