Automated Test Instruments Enable Seamless Working

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For quicker measurement, control and data analysis in professional engineering labs

EDWIN HOH


The demand for test and measurement instruments to meet the lab infrastructure needs of professional engineering colleges is inevitably on the rise. To cater to various engineering fields offered, labs are equipped with a multitude of test and measurement instruments ranging from high-end oscilloscopes and spectrum analysers to common equipment such as digital multimeters and power supplies.

Traditionally, measurements are taken from a single instrument one at a time, recording the values. The measurement data is transferred to a PC to perform further data analysis. However, today, when measurements have become complex and integration of multiple instruments is required, this method is impractical as it is time-consuming and inefficient. Educators are therefore looking at integrating instruments into lab stations so that various tasks such as measurements, data analysis and data storage can be performed in a single PC.

Building an automated lab station
Building an automated instrument lab station requires consideration of three major components, namely, the software, hardware connectivity and instruments (see Fig. 1). The software on a PC is used to control the instrument that is connected to it using a connectivity hardware via an instrument control bus. Understanding each of these components helps in deciding which option is best suited for your application. Key considerations when building such a system are the ease of connectivity and scalability, performance and reliability.

Fig. 1: Major components of an automated instrument lab station
Fig. 1: Major components of an automated instrument lab station
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Software. The first component to consider in designing an automated lab station is the software. It consists of three sub-components: The application development environment (ADE), instrument driver and input/output (I/O) software.

The ADE can either be a textual (C++, C# and VB.NET) or graphical programming language (National Instruments’ LabVIEW and Agilent’s VEE). In deciding which ADE is the most suitable for your application, factors such as the learning curve, ease of integration with other software and hardware, robust data analysis and management, reporting capabilities and support and maintenance costs are important.

The instrument driver is essentially a set of software routines that allows quick communication with an instrument. Each routine corresponds to a programmed operation, such as configuring, writing to, reading from and triggering the instrument.

Two types of instrument drivers are prevalent today: Interchangeable virtual instrument (IVI) driver and plug-and-play drivers. The IVI standards specify an instrument driver architecture that provides compatibility with popular ADEs, common command syntax across instrument families and members and supports PC industry standards like COM (Component Object Model). The two architectures of IVI drivers are IVI-COM, which is based on Microsoft’s COM standard, and IVI-C, which is based upon VXIplug&play specifications. Both IVI-COM and IVI-C consist of a set of instrument classes and provide instrument interchangeability independent of the instrument vendor.

Available automation software

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Agilent VEE. Agilent VEE (Visual Engineering Environment) is a high-level object-based dataflow graphical programming software for automated test, measurement, data analysis and reporting. It is designed to work seamlessly with T&M instruments and comes packed with all the desired features for an educational lab station, such as ease of connection to various software and hardware devices from multiple vendors, data manipulation and display utilities, runtime deployment capability and built-in MATLAB, Microsoft Excel and database integration engines.

VEE is finding increased acceptance in the education sector in India due to the ease in instrument programming and provides the right platform for students to learn test automation prior to entering the industry. To know more about Agilent VEE, visit www.agilent.com/find/vee

National Instruments’ LabVIEW. LabVIEW is a graphical programming environment used by millions of engineers and scientists to develop sophisticated measurement, test and control systems using intuitive graphical icons and wires that resemble a flow-chart. It offers integration with thousands of hardware devices. Also, it provides hundreds of built-in libraries for advanced analysis and data visualisation—all for creating virtual instrumentation. To know more about NI LabVIEW, visit www.ni.com/labview

Plug-and-play drivers, such as VXIplug&play and LabVIEW’s proprietary Plug and Play drivers, specify common sub-routines to access an instrument via a programming language.

If an instrument driver is not available, or is not required, you can directly connect and control instruments using Direct I/O method as well. Direct I/O uses specific instrument commands (called SCPI (Standard Commands for Programmable Instrumentation)) to directly communicate with the instrument and, in many cases, it is proven to deliver better performance than instrument drivers.

To complete the software component requirement, an input/output (I/O) software is required. Virtual Instrument Software Architecture (VISA) was created by the IVI Foundation to standardise I/O software across physical interfaces and instrument vendors. VISA I/O software uses common terminology and syntax to connect and control instruments. A VISA library supports complete control of instruments across the physical interfaces of GPIB, USB, Ethernet, RS-232 and VXI. I/O software include such utilities as configuration of hardware, connection and control GUI, bus monitoring and troubleshooting.

Choosing the best combination of the three software sub-components to work seamlessly will help you accomplish two goals: Get your test system up and running in the fastest time and get the throughput you require.

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Hardware connectivity. Most instrument control systems are hybrids. These comprise instruments from multiple vendors and use multiple instrument control buses to connect the instruments to the PC. Because most instruments offer multiple bus options, the challenge is deciding which bus provides the best performance for your application.

Typically, connectivity options on the backplane of an instrument are GPIB (general-purpose instrumentation bus), USB (universal serial bus), LAN (local-area network) and RS-232. These options connect to various interfaces available on the PC, namely, USB, LAN, PCI (peripheral component interconnect) and PCIe (PCI Express).

For decades, the IEEE-488 bus, commonly known as GPIB, has been the standard interface for connecting test instruments to computers. It is the most common and reliable interface for programmable test-and-measurement instruments and is maximised for a variety of block sizes. Connecting GPIB instruments to a PC requires an interface converter such as a USB/GPIB adaptor or PCI (or PCIe)/GPIB interface card.

In applications where reliability is not a major concern, USB interface is the popular choice. USB devices are plug-and-play—you don’t have to shut down your PC to plug in or unplug an instrument—and the cables are significantly cheaper than the GPIB counterparts.

Ethernet (LAN) connections are gaining popularity today as educators look to remotely control instruments from different locations. Using interface converter hubs, such as the LAN/GPIB gateway or LAN/USB hubs, enables GPIB and USB instruments to be accessed remotely as well.

Fig. 2: Desired features of application development software
Fig. 2: Desired features of application development software

Instrument. Depending on your intended application, there are various factors to consider when choosing test and measurement instruments. With the goal of having an automated lab station, educators look for instruments that are programmable, scalable and supportable, provide a variety of bus interfaces (typically, GPIB, USB, LAN), and work with a variety of programming languages. The good news is that most test and measurement vendors today provide customised instrument bundles that suit a particular engineering field for educational institutions.

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Desired software features for educational lab station
Choosing the right application software for your ADE is important as you will be spending most of your time working on the instruments with it. As mentioned earlier, the software should ideally be easy to learn and use, and provide painless integration with other software and hardware devices, data analysis, management, and deployment and reporting capabilities.

The primary requirement when selecting an application software is ease of connection to instruments and other software. You should not be bogged down by the intricacies of low-level connectivity programming but instead focus on your measurement tasks. Having a built-in instrument auto-detection feature with seamless link to a standard I/O library (VISA interface) is a must. The software must also provide instrument programming utilities to control and take measurements using industry-standard instrument drivers like IVI-COM or Direct I/O (SCPI programming). In most educational institutes, research labs require the software to integrate with other complex tools such as MATLAB or with external components via ActiveX, C dynamic link libraries (dll) or Microsoft .NET framework.

Apart from ease of connection, the software itself must be easy to learn and use. Graphical programming software is usually preferred as graphical objects are easily understood and not bugged down by programming syntax of textual programming languages. Built-in data manipulation features such as loops, arrays and datatypes conversion and display utilities such as graphs and graphical user interface panels enable educators to build meaningful programs for use in teaching labs.

Having the data collected from instruments is usually not meaningful as there is no means to store it. Educators will require data reporting and storage utilities such as export functions to Microsoft Excel or to industry-standard databases such as Microsoft SQL Server and Oracle.

Lastly, the software should allow for deployment to other PCs in labs where each teaching lab station will have the same program running. In this context, the software will need to facilitate generation of program runtime versions that are robust and easily distributable to a large number of PCs.


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