基于LabVIEW综合实验室的设计

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设计(论文)题目: 基于LabVIEW综合实验室的设计专业与班级:

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LabVIEW

1．overview

LabVIEW is a program development environment, by the national instruments (NI) research and development company, similar to the C and BASIC development environment, but with other computer language LabVIEW significant difference is: other computer language is based on the text, and the language code of graphical LabVIEW use scripting language G program, application is in the form of block diagram.

A complete, LabVIEW virtual instrument system of open application software development, and use it to form instrument testing system and data collecting system can simplify the design procedure. With Visual C++ LabVIEW, Visual Basic,LabWindows/CVI, etc, which adopts different programming language is based on the text language program Code (Code), and abVIEW L is using graphical programming language), Graphic (G instead of the traditional diagram of the Code. The Lab VIEW of equipment with the scientists and engineers icon in the habit of basic agreement, this makes the icon programming process and thinking process is very similar.

LabVIEW convenient calls Windows DLL and user-defined function in the DLL, LabVIEW also provides CIN (C) Node with any users can use by C + + language or, if the ANSI C, compiled program modules, makes a open LabVIEW development platform. LabVIEW also directly support dynamic data exchange (DDE), structured query language (SQL), TCP and UDP network protocol. In addition, the LabVIEW also provides special used for program development kit, users can easily set breakpoints, dynamic program execution to very intuitive image observation data transmission process, and convenient debug.

The operation mechanism is LabVIEW macroeconomic sense is no longer the von neumann traditionally computer system structure of the method. The traditional computer language (such as C) to the order of execution by parallel structure in LabVIEW mechanism; Essentially, it is a kind of control Flow structure with graphical Data Flow pattern (Data Flow Mode), this kind of means to ensure the process of any Node Function in hire those knowledgeable programmers only after all it can only be executed Data.

That is to say, in the data flow in the concept of program execution, and it is the data driven by operating system, calculate machine and so on.

Since LabVIEW program is data flow driven, data flow design program, a goal only when it's all input can only be effective, And the goal of output only when it is complete. So, in VIEW of the Lab is connected the data flow between nodes function control program execution sequence, and don't like text program execution sequence by rows of constraint. Thus, we can be connected through the rapid development of concise function node applications, even can have multiple data synchronization operation channel, the so-called Multithreading (Multithreading).

2．Data Storage and Reporting with NI LabVIEW

The continued increase in processing and storage capacity and the decrease of hardware and software costs has resulted in an explosion of collected data being acquired. But while technology is enabling faster and richer data retention, storing, managing, and sharing data remains the real challenge. Traditional software packages tend to take one of two limiting approaches: 1) they force you into a particular format that is not exchangeable with other applications or users or 2) saving data is left so open ended you waste time trying to determine the best way to organize and save your data to disk so you can share it.

NI LabVIEW, designed for the entire engineering process, includes built-in functionality to help you easily save data to disk and create professional reports. By providing easy yet robust interfaces for file I/O and reporting, you can make the most of your acquired data to make decisions faster.

(1)File I/O Designed Specifically for Engineering Data

Despite the fact that LabVIEW offers a wide variety of file I/O options, these traditional file types rarely meet all the criteria you need in a file format. For example, ASCII files are exchangeable, but are very large and slow to read and write. On the other hand, binary file read and write speeds can keep up with high-speed hardware, but are difficult to share with others.

Because of the drawbacks of traditional file I/O, National Instruments developed the Technical Data Management Streaming (TDMS) file format to meet the specific needs and high demands of engineers and scientists. TDMS files are based on the TDM data model for saving well-organized and documented test and measurement data. The TDM data model offers three levels of hierarchy, as shown in Figure 2 – file, group, and channel. The file level can contain an unlimited number of groups, and

each group can contain and unlimited number of channels. Because of this channel grouping, you can organize your data to make it easier to understand. For example, you may have one group for your raw data and another group for your analyzed data within one file, or you may have multiple groups that correspond to sensor types or locations.

Figure 1. The TDM data model meets the specific requirements of measurement

data.

Also, you can insert your own custom properties at each of the three levels. Each level accepts an unlimited number of custom-defined attributes to achieve well-documented and search-ready data files. The descriptive information located in the TDMS file, a key benefit of this model, provides an easy way to document the data much like you would document code. As your documentation requirements increase, you do not have to redesign your application, you simply extend the data model to meet your needs.

(2)Multiple Easy-to-Use Programming Interfaces

Because it was developed to meet the needs of all engineers, TDMS offers ease of use, high-speed streaming, and exchangeability. Like many operations in LabVIEW, you can use multiple interfaces to write TDMS files. You can quickly read and write TDMS files using a virtual instrument (VI) such as the Write To Measurement File Express VI or, for the best performance and customization, use the primitive TDMS VIs from the File I/O palette. Also, when using LabVIEW with NI-DAQmx, you can use the Configure Logging VI from the DAQ palette or log directly from the NI DAQ Assistant

(3)Files Exchangeable with Other Programs such as Microsoft Excel

Because you may be required to work in additional applications, TDMS is easily

exchangeable across other programs. You can open TDMS files in Microsoft Excel using the TDM Excel Add-In, which installs with NI software and is available free at https://www.360docs.net/doc/566351111.html,. You also can use a C DLL for reading and writing TDMS files in other programming languages. NI is committed to helping you write well-organized and documented data using the TDMS file format, regardless of which products you use.

(4)Custom and Legacy File Format Reading and Writing

Although ideally you can choose the file format for each application you work on, you may still be restricted to reading and writing in a custom format due to legacy files or hardware that uses custom formats. Understanding that many engineers face this challenge, NI developed the DataPlugin technology so that you can use these custom formats in LabVIEW. As seen in Figure 4, a DataPlugin acts as a file parser that tells LabVIEW and other NI software how to read your custom file formats and maps them to the TDM hierarchy model in memory.

Figure 2. Using a DataPlugin, you can map any file format onto the TDM data

model.

National Instruments provides more than 200 free, downloadable DataPlugins for the most common file formats. For custom formats, you can create your own DataPlugins in LabVIEW and NI DIAdem software using a documented API, or request that an NI expert create a DataPlugin for you. Using DataPlugins, you are no longer limited by custom formats and applications, and have options for how to use your data.

3．Organizing and Managing Y our Data with DataFinder Technology With many applications, the amount of data being collected can quickly become overwhelming. Typically, at that point, you might turn to a database to begin storing your data for faster search and trending. National Instruments makes it easy to interact with a database using the LabVIEW Database Connectivity Toolkit by abstracting the

low-level structured query language (SQL) queries. However, moving your existing data to a database, maintaining the database, and creating applications for accessing data can become extremely costly and time-consuming.

In response to this challenge, NI developed NI DataFinder technology, included in the LabVIEW DataFinder Toolkit and DIAdem, for managing test files without the headache and expense of setting up and maintaining a large database. With NI DataFinder, you can perform Internet-like searches across all your data files, regardless of format and location within your company intranet. Simply point NI DataFinder to the location of your data files, and within seconds you can search for your files just as you would search for information on the Internet.

NI DataFinder automatically builds and maintains an index of all files that meet the file type and location criteria in the NI DataFinder configuration. You can use properties automatically stored in the NI DataFinder index in query conditions. When a valid data file is created, deleted, or edited, NI DataFinder automatically notices and reindexes the hierarchy and properties of the file. When you save properties not yet in NI DataFinder in a newly created file, these properties are automatically added to the index. NI DataFinder dynamically manages its own data tables and updates them based on file events and the contents of each file. Therefore, unlike many expensive database solutions, you can change and add information as your needs change without redesigning your data management solution. Using the NI DataFinder, you can quickly find trends and correlations in the large amounts of data you have saved during your tests.

4.Multiple Programming Approaches in NI LabVIEW

NI LabVIEW is a graphical dataflow programming environment. When using dataflow in LabVIEW, you define an execution flow in code by creating diagrams that show how data moves between functions (known as virtual instruments, or VIs). However, with LabVIEW, you can combine multiple programming approaches besides graphical data flow (G) in a single application. Use this flexibility to select your tool of choice for creating algorithms and solving an infinite variety of engineering problems.

(1)Defining Programming Approaches

The phrase …programming approaches? encompasses different languages for programming, models of computation, levels of abstraction, methods for interacting with existing code, and ways for representing algorithms. Over the years, National

Instruments has added interfaces and methods for communication in LabVIEW to extend the number of approaches that are available.You can write and import multiple approaches into the same block diagram as the familiar G dataflow language. LabVIEW compiles all of these approaches for the appropriate hardware target, which can span desktop computers, real-time OSs, field-programmable gate arrays (FPGAs), mobile devices, and embedded processors such as ARM.1

(2)Programming in G

Data flow, the fundamental LabVIEW programming method, was the original, and only, programming approach when NI introduced LabVIEW 1.0 in 1986. Unlike sequential-style programming, the flow of data in a dataflow program dictates when, and in what order, operations are executed. In sequential languages such as C and C++, the order of the commands in the source code (as opposed to the availability of data) determines the order in which execution will occur.

G follows a dataflow model for running functions and primitives, or VIs. A block diagram function or node executes when all its inputs are available. When a node completes execution, it supplies data to its output terminals and passes the output data to the next node in the dataflow path.

Figure 3. A and B are added, and the result is multiplied by C and displayed.

The graphical code in Figure 2 shows how a mathematical equation can be represented in G. This diagram consists of two nodes (an add node and a multiply node), and has three numerical inputs (A, B, and C). First, A and B are added. The multiplication node does not execute until both inputs are provided, so it depends on the addition node to complete and provide the result of A + B, at which point it computes the result – (A+B)*C.

Although it is possible to explicitly define variables in G, one of the most obvious differences between G code and other languages is that the functional equivalent of a traditional variable is a wire. Instead of passing variables between functions, wires define the functions to which a value is passed. Other familiar programming concepts such as While Loops, For Loops, conditional code, callback

functions, and digital logic are all part of the G dataflow programming language

(3)Using Configuration-Based Programming

In 2003, National Instruments released NI LabVIEW 7 Express, which featured Express VIs – a new technology designed to further simplify common programming tasks and algorithm creation. Unlike traditional VIs, Express VIs abstracted tasks by offering a configuration-based approach to programming.

LabVIEW distinguishes Express VIs with large blue icons. When you place an Express VI on the block diagram, a dialog appears so you can configure how the function executes. After completing the configuration, the LabVIEW development environment writes the necessary code (represented by the Express VI) for you. You can view and modify this code, and you can change the Express VI configuration by simply double-clicking the Express VI icon.

Consider the task of reading real-world signals into software for analysis. LabVIEW is designed to make integration with hardware for I/O simple and easy thanks to native drivers and support for thousands of instruments. However, even a task that would otherwise take a handful of VIs to execute can be simplified to a single Express VI. The DAQ Assistance Express VI prompts you to select the channels you want to send and receive I/O to and from, and configure parameters such as sample rate, terminal configuration, scales, triggering, and synchronization. You also can preview the data within the interface before saving the configuration.

Express VIs do not offer the same low-level control as VIs, which is why you may prefer to write the code entirely using VIs. New users interested in learning low-level constructs can easily convert an Express VI to the underlying G code by right-clicking the Express VI and selecting Open Front Panel. Normal VIs can do everything an Express VI can do. The LabVIEW Professional Development System also includes a utility for creating custom Express VIs.

(4)Incorporating C-Based Syntax

We can incorporate sequentially executed text-based syntax into a VI block diagram using one of several techniques. The Formula Node offers an inline structure that supports a syntax similar to traditional C programming. Much like C, every line ends with a semicolon and variables must have a defined scope.

The Inline C Node is similar to the Formula Node with additional support and functionality for low-level programming and header files without the overhead of a

function call. You can use the Inline C Node for any C code, including assembly directives and #defines, that syntactically is between the curly braces in a C file.

The Inline C Node is available only for targets that use generated C code. The Inline C Node is not supported for desktop Windows targets.

(5)Interfacing with Built Assemblies

Instead of importing source code to a LabVIEW block diagram, you may want to call into built assemblies or reuse built LabVIEW applications in other environments. Applications written in LabVIEW can easily reuse existing code and algorithms developed in other languages or programming approaches. Additionally, you might need to build an assembly from LabVIEW code, which includes the programming approaches discussed above, to be called by a different environment.

LabVIEW offers multiple solutions for both scenarios. LabVIEW can call external code in DLLs or shared libraries and code exposed through ActiveX or .NET interfaces. In addition, you can reuse LabVIEW code in other programming languages by building a LabVIEW DLL or shared library, or by using ActiveX.

If you have existing C code and need to reuse it in LabVIEW, one technique is to build the code as a DLL and call it using the Call Library Function Node. In fact, based on your C application architecture, you can use simple LabVIEW parallel programming to run two or more existing C routines in parallel without the additional complexity of C-based multithreaded programming. To make importing external libraries simple, LabVIEW includes the Import Shared Library Wizard, which automatically creates or updates a LabVIEW wrapper VI project library for Windows .dll file, Mac OS .framework file, or Linux .so file functions.

Interfacing with the command-line is also possible with the System Exec.vi, which provides OS-specific interfaces for calling executables and other build libraries.

(6)aking Advantage of Flexible Programming

The combination of multiple programming approaches in a single development environment offers the advantage of reusing existing code and algorithms developed in other languages. It also makes it possible to combine simple, high-level abstractions with lower-level code that gives you more visibility and control of your application. These abstraction layers represent highly complex operations in simple, easy-to-read representations, but can be coupled with functions that give low-level control over application behavior and hardware interfaces. Thanks to tight integration

with I/O, you can combine these approaches with real-world signals to take advantage of the most recent hardware technology such as multicore CPUs, FPGAs, and embedded processors.

5．The Benefits of Programming Graphically in NI LabVIEW Graphical program design and programming simple, intuitive, and development of high efficiency. With the continuous development of the virtual instrument technology and graphical programming language test and control will become the most promising field development direction.

Graphical programming language, which is also known as "G" language. Use this kind of language programming, basically don't write code, instead of chart or diagram. It was possible use technical personnel, scientists, engineers, familiar terminology and concepts, therefore, ICONS, LabVIEW is a tool for end users. It can enhance your own science and engineering construction, provides realizing instrument programming and convenient way of data acquisition system. Use it to research, design, testing principle and realization instrument system, can greatly improve the work efficiency.

(1)abVIEW: Graphical, Dataflow Programming

LabVIEW is different from most other general-purpose programming languages in two major ways. First, G programming is performed by wiring together graphical icons on a diagram, which is then compiled directly to machine code so the computer processors can execute it. While represented graphically instead of with text, G contains the same programming concepts found in most traditional languages. For example, G includes all the standard constructs, such as data types, loops, event handling, variables, recursion, and object-oriented programming.

The second main differentiator is that G code developed with LabVIEW executes according to the rules of data flow instead of the more traditional procedural approach (in other words, a sequential series of commands to be carried out) found in most text-based programming languages like C and C++. Dataflow languages like G (as well as Agilent VEE, Microsoft Visual Programming Language, and Apple Quartz Composer) promote data as the main concept behind any program. Dataflow execution is data-driven, or data-dependent. The flow of data between nodes in the program, not sequential lines of text, determines the execution order.

This distinction may seem minor at first, but the impact is extraordinary because it renders the data paths between parts of the program to be the developer?s