Rockwell Automation T3833 User Manual

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ICS Regent

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PD-6043

Math Package for

INTERPRET

Floating Point Math Function Block

(T3833)

Issue 1,

The Math pac package which allows the user to create Floating Point Math function blocks for Regent application programs. When installed on the PC, the math package is seamlessly integrated with the base WINTERPRET

Floating point math function blocks are used to perform mathematical calculations that require floating point precision or use values that exceed the 16-bit signed integer range (-32768 to +32767) used in ladder logic math operations. The expressions that can be used in floating point math function blocks include addition, subtraction, division, multiplication, exponentiation, logarithms, and square root.

kage for W

INTERPRET

is an add-in software

software.

March, 06

Software Installation

The Math package is installed on the PC running the W

INTERPRET

package provides the necessary installation software to install this add-in math package. The math package should be installed at the same time or after you have installed the W

INTERPRET

Installation Procedure

The files on the Math package diskette are in compressed

form. You cannot simply copy the files to your hard drive — they must be decompressed before they will run. You must have the WINTERPRET base package distribution disk in order to run the setup procedure to install the Math package.

To install the Math package, use the following sequence:

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application software. The W

base package.

INTERPRET

base

Math Package for

1. Insert the WINTERPRET base package distribution disk into

INTERPRET

drive A: or B:

(T3833)

2. Start Windows (if it isn’t already running).

3. Choose Run from the Program Manager’s File menu.

4. Type a:\

INTERPRET base package disk in drive B: type

b:\setup.exe

5. In the WINTERPRET Setup dialog box enter the name of the

directory in which you have installed the WINTERPRET base package (This assumes that you have already installed WINTERPRET). Choose Continue.

6. In the WINTERPRET Installation dialog box check the Math

package box.

7. Choose OK to have the setup program install the Math

package software.

When the installation is completed, you can run the W

INTERPRET application and create floating point math

function blocks in you application programs.

setup.exe

.) Choose OK or press ENTER.

in the text box. (if you inserted the

Working with Floating Point Math Function Blocks

Floating point math function blocks are created as part of an application program which may also contain other types of function blocks. A single application program is made up of as many as 50 function blocks of any type or combination.

When you installed the Math package, additional sof was added to W point math function blocks. With this additional software you can create floating point math function blocks by opening a project, opening a program and opening (or creating) a function block.

For an overview about Regent application programs and function blocks and how to create them using WINTERPRET refer to Section 5, Working with Programs and Function Blocks in the Regent User’s Guide.

INTERPRET

to allow you to work with floating

tware

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Math Package for

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Using Floating Point Math Statements

In floating point math function blocks you enter mathematical equations and expressions in the form of statements. Each line can contain one statement that calculates the result of a mathematical equation. For example, consider the quadratic equation below.

y = 1.6x2 +8x -22.4

Using floating point math the statement representing this equation would be:

Y = 1.6*X^2 + 8*X - 22.4

You can also enter comments in any line by entering a semicolon (;) and placing your comments after the semicolon as shown below.

= 1.6*X^2 + 8*X - 22.4 ; This is a comment.

Floating point math also allows you to create conditional statements using IF, ELSE, ENDIF, WHILE, ENDW, AND and OR operations. Below is an example of using IF, ELSE and ENDIF to calculate the absolute value of the difference between two variables.

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IF AI1 > AI2 DIFF = AI1 - AI2 ELSE DIFF = AI2 - AI1 ENDIF

Using combinations of conditional statements and mathematical operations allows you to configure floating point function blocks to meet a wide range requirements.

Mathematical Operations

of control

The mathematical operators perform arithmetic and functional operations.

Math Package for

Operator Operation

^ Exponentiation * Multiplication /

Division

Addition

- Subtraction

Operator Operation

SQRT(x)

Returns the square root of x

EXP(x)

Raises e to the x power

LOG(x)

Returns the logarithm of x

LN(x)

Returns the natural logarithm of x

Note:

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Arithmetic Operations

Table 1 shows the arithmetic operators recognized by floating point math listed in their default order of precedence.

Table 1. Arithmetic Operators.

Multiplication and division have equal precedence from

right, as do addition and subtraction.

The exponent, X, in an exponential expression (

Y^X

left to

) is always

evaluated as an integer (fractional portion is truncated). Do not use the exponentiation operator to perform square root calculations, instead use the below.

SQRT(X)

function described

Parentheses may be used to clarify the order of operation: operations within parenthesis are performed first. Inside the parentheses, the usual order of precedence is maintained.

Functional Operators

A functional operator is used in an expression to perform a predetermined operation that is to be performed on one or more operands. The Regent’s floating point math has four standard functions that reside in the system as shown in Table 2.

Table 2. Functional Operators.

In each function you can enter a variable or arithmetic expression within the parenthesis of the function. For example the following statement is valid.

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Math Package for

Note:

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The exponentiation operator (

integer power X. If you need to calculate values of X you can use the shown below.

Conditional Statements

ROOT1 = (-B + SQRT(B^2 - 4*A*C)) / (2*A)

Y^X

) can only raise Y to an

YX for non-integer

LN(X)

and

EXP(X)

functions as

Y_2_THE_X = EXP(X*LN(Y))

The statements available in the floating point math let you alter program flow base

IF, ELSE, and ENDIF

d on testing of conditions.

The IF statement is used to make a decision regarding program flow based on the result returned by an expression. The expression can include mathematical and logical operators. The use of ELSE within the lines controlled by the IF statement is optional.

Syntax:

IF expression

•

• ELSE (optional)

•

• ENDIF

IF, ELSE, and ENDIF statements must not the same line.

WHILE and ENDW

be combined on

The WHILE statement executes a series of statements in a l

oop as long as the expression is true. The expression can

include mathematical and logical operators. Syntax:

WHILE expression

•

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• loop statement

Math Package for

Operator

Relation Tested

Expression

Equality

X = Y <> Inequality

X <> Y

Less than

X < Y

Greater than

X > Y <= Less than or equal to

X <= Y

>= Greater than or equal to

X >= Y

Important!

If the expression is true (not zero), loop statements are executed until the ENDW statement is encountered. Floating point math then returns to the WHILE statement and checks expression. If expression is still true, the process is repeated. If the expression is not true, execution resumes with the statement following the ENDW statement.

To avoid infinite loops, the expression must be modified (its

value changed) during repeated execution to make the expression false and exit the loop.

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•

• ENDW

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WHILE and ENDW statements may be nested.

Relational and Logical Operators

Relational and logic operators are often used in the expressions for IF and WHILE statements to control the execution of other mathematical statements.

Relational Operators

Relational operators compare two values. The result of the comparison is either true (1) or false (0

). The result can then be used to make a decision regarding program flow. The relational operators are shown in Table 3.

Table 3. Relational Operators.

When arithmetic and relational operators are combined in one expression, the arithmetic is always p

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erformed first.

Math Package for

Value

Result

A AND B

Result

A OR B

T T T T T F F T F T F T F F F

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Logical Operators

Logical operators perform logical, or boolean, operations on numeric values. Just as the relational operators are usually used to make decisions regarding program flow, logical operators are used to connect two or more relations and return a true or false value to be used in a decision.

A logical operator takes a combination of true/false values and returns a true or false result. An operand of a logical operator is considered to be true if it is not equal to zero, or

false if it is equal to zero. The result of the logical operation is a number which is, again, true if it is not equal to zero, or false if it is equal to zero.

In an expression, logical operations are performed after arithmetic and relational operations.

Table 4. Logical Operators.

Using Variables and Constants

Constants

Constants are static values used by the floating point math function blocks during execution of your program. All constants are numeric.

Numeric constants can be either positive or negative. Numeric constants must not contain commas. For example, if the number 20,000 is needed as a constant, it should be typed in the floating point math statement as 20000.

There are two types of numeric constants: integer and floating point.

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Math Package for

INTERPRET

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Integer Constants

Integer constants are constants entered as whole numbers that do not contain decimal points or commas. Entering

an integer constant greater than 7 numerals long is allowed but the precision of the actual number stored and used in the Regent is limited to 7 significant digits. For example, the integer constants 12345678 and 12345679 may result in an equal values when converted and stored in the Regent.

Floating Point Constants

Floating point constants are positive and negative numbers represented in exponential form (similar to scientific notation). A floating point constant consists of an optionally signed integer or fixed point number (the mantissa) followed by the letter "E" and an optionally signed integer (the exponent). The "E" means "times ten to the power of."

For example:

33E-2

Here, 33 is the mantissa, and -2 is the exponent. This number could be read as "thirty-three times ten to the power of negative two." You could also write this number as 0.33 in regular fixed point notation.

You can represent any number from -1.175494E-38 to

3.402823E38 as a floating point constant.

Variables

Variables are names representing values used in the float

ing point math function blocks. All of the variables you use in a floating point math function block must be shared variables, I/O points, or local variables used by floating point math function blocks only. For example, if you scale an analog input value to a register, the register should be defined as a shared variable register if you want to use the scaled result in a floating point function block.

The floating point math compiler assumes that any local var

iables found in the function block will be local floating point registers. If a local variable is used in both a floating point math and other type of function block, a local data allocation error will be reported when you attempt to load the

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Math Package for

INTERPRET

(T3833)

application program in the Regent. This will prevent the program from being loaded into the Regent.

For more information about Regent variable types, see Regent Variable Types and Memory, in Section 4, Working with Projects, in the Regent User’s Guide.

Floating point math function blocks recognize the following variable types:

Logical Variables

Logical variables are used for digital output, shared control relays, and local control relays. Logical values are always 1 (on) or 0 (off).

Analog Variables

Analog variables are used for analog inputs and outputs. Analog variables must be within the range 0 to 4095. Thermocouple and RTD inputs are within the range of -16384 and 16383.

Integer Variables

Integer variables are used for shared registers and local regist and 32767.

Floating Point Variables

ers. Integer values must be within the range -32768

Floating point variables are used for floating point shared registers and floating point local registers. Floating point values must be within the range -1.175494E-38 and

3.402823E38.

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Coercion (Type Conversion)

Regardless of the variable type, all calculations performed in floating point math are done using floating point numbers. When logical, analog, or integer type variables are used, code is created in the fun to a floating point number for calculation in the Regent.

ction block to convert the variable value

When storing the result of a calculation, the value is converted to the type of the destination variable.

When performing variable conversions, the rules in Table apply:

Math Package for

Logical to analog

False to 0, true to 1.

Logical to integer

False to 0, true to 1.

Logical to floating point

False to 0.0, true to 1.0

Analog to logical

0 to

false, otherwise true.

Analog to integer

Valid for all analog values.

Analog to floating point

Valid for all analog values.

Integer to logical

0 to false, otherwise true.

Integer to analog

Valid for all integers between 0 and 4095 (-16384 to +16384 for T/C and RTD inputs). Otherwise a conversion error is reported.

Integer to floating point

Valid for all integers.

Floating point to logical

0.0 to false, otherwise true.

Floating point to analog

Valid for all floating point number

s between 0.0 and 4095.0 (-16384.0 to +16384.0 for T/C and RTD inputs). Otherwise a conversion error is reported.

Floating point to integer

Valid for all floating point numbers between -32768.0 and +32767.0. Otherwise a conversion error is reported.

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Table 5. Conversion Rules.

Error Handling

In a floating point math function block, errors may occur during floating point calculations as the values used in the equations change. An example of a math error is the square root of a negative number. For each function block the us must define two tag names which are used to report the line number and error code of the math error. These tag names may be used in the function block to annunciate errors and optionally execute user defined actions if math errors occur.

Hold Last Valid Value

When a math error occurs during a calculation, the result of the equation retains the last valid value.

For example, consider the equation:

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Math Package for

Scan B

SQRT(B)

Result, A

1 25 5 5 2 16 4 4 3 2

1.414213

1.414213 4 -7

<error>

1.414213 5 1 1 1

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A = SQRT (B)

During execution in the Regent, the value of B may change from one scan cycle to the ne

xt. Table 6 illustrates the values of B the result stored in A for a series of scan cycles to illustrate the effects of a math error (square root of a negative number).

Table 6. Example of Math Error and Result Values.

During scan 4, the square root of -7 produces an error, and the result, A, retains its last valid value (1.414213

). In scan 5, the square root of 1 is valid so the result, A, is updated with the new value square root of 1 = 1.

User-Supplied Error Handling Logic

Each floating point math function block contains two registers in which error codes are placed by the Regent during execution. Error codes indicate what type of error occurred and the line number on which it occurred. This error information can be tested in the function block as desired.

Error Code Variable

The error code variable must be assigned a name

. This name will hold the error code. Four error codes are generated as shown in Table 7.

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Math Package for

Error Code

Description Example

1 Underflow

C = A / B; |A/B| < 1.175494E-38

2 Overflow

C = A * B; A * B > 3.402823E38

C = A/B; B = 0

Not a number

C = SQRT A; A < 0

Conversion AO = 3000 + 2000

(where AO is an analog output)

Scan AI

AI+300

Comments

1 3000

3300

No error

2 3200

3500

No error

3 3700

4000

No error

4 3900

4200

4000

Error Code 4, last value used

5 4000

4300

4000

Error Code 4, last value used

6 3780

4080

No error

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Table 7. Error Codes.

In most floating point equations, the results do not approach the error limits of floating point math. When equations are used that can produce floating point errors, the variable on the left side of the equal sign will not be changed and it will contain the last valid result. If under error conditions this last value is not the best answer and a better answer can be determined by the error code, then the error term should be examined.

Example:

AO = 300 + AI

where,

AO is analog output (maximum 4095) AI

is analog input (0 - 4095)

if AI > 3795 then an error will occur.

Table 8. Examp

le of Conversion Error, Error Code 4.

The most desirable answer for scans 4 and 5 would probably be AO max = 4095, not the last value of 4000. To alter this value, you may use the error code to examine the error term to determine a bett

er value.

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Math Package for

Line Equation

Comments

1 LINE = 0

Reset line number variable to 0 to clear status each scan.

2 ERROR = 0

Reset error code variable to 0 to clear status each scan.

3 A = EQUATION 1

Equation that generates an error, a better answer is pre

dictable:

4 IF (ERROR <> 0 AND LINE = 3)

If line 3 produces an error, a better value for A should be determined.

5 A = BETTER VALUE

Equation that sets A to a better value than calculated in line 3.

6 ENDIF

7 B = EQUATION 2

Equation not requiring special error handling.

8 C = EQUATION 3

Equation not requiring special error handling.

9 D = EQUATION 4

Equations not requiring special error handling.

10 E = EQUATION 5

Next equation requiring better error handling.

11 IF (ERROR <> 0 AND LINE = 10)

If line 10 produces an error, a better value for E should be determined.

12 E = BETTER VALUE

Equation that sets A to a better value than calculated in line 10.

13 ENDIF

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Table 9 shows a general example of how the error variables can be used in a floating point function block to check for error conditions and conditionally execute alternate equations that calculate a more appropriate result than leaving the value at its last valid value. For example, if our analog output equation, AO = 300 + AI, was the equation in line 3, we could use the equation, AO maximum value for the analog output when AI > 3795.

4095, in line 5 to always produce a

Table 9. Using Error Variables.

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When multiple lines in the function block have math errors, the error code variable and line number variable will change during the execution of the function block. For each equation that you identify a potential for a math error, you must test for errors before executing any other equations which may also generate errors. At the end of the scan, the error variables will have the value of the last math error.

Math Package for

The Regent does not reset the values of the line number and error code variables when n When the error condition ceases, these variables contain the values for the last error. You should include equations to reset the error variables (as shown in lines 1 and 2 in Table 9. Otherwise, once an equation generates an error, the test for error will remain true for that equation until a different line number generates a math error.

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o more math errors are present.

Using the Floating Point Math Editor

Floating Point Math function blocks are created using the Add Function Block or Insert Function Block from the Program Editor. After you have created a new math function block the Floating Point Math Editor window is opened as shown in Figure 1.

Figure 1. The Floating Point Math Editor Window.

Using the drop-down menus you can select commands to create floating point math statements, define error variables, perform cut, copy and paste operations, print the function block and a host of other configuration operations.

The F floating point math function blocks. When you create a math function block you will enter your equations line by line in a simple text-based editor.

loating Point Math Editor lets you create and edit

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Math Package for

Note:

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The floating point math editor allows you to create up to 6500 lines in a single function block. The size of each compiled function block is limited to 64 kbytes of code which provides up to 1300 lines which contain floating point math statements (a simple statement like A = 1 occupies approximately 50 bytes).

Statement Lines

Each line of the function block may contain up to 72 characters that form a floating point math statement. Additional comment characters may also be included (see Comments below). Statements cannot be extended from one line to the next.

Comments and Blank Lines

In-line comments may be included on any line of the floating point math function block.

Comments begin with a semicolon (;). Anything following a semicolon will be interpreted as a comment. All characters to the right of a

semicolon will be interpreted as comments and will not be used to generate code that is loaded and executed in the Regent. A line beginning with a semicolon is completely a comment line.

Blank lines may be used to make the function block more easily readable by separating sequential lines from others. Blank lines and lines that are completely comments do not generate any executable code, but do require 2 bytes of function block local data.

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The editor allows you to enter up to 1024 characters per

line,

however, when the function block is printed only the first 125 characters of each line are printed. Avoid entering lines longer than 125 characters wide.

An floating point math example which includes comments and blank lines is shown in Figure 2.

Math Package for

INTERPRET

Figure 2. Example of the Floating Point Math Editor

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Window.

File Menu

The File Menu gives you access to the standard function block file commands which include: Save Function Block, Revert to Last Saved, Compile, View Error Messages, Edit Function Block Description, Edit Function Block Details, Print Function Block, Print Setup, Log Off and Exit. For more information on all of these commands refer to Commands Common to all Function Blocks in Section 5 of the Regent User’s Guide.

Edit Menu

From the Edit Menu the user can select a variety of commands such as cut, copy and paste of the currently selected text in the editor.

Undo

Use the Undo command to restore the text in the editor to its original state before performing a Cut, Copy, Paste or delete.

Cut

The Cut command can be used to remove the currently selected text from the editor. Subsequently the text can be inserted into the function block using the Paste command.

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Math Package for

INTERPRET

(T3833)

Click and drag the mouse to select the desired text to cut. Choose Cut from the Edit Menu to remove the selected text.

Copy

The Copy command can be used to copy the currently selected text to the Windows clipboard. Copied text can later be inserted into the function block using the

Paste command.

Click and drag the mouse to select the desired text to copy. Choose Copy from the Edit Menu to copy the selected text to the clipboard.

Paste

The Paste command is used to insert the current contents of the clipboard at the currently selected position. Paste is normally used in conjunction with the Cut and Copy commands.

After using the Cut or Copy command, place the cursor at the position that you wish to insert the text. Choose Paste from the Edit Menu to insert the contents of the c

Note:

lipboard.

The Paste command can be used to replace text in the function block. Use the mouse to select the range of text that you wish to replace. Choose Paste from the Edit Menu to replace the selected text with the text previously selected by Cut or Copy.

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Select All

Choose Select All to select all of the lines in the function block. This performs the same operation as selecting all of the lines by clicking and dragging the cursor from the start of the first line to the end of the last line in

Error Variables

the editor.

Use the Error Variables command to define the line number and error code variable names for floating point math error reporting. For additional information about error variables and how they can be used in the function block see Page 10, Error Handling.

When you select the Error Variables command from the Edit menu the following dialog box is opened:

Math Package for

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Figure 3. Floating Point Math Error Variables.

Line number va

riable

Enter the tag name for the line number variable. The variable is used to report line numbers that generate math errors if they occur during execution in the Regent.

Error code variable

Enter the tag name for the error code variable. The variable is used to report the error code for math errors if they occur during execution in the Regent.

Search Menu

Go to Line

The Go to Line command lets you quickly move to different lines in the floating point math function block. From the Floating Point Math Editor's Search menu choose Go to Line (

ALT,S,G

Figure 4. Floating Point Math: Go to Line.

For your convenience, the dialog displays the number of lines currently defined in the function block.

Line number

Enter the line number that you want to go to.

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Math Package for

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Choose Go to move to the line number that you entered in the Line Number text box.

First

Go to the first line in the function block.

Last

Go to the last line in the function block.

Find

The Find command lets you quickly loca

te text strings in the floating point math function block. For example, you can search for a tag name and have the editor locate the line of the function block where the tag name is used. From the Floating Point Math Editor's Search menu choose Find (

ALT,S,F

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Find Next

Figure 5. Floating Point Math: Find.

The Find Next command repeats the last selected Find operation. From the Floating Point Math Editor's Search menu choose Find Next (

ALT,S,N

) or simply press F3.

Math Package for

INTERPRET

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Window Menu

The Wi W Window menu commands see Commands Common to all W W

ndow menu commands are standard throughout all

INTERPRET windows. For more information on using the

INTERPRET Windows in Section 3, Installing the INTERPRET Application of the Regent User’s Guide.

Help Menu

The Help menu commands are standard throughout all W

INTERPRET windows. For more information on using the

Help menu commands see Commands Common to all W

INTERPRET Windows in Section 3, Installing the

INTERPRET Application of the Regent User’s Guide.

Using the Floating Point Math Monitor

When you have selected a Floating Point Math function block in the Program Monitor window and choose the Monitor command from the Control Menu, the Floating Point Math Monitor window is opened as shown in Figure 6.

Figure 6. Floating Point Math Monitor Window.

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Math Package for

INTERPRET

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Normally you will use the Floating Point Math Monitor Window to observe results of the floating point math calculations. You can also select a single line and d values of all the variables used in the selected line.

isplay the