Lab 1: Getting familiar with LabVIEW: Part I
Contents
1. Numeric Knob Adjust the size of the knobs by using the Positioning tool Properties of knobs such as precision and data type can be modified by right clicking and choosing Properties from the shortcut menu A Knob Properties dialog box is brought up and an Appearance tab is shown by default Edit the label of one of the knobs to read Input 1 Select the Data Range tab and click Representation to change the data type from double precision to byte by selecting Byte among the displayed data types This can also be achieved by right clicking on the knob and choosing Representation Byte from the shortcut menu In the Data Range tab a default value needs to be specified In this example the default value is considered to be 0 The default value can be set by right clicking on the control and choosing Data Operations Make Current Value Default from the shortcut menu Also this control can be set to a default value by right clicking and choosing Data Operations Reinitialize to Default Value from the shortcut menu Label the second knob as Input 2 and repeat all the adjustments as done for the first knob except for the data representation part The data type of the second knob is specified to be double precision in order to demonstrate the difference in the 13 outcome As the final step of configuring the FP align and distribute the objects using the appropriate buttons on the FP toolbar To set the outputs locate and place a N2. number Oto 1 2 bose 3H poe E 3 nu E3 number Oto 1 0 526559 Figure 2 32 Probe tool 21 L1 5 Bibliography 1 National Instruments LabVIEW User Manual Part Number 320999E 01 2003 L1 6 Lab Experiments Carry out the following experiments with and without the MathScript feature of LabVIEW 8 1 Build a SubVI to compute the product sum and difference of two given square matrices A and B 2 Build a SubVI to compute and display the roots of the quadratic equation 2 ax bx C for given coefficients a b and c 3 Build a SubVI to generate the first 20 numbers of the Fibonacci sequence and store them using an indexing array 4 Build a SubVI to compute the sum of the first n natural numbers for a given value of n 22
3. Lab 1 Getting familiar with LabVIEW Part I The objective of this first lab is to provide an initial hands on experience in building a VI For detailed explanations of the LabVIEW features mentioned here the reader is referred to 1 LabVIEW 8 0 can get launched by double clicking on the LabVIEW 8 0 icon The dialog window shown in Figure 2 17 should appear Getting Started File Tools Help 3 LabVIEW mi Blank VI ec Empty Project wd VI From Template C3 Mors zu C 00k Updates Chapter24ddExample vi zu Ci LabVIEW Book Updates addExample vi mi C1 AbalaramalDesktopllabi p1 1 mad vi mi C ings balaramalDesktopilabl p1 1 vi ini C s MIMMAOT2esEIMAOQInconsistency vi cu Ci Applications Barcode Example vi ru C s Vision IMAG vision AVI Folder vi mi Ci Settings balarama Desktop test vi mei Cr FioniMeuralMebwork DBD Revisonz vi m CH Labs LabOo D5K6416 FFT FFT DSF vi C3 Browse Licensed For Professional Version New To LabVIEW Getting Started with LabVIEW LabVIEW Fundamentals Guide to LabVIEW Documentation LabVIEW Help Upgrading Lab IEW LabVIEW Projects Changes to Existing VIs and Functions New Palette Organization List of All New Features Web Resources Discussion Forums Training Courses LabVIEW Zone Examples Q Find Examples Figure 2 17 Starting LabVIEW L1 1 Building a Simple VI To become familiar with the LabVIEW programming environment it is
4. Numeric Constant Enter 9 in the numeric constant Then wire the Round LED labeled as Warning to the x y terminal of this function to provide a Boolean value In order to run the VI continuously a While Loop structure is used Choose Functions Programming Structures While Loop to create a While Loop Change the size by dragging the mouse to enclose the objects in the While Loop as illustrated in Figure 2 29 15 Ex Structure and SubVI vi Block Diagr Sele Figure 2 29 While Loop enclosure Once this structure is created its boundary together with the loop iteration terminal Li and conditional terminal get shown on the BD If the While Loop is created by using Functions Programming Structures While Loop then the Stop Button is not included as part of the structure This button can be created by right clicking on the conditional terminal and choosing Create Control from the shortcut menu A Boolean condition can be wired to a conditional terminal instead of a stop button in order to stop the loop programmatically As the final step tidy up the wires nodes and terminals on the BD using the Align object and Distribute object options on the BD toolbar Then save the VI ina file named Structure and SubVI vi 16 Now run the VI to verify its functionality After clicking the Run button on the toolbar adjust the knobs to alter the inputs Verify whether the average and sum are displayed correctly
5. Tools Palette from the menu bar Choose the Labeling tool and click on the default labels Numeric and Numeric 2 in order to edit them Alternatively if the automatic tool selection mode is enabled by clicking Automatic Tool Selection in the Tools palette the labels can be edited by simply double clicking on the default labels Editing a label on the FP changes its corresponding terminal icon label on the BD and vice versa Similarly the outputs are created by locating two Numeric Indicators Controls Modern Numeric Numeric Indicator on the FP Each numeric indicator automatically places a corresponding terminal icon on the BD Edit the labels of the indicators to read Sum and Average For a better visual appearance objects on a FP window can be aligned distributed and resized using the appropriate buttons appearing on the FP toolbar To do this select the objects to be aligned or distributed and apply the appropriate option from the toolbar menu Figure 2 19 shows the configuration of the FP just created Figure 2 19 FP configuration Now let us build a graphical code on the BD to perform the summation and averaging operations Note that lt Ctrl E gt toggles between a FP and a BD window If one finds the objects on a BD are too close to insert other functions or VIs in between a horizontal or vertical space can be inserted by holding down the Ctrl key to create space horizontally and or vertically As an examp
6. eration count which is read from the iteration terminal starts at index 0 and ends at index 9 Place a Random Number 0 1 function Functions Programming Numeric Random Number 0 1 inside the For Loop and wire the output terminal of this function number 0 to 1 to the border of the For Loop to create an output tunnel The tunnel appears as a box with the array symbol inside it For a For Loop auto indexing is enabled by default whereas for a While Loop it is disabled by default Create an indicator on the tunnel by right clicking and choosing Create Indicator from the shortcut menu This creates an array indicator icon outside the loop structure on the BD Its wire appears thicker due to its array data type Also another indicator representing the array index gets displayed on the FP This indicator is of array data type and can be resized as desired In this example the size of the array is specified as 10 to display all the values considering that the number of iterations of the For Loop isset to be 10 Create a second output tunnel by wiring the output of the Random Number 0 1 function to the border of the loop structure then right click on the tunnel and 18 choose Disable indexing from the shortcut menu to disable auto indexing By doing this the tunnel becomes a filled box representing a scalar value Create an indicator on the tunnel by right clicking and choosing Create Indicator from the shortcut me
7. found to be more effective if one goes through a simple example The example presented here consists of calculating the sum and average of two input values This example is described in a step by step fashion below L1 1 1 VI Creation To create a new VI click on the Blank VI under New as shown in Figure 2 17 This step can also be done by choosing File New VI from the menu As a result a blank FP and a blank BD window appear as shown in Figure 2 18 It should be remembered that a FP and a BD coexist when building a VI untitled 1 Block Diagram Iof x File untitled 1 Front Panel File Edit view Project Operate Tools Window Help m ES Figure 2 18 Blank VI Clearly the number of inputs and outputs to a VI is dependent on its function In this example two inputs and two outputs are needed one output generating the sum and the other the average of two input values The inputs are created by locating two Numeric Controls on the FP This is done by right clicking on an open area of the FP to bring up the Controls palette followed by choosing Controls Modern Numeric Numeric Control Each numeric control automatically places a corresponding terminal icon on the BD Double clicking on a numeric control highlights its counterpart on the BD and vice versa Next let us label the two inputs as x and y This is achieved by using the Labeling tool from the Tools palette which can be displayed by choosing View
8. gure 2 26 b illustrates the BD with an inserted subVI This subVI can be opened and edited by double clicking on its icon on the BD Save this subVI as Sum and Average vi This subVI performs the same function as the original Sum and Average VI 11 b Figure 2 26 Creating a subVI a selecting nodes to make a subVI and b inserted subVI icon In Figure 2 27 the completed FP and BD of the Sum and Average VI are shown Operate Tools Browse Window Help E m 130 Application Font 13pt Application Font 13pt Application Font cepmpcpspsrepedE esee E EEEEELEEELEELELEL a Sum and Average vi Block Diagram JP a m JJ Ej Ex KA Avg HE Edit sie Tools Browse Window Help nig bal Po 1 one All Figure 2 27 Sum and Average VI 12 L1 2 Using Structures and SubVIs Let us now consider another example to demonstrate the use of structures and subVIs In this example a VI is used to show the sum and average of two input values in a continuous fashion The two inputs can be altered by the user If the average of the two inputs becomes greater than a preset threshold value a LED warning light is lit As the first step to build such a VI build a FP as shown in Figure 2 28 a For the inputs consider two Knobs Controls Modern
9. he automatic tool selection mode Figure 2 24 a illustrates assigning a terminal of the Sum and Average VI to a numeric control The completed connector pane is shown in Figure 2 24 b Notice that the output terminals have thicker borders The color of a terminal reflects its data type amp Sum and Average vi Front Panel Sele File Edit Operate Tools Browse Window Help H P Sum and Average vi Front Panel m z E sj O m ee reann b Figure 2 24 Connector pane a assigning a terminal to a control and b terminal assignment completed Considering that a subVI icon is displayed on the BD of a higher level VI it is important to edit the subVI icon for it to be explicitly identified Double clicking on the top right corner icon of a BD brings up the Icon Editor The tools provided in the Icon Editor are very similar to those encountered in other graphical editors such as Microsoft Paint An editing of the icon for the Sum and Average VI is illustrated in Figure 2 25 10 E Icon Editor File Edit Help Copy Fram Black amp White 16 Colors 256 Colors 16 Colors Sum amp Aug Show Terminals OK 256 Colors Cancel Sum amp Aug Figure 2 25 Editing subVI icon A subVI can also be created from a section of a VI To do so select the nodes on the BD to be included in the subVI as shown in Figure 2 26 a Then choose Edit Create SubVI This inserts a new subVI icon Fi
10. in the gauge and numeric indicators Note that only integer values can be entered via the Input 1 knob while real values can be entered via the Input 2 knob This is due to the data types associated with these knobs The Input 1 knob is set to byte type i e I8 or 8 bit signed integer As a result only integer values within the range 128 and 127 can be entered Considering that the minimum and maximum value of this knob are set to 0 and 10 respectively only integer values from 0 to 10 can thus be entered for this input Structure and SubVl vi Seles File Edit Operate Tools Browse Window Help Average 18 3893 Warning ae 1 ae e e e Figure 2 30 FP as VI runs i When the average value of the two inputs becomes greater than the preset threshold value of 9 the warning LED will light up see Figure 2 30 Click the stop 17 button on the FP to stop the VI Otherwise the VI keeps running until the conditional terminal of the While Loop becomes true L1 3 Create an Array with Indexing Auto indexing enables one to read write each element from to a data array in a loop structure In this section this feature is covered Let us first locate a For Loop Functions Programming Structures For Loop Right click on its count terminal and choose Create Constant from the shortcut menu to set the number of iterations Enter 10 so that the code inside it gets repeated 10 times Note that the current loop it
11. l or input This locates a numeric control on the FP as well as a corresponding terminal icon on the BD The label is automatically set to x Create a second numeric control by right clicking on the y terminal of the Add function Next right click on the output terminal of the Add function and choose Create Indicator from the shortcut menu A data type terminal icon labeled as x y is created on the BD as well as a corresponding numeric indicator on the FP Next right click on the y terminal of the Divide function to choose Create Constant from the shortcut menu This creates a Numeric Constant as the divisor and wires its y terminal Type the value 2 in the numeric constant Right click on the output terminal of the Divide function labeled as x y and choose Create Indicator from the shortcut menu In case a wrong option is chosen the terminal does not get wired A wrong terminal option can be easily changed by right clicking on the terminal and choosing Change to Control or Change to Constant from the shortcut menu To save the created VI for later use choose File Save from the menu or press lt Ctrl S gt to bring up a dialog window to enter a name Type Sum and Average as the VI name and click Save To test the functionality of the VI enter some sample values in the numeric controls on the FP and run the VI by choosing Operate Run by pressing lt Ctrl R gt or by clicking the Run button on the toolbar From the di
12. le Figure 2 20 b illustrates a horizontal space inserted between the objects shown in Figure 2 20 a Untitled 1 Block Diagram Seles Untitled 1 Block Diagram Seles Figure 2 20 Inserting horizontal vertical space a creating space while holding down the Ctrl key and b inserted horizontal space Next place an Add function Functions Express Arithmetic amp Comparison Express Numeric Add and a Divide function Functions Express Arithmetic amp Comparison Express Numeric Divide on the BD The divisor in our case 2 needs to be entered in a Numeric Constant Functions Express Arithmetic amp Comparison Express Numeric Numeric Constant and connected to the y terminal of the Divide function using the Wiring tool To have a proper data flow functions structures and terminal icons on a BD need to be wired The Wiring tool is used for this purpose To wire these objects point the Wiring tool at a terminal of a function or a subVI to be wired left click on the terminal drag the mouse to a destination terminal and left click once again Figure 2 21 illustrates the wires placed between the terminals of the numeric controls and the input terminals of the add function Notice that the label of a terminal is displayed whenever the cursor is moved over it if the automatic tool selection mode is enabled Also note that the Run button on the toolbar remains broken until the wiring proce
13. nu This sets up an indicator of scalar data type outside the loop structure on the BD Next create a third indicator on the Number 0 to 1 terminal of the Random Number 0 1 function located in the For Loop to observe the values coming out To do this right click on the output terminal or on the wire connected to this terminal and choose Create Indicator from the shortcut menu Place a Time Delay Express VI Functions Programming Timing Time Delay to delay the execution in order to have enough time to observe a current value A configuration window is brought up for specifying the delay time in seconds Enter the value 0 1 to wait 0 1 seconds at each iteration Note that the Time Delay Express VI is shown as an icon in Figure 2 31 in order to have a more compact display 19 B Indexing Example vi Front Panel File Edit Operate Tools Browse Window Help i a 13pt o Current output tpi T fosizo4 eho jd Output w o indexing iii i LES Indexing rs ETHER Block Diagram SESE Ele Edit Operate Tools Browse Window Help FERRE il e n Pale a2 1 sk Fo 1 lI s BSS came BIKE BE L m Figure 2 31 Creating array with indexing Save the VI as Indexing Example vi and run it to observe its functionality From the output displayed on the FP a new random number should get displayed every 0 1 seconds on the indicator residing inside the loop struc
14. splayed output values in the numeric indicators the functionality of the VI can be verified Figure 2 23 illustrates the outcome after running the VI with two inputs 10 and 30 gt Sum and Average vi Front Panel BHA Fie Edit Operate Tools Browse Window Help a 13pt Application Font m Surm Average Do Figure 2 23 VI verification L1 1 2 SubVI Creation If a VI is to be used as part of a higher level VI its connector pane needs to be configured A connector pane assigns inputs and outputs of a subVI to its terminals through which data are exchanged A connector pane can be displayed by right clicking on the top right corner icon of a FP and selecting Show Connector from the shortcut menu The default pattern of a connector pane is determined based on the number of controls and indicators In general the terminals on the left side of a connector pane pattern are used for inputs and the ones on the right side for outputs Terminals can be added to or removed from a connector pane by right clicking and choosing Add Terminal or Remove Terminal from the shortcut menu If a change is to be made to the number of inputs outputs or to the distribution of terminals a connector pane pattern can be replaced with a new one by right clicking and choosing Patterns from the shortcut menu Once a pattern is selected each terminal needs to be reassigned to a control or an indicator by using the Wiring tool or by enabling t
15. ss is completed Untitled 1 Block Diagram Figure 2 21 Wiring BD objects For better readability of a BD wires which are hidden behind objects or crossed over other wires can be cleaned up by right clicking on them and choosing Clean Up Wire from the shortcut menu Any broken wires can be cleared by pressing lt Ctrl B gt or Edit Remove Broken Wires The label of a BD object such as a function can be shown or hidden by right clicking on the object and checking or unchecking Visible Items Label from the shortcut menu Also a terminal icon corresponding to a numeric control or indicator can be shown as a data type terminal icon This is done by right clicking on the terminal icon and unchecking View As Icon from the shortcut menu Figure 2 22 shows an example where the numeric controls and indicators are shown as data type terminal icons The notation DBL represents double precision data type Figure 2 22 Completed BD It is worth pointing out that there exists a shortcut to build the above VI Instead of choosing the numeric controls indicators or constants from the Controls or Functions palette the shortcut menu Create activated by right clicking on a terminal of a BD object such as a function or a subVI can be used As an example of this approach create a blank VI and locate an Add function Right click on its x terminal and choose Create Control from the shortcut menu to create and wire a numeric contro
16. ture However no data should be available from the indicators outside the loop structure until the loop iterations end An array of 10 elements should be generated from the indexing enabled tunnel while only one output the last element of the array should be passed from the indexing disabled tunnel L1 4 Debugging VIs Probe Tool The Probe tool is used to observe data that are being passed while a VI is running A probe can be placed on a wire by using the Probe tool or by right clicking on a wire 20 and choosing Probe from the shortcut menu Probes can also be placed while a VI is running Placing probes on wires create probe windows through which intermediate values can be observed A probe window can be customized For example showing data of array data type via a graph makes debugging easier To do this right click on the wire where an array is being passed and choose Custom Probe Controls Modern Graph Waveform Graph from the shortcut menu As an example of using custom probes a Waveform Chart is used here to track the scalar values at probe location 1 a Waveform Graph to monitor the array at probe location 2 and a regular probe window at probe location 3 to see the values of the Indexing Example VI These probes and their locations are illustrated in Figure 2 32 3m 2 Probe Poo ZA E Indexing Example vi Block Diagram E ile Edit Operate Tools Browse Window He E 1 number 0 to 1
17. umeric Indicator a Round LED Controls Modern Boolean Round LED and a Gauge Controls Modern Numeric Gauge Edit the labels of the indicators as shown in Figure 2 28 a my i i F Lr i Structure and Sub l vi Glock Diagram Sele Structure and SubYl vi Front Panel Seles rr b Figure 2 28 Example of structure and subVI a FP and b BD Now let us build the BD There are five control and indicator icons already appearing on the BD Right click on an open area of the BD to bring up the Functions palette and then choose Select a VI This brings up a file dialog box Navigate to the Sum and Average Vl in order to place it on the BD This subVI is displayed as an icon on the BD Wire the numeric controls Input 1 and Input 2 14 to the x and y terminals respectively Also wire the Sum terminal of the subVI to the numeric indicator labeled Sum and the Average terminal to the gauge indicator labeled Average A Greater or Equal function is located from Functions Programming Comparison Greater or Equal in order to compare the average output of the subVI with a threshold value Create a wire branch on the wire between the Average terminal of the subVI and its indicator via the Wiring tool Then extend this wire to the x terminal of the Greater or Equal function Right click on the y terminal of the Greater or Equal function and choose Create Constant in order to place a
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