Lab 2: Getting familiar with LabVIEW: Part II
Contents
1. edit the labels to read Original and Scaled using the Labeling tool The changing of the properties of the Waveform Graph can also be accomplished by using its properties dialog box This box is brought up by right clicking on the Waveform Graph and choosing Properties from the shortcut menu The completed FP is shown in Figure 2 40 With this version of the VI the frequency of the input signal and the gain of the output signal can be controlled using the controls on the FP es Lab02_Express with Controls vi Front Panel File Edit Operate Tools Browse Window Help gt 5 m 13pt Application Font w Tar A Original Waveform Graph Scaled Frequency Gain 1000 HS 800 6004 400 3 200 iE a g 2 a a O m w e Tesetecebecetoeedone Figure 2 40 FP of signal generation and amplification system with controls L2 2 Building a System with Regular Vis In this section the implementation of the same system discussed above is achieved by using regular VIs After creating a blank VI place a While Loop Functions Programming Structures While Loop on the BD which may need to be resized later To provide the signal source of the system place a Basic Function Generator VI Functions Programming Waveform Analog Waveform Waveform Generation Basic Function Generator inside the While Loop To configure the parameters of the signal appropriate controls and constants2. 3 Profile VI The Profile tool is used to gather timing and memory usage information Make sure the VI is stopped before setting up a Profile window Select Tools Profile Performance and Memory to bring up a Profile window Place a checkmark in the Timing Statistics checkbox to display timing statistics of the VI The Timing Details option provides more detailed statistics of the VI such as drawing time To profile memory usage as well as timing check the Memory Usage checkbox after checking the Profile Memory Usage checkbox Note that this option can slow down the execution of the VI Start profiling by clicking the Start button on the profiler then run the VI A snapshot of the profiler information can be obtained by clicking on the Snapshot button After viewing the timing information click the Stop button The profile statistics can be stored into a text file by clicking the Save button An outcome of the profiler is exhibited in Figure 2 44 after running the Lab02_Regular VI More details on the use of the Profile tool can be found in 3 15 Profile Performance and Memory Sub VIs Time Total Time Runs JV Timing statistics lV Profile memory usage JV Timing details V Memory usage Time unit Size unit J milliseconds gt kilobytes Profile Data VI Time Lab02_Regular vi 171 9 0 0 ma_Updatet0 timestamp vi 0 0 0 0 ma_patchErrorCode or Caller as Source vi 0 0 0 0 ma_Trap Fgen Parameter Errors vi 0 0 0 0 B
3. Figure 2 34 Different types of signals including sine square triangle sawtooth or DC can be generated with this VI Enter and adjust the parameters as indicated in Figure 2 34 to simulate a sinewave having a frequency of 200 Hz and an amplitude swinging between 100 and 100 Set the sampling frequency to 8000 Hz A total of 128 samples spanning a time duration of 15 875 milliseconds ms are generated Note that when the parameters are changed the modified signal gets displayed instantly in the Result Preview graph window gt Configure Simulate Signal Simulate Signal Signal Result Preview Signal type Sine Frequency Hz Phase deg 200 0 Amplitude Amplitude Offset 100 0 C Add noise Noise type Time Stamps Relative to start of measurement Timing A a ey Absolute date and time 8000 Simulate acquisition timing Reset Signal Number of samples Run as fast as possible O Reset phase seed and time stamps 128 C Automatic Use continuous generation C Integer number of cycles Signal Name Actual number of samples V Use signal type name Signal name Actual frequenc Sine Figure 2 34 Configuration of Simulate Signal Express VI Next place a Scaling and Mapping Express VI Functions Express Arithmetic amp Comparison Scaling and Mapping to amplify or scale this simulated signal When its configuration dialog is brought up see Figure 2 35 choose Linear Y mx b and enter 5
4. need to be wired To create a control for the signal type right click on the signal type terminal of the Basic Function Generator VI and choose Create Control from the shortcut menu Note that an enumerated Enum type control for the signal gets located on the FP Four items including sine triangle square and sawtooth are listed in this control Next right click on the amplitude terminal and choose Create Constant from the shortcut menu to create an amplitude constant Enter 100 in the numeric constant box to set the amplitude of the signal In order to configure the sampling frequency and the number of samples create a constant on the sampling information terminal by right clicking and choosing Create Constant from the shortcut menu This creates a cluster constant which includes two numeric constants The first element of the cluster shown in the upper box represents the sampling frequency and the second element shown in the lower box represents the number of samples Enter 8000 for the sampling frequency and 128 for the number of samples Note that the same parameters were used in the previous section Now toggle to the FP by pressing lt Ctrl E gt and place two Vertical Pointer Slide controls on the FP by choosing Controls Modern Numeric Vertical Pointer Slide Rename the controls Frequency and Gain respectively Set the maximum scale values to 1000 for the Frequency control and 5 for the Gain
5. to 400 Hz and set the amplitude ranges from 20 to 200 Generate a third signal with the frequency fs mod lem f f2 400 100 Hz where mod and lem denote the modulus and least common multiple operation respectively and the amplitude As being the sum of the amplitudes A and A2 Use the same sampling frequency and number of samples as used for the first two signals Display all the signals using the legend on the same waveform graph and label them accordingly When not using the MathScript feature it is easier to use the Express VIs Build a VI to check whether a given positive integer n is a prime number or not and display a warning message if it is not a prime number Build a VI to generate two sinusoid signals the same as the ones in Experiment 2 Generate a third signal with the frequency fs gcd f f2 mean f f2 Hz where gcd and mean denote the greatest common divisor and the average operation respectively and the amplitude As being the sum of the amplitudes Ai and A2 Use the same sampling frequency and number of samples as used for the first two signals Display all the signals using the legend on the same waveform graph and label them accordingly When not using the MathScript feature it is easier to use the Express VIs Build a VI to generate the first n prime numbers and store them using an indexing array Display the outcome 17
6. 10 control The Vertical Pointer Slide controls create corresponding icons on the BD Make sure that the icons are located inside the While Loop If not select the icons and drag them inside the While Loop The Frequency control should be wired to the frequency terminal of the Basic Function Generator VI in order to be able to adjust the frequency at run time The Gain control is used at a later stage The output of the Basic Function Generator VI appears in the waveform data type The waveform data type is a special cluster which bundles three components t 0 dt and Y together The component t 0 represents the trigger time of the waveform dt the time interval between two samples and Y data values of the waveform Next the generated signal needs to be scaled based on a gain factor This is done by using a Multiply function Functions Programming Numeric Multiply and a second Vertical Pointer Slide control named Gain Wire the generated waveform out of the signal out terminal of the Basic Function Generator VI to the x terminal of the Multiply function Also wire the Gain control to the y terminal of the Multiply function Recall that the Merge Signals function is used to combine two signals having dynamic data types into the same wire To achieve the same outcome with regular VIs place a Build Array function Functions Programming Array Build Array to build a 2D array i e tw
7. Lab 2 Getting familiar with LabVIEW Part Il Now that an initial familiarity with the LabVIEW programming environment has been acquired in Lab 1 this second lab covers an example where a simple DSP system is built thus enhancing the familiarity of the reader with LabVIEW This example involves a signal generation and amplification system The shape of the input signal sine square triangle or saw tooth as well as its frequency and gain are altered by using appropriate FP controls The system is built with Express VIs first then the same system is built with regular VIs This is done in order to illustrate the advantages and disadvantages of Express VIs versus regular VIs for building a system L2 1 Building a System VI with Express Vis The use of Express VIs allows less wiring on a BD Also it provides an interactive user interface by which parameter values can be adjusted on the fly The BD of the signal generation system using Express VIs is shown in Figure 2 33 gt LabO2_Express vi Block Diagram DAR File Edit Operate Tools Browse Window Help o m Elkala z Simulate Signal Mapping eal Signals Scaled Signals rb SSS ys f Scaling and Figure 2 33 BD of signal generation and amplification system using Express VIs 1 To build this BD locate the Simulate Signal Express VI Functions Express Input Simulate Signal to generate a signal source This brings up a configuration dialog as shown in
8. asic Function Generator vi 0 0 0 0 ma_Updatet0 DBL vi 0 0 0 0 Triangle Wave vi 0 0 0 0 Sine Wave vi 0 0 0 0 Sawtooth Wave vi 0 0 0 0 Square Wave vi 0 0 0 0 ma_basicErrorCode2ErrorCluster vi 0 0 0 0 Select Application Instances 171 9 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 142 a 142 142 0 0 142 0 0 142 Average Shortest Longest 171 9 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 171 9 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 171 9 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Application Instances Loix Diagram Di 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 a N 9 9 9 9 9 9 9 9 9 9 ofa Stop Snapshot Save Close Help Figure 2 44 Profile window after running Lab02_Regular VI L2 4 Bibliography 1 National Instruments Getting Started with LabVIEW Part Number 323427A 01 2003 2 National Instruments LabVIEW User Manual Part Number 320999E 01 2003 3 National Instruments LabVIEW Performance and Memory Management Application Note 168 Part Number 342078B 01 2004 L2 5 Lab Experiments Carry out the following experiments with and without the MathScript feature of LabVIEW 8 1 Build a VI to generate two sinusoid signals with the frequencies f Hz and f2 Hz and the amplitudes Ai and Az based on a sampling frequency of 8000 Hz with 16 the number of samples being 256 Set the frequency ranges from 100 Hz
9. e two labels and markers The use of the dynamic data type sets the signal labels automatically To run the VI continuously place a While Loop Position the While Loop to enclose all the Express VIs and the graph Now the VI is ready to be run i gt LabO2_Express vi Front Panel File Edit Operate Tools Browse Window Help ima JA iOl TT 13pt Application Font tor F A Sine K waveform Graph Sine Scaled v a 3 a lt I 1 1 0 01 0 015 0 02 Time Figure 2 36 FP of signal generation and amplification system Run the VI and observe the waveform Graph The output should appear as shown in Figure 2 36 To extend the plot to the right end of the plotting area right click on the waveform Graph and choose X Scale then uncheck Loose Fit from the shortcut menu The graph shown in Figure 2 37 should appear LabO2_Express vi Front Panel File Edit Operate Tools Browse Window Help imi AE E j 13pt Application Font tor E Gl a Sine w Waveform Graph Sine Scaled a 3 3 2 Tat lt 1 Figure 2 37 Plot with Loose Fit If the plot runs too fast a delay can be placed in the while Loop To do this place a Time Delay Express VI Functions Programming Timing Time Delay and set the delay time to 0 2 in the configuration window This way the loop execution is delayed by 0 2 seconds in the BD shown in Figure 2 33 Although this system runs successfully no control of t
10. form vi and run it Change the signal type gain and frequency values to see the original and scaled signal in the Waveform Graph 12 LabO2_Regular_Waveform vi Block Diagram File Edit Operate Tools Browse Window Help LabO2_Regular_Waveform vi File Edit Operate Tools Browse Window Help Waveform Graph signal type z Sine Wave Frequency Gain 1000 5 8 8 5 Ke N wo A A Amplitude Figure 2 42 Original and scaled output signals 13 The waveform data type is not accepted by all the functions or subVIs To cope with this issue the Y component data value of the waveform data type is extracted to have the output signal as an array of data samples This is done by placing a Get Waveform Components function Functions Programming Waveform Get Waveform Components Then wire the signal out terminal of the Basic Function Generator VI to the waveform terminal of the Get Waveform Components function Click on t0 the default terminal of the Get Waveform Components function and choose Y as the output to extract data values from the waveform data type see Figure 2 43 The remaining steps are the same as those done for the version shown in Figure 2 41 In this version however the processed signal is an array of double precision samples LabO2_Regular vi Block Diagram DAR File Edit Operate Tools Browse Window Help M i S iii S n Gale 0 AA Figure 2 43 Matching data types 14 L2
11. he default values for these controls to 200 and 2 respectively By running this modified VI it can be observed that the two signals get displayed with the same label since the source of these signals i e the Sine terminal of the Simulate Signal Express VI is the same Also due to the autoscale feature of the Waveform Graph the scaled signal appears unchanged while the Y axis of the Waveform Graph changes appropriately This is illustrated in Figure 2 39 i LabO2_Express with Controls vi Front Panel File Edit Operate Tools Browse Window Help D E oO u 13pt Application Font x So ta 2 eo Waveform Graph Frequency Gain 1000 8002 600 Z 4004 200 iE v D Z 5 a 1 O NUA Vevoteseteeebevetons Figure 2 39 Autoscaled graph of two signals shown together Let us now modify the property of the Waveform Graph In order to disable the autoscale feature right click on the Waveform Graph and uncheck Y Axis AutoScale Y The maximum and minimum scale can also be adjusted In this example 600 and 600 are used as the minimum and maximum values respectively This is done by modifying the maximum and minimum scale values of the Y axis with the Labeling tool If the automatic tool selection mode is enabled just click on the maximum or minimum scale of the Y axis to enter any desired scale value To modify the labels displayed in the plot legend right click and choose Ignore Attributes Then
12. he signal frequency and gain is available during its execution since all the parameters are set in the configuration dialogs of the Express VIs To gain such a flexibility some modifications need to be made To change the frequency at run time place a Vertical Pointer Slide control Controls Modern Numeric Vertical Pointer Slide on the FP and wire it to the Frequency terminal of the Simulate Signal Express VI The control is labeled as Frequency The Express VI can be resized to show more terminals at the bottom of the expandable node Resize the VI to show an additional terminal below the Sine terminal Then click on this new terminal error out by default to select Frequency from the list of the displayed terminals Next replace the Scaling and Mapping Express VI with a Multiply function Functions Programming Numeric Multiply Place another Vertical Pointer Slide control and wire it to the y terminal of the Multiply function to adjust the gain This control is labeled as Gain These modifications are illustrated in Figure 2 38 P LabO2_Express with Controls vi Block Diagram DAR Eile Edit Operate Tools Browse Window Help if requenc Simulate Signal Sine gt Frequent ESS SSeS Figure 2 38 BD of signal generation and amplification system with controls Now on the FP set the maximum range of each slide control to 1000 for the Frequency control and 5 for the Gain control respectively Also set t
13. in Slope m to scale the input signal 5 times Wire the Sine terminal of the Simulate Signal Express VI to the Signals terminal of the Scaling and Mapping Express VI Note that a wire having a dynamic data type gets created Configure Scaling and Mapping Scalin Scaling or Mapping Type O Normalize Lowest peak Highest peak Linear Y mx b Slope m _ Yintercept b 5 lo O Logarithmic dB reference O Interpolated Define Table Figure 2 35 Configuration of Scaling and Mapping Express VI To display the output signal place a Waveform Graph Controls Modern Graph Waveform Graph on the FP The Waveform Graph can also be created by right clicking on the Scaled Signals terminal and choosing Create Graph Indicator from the shortcut menu Now in order to observe the original and the scaled signal together in the same graph wire the Sine terminal of the Simulate Signal Express VI to the Waveform Graph This inserts a Merge Signals function on the wire automatically An automatic insertion of the Merge Signals function occurs when a signal having a dynamic data type is wired to other signals having the same or other data types The Merge Signals function combines multiple inputs thus allowing two signals consisting of the original and scaled signals to be handled by one wire Since both the original and scaled signals are displayed in the same graph resize the plot legend to display th
14. o rows or columns of one dimensional signal Resize the Build Array function to have two input terminals Wire the original signal to the upper terminal of the Build Array function and the output of the Multiply function to the lower terminal Remember that the Build Array function is used to concatenate arrays or build n dimensional arrays Since the 11 Build Array function is used for comparing the two signals make sure that the Concatenate Inputs option is unchecked from the shortcut menu More details on the use of the Build Array function can be found in 2 A Waveform Graph Controls Modern Graph Waveform Graph is then placed on the FP Wire the output of the Build Array function to the input of the Waveform Graph Resize the plot legend to display the labels and edit them Similar to the example in the previous section the AutoScale feature of the Y axis should be disabled and the Loose Fit option should be unchecked along the X axis Place a Wait ms function Functions Programming Timing Wait inside the While Loop to delay the execution in case the VI runs too fast Right click on the milliseconds to wait terminal and choose Create Constant from the shortcut menu to create and wire a Numeric Constant Enter 200 in the box created Figure 2 41 and Figure 2 42 illustrate the BD and FP of the designed signal generation system respectively Save the VI as Lab02_ Regular_Wave
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