The automotive industry is highly competitive, and the entire industry has been under pressure to improve quality while reducing costs. As a result, beneficial and demanding activities such as Electronic functional testing are often seen as “essential nuisances” and such investments must provide high returns.
We will introduce LAN Interface Based Instrumentation Extensions (LXI), a solution for next-generation test systems. First, LXI is a test system architecture based on proven and widely used standards, such as the Ethernet standard. These time-tested standards provide the “just right” cooling, power, shielding and physical size for efficient measurements without sacrificing performance, while offering a modular design and traditional form factor. The LXI concept has been used in benchtop instruments to further enhance the appeal of LXI, which has been selling far more than card slot instruments, while offering good performance at a very competitive price.
Because of these advantages, system designers tasked with testing automotive electronics can use LXI to maximize performance, minimize cost, and plan for the future. As stated in the April 2006 issue of LXI Connexion magazine, there are at least 10 good reasons to consider LXI.These reasons apply to both current and future test systems: Ease of Use Performance Cost Expansion Capacity Lifetime Flexibility Rack Space Distributed Systems IEEE-1588 Synchronized Instrumentation
A deeper understanding of these 10 reasons will help illustrate the value of LXI test systems to the automotive industry.
Ease of use
With new models changing every year, automotive electronics manufacturers have to bring new products to market in a very short period of time. Anything that hinders rapid development of test systems or reduces production run time will not be tolerated. Therefore, setting up the system quickly depends on connecting the instruments and putting the system into operation as quickly as possible. Not only does this save time, it also allows manufacturers to focus on the more important task of functional verification of modules and subassemblies.
Today, many systems are built using VXI-based or PXI-based hardware. Since these systems must be controlled using an embedded PC or a standalone PC connected via interface cards and cables, developers face four main problems, which LXI addresses:
Interface: LXI uses not the MXI or GPIB interface, but the long-standing standard interface in the computer field—Ethernet. Therefore, users do not need to install additional interface cards in the PC, do not need to install special cables, and do not need to install special software. That alone can get the system up and running in minutes instead of hours.
PC configuration: Since the PXI card slot is an extension of the PC backplane, the entire system must be rebooted every time a card is inserted or removed. LXI doesn’t need to do this: it uses a LAN connection and doesn’t have to restart the PC when connecting or disconnecting an instrument. Additionally, some modular LXI instruments, such as the Agilent 34980A Multifunction Switch/Measure Unit, support “hot swapping” or card insertion and removal while the power is on.
Drivers: When a PXI system reboots, the PC goes through a device discovery process to identify newly connected devices, which usually requires downloading and installing device drivers. Driver limitations can cause problems that can be time consuming, as described later. The LXI standard specifies the use of IVI-COM drivers, which makes it easier to work in various development environments. However, when higher functionality or performance is required, some LXI instruments can be programmed directly through Standard Programmable Instrument Commands (SCPI). (SCPI is an established standard that can be used in any computer language with a simple VISA function.)
User Interface: The lack of a front Panel makes it sometimes difficult to use PC-based software to diagnose problems in PXI and VXI devices. When a developer first learns the capabilities of a new device, a thorough reading of the product manual is often required. In benchtop LXI instruments, the front panel allows the user to easily operate the instrument and understand how it works. Of course, most modular LXI instruments do not have front panels, but their built-in web interface allows users to learn instrument functions by simply opening a web browser on a connected PC. Thanks to browser capabilities, users can also more easily see what’s happening on their device anywhere in the world, simplifying system support and helping to ensure higher system availability. As shown in Figure 1.
Figure 1: Many Agilent LXI instruments include front panels, making them easy to learn and debug without having to connect to a computer.
Automotive electronics testing involves everything from complex powertrain control modules that require thousands of tests to simple airbag modules that may require the transmission of large amounts of data. These tests are demanding and often challenge the transfer speeds of GPIB, which has a maximum data rate of about 1 MB/s. In local area networks, I/O transfer speed is no longer an issue, as 1Gbit/s connections are becoming more common and 10Gbit has begun to appear.
I/O performance should not be an issue for LXI devices in typical automotive applications that require both interactive programming and the transfer of large amounts of data. Clearly, the speed advantage of a local area network is apparent when transferring large chunks of data, such as waveforms captured by a digitizer. In the interactive programming, there is a delay problem in the local area network that people already know very well. The computer industry is looking for a solution to this problem, as it is also a problem for storage networks. Instrument vendors are also reducing the number of communication cycles required by pre-storing instructions in LXI devices.
Minimizing the overall cost of testing requires fast and reliable testing at the lowest possible price. Some trade publications claim that functional testing adds no value: because it is at a later stage in the manufacturing process, the manufacturer has already inspected parts entering this stage, performed X-ray inspections, and completed in-circuit testing. In fact, these steps do improve product quality, but do not eliminate the need for functional testing, as they fail to detect early device defects, design errors (such as determining tolerances), and unreachable nodes (usually due to failure to perform testability) problems caused by design).
This is further complicated by seemingly contradictory demands from automakers, who can be penalized for delayed shipments and high defect rates. To solve this problem, the instrument is required to provide optimal function and performance with limited capital (Figure 2). It also requires careful consideration of hardware acquisition costs and subsequent costs, such as spare parts, warranties, local or depot repairs, availability of rental equipment, and more. In many cases, instrument-by-instrument price comparisons show that LXI can cost up to 40% less hardware than PXI.
Figure 2: The 34980A LXI Multifunction Switch/Measure Unit is a low-cost 8-slot mainframe with an optional built-in DMM, making it an economical switch subsystem alternative.
The learning curve cost of card slot instruments compared to LXI should also be considered. Card slot instruments require different software drivers for each development environment, such as LabVIEW, Visual Basic, C++, etc. LXI instruments usually provide an option to allow the use of drivers or SCPI. For developers familiar with SCPI, the learning curve for instrumentation is generally very short. Of course, the IntelliSense help function and online documentation for the .NET environment help simplify programming with drivers.
Figure 3 is a typical automotive electronic functional test system built with LXI equipment: an expandable reed relay matrix, multiple armature relay load switches, multiple arbitrary waveform output channels, and multiple digital-to-analog conversion channels.
Figure 3: In automotive test systems, LXI enables greater scalability and flexibility to meet current and future needs.
In a card-slot-based system, these devices quickly fill each slot, requiring another chassis and computer interface to add even one more device. For simple systems requiring only a few boards, card slots add cost and take up space, although empty slots can be expanded in the future. LXI instruments provide just the functionality needed and can easily add functionality later without adding card slots or additional computer interfaces. The system requires at most one low-cost LAN switch to provide more ports for the newly added LXI devices.
Hewlett-Packard’s Test and Measurement Division (now Agilent Technologies) invented GPIB in the mid-1970s, and the interface is still the industry standard. Local area networks have been around since the 1970s, starting with the ARPANET. Figure 4 compares the various interfaces that have emerged over the past 30+ years. Most notably, the performance of LANs is constantly improving while maintaining backward compatibility. The widespread use of local area networks suggests that it will continue to be the dominant force in the computer industry in the long term.
Figure 4: LANs are constantly evolving and remain backward compatible, while other interfaces are constantly changing.
The extended functionality designed into the LXI standard ensures that it will meet the needs of the test and measurement industry over the long term. The automotive electronics industry must be able to provide active support for auto repair and maintain a long service life of the products, which inevitably places high demands on service life. LXI is designed to provide a stable, long-life test environment for this environment.
Slot-based solutions limit the optimal placement of the instrument in the test rack. For example, it is better to put switching instrumentation in one low-cost subsystem and excitation/measurement instrumentation in another, which simplifies service without the inefficient use of high-cost, high-performance backplanes to control low-speed Relays (this usually happens in PXI or VXI card slots).
LXI instruments implement a better approach. The Agilent 34980A features a built-in DMM and a choice of switch cards, providing a low-cost, dedicated way to create switch subsystems. LXI-based instrumentation subsystems can also be placed elsewhere.
Functionality can also be an issue: Few of the slot-based power supplies meet the current requirements of automotive electronics. This requires the use of external power supplies based on different structures. A better alternative is an up-to-date power supply that happens to meet the LXI standard. For example, Agilent has updated proven designs to meet the LXI standard while adding other improvements such as fast up/down programming, building and monitoring waveforms with power, and compact chassis such as the Agilent N6700 Modular Power Supply and N5700 series high-power power supplies (Figure 5).
Figure 5: Some LXI power supplies are better in size and functionality than GPIB and PXI power supplies.
In automotive applications, LXI-based functional test systems can be assembled in racks with a height of only 400 mm (Figure 6). This high space utilization is achieved in part due to its use of LXI-based devices such as the 1U Agilent N6700B modular power system and the 8-slot Agilent 34980A with integrated DMM.
Figure 6: In LXI, functional test systems can be housed in racks with a height of only 400 mm.
To achieve maximum density, system developers typically use card slot-based instruments. In VXI, a single C-card slot can hold up to 12 high-performance instruments in about 6U, but the cost of this solution is often high. PXI also achieves high density, but its compact 4U form factor has four major drawbacks:
Card size: Due to the size of PXI cards, it is sometimes necessary to use more than one slot to achieve the desired functionality.
LXI instruments, on the other hand, can be created in a variety of sizes, guaranteed to meet their intended use.
Shielding: PXI cards are subject to various interference issues. For example, an SCXI power supply that emits high magnetic interference may degrade the performance of an adjacent PXI DMM, possibly reducing the DMM’s resolution by a full bit. VXI avoids these problems because it requires shielded enclosures for all cards. Similarly, LXI devices are shielded themselves because they are completely self-contained devices.
Cooling and Power: The card slot must provide sufficient cooling and power capacity to handle the maximum number of instruments or relays simultaneously. In demanding systems, it may be necessary to upgrade to one or more more expensive chassis that provide the required cooling and power. Additionally, applications in automotive electronics often require instrument output voltages that exceed the voltage capabilities of many PXI hosts. In general, LXI instruments are designed to provide the required power, voltage, and cooling for the target application.
Automotive production test systems typically put all the instruments together. However, being able to place LXI instruments where measurements need to be made will bring many benefits to durability test systems, R&D test systems, and production inspection systems. For example, an LXI instrument can be placed next to the environmental chamber and connected via a wireless LAN link to a PC on the test engineer’s desktop.
Production test systems can also benefit from remote test heads. By using the best-selling LXI switch modules, test fixtures can be created that automatically adapt to any engine control module on the line, regardless of which pinout is used. It can be installed inside the case and connected to the inside of the automatic machine finished test case.
Only LXI can place excitation and measurement instruments where they are needed, minimizing or even eliminating the need for cabling back to the core of the system. The Agilent L4400A series (1U height, no front panel) modules are designed for such remote or distributed applications (Figure 7).
Figure 7: Agilent L4400A Series LXI switch modules can build powerful remote test systems
Another factor in favor of LXI is remote debugging and diagnostics. Service technicians with remote access can diagnose the test system from almost anywhere in the world with just a web browser. Adding a LAN-connected network camera to the system allows remote technicians to see what’s going on in the system while they’re diagnosing the system elsewhere.
In a high-volume production line, a reduction in test time of just one second per module can result in a benefit of several thousand dollars. In this case, any hardware or software changes that result in longer test execution times are overall unacceptable.
LXI addresses this need with extensive triggering capabilities. It originally provided a standardized trigger bus in Class A LXI instruments. As LXI continues to evolve, it offers a whole new way to improve test execution time: self-triggered measurements from instrument to instrument based on high-precision real-time clock synchronization. With this feature, the IEEE-1588 High Precision Time Protocol, complex and time-consuming measurements can be performed without the intervention of a host computer. This minimizes (or eliminates) trigger wiring in the test system, reducing I/O bottlenecks. This new capability is not currently available on all LXI devices, but is expected to be available in more and more LXI devices, so it deserves further study.
As cars become the rolling connectivity hubs of the internet, cell phones and GPS, they are taking on multiple forms of wireless communication. As a result, test requirements in the automotive industry are beginning to converge with those of the telecommunications and aerospace/defense industries, and in the future, more and more RF test instruments are likely to find their way into automotive electronics test systems.
Driven by the U.S. Navy’s NxTest (“The Next Test”) initiative, the aerospace/defense industry requires the use of discrete instrumentation components such as RF amplifiers, up- and down-converters, and digitizers that are in use during Can be easily arranged and rearranged to provide functions such as oscilloscope, network analyzer, spectrum analyzer, and more. Agilent is a leader in this field and already offers LXI-based synthetic instruments (Figure 8).
Figure 8: The Agilent N8201A 26.5 GHz high-performance downconverter is an LXI-based synthetic instrument module
From the above, we can clearly see that LXI is built for long-term requirements and is particularly suitable for automotive electronics testing. Its main advantages include cost, scalability and ease of use, while also providing advantages in performance, longevity, flexibility, synchronization and rack space. Leaders in the test and measurement industry support this standard, giving developers confidence that LXI is a viable architecture today and into the future.
The Links: SKM200GB128D NL6448BC33-31D