BY：Tom afrid From:SCIENCE OF NEW JERSEY DAILY 2010.1 Computer Science Department
college of new jersey Institute of technology USA.
Email: Tom afrid@nze.edu
Abstract
Strain test is one of the most widely applied technologies in mechanical engineering. Nowadays, the conventional strain test technology gradually can’t keep up with the step of
modern test technology’s development. Virtual Instrument, whose core is computer, is becoming the main trend of test technology instead of conventional instruments. But the software
development of virtual Instrument is rather complicate, it limits the application and development of virtual instrument technology in strain test field.In order to solve the problem mentioned above, a strain test software system was developed in LabVIEW 8.0. First, functional module design method was adopted to construct the software system based on studying the test method using traditional instruments. In the process of realizing functional module,“event-loop-state
machine”model was designed. Second, the running procedure of software system was designed based on studying the conventional test process. Third, based on the strain test hardware system consisting of NI SCXI-1520 etc., the modules including parameter initialization, bridge balance, shunt calibration, filter, stress and load display, time domain analysis, frequency domain analysis, data storage, signal replay, experiment report generation and static calibration of system were developed to implement the test and control assignment. Finally, some experiments were done to validate the system’s reliability.The user was capable of carrying out the strain test and analysis task using the corresponding software test system constructed only through clicking the functional buttons on the system’s main board according to the test requirement. It makes user far away from the complicate software development.
LabVIEW (short for Laboratory Virtual Instrumentation Engineering Workbench) is a platform and development environment for a visual programming language from National Instruments. The graphical language is named \"G\". Originally released for the Apple Macintosh in 1986, LabVIEW is commonly used for data acquisition, instrument control, and industrial automation on a variety of platforms including Microsoft Windows, various versions of UNIX, Linux, and Mac OS X. The latest version of LabVIEW is version LabVIEW 2010, released in August 2010.
Dataflow programming
The programming language used in LabVIEW, also referred to as G, is a dataflow programming language. Execution is determined by the structure of a graphical block diagram (the LV-source code) on which the programmer connects different function-nodes by drawing wires.
These wires propagate variables and any node can execute as soon as all its input data become available. Since this might be the case for multiple nodes simultaneously, G is inherently capable of parallel execution. Multi-processing and multi-threading hardware is automatically exploited by the built-in scheduler, which multiplexes multiple OS threads over the nodes ready for execution Graphical programming
LabVIEW ties the creation of user interfaces (called front panels) into the development cycle. LabVIEW programs/subroutines are called virtual instruments (VIs). Each VI has three components: a block diagram, a front panel, and a connector panel. The last is used to represent the VI in the block diagrams of other, calling VIs. Controls and indicators on the front panel allow an operator to input data into or extract data from a running virtual instrument. However, the front panel can also serve as a programmatic interface. Thus a virtual instrument can either be run as a program, with the front panel serving as a user interface, or, when dropped as a node onto the block diagram, the front panel defines the inputs and outputs for the given node through the connector pane. This implies each VI can be easily tested before being embedded as a subroutine into a larger program.
The graphical approach also allows non-programmers to build programs by dragging and dropping virtual representations of lab equipment with which they are already familiar. The LabVIEW programming environment, with the included examples and the documentation, makes it simple to create small applications. This is a benefit on one side, but there is also a certain danger of underestimating the expertise needed for good quality \"G\" programming. For complex algorithms or large-scale code, it is important that the programmer possess an extensive knowledge of the special LabVIEW syntax and the topology of its memory management. The most advanced LabVIEW development systems offer the possibility of building stand-alone applications. Furthermore, it is possible to create distributed applications, which communicate by a client/server scheme, and are therefore easier to implement due to the inherently parallel nature of G-code.
Benefits
One benefit of LabVIEW over other development environments is the extensive support for accessing instrumentation hardware. Drivers and abstraction layers for many different types of instruments and buses are included or are available for inclusion. These present themselves as graphical nodes. The abstraction layers offer standard software interfaces to communicate with hardware devices. The provided driver interfaces save program development time. The sales pitch of National Instruments is, therefore, that even people with limited coding experience can write programs and deploy test solutions in a reduced time frame when compared to more conventional or competing systems. A new hardware driver topology (DAQmxBase), which consists mainly of G-coded components with only a few register calls through NI Measurement Hardware DDK (Driver Development Kit) functions, provides platform independent hardware access to numerous data acquisition and instrumentation devices. The DAQmxBase driver is available for LabVIEW on Windows, Mac OS X and Linux platforms.
In terms of performance, LabVIEW includes a compiler that produces native code for the CPU platform. The graphical code is translated into executable machine code by interpreting the
syntax and by compilation. The LabVIEW syntax is strictly enforced during the editing process and compiled into the executable machine code when requested to run or upon saving. In the latter case, the executable and the source code are merged into a single file. The executable runs with the help of the LabVIEW run-time engine, which contains some precompiled code to perform common tasks that are defined by the G language. The run-time engine reduces compile time and also provides a consistent interface to various operating systems, graphic systems, hardware components, etc. The run-time environment makes the code portable across platforms. Generally, LV code can be slower than equivalent compiled C code, although the differences often lie more with program optimization than inherent execution speed.
Many libraries with a large number of functions for data acquisition, signal generation, mathematics, statistics, signal conditioning, analysis, etc., along with numerous graphical interface elements are provided in several LabVIEW package options. The number of advanced mathematic blocks for functions such as integration, filters, and other specialized capabilities usually associated with data capture from hardware sensors is immense. In addition, LabVIEW includes a text-based programming component called MathScript with additional functionality for signal processing, analysis and mathematics. MathScript can be integrated with graphical programming using \"script nodes\" and uses a syntax that is generally compatible with MATLAB[citation needed].
The fully modular character of LabVIEW code allows code reuse without modifications: as long as the data types of input and output are consistent, two sub VIs are interchangeable.
The LabVIEW Professional Development System allows creating stand-alone executables and the resultant executable can be distributed an unlimited number of times. The run-time engine and its libraries can be provided freely along with the executable.
A benefit of the LabVIEW environment is the platform independent nature of the G code, which is (with the exception of a few platform-specific functions) portable between the different LabVIEW systems for different operating systems (Windows, Mac OS X and Linux). National Instruments is increasingly focusing on the capability of deploying LabVIEW code onto an increasing number of targets including devices like Phar Lap or VxWorks OS based LabVIEW Real-Time controllers, FPGAs, PocketPCs, PDAs, and Wireless sensor network nodes.
There is a low cost LabVIEW Student Edition aimed at educational institutions for learning purposes. There is also an active community of LabVIEW users who communicate through several e-mail groups and Internet forums.
Criticism
LabVIEW is a proprietary product of National Instruments. Unlike common programming languages such as C or FORTRAN, LabVIEW is not managed or specified by a third party standards committee such as ANSI.
As of version 8, all LabVIEW installations on Windows computers require customers to
contact National Instruments by Internet or phone to \"activate\" the product. Macintosh and Linux users are not subject to this requirement.
Building a stand-alone application with LabVIEW requires the Application Builder component which is included with the Professional Development System but requires a separate purchase if using the Base Package or Full Development System.Compiled executables produced by the Application Builder are not truly standalone in that they also require that the LabVIEW run-time engine be installed on any target computer on which users run the application.The use of standard controls requires a runtime library for any language and all major operating system suppliers supply the required libraries for common languages such as C. However, the runtime required for LabVIEW is not supplied with any operating system and is required to be specifically installed by the administrator or user. This requirement can cause problems if an application is distributed to a user who may be prepared to run the application but does not have the inclination or permission to install additional files on the host system prior to running the executable.
According to the National Instruments license agreement an executable built with LabVIEW should contain a note that the software is written in LabVIEW.
There is some debate as to whether LabVIEW is really a general purpose programming language (or in some cases whether it is really a programming language at all) as opposed to an application-specific development environment for measurement and automation.Critics point to a lack of features, common in most other programming languages, such as, until version 2009, native recursion and, until version 8.20, native object oriented features.
Also, for an environment heavily targeted for test, LabVIEW includes no built-in functions for formally testing limits, reading a limits file, and conveniently tracking the passing or failing results. Companies tend to build their own proprietary functions for this basic feature if they choose not to use TestStand.
Timing System
LabVIEW uses the January 1, 1904 Epoch (reference date) as its \"zero\" time. Other programs that use the January 1, 1904 epoch are Apple Inc.'s Mac OS through version 9, Palm OS, MP4, and Microsoft Excel
Labview is above，now let us disuss the strain.Due to external objects (stress, humidity, temperature changes, etc) and deformation, the object between the parts produced within the internal interaction to resist the external cause role, and tried to make the object from the deformation after position revert to deformation previous position. In the section some investigation on unit area of internal force called stress. With section of vertical called normal stress or method to stress, with section tangent called shear stress or shear stress. Stress increases with the external growth, with a particular kind of material, the build-up of stress is limited, exceed this a limit, material will be destroyed. For a certain materials for, stress can be reached this plateau called the materials of ultimate stress. Ultimate stress value through the material mechanics test to determine. Will determine the limit should be reduced, set the masterpiece of appropriate materials can safe work stress, this is the maximum allowable stress. Materials to the safe use, when use inside the stress should be less than its ultimate stress, otherwise materials will
occur when use destruction. Engineering components, most cases, internal force is not evenly distributed, usually \"destruction\" or \"failure\" tend to be aged from internal force set degree the most pound-foolish beginning, so, it is necessary to distinguish and define stress concept.
Some materials at work, its by external changes with time, when their internal stress is changeless, called static stress, There are some material, its by external over time in a cyclical change, at this moment internal stress also over time to a periodic variation, called alternating stress. Materials in alternating stress under the action of the destruction of fatigue damage occurred called. Usually materials under the alternating stress is far less than that of the static load the intensity limit, destruction may occur. Other materials will be due to section size change and cause stress local increases, this phenomenon is called stress concentration. For the organization uniform brittle material, stress concentration will greatly reduce the strength of this component in the component design should pay special attention to.
Objects mechanical deformation, the body each point deformation degree generally are not identical. A term used to describe a little place deformation degree of mechanical quantity is accepts the strain. This can be in place to find a problem-dependent compared before and after the body of the cell, deformation of the body of the cell size and shape changes. Namely strain is from load, temperature and humidity causes of object local relative deformation. Main cable strain and cut strain two kinds.
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