The Equation Builder is WinSPC's tool for creating equations. Equations are sometimes used to calculate values, limits and targets for a variable, and even can be used in user-defined tests and triggers.

Displaying the Equation Builder

You can use the Equation Builder to develop an equation for any of the following… 

• URL, USL, Target, LSL, LRL – Open the Properties window for the variable that you would like to build the equation for.  Click on the Advance button.  Select the Equation radio button for the limit or target and click the Equation Builder icon beside that button. The Equation Builder icon consists simply of three dots. The Equation Builder icon consists simply of three dots […].
• Calculate Variables - Open the Properties window for the variable that you would like to build the equation for.  Click on the Advance button.  Select the Settings tab.  Check the Calculated checkbox and then click the Equation button.
• Sample Level Test - In the Administrator window, double-click on a User-Defined sample level test. When this is done, the name given to the dialog box that appears is Sample Level Test Setup. Other than this name, this dialog box is identical to the Equation Builder.
• Trigger Setup - - In the Administrator window, double-click the Control Test Template and select a test in the left pane and click the green plus sign [+] near the upper right of the dialog box. When this is done, the name given to the dialog box that appears is Sample Level Test Setup. Other than this name, this dialog box is identical to the Equation Builder.  The following triggers have the equation builder option to choose from : Log, E-Mail, Message Box, Serial Message, File, Poke DDE Item, Set OLE Auto Property, and Write OPC Item.  After you have made one of the above selections, click on the Insert Equation… button.

Building an Equation

1. In the Equation Builder (see Figure 1), from the Functions, Operators, Statistics and Variables lists, double-click the function, operator, statistic or variable you want to appear first in the equation. This copies the function, operator, statistic or variable to the right of Result = in the Calculation Text area. If preferred, you may drag-and-drop a list item to the Calculation Text area or enter the equation using your keyboard. If you enter the equation using your keyboard, notice that, as the characters you type match list items, those items become highlighted. Once only one highlighted item remains, pressing the [Space Bar] auto-fills the remaining characters of that item into your equation.
2. Double-click other functions, operators, statistics and variables as appropriate in the order in which you want them to appear in the equation.
3. If desired, create an interpolation table by completing the Creating and using a Look-Up table procedure below.
4. Click the OK.

Creating and using a Look-Up table

A look-up table is a table used to match an input value with a standard set of predefined values.

1. In the Equation Builder that is displayed, click the Table button (see Figure 2).
2. In the Table Editor that is displayed, single-click the first cell in the A value of column and enter a value that, upon collection, will be replaced by a pre-defined value.
3. Single-click the first cell of the Results in column and enter a value that which the variable value is to be replaced.
4. Repeat the preceding two steps for other and pre-defined values as desired. Notice that, as you do, a curve is displayed and updated in the right half of the Table Editor.  If, at any point, you want to edit a previously entered value, single-click the cell and enter the new value. If, at any point, you want to delete an input value and its corresponding predefined value, single-click either value, and click the Delete button in the lower left corner.  If, at any point, you want to edit a previously entered value, single-click the cell and enter the new value. If, at any point, you want to delete an input value and its corresponding predefined value, single-click either value and click the Delete button in the lower left corner.
5. Click the OK. The Table Editor closes and the value pairs you entered in the table are copied to the Calculation Text pane of the Equation Builder, the first item of the pair being the variable value and the second being the pre-defined value.
6. Double-click on the function, from the Functions list, that you want to use with the look-up table. The applicable options are:     

• Lookup: When a variable value is collected or calculated during Data Collection, this function scans the values in the extrapolation table's A value of column for that value. If a match is found, it returns the matching pre-defined value. If a match isn't found, it returns 0 (zero).
• LookupNearest: This function works similarly to the Lookup function but returns the value nearest to the input value if a matching value isn't found.
• LinearInterpolate: This method uses the intercept of straight lines between points defined in the Table Editor. Points beyond the start and end points will be in a straight line.
• CubicInterpolate: This method use the intercept of a smooth curve (cubic spine interpolation) between points defined in the Table Editor. Points beyond the start and end points will be in a straight line.
• IsExtrapolated: Returns 1 (True) if the result was extrapolated from the table.  It will return 0 (False) if it was not extrapolated from the table (Value was in the table).
• IsInTable: Returns 1 (True) if the value is in the table, else it returns 0 (False) if it is not in the table.

7. Double-click the opening parenthesis “(” from the Operators list. Alternately the opening parenthesis can be entered from the keyboard.
8. Double-click the name of the variable, from the Variables list, to which the interpolation will be applied.
9. Double-click the closing parenthesis “)” from the Operators list. Alternately the closing parenthesis can be entered from the keyboard.

10. Click the OK button to exit the Equation Builder.

Understanding the Equation Builder Statistics