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Lab no. 1  – Solving the quadric equation 

Defining the problem

You have to build a Virtual Instrument (VI) that displays the roots of a quadratic (equation)

and indicates if those roots are real or not. The coefficients of the equation (a, b and c) will bespecified by the user. 

Description of virtual instrument

The user will use three Horizontal Pointer Slide elements to specify the values of the three

coefficients (a, b, and c) of the equation. The a, b and c  coefficients can take integers valuesbetween [-10, 10]. The Horizontal Pointer Slide elements will have visible digital displays.

Virtual instrument will display numerical values representing the roots of the equation X1 andX2 as numerical indicator elements.

Virtual instrument will signal by lighting a red Round LED and will display the message "NaN"  through the X1  and X2  numerical indicator elements if the equation has not real solutions.Round LED Boolean indicator turns green if the equation has real solutions.

Front Panel example

Fig. 1.1. Front Panel example

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Indications

Complete the following steps to launch a LabVIEW program: START ProgramsNational Instruments LabVIEW … (figur e 1.2).

Fig. 1.2. Launching LabView 

The  Getting Started  window, shown in Figure 1.3, appears when you launch LabVIEWprogram. Use this window to create a new VI (click the Blank VI link in the New section). 

Fig. 1.3. The Getting Started window

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When a new Virual Instrument will open, LabVIEW displays two windows: the Front Panelwindow and the Block Diagram window. The Front Panel appears with a gray background

and the Block Diagram window appears with a white background (figure 1.4).

Fig. 1.4. The Front Panel window and the Block Diagram window

For defining the coefficients a, b and c of the equation, you have to add three numericalcontrol elements - Horizontal Pointer Slide  –  from the Front Panel (right-click on the FrontPanel select Modern menu from Controls Palette  select Numeric  Numeric control

Horizontal Pointer Slide) (figure 1.5). You have to click on the Horizontal Pointer Slide

element and after you can place it on the Front Panel and type the name a. Then repeat thesteps for defining the other coefficients b and c or you can copy twice the Horizontal PointerSlide who you just added on  the Front Panel pressing CTRL + left button mouse and

dragging down the element and then you can rename elements, b respectively c  (figure 1.5).

Fig. 1.5. Numeric control elements

The specified values by the user for a, b and c have to be integers. For setting this, right-clickover the element a  and then select Representation Byte (figure 1.6).

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Fig. 1.6. Representation numerical values

The numerical values have to be included into the range [-10, 10]. In this order, you canselect option Data Entry from the contextual menu of the Horizontal Pointer Slide element,

and then you can uncheck Use Default Limits option from the window which appears.

Complete the Maximum, Minimum and Increment values like in figure 1.7.

Fig. 1.7. Configuration of the numeric control elements

The user should also specify the values for the a, b and c coefficients by typing values intodigital displays of the three Horizontal Pointer Slide elements. For making digital displays to

be visible you should selects Visible Items - Digital Display option from the contextual menu

of the elements (figure 1.8).

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Fig. 1.8. Showing digital display

The output data of the program represented by numerical solutions of the equation X1 and X2

(the roots) can be defined in the Front Panel by right-click mouse on the Front Panel  Controls Palette   Modern   Numeric  Numeric indicator ) (Figure 1.9).

Fig. 1.9. Adding numeric indicator elements

The other output data of the program is a led which will indicate if the equation’s roots are realor complex. For defining the led you have to add a Round LED element on the Front Panelgo to Controls Palette  Modern   Boolean Round Led) (figure 1.10). 

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Fig. 1.10. Adding Boolean indicator element

The Front Panel of the virtual instrument for solving of the quadric equation is shown in figure

1.11.

Fig. 1.11. The Front Panel of the virtual instrument 

 After the Front Panel is done the next step is to build the program’s algorithm in the Block

Diagram.

When the control or indicator elements are added on the Front Panel, the terminals of the

elements appear on the Block Diagram (figure 1.12).

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Fig 1.12. Terminals of the elements 

For the calculation of the solutions  X1 and X2 of the equation, according with  a, b and c

values,  you must add the functions which will be used for calculus and then you must wire theelements together for building the data flow of the virtual instrument. The relations that will be

used are the following:

  (1.1)

√

  (1.2)

√

  (1.3)

For the calculation of the discriminant Delta value, first, you must calculate b2  value.The multiply function will be added on the Block Diagram (right-click mouse on the BlockDiagram , from Functions Palette  select Programming menu Numeric  Multiply) and

then you have to wire objects together (figure 1.13).

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Fig. 1.13 . Multiply function

For calculating the term 4ac you can use Compound Arithmetic  function (right-click mouse

on the Block Diagram , from Functions Palette select Programming menu Numeric Compound Arithmetic) (figure 1.14).

Fig. 1.14. Adding Compound Arithmetic function on Block Diagram

Compound Arithmetic function has two input terminals available by default, which allows the

calculation of the two numerical values. To manipulate three terms (inputs) you have to dragthe lower border and add another input of the Compound Arithmetic function (Figure 1.15).

Fig. 1.15. Adding input terminals to the Compound Arithmetic function 

By default, Compound Arithmetic  function performs the operation of addition. To change itto multiply select from the context menu of the function the Change Mode option and click onMultiply (Figure 1.16). Then wire terminals in order to calculate the 4ac result.

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Fig. 1.16.  Compound Arithmetic fuction

Using Subtract  function (that is available in Functions palette, Numeric menu) you will

calculate Delta value, according to relation 1.1 (figure 1.17).

Fig. 1.17. Subtract function

If the Delta  value will be greater than zero, the equation will have real solutions. Use theGrater or Equat to 0?  Function (available in the Comparison  menu)in order to comparesDelta value with zero value (figure 1.18).

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The Virtual Instrument will light on red the element LED Round  if the equation does not havereal solutions. The Boolean Round LED  indicator turns green if the equation has real

solutions.

Fig. 1.18. Grater Or Equal To 0? Function

X1 solution of the equation will be calculated according to the relation 1.2 using the following

functions: Negate, Square Root, Add, Multiply, Divide. You have to wire the terminals andthe value obtained from the output terminal of the function Divide  will be connected to the

input terminal of the numeric indicator element called “X1" (Figure 1.19). 

Fig. 1.19. Calculus of the X1 solution

X2 solution of the equation will be calculated according to the relation 1.3 using the following

functions: Negate, Square Root, Subtract, Multiply, Divide. You have to wire the terminals

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and the result obtained to the output terminal of the function Divide will be connected to the

input terminal of the numeric indicator element called “X2" (Figure 1.20). 

Fig. 1.20. Calculus of the X2 solution

Running modes

Running a virtual instrument will execute the algorithm designed in the Block Diagram of theprogram. You can run a virtual instrument if the Run button on the toolbar appears as a solid

white arrow. If there is any error in the program the Run button will look like a broken arrowand if you will press it than the list of errors will be displayed.

Complete the following steps to run the virtual instrument:

- display the Front Panel by pressing the CTRL - E keys or by clicking the front panel;- give values fro the input data by entering values into digital displays of the a, b and c  

Horizontal Pointer Slide elements or you can change the value of the controls using

operating tool;- click the Run  button or press the CTRL - R keys to run the virtual instrument once

(figure 1.21). The VI will be executed once and it will stop when the VI completes its

data flow.

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Fig. 1.21. Running the virtual instrument

Running continuously

Clicking the Run Continuously  button runs the virtual instrument continuously until you stopit manually by pressing the red button Abort Execution. In this running mode it is possible to

follow the data flow (Figure 1.22).

Fig. 1.22. Running continuously a virtual instrument

The Abort Execution  button stops the virtual instrument immediately, before the program

finishes the current iteration (figure 1.23).

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Fig. 1.23. Abort execution

If you want to follow the data flow of the virtual instrument then you can press HighlightExecution button from the Block Diagram (figure 1.24).

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Fig. 1.24. Data flow of the virtual instrument

If you want to temporary Stop running the application you can use Pause  button from both

Front Panel or Block Diagram toolbar (Figure 1.25). 

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Fig. 1.25. Stop temporary the virtual instrument

Save virtual instrument

Save the virtual instrument pressing the CTRL  – S keys or selecting Save from File menu inthe Front Panel or in the Block Diagram .

Choosing Save as  option, the virtual instrument can be saved with another name (figure

1.26).

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Fig. 1.26. Save the virtual instrument

Learning outcomes

Open a new virtual instruments

Using the Front Panel window and Block Diagram windows and switching between them

Defining numerical and Boolean controls and indicators as input and output data. 

Customizing control and indicators in the front panel. 

How to define functions on the Block Diagram.

Using scalar functions function according to the data types and operations needed 

Make connections between functions and terminals of the elements

Identifying errors and solving the bad connections. Using different running modes

Save the virtual instrument