Virtual Instrumentation for Next Generation Test

The New Needs for Test
Never has the need for test been greater. As the pace of innovation has increased, so too has the pressure to get new, differentiated products to market quickly. Consumer expectations continue to increase; in electronics markets, for example, integration of many disparate functions is required in a small space and at a low cost. The economic downturn of the past three years has not curbed the need to innovate, but instead has only added the restraint of fewer resources. Meeting these demands is now a factor in business success; whomever can meet these demands fastest, most consistently, and most reliably, has a decided advantage over their competition


All of these conditions drive new needs for validation, verification, and manufacturing test. A test platform that can keep pace with this innovation is not optional; it is essential. The platform must include rapid test development tools adaptable enough to be used throughout the product development flow. The need to get products to volume quickly and manufacture them efficiently requires high-throughput test. To test the complex multifunction products that consumers demand requires precise, synchronized measurement capabilities. And as you incorporate innovations to differentiate your products, your test system must quickly adapt to test the new features.

Virtual instrumentation is an innovative solution to these challenges. Virtual instrumentation combines rapid development software and modular, flexible hardware to create user-defined test systems. Virtual instrumentation delivers:

• Intuitive software tools for rapid test development;
• Fast, precise modular I/O based on innovative commercial technologies; and
• A PC-based platform with integrated synchronization for high accuracy and throughput.

Rapid Test Development Software
As automation has increasingly become a requirement to quickly test complex products, software has become an essential element in all test systems – from design verification through highly automated manufacturing test. To quickly deliver test systems that can adapt to testing new functions requires an integrated set of test development tools. As shown in Figure 1, these tools include test management, test development, and I/O drivers.

Test Management software provides a framework for highly automated test systems, including sequencing, branching/looping, report generation, and database integration. The test management tool must also provide tight integration into the test development environments where the application-specific tests are created. National Instruments TestStand, the industry’s leading test management environment, includes connectivity to all common test development environments, and can pass data freely to and from these environments to create a fully integrated system. The architecture of TestStand is shown in Figure 2. Because many of the needs of the test management environment vary by application, it is a flexible framework – the operator interface, reporting format, and execution model, for example, can all be customized to individual application needs.


For many automated test applications, the high number of stimulus and measurement channels necessitates a switching matrix to connect I/O to the device under test (DUT). As device complexity grows, so does the channel count of these systems. In order to effectively manage a large number of switching routes, as well as change them quickly to adapt to new product designs, switch management software is imperative. NI Switch Executive, the industry’s only commercial switch management environment, provides an environment for configuring and documenting switching routes in an automated test system, for example. Switch Executive delivers tight connectivity to NI TestStand so that the switching routes can be tied to a particular test step, promoting a modular “connect, test, and disconnect” architecture in the test system.

The test development environment is the most important component for meeting the need of rapid test deployment. It is essential that this environment provides the tools to rapidly develop the “code” or procedure for the test. Over the years, an important software technology that has emerged which delivers faster development is graphical programming. Graphical programming uses “icons” or symbolic functions that pictorially represent the action to be performed. These symbols are connected together through “wires” that pass data and determine order-of-execution. Because the test procedure can be viewed instead of read, the overall development and comprehension of the test is rapid. NI LabVIEW provides the industry’s most used and most complete graphical development environment. LabVIEW's hierarchical dataflow language also promotes a high degree of reuse between test programs.

The I/O driver software, though often overlooked, is one of the most crucial elements of a rapid test development strategy. This software provides the connectivity between the test development software and the hardware for measurement and control. It includes instrument drivers, configuration tools, and rapid I/O assistants.

Instrument drivers provide a set of high-level, human-readable functions for interfacing with instruments. Each instrument driver is specifically tailored to a particular model of instrument to provide an interface to its unique capabilities. Of particular importance in an instrument driver is its integration with the test development environment so that the instrument commands are a seamless part of test development. As a test developer, you need instrument driver interfaces optimized for your development environment of choice. The Instrument Driver Network, on ni.com, for example, contains drivers for more than 4,000 different instruments, with interfaces to LabVIEW, C, C++, and Visual Basic.

Configuration tools, such as NI Measurement & Automation Explorer, include tools for configuring and testing I/O, as well as storing scaling, calibration, and channel aliasing information. These tools are important for achieving fast time to first measurement and for troubleshooting and maintenance of the test system.

I/O assistants are interactive tools for very rapidly creating a measurement or stimulus applications. Examples are the Instrument I/O Assistant and DAQ Assistant in LabVIEW 7 Express. DAQ Assistant, as shown in Figure 3, presents a panel to the user for configuring common data acquisition parameters without programming. The combination of easy-to-use assistants and powerful programming environments is necessary to provide both rapid development and the capabilities to meet a breadth of application requirements.


Modular I/O
The second essential technology for test is modular I/O, including technologies such as modular instruments and data acquisition. This measurement hardware resides on a printed circuit board that can be plugged into a PC or PXI backplane. Modular I/O uses commercial chip technologies to create virtual instruments with high performance at a low cost. The explosion of widely used commercial technologies such as ADCs, DACs, FGPAs, and DSPs, has resulted in rapid growth of functionality and performance in modular I/O. Figure 4 shows the current performance capabilities of modular digitizers, for example, mapped out by frequency (the speed of signal they can digitize) and bits (the accuracy to which they can digitize). In many cases the accuracy of virtual instrumentation exceeds that of traditional instruments.

Modular I/O, because of its use of bus and processor technologies, is capable of high-speed measurement and high throughput to PC memory. The PCI bus, for example, is capable of throughput of 132 MB/s – more than 100 times faster than the GPIB bus used to connect to most traditional instruments. In virtual instrument systems, GHz PC processors are used to analyze the data and make measurements using software. The result is measurements at 10 to 100 times the throughput of a test system built solely on traditional instrumentation, which include built-in vendor defined firmware and application-specific processors. In many systems, where test is a bottleneck, multiple redundant instruments are used to keep up with throughput requirements. Tightening budgets are straining this “brute force” approach to throughput. A system based on PXI modular I/O, though, can continuously stream digitizer data to the PC at more than 100 MB/s, or take up to 3000 5 1/2 digit DMM measurements per second. Today’s requirement for high-volume testing make these throughput gains and cost savings essential to remain competitive.

PC-Based Test Platform
Today, all modern test systems include a PC. Increasingly, though, the PC is becoming not just a part of the test system, but the essential integrating platform – the center of the test system. GHz processors, high speed buses, widely available software, constantly increasing performance, and extremely low price, make the PC, in fact, an ideal test platform. As an example, consider the performance advances the PC has undergone in the past 20 years, shown in Figure 5. The only other element of test systems that have undergone a performance increase of this magnitude is perhaps the DUT itself.



Virtual Instrumentation has embraced the PC and PC technologies to deliver similar advances in performance to test applications. In a virtual instrumentation system, when you upgrade your PC, the entire test system benefits from the faster processor, memory, and peripherals.

PXI (CompactPCI eXtensions for Instrumentation) is a standard for modular I/O built on PC technologies. PXI adds integrated timing and synchronization, industrial ruggedness, and increased channel count to a PC-based architecture. PXI is a multivendor standard supported by more than 65 vendor companies.

The timing and synchronization architecture offered by PXI is another essential technology for test. Using these features, the timing characteristics of multiple modular I/O devices can be tightly synchronized to achieve greatly improved accuracy and throughput. A PXI backplane includes shared triggers, a shared low-skew clock and a set of low-skew star-trigger lines, as shown in Figure 6.


One example of how timing and synchronization can increase the throughput of a test system is the use of DMMs and switches to scan a set of DC measurements. One of the key features of scanning switches and DMMs is the ability to handshake during the execution of testing multiple points. With handshake scanning, the DMM receives a digital pulse from the switch (“Scanner Advanced”), takes a measurement, and then generates a digital pulse (“Measurement Complete”). When the switch receives the "Measurement Complete" pulse, it advances to the next entry in its onboard scan list. Once the relays of the switch module have settled, the switch sends a “Scanner Advanced” pulse and triggers the DMM for a new measurement, starting the process again as described above. The process repeats itself until the scanning list is exhausted. The handshaking signals can be directly sent over the PXI trigger bus. In this manner, PXI-based switch/DMM systems can optimize test time by more than 50 percent versus a software-timed approach.

Virtual Instrumentation in Action
Thousands of companies have successfully deployed virtual instrumentation into their design labs and manufacturing floors to realize the increased performance, flexibility, and productivity discussed above. Each of the following examples illustrates how these technologies are essential for companies that have recognized how they can make test a strategic advantage.

Lexmark Improves Accuracy of Ink Cartridge Tests
Lexmark is a global leader in the development and manufacturing of printing solutions, including inkjet and laser printers and related consumable supplies. To meet their requirements for high throughput and low test, Lexmark turned to a PC-based solution using LabVIEW and NI modular instrumentation.

Lexmark has been able to scale their test solution as their needs have changed. In 1997, the system used an 8-bit, 20 MS/s digitizer (the NI PCI-5102) and LabVIEW 4.1. As the technology of inkjet print heads has changed, however, Lexmark’s requirements for speed and resolution have increased. Today’s manufacturing system uses LabVIEW 7 Express and a PXI-based system, including the latest 14-bit, 100 MS/s digitizer (NI PXI-5122) and 100 MHz digital waveform generator/analyzer (NI PXI-6552). While increasing the test system’s performance, Lexmark actually was able to decrease the equipment cost using the latest measurement technology. Most importantly, by using a software-based virtual instrumentation architecture, they were able to upgrade the system as requirements changed with minimal software rework.

	1997	2001	2003
Digital Waveform Generation	Third-party ISA Board (25 MHz)	NI PCI-6534 (20 MHz)	NI PXI-6552 (100 MHz)
Digitizer for Resistance Measurements	NI PCI-5102 (10 MS/s, 8-bit) NI-SCOPE	NI PCI-5911 (12.5 MS/s, 12-bit) NI-SCOPE	NI PXI-5122 (100 MS/s, 14-bit) NI-SCOPE
Software	LabVIEW 4.1	LabVIEW 6i	LabVIEW 7 Express

U.S. Air Force Increases Mission-Capable Rates with Virtual Instrumentation
In 2002, ManTech Test Systems was awarded a multimillion dollar contract for development, production, and support of test equipment for LANTIRN systems. LANTIRN (Low-Altitude Navigations and Targeting Infrared for Night) is a system used on U.S. Air Force premier fighter aircraft, including the F-15E Eagle and F-16C/D Fighting Falcon. LANTIRN significantly increases the combat effectiveness of these aircraft, so they can fly at low altitudes, at night, and under the weather to attack ground targets with a variety of precision-guided and unguided weapons.

The original LANTIRN test system dates back to the late 1980s, and was based on MicroVAX computers tied to stand-alone instrumentation. Not only was the system large, requiring seven complete racks of space, but the Air Force faced a host of reliability and maintenance problems from the growing obsolescence of test system components.

Using PXI and NI modular instrumentation, ManTech used commercial off-the-shelf technology to reduce the size of the test system by more than 50 percent, while meeting stringent military requirements for operating and nonoperating conditions.

Lowering Manufacturing Test Cost for 3G Mobile Handsets
Xin Wei Co. LTD is a Chinese telecommunications company that has pioneered and co-developed the SCDMA standard. The SCDMA protocol is one of the foundations of TD-SCDMA, the 3G protocol developed in China. Xin Wei’s SCDMA operates on 1.8 GHz bandwidth and offers a low-cost wireless access and message services to small cities.

Working with Xin Wei Co. Ltd, VI Services (an NI Alliance Partner) successfully developed a SCDMA mobile phone online test station using the PXI-5660 RF signal analyzer, LabVIEW, and VI Services’ Wireless Test Toolset. For each mobile phone product line, Xin Wei Co. Ltd has replaced test systems based on stand-alone communications test sets with one new virtual instrumentation-based test station. Simultaneously, the test throughput has nearly doubled on each production line, resulting in almost 4x performance improvement using a virtual instrumentation approach.

Because the system uses software to perform the signal analysis, it can be upgraded as new cellular standards emerge, without requiring the purchase of additional test equipment.

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