Home

LabVIEW Reference

1. The for loop in LabVIEW operates just like a for loop would in another programming language In the top left corner is a boxed N It is an input connector that accepts a integer data type represented by the color blue and the loop will complete as many iterations as the value wired to it In the lower left corner is a boxed i It is an output terminal that also outputs an integer data type Use this terminal to keep track of the current iteration number beginning at zero or to do calculations with its value The loop will iterate as long as long as i lt N N Insert LabVIEW Code Here H gt Figure 12 For Loop Structure 12 While Loop Structure To place the while loop select Functions gt gt Structures gt gt While Loop After picking the while loop structure drag out an area on the block diagram that the structure will take up Anything on the block diagram within the boundary of the while loop will be included in the while loop Like the for loop the while loop has a terminal in the lower left corner a boxed i which increments with each iteration beginning at zero The while loop however does not have a boxed N because it operates not a specific number of times but instead until the conditional terminal receives a certain Boolean value The conditional terminal is in the lower right of the while structure represented by either a boxed circular arrow or a boxed stop sign If the condition
2. Write To Spreadsheet File To create a generic text based file is more difficult First you have to place the New File node on the block diagram Functions gt gt File I O gt gt Advanced File Functions gt gt New File or use the Open File node Functions gt gt File I O gt gt Advanced File Functions gt gt New File if the file already exists Wire this node to a file path control constant Next place the Write File node Functions gt gt File I O gt gt Write File on the block diagram and wire the refnum output connector from the New File node to the refnum input connector on the Write File node Also wire in some data of any data type Finally close the file using Close File Functions gt gt File I O gt gt Close File again wiring a refnum from the Write File to Close File NOTE these operations will happen in the correct order because each node must wait until the previous node sends it data in the form of a refnum if you wired the refnum from the Open File node to the Close File node instead of from the Write File to the Close File the file may be closed before it is written see the section on Data Transfer The Write To Spreadsheet File node does all of these steps for you 15 Figure 18 Creating a File ata Acquisition To acquire data from the breakout boards use the Analog Input and Output nodes found in Functions gt gt Data Acquisition gt gt Analog Input or Analog Output You will need to wi
3. in the following format 1 0 1 where 1 is the current frame and there are two frames the first called and the second 1 In the blank space within the second frame frame number 1 place the nodes that you want to operate after the first frame has completed You can continue to add more frames and code by right clicking the border gt gt Add Frame After or Add Frame Before whichever frame is currently displayed 11 Figurel1 Frame 0 and Frame 1 of a Sequence There will be times when you want to use sequence structures and data transfer at the same time i e pass data between the frames of a sequence This is easily done by creating sequence locals Sequence locals are variables on the boundary of the sequence that are available to all frames Place one by right clicking the boundary gt gt Add Sequence Local On one of the frames the data will be loaded into the sequence local by wiring a node to that sequence local and then any of the nodes on the frames after the frame from which the data is loaded can access that data by wiring from the sequence local to an input connector on the correct node Repetition For Loop Structure To place a for loop select Functions gt gt Structures gt gt For Loop After picking the for loop structure drag out an area on the block diagram that the structure will take up Anything on the block diagram within the boundary of the for loop will be included in the for loop
4. new VI two windows will pop up The first window is known as the front panel and the second as the block diagram Front Panel The purpose of the front panel is user interface On the front panel you will place the controls indicators charts and graphs etc that the user needs to see and possibly use You can access the front panel from the block diagram by selecting Window gt gt Show Panel You can align controls on the front panel using the Align Objects pull down button on the tool bar Block Diagram The block diagram contains the meat of the program Herein lie all the internal workings and background operations of the code On the block diagram you will place nodes wires structures etc You can access the block diagram from the front panel by selecting Window gt gt Show Diagram Palettes To display a palette select Window gt gt Show Palette Name Palette This will display the palette in locked mode which means that the palette will remain in that position until it is closed if you are using the controls palette and switch to the block diagram the controls palette will be closed and the functions palette opened Another way to display the controls palette functions palette is to right click using any tool on either the front panel or block diagram and the corresponding palette will be displayed in unlocked mode When I direct you to Controls Palette or Functions Palette to access a certain control or Function I wi
5. LabVIEW Reference l LabVIEW Help To access the LabVIEW help reference click LabVIEW Tutorial on the startup box Find Examples is also a helpful resource with example VIs or select Help gt gt VI Function amp How To Help from either the front panel or block diagram There are also LabVIEW manuals under Help gt gt Search the LabVIEW Bookshelf for an even more in depth study of LabVIEW mechanics To access help on individual nodes of a VI select Help gt gt Show Context Help to display context help Context help is a window that displays reference information for the LabVIEW element near the cursor It will help you figure out what each node does and understand how the VI LabVIEW code has a vi extension works when you are trying to examine example code It also contains a link to more information about the element The LabVIEW help reference is an incredible resource for learning and understanding LabVIEW mechanics Included in the reference are a number of example VIs and many step by step tutorials You will most likely be able to find an example somewhere that nearly implements the function you want to program using Lab VIEW the Internet is a good resource as well The LabVIEW help reference is nearly all you will need to learn LabVIEW This reference sheet will point out the things that LabVIEW can do and describe some of its mechanics without the depth the LabVIEW help reference has ll Interface When you create a
6. Nodes Formula Node hel result x constant ixe 14 esult Figure 10 An Example of a Mathematical Operation Using a Formula Node Figure 10 shows the operation x 2 x2 1 using a formula node two numeric controls x and x2 and a constant equal to 2 00 A numeric indicator displays the result on the front panel To add input or output variables to a formula node right click the border of the node gt gt Add Input or Add Output Then type a name for the variable and wire it to the output connector of another node or a constant if the variable is an input or an input connector of another node if the variable is an output Now enter mathematical statements you want the node to execute inside the node using the edit text tool end statements with a semicolon The formula can do operations similar to those used in C code 10 Matlab Node The Matlab node is just like the formula node except that a VI with a Matlab node in it requires that Matlab be running in the background open in order operate correctly and the statements must be written in the format of a Matlab script VI Programmatic Control When you want to control how your program operates or the order of events use the following techniques Sequential Control Data Transfer The first obvious form of control over the order of operations in LabVIEW 1s data transfer Before any node runs it waits for data to be passed to all the connectors that are wir
7. The design of the Boolean controls is generally in the form of push buttons or switch Use these with case structures event structures connected to a while loop s conditional terminal etc Boolean controls are accessed from Controls gt gt Boolean gt gt Control Name The data type of a Boolean control is Boolean Array Controls Array controls are just like numeric controls only in an array format Graphs and Charts Graphs and charts are accessed from Controls gt gt Graph gt gt Graph or Chart Name They are used to display a plot of data Graphs and charts differ in the way they display and update data VIs with graphs usually collect the data in an array and then plot the data to the graph which is similar to a spreadsheet that first stores the data then generates a plot of it In contrast a chart appends new data points to those already in the display On a chart you can see the current reading or measurement in context with data previously acquired LabVIEW User Manual Random Signal o 24 Figure 6 A Chart Displaying a Random Signal and a Digital Readout If you feed a graph a 1D array the graph will display the data with the values on the x axis representing the index of the data element beginning with zero That is if the graph shows a point at 2 5 this means that the third number in the array is a five The same goes for charts If you feed a graph a 2D array the graph will display multiple plot
8. al terminal is a circular arrow then the while loop is set to run until a False Boolean data type is passed to the terminal If the terminal is a stop sign the loop is set to run only as long as a False is passed to the terminal Change this setting by right clicking the terminal gt gt Stop If True or Continue If True You must wire this terminal to some control for the VI to run If you want the loop to run forever simply right click the terminal gt gt Create Constant and switch the constant to the correct value with the operate value tool Conditional Terminal Figure 13 While Loop Structure Tunnels If you want a while loop or a for loop to build an array as it cycles simply wire a number generator from inside the loop to outside the loop Where the wire crosses the boundary of the loop LabVIEW will create a tunnel On the tunnel right click gt gt Enable Indexing and the output will become the data type of a 2D array There is a random number generator node in Functions gt gt Numeric Figure 14 For Loop With a Random Number Generator Node 13 Feedback If you want feedback in your loop that is you want to use a variable that your loop updated on its last cycle use shift registers On the boundary of your loop right click gt gt Add Shift Register The left shift register will produce the value that was sent to the right shift register on the last cycle of the loop If you do not initialize the register
9. ed Therefore any node which has an output connector wired to another node s input connector will complete its operation before the other node can begin Any node that has no input connectors wired will automatically operate as soon as the VI is started unless the VI contains another form of programmatic control discussed in the following sections Sequence Structure Sometimes however you need two or more operations to happen sequentially even though they are not wired together To do this place a sequence structure on the block diagram Functions gt gt Structures gt gt Sequence After picking the sequence structure drag out an area on the block diagram that the structure will take up Anything on the block diagram within the boundary of the sequence structure will be included in the current frame of the sequence At this point there is only one frame in the sequence LabVIEW will run only one frame at a time and move to the next frame only after every node on the current frame has ended its operation To add another frame after this one right click on the border of the sequence structure gt gt Add Frame After A new empty frame will be displayed and all of the nodes on the first frame will be hidden Also a heading is added to the structure On the outsides of the heading are arrows Click on them to browse through the frames of the sequence In the middle 1s written the current frame number followed by the set of possible frames
10. ll write it like Controls gt gt Section gt gt Control Name or Functions gt gt Section gt gt Function Name To change a palette to locked mode click the pushpi in the upper left corner 7 Pushpin gt Functions E Controls 7 m Wi T hal a mn ws rs We pE r a o m m pas HE gt F as i sa E at E H x ame A eS pry D me 8 i t i h jem F Dooe ooo a a l r 1 F T Figure 1 Functions Palette Figure 3 Tools Palette Tools and Shortcuts LabVIEW uses different tools to program your VI These can be accessed from the Tools Palette if it is open or by pressing tab until the tool you want is displayed as the cursor I have set the small button on the left side of the mouse in this lab as the tab button to make this oft used task quicker To display the Tools Palette select Window gt gt Show Tools Palette Below is a description of the tools in the Tools Palette From this list only the operate value position size select edit text and connect wire tools are available when using the tab key in the block diagram and only the operate value position size select edit text and set color tools are available when using the tab key in the front panel 7 E Automatic Tool Selection This option is the top button of the Tools Palette p p It automatically selects the tools based o
11. methods Select them from the Controls palette if it is open and click on the front panel at the location that you want it or right click anywhere on the front panel to display the Controls palette Another way to create controls or indicators from the block diagram is to right click on a node s connector that you want wired to the control indicator gt gt Create Control or Create Indicator You can also create constants which are manipulated only from the block diagram NOTE the controls and indicators on the front panel are also displayed on the block diagram and can be wired to other nodes however you can only delete controls and indicators from the front panel if you are working in the front panel and would like to display the location of a control or indicator on the block diagram or vice versa either right click the control or indicator gt gt Find Control or Find Indicator or double click the control or indicator Controls Controls allow the user to input information that the VI needs to do a calculation or complete a task They usually need to be changed by the user before the program runs or updated on each cycle of a loop There are five basic types of controls that you will use numeric Boolean string and path list and ring controls List and ring controls differ only in format and are used for similar tasks a eControls Numeric Controls Boolean Controls g Ha Aii String and Path Controls List Cont
12. n the context of the cursor location Mo perate Value Use this tool to change the value of a control or constant click on buttons switch between the frames of a structure etc This will be one of the tools along with the probe data tool available when the VI is running lposition Size Select This is the tool you will use most often Use it to position nodes move wires resize structures and constant boxes switch between the frames of a structure resize a node to include more input output connectors select a section of code to copy it with Ctrl C etc Acai Text This tool edits any text in the VI including values in a control or constant that aren t symbolic and case headings Bconnect Wire This tool is only used on the block diagram Use it to connect nodes in the block diagram by selecting one output connector and one input connector When you place the connect wire tool over a node the connector that you are on top of will begin blinking Also if context help is open the connector will blink in that window as well This will help you make sure to select the correct connector After you connect two connectors one of two things will happen Either a wire will form between them color coded with the data type it is carrying or the wire will become a dashed line If the wire is a dashed line this means that you have made an error Usually the error will be that you connected two different data types or y
13. of each case NOTE There must be a case for each possible value that the structure may receive To do this make one of the cases a default case by right clicking on the case gt gt Make This Case the Default and in this case simply wire the input tunnels to the output tunnels without modifying the data You can add cases in the same way that you add frames in a sequence structure right click on the case gt gt Add Case After or Add Case Before The case structure by default has two cases True and False and accepts Boolean values Boolean case structures do not need a default case Change this by wiring a different data type to the question mark terminal To change the name of each case use the edit text tool 14 Rn a a ie A Figure 16 The Case Structure VII Input Output Files The two most common methods of saving data in LabVIEW are in text format and spreadsheet format You can create a file in LabVIEW using either method and it will be accessible to Excel To create a spreadsheet file format you must have data in array form Use the Write To Spreadsheet File node Functions gt gt File I O gt gt Write To Spreadsheet File and wire it to array data and a file path The Write To Spreadsheet File node also allows other functionality such as appending to a file that already exists saving the data in a certain format that your spreadsheet program requires etc File path constankidialog if empt Figure 17 Using
14. ou connected two input connectors or two output connectors together If you hold the connect wire tool over a wire context help will show you what data type is flowing through the wire If you hold the tool over a dashed wire a dialog will appear describing the error that is causing the wire to be dashed Alon ect Shortcut Menu This tool is the same thing as a right click using any tool on either the front panel or block diagram It displays the Controls Palette Functions Palette depending on whether you are in the front panel or block diagram scroll Window This tool has the same function as the hand in Adobe Acrobat it allows you to move around the front panel block diagram by clicking and dragging cetctear Breakpoint This tool represented by the stop sign is used for troubleshooting the VI Refer to the LabVIEW help reference probe Data This tool represented by the circled p with an arrow through it is used for troubleshooting the VI Refer to the LabVIEW help reference lA cet Color This tool is useful for changing background colors in the VI Ch Color This tool is useful for changing background colors in the VI lil Data Types Below is a list of the data types used in LabVIEW The first image before each data type represents a control on the block diagram which outputs that data type note the solid outer line The second image represents an indicator on the block diagram which input
15. re them the device number usually 1 and the channel number usually 0 using constants or controls see the section on Controls and Indicators The Analog Input nodes will output the voltage it read from the specified input channel at the time it ran and the Analog Output nodes will output a voltage to some specified output channel reference the National Instruments breakout board reference card to find which channels are input and which are output and where they are on the board You can also use the Acquire Waveform node and average the array it outputs with the Mean node Figure 19 Using The Acquire Waveform Node
16. rols sa T i HE za EEEE Ring Controls Fra gt A a tl m HLH Figure 4 Basic Controls On the block diagram a control is indicated by a rectangle with the data type written on the inside color coded according to data type and a solid line around the outside of the rectangle e g represents a control of the type double The value of a control is changed using the operator tool To change the default value of a control on the control right click gt gt Make Current Value Default NOTE not all the nodes in the Controls palette are controls by default some are indicators If you aren t sure place the control on the front panel and look at the block diagram to evaluate if a node is a control or an indicator based on the symbols given in the Data Types section However indicators can generally be changed to controls with the same design by simply right clicking the node after it has been created from either the front panel or block diagram and selecting Change to Indicator or vice versa e7eNumeric Indicators Controls Ties fi Figure 5 Numeric Controls Palette Numeric Controls Use numeric controls when a calculation needs to be performed or a decimal number is required Numeric controls are accessed from Controls gt gt Numeric gt gt Control Name The data type of a numeric control is numeric Boolean Controls A Boolean control is a switch it is either on or off 1 or 0
17. rray the array data type represents the number of dimensions of the array by the size of the wire 2D Array An array is color coded according to the data type that the array consists of e g the data on the left are double while the type could also be numeric or cluster as shown below 3D Array 4D Array Cluster A cluster is a data type that contains elements of other data types It is generally used to group related data elements together to eliminate clutter on the block diagram You can use the Build Cluster node to input data into a graph or chart since they have only one connector and require multiple data but you don t have to see Graphs and Charts You can think of a cluster as a bundle of wires LabVIEW User Manual Cluster of Arrays There is a special cluster that represents error data File input and output nodes have connectors for error in and error out The wire representing an error cluster 1s File Path Refnum Signal Conversions If you are trying to connect different data types that are closely related and LabVIEW won t let you try using a conversion node for example if you are trying to convert from a character string to a file path There are conversion nodes in the numeric Boolean array cluster and string sections of the Functions palette IV Controls and Indicators When the front panel is being displayed you can add controls and indicators using one of two
18. s that data type Both symbols are rectangles color coded and the data type is written on the inside LabVIEW also draws an arrow on either the right or the left side of these symbols to indicate if the symbol represents an input or an output connector e g represents an output connector of the type double and represents an input connector of the type double Dashed Line indicates an error either in mismatched datatypes or connector types Polymorphic means that this node can accept multiple data types A POLY indicator in brackets Indicates an array of any data type It is the generic data type for most of the array nodes Numeric there are many numeric data types unsigned integer signed integer double extended complex etc and you can change the type of a numeric control connector or indicator by right clicking the control etc gt gt Representation gt gt data type Non integer data types are color coded orange e g types are color coded blue while integer data Enum is a special data type that allows you to assign values to menu selections After placing an Enum control use the edit text tool to change the name of the first item in the list Then right click gt gt Add Item After and type a name for every additional item you want added to the list To wire two enum connectors together the items in each list must be equivalent a I2 Boolean Character String DEL 1D A
19. s using the same scheme as for a 1D array e the values on the x axis will increment by one for each element in the array You can also feed the graph cluster data using a Bundle node Figure 7 Cluster the initial x value you want your graph to start with the amount you want to increment x for each point and an array of y values This specific bundle of xo Ax y array is classified as WDT waveform data type The AI Acquire Waveform node and other nodes like it outputs this type of data so you can wire it directly to a chart g DEL AM ae ooo Waveform Graph J array Figure 7 WDT Bundle V Mathematics There are multiple ways of doing mathematic operations in LabVIEW depending on your design intent If you only need to do a few simple mathematical operations add multiply increment etc use the operator nodes you need to do some complex math or a lot of operations at a time use either the formula node or the Matlab node 1f you need the functionality of Matlab Operator Nodes Figure 8 An Example of a Mathematical Operation Using Operator Nodes Figure 8 shows the operation x 2 x2 1 using operator nodes two numeric controls x and x2 and a constant equal to 2 00 A numeric indicator displays the result on the front panel When the block diagram is being displayed you can place operator nodes using one of two methods Select them from the Functions Palette if it is open and click on the front panel a
20. t the location that you want it or right click anywhere on the front panel to display the Functions palette Arrays You can use a for loop to build an array see the section on for loops or you can initialize an array with Functions gt gt Array gt gt Initialize Array The Initialize Array node will initialize an array of the size you tell it by wiring constants to the right connectors with the value you set in every index Use the position size select tool to make a higher dimension array by dragging the bottom of the node down to reveal more connectors You can also build an array by feeding many elements or arrays to the Build Array node Functions gt gt Array gt gt Build Array If you are feeding the Build Array node arrays select whether you want the node to concatenate the arrays or not by right clicking on the node gt gt Concatenate Inputs If you do not choose to concatenate inputs Build Array will add a new dimension to the output array make sure all input arrays have the same dimensions For example if you connect two 2D arrays to a build array node the node will output a 3D array if you do not concatenate inputs but if you select concatenate inputs the node will output a larger 2D array E Ee array element rH ah element appended array dimension size 0 __ E initialized array element W a Drag down to Create Build Array Initialize Array Higher Dimension Array Figure 9 Build Array and Initialize Array
21. the loop uses the value written to the register when the loop last executed or the default value for the data type if the loop has never executed LabVIEW help reference To initialize the register wire an input from outside the loop to the left register NOTE if you are using nested loops or running a loop more than once during the time the VI is run the shift register will start the new loop with the value that it ended with the last time the loop was executed Figure 15 shows how to use a while loop with a Build Array node to build an array using feedback Array is a control of the type 1D array and Array 2 is an indicator of the type 2D array because the Build Array node is not set to concatenate inputs Shift Registers Figure 15 Using Feedback in a While Loop Conditional Control Case Structure The case structure has one or more subdiagrams or cases exactly one of which executes when the structure executes Whether it executes depends on the value of the Boolean string or numeric scalar you wire to the external side of the terminal or selector LabVIEW help reference The case structure allows conditional control in a VI lke an 1f then statement On the left side of the case structure is a question mark terminal Wire into this terminal any numeric Boolean or string data During runtime the VI will wait for data to be passed to the case structure and then compare the data it receives to the titles

LabVIEW Reference

Contents

Download Pdf Manuals

Related Search

Related Contents