LXI and Other Test Platforms
By David Owen and Bob Stasonis, Pickering Interfaces, January 2011
In the test and measurement ecosystem, there are many species—better known as platforms. We’re talking about GPIB, VXI, PCI, PXI, and LXI. All of them have their application niches, and more importantly, they all need to coexist and work together. Each platform has its place in the test ecosystem, especially in implementing a hybrid test system design.
And just like other ecosystems, platforms evolve and often replace other platforms. It may result from a rehosting of a system, replacing instruments that are no longer available, or designing the next-generation test system.
It is important to understand that changing platforms usually is not the direction of choice. Change requires time—evaluation of the choices, potential new vendors, programming issues, and interconnections. The list goes on.
So why change? There can be many reasons.
- Simple obsolescence: The instruments, switching systems, or software drivers for newer programming environments may not be available.
- Upgrading a test system to accommodate new test programs: Perhaps the original instruments don’t have the bandwidth, or the switching system is not expandable to address new requirements.
- Size and ease of use: Adapting older platforms to address new needs or taking a platform that does not lend itself well to a new application could create a system that is physically too large and potentially unwieldy. Cabling also must be considered. Will the platform create interconnection issues that can affect reliability and add cost?
- Price: Management may require change to address a smaller budget as profit margins are squeezed.
- Evolution of manufacturing technology: As manufacturing and the products evolve, the test requirements and objectives change.
In many cases, these considerations suggest that a system with multiple platforms, or rather a hybrid system, is needed. In upgrading an existing system, it might be impractical to replace the entire system with a new design. For example, using a new instrument instead of the obsolete portion of the test system would be the pragmatic thing to do.
New designs might need several different platforms to work together. The reasons include selecting the best instrument for the job or a switching platform that is more flexible for the application or utilizing surplus test equipment in stock to save on new capital investment.
Fortunately, standardized test platforms are designed to work with other platforms. Software programming environments also feature tools to support multiple platforms. Good drivers from the instrument vendors also would help.
To illustrate, we have selected several applications focusing on companies that incorporated LXI into their test strategies; more specifically, the LXI choices are all switching systems. In each application there is a change of or a migration from one platform to another, either partially or entirely. In many cases, the end result is a hybrid system with platform combinations using GPIB, VXI, PXI, and LXI instruments and systems.
You need not limit your test strategy to a single platform for either new systems or upgrades. Each test platform has its strengths and weaknesses. You need to balance budget, specs, and size against your test plan.
Switching and Safety
Customer: A world leader in the development and supply of intrinsic safety explosion protection devices.
Application: The customer wanted to develop a fully automated version of its existing functional test rig for a new range of intrinsic safety isolators. One aspect of this was replacing the existing VXI-based low-thermal EMF switch matrix due to its slow switching speed and obsolescence considerations.
Problem: Constructing a 55x33 matrix is cumbersome with small form-factor modules such as those used in PXI. Connecting multiple modules together to expand the X-axis and Y-axis dimensions requires many modules and awkward cable assemblies that result in the solution being both large and expensive. The large size and complex interconnect could possibly generate thermal EMFs, a parameter the user was concerned about since the matrix was to work with low-voltage signals as well as larger voltage signals.
Solution: With no COTS solutions available on the market, Pickering designed a product to suit the specific switching requirements. Due to >1,800 crosspoints and the stringent thermal considerations, the new matrix was housed in a 2U-high 19" rack-mount LXI-compliant chassis.
LXI was chosen over a modular form factor because it does not add physical constraints; we could design the matrix using an optimal layout. The rest of the test system consisted of several GPIB-based instruments that were used on the original tester and an LXI DMM.
Test Systems for Voice Routing
Customer: This application focuses on the financial sector within the U.K. rather than the traditional test and measurement markets for LXI. The customer is a global provider of voice logging and communications recording solutions to the public safety, financial services, and call center markets.
Application: A major international bank tender required that a digital voice-recording system to record dealer room activity include backup capabilities. If a recorder were to fail, the trunk-line circuits to that recorder needed to be switched automatically to a standby recorder. To minimize cost, power, and footprint of the proposed system, the customer wanted each standby recorder to support multiple primary recorders. Accordingly, a multiplexer switch was needed to automatically route the phone channels of the faulty primary recorder through to the standby under appropriate alarm conditions. To facilitate integration and control of the switch in the recorder server, the customer’s preferred method of communications was Ethernet.
Solution: Following joint technical discussions and field trials, it was determined that Pickering’s high-density PXI multiplexer modules with screened reed relays were suited to the switching task. The ability to use these in the modular LXI chassis together with shielded module-mounted connector blocks provided the customer with an easy-to-integrate, scalable solution. It now has become the standard switching option for standby recording at a much lower cost than traditional systems. It also improved the time to market because the company could use an existing design.
Customer: A leading systems integrator and manufacturer of military aircraft and defense electronics.
Application: The customer needed to replace an existing dual VXI 90-channel RF multiplexer switching system used for testing PCB backplanes. The switching system was used to multiplex a vector network analyzer (VNA) to characterize different paths on a PCB backplane. Not only was the VXI platform large, it also was expensive.
Solution: A modular LXI solution was proposed which gave the customer the flexibility to change the size of the multiplexers by adding or removing a module from the chassis. An evaluation unit comprising a seven-slot LXI chassis with a 16x1 multiplexer was provided to the customer to back up technical discussions.
For the application, the customer is using an LXI-based VNA and one 18-slot LXI chassis with 16 16x1 multiplexer modules and one dual 8x1 multiplexer allowing two 128x1 multiplexers to connect to each port of the VNA. The use of LXI provided a system that was much smaller than the existing VXI system and at a lower cost.
Large Matrix for Aircraft Testing
Customer: A leading systems integrator for aerospace applications who provides functional testers for civilian and military aircraft.
Application: The customer needed to replace an old specific VXI system with a generic tester that could test a range of cards for several different aircraft electronic control units (ECUs). This system required more than 9,000 points of switching to test all the different cases.
Covering a large variety of applications with a single tester is more economical than creating several smaller testers. Two of the main objectives were to reduce the size of the full cabinet and the quantity of cabling to get the best flexibility and repeatability at a competitive price.
Solution: Despite the fact that the customer was attracted by the modularity of PXI, building a tester with 9,000 points of switching would be less effective, the labor cost would be higher, and it would take much more space than an LXI solution. A PXI solution for the matrix switching section would require more than 18 PXI cards with 512 relays and many cabling connections between the modules to implement the full matrix.
For this application, the customer has used a PXI chassis for all the instrumentation resources including a DMM, serial bus, scope, DIO, and avionic cards and six LXI 64x24 modules configured as a 384x24 matrix using integral loop-thru connections designed into the matrix. Again, the mechanical freedom of LXI allowed the designers to add loop-thru connections which greatly simplified the cabling compared to a PXI solution.
The resulting system has much less cabling with better performance than the original VXI system. It also is an example of a user selecting two different but complimentary platforms, PXI and LXI, to implement different parts of the system to obtain the most effective test solution.
Matrix for Healthcare Production
Customers: A provider of medical equipment, specifically X-ray systems, and its systems integrator.
Application: The medical equipment company needed to check electrical cabinets at the end of a production line. These cabinets drove the X-ray machines produced on the line. The systems integrator was required to implement a test to check electrical continuity and the absence of short circuits between the pins of different connectors. There were more than 1,000 resistance measurements to perform in an automatic self test.
Solution: The main difficulties were the number of resistance measurements and the precision of these measurements. Subsequently, the systems integrator used an Agilent LXI DMM with a Pickering LXI matrix. The full matrix was composed of nine 128x2 matrices to create a 1,152x2 matrix in an LXI switching chassis. A built-in automatic self-test measures all the switch paths for assurance of an accurate test.
The systems integrator used two cabinets. The first contained the data-processing devices such as a PC and printers. The second housed the measuring devices in an enclosed cabinet containing the LXI DMM and LXI chassis. This solution was developed in three months and duplicated in a second system.
Flexible Matrix for Avionics Use
Customer: An avionics systems integrator.
Application: A new generation of flexible and easily reconfigurable test systems for the avionics industry had been requested from the integrator’s end customer. The main goal was to simplify test installations and cover all functional tests for a very high variation of UUTs at a voltage up to 750 V and with a much faster test time than previous systems.
Problem: The size of the test system’s switching system is driven by the amount of UUT pins, instrument leads, and concurrent interconnected signals. Previous switching systems were either too large and therefore very expensive or too small to meet all requirements in one setup. Use of small switching systems resulted in long test times because of the lack of concurrent signal switching.
Solution: With no COTS solutions available on the market, our company agreed to design a new product to suit the specific switching requirements. Each test system’s switching network was configured from multiple 75x4 two-pole high-voltage matrices in an LXI chassis. Each of the 75x4 matrices has its own isolation relays on the X axis and the Y axis to allow the overall matrix to be configured to the size required by the different test targets.
Large Matrix Avionics Test
Customer: A large manufacturer of private aircraft.
Application: The company was streamlining its test process of various aircraft electronics subassemblies. The plan was to replace many separate test systems with one common-core tester.
A large matrix would be able to configure multiple instruments and test hardware, allowing for a single test system. This would save bench space, reduce the number of wire bundles since the unit would have a universal connector, simplify test procedures, and reduce maintenance in the long run. The matrix needed to be a 100x100 configuration and to carry voltages up to 250 VAC at a maximum of 2 A. Bandwidth was not critical since the highest frequency would be about 100 kHz for the ARINC serial buses.
Solution: Initially, the customer looked at PXI. That was dismissed for several reasons. First, the form factor limited the number of relays per module. As a result, the systems would require four PXI chassis, creating a test system that was 18U high. Second, the custom cabling to interconnect the modules and create the large matrix would be very complex and expensive.
In the end, the customer purchased four Pickering 50x50 matrices with loop-thru connections to allow for expansion. The total system was only 4U high. Four low-cost loop-thru cables connected the X axis and Y axis together to achieve the 100x100 configuration. The end result was about 40% lower in cost than the PXI solution and less than one-quarter the size.
Cable Testing in Airframe
Customer: An aviation application for a systems integrator in France supporting a major airline.
Application: After thousands of flying hours, every private or commercial airplane must be dismantled and fully checked to ensure it continues to be airworthy. A commercial airplane company required a switching system that would provide the capability to test for continuity and insulation integrity of cables in the entire aircraft.
Insulation tests needed to be performed at voltages up to 1 kV. The switching system used for the test had to support cold switching at 1 kV and be suitable for use with low voltages consistent with continuity testing. The switching system needed to be an 800x2 two-pole matrix.
Problem: The first approach was based on a GPIB backplane chassis with several switch cards using high-voltage reed relays. This solution was much too expensive and occupied more than 18U of rack space. There also was a solution based on the use of PXI modules. The PXI solution required four chassis with 52 PXI cards, about the same rack space needed for a GPIB solution. The end cost of the PXI solution also was prohibitive.
Solution: Pickering Interfaces proposed an LXI solution to reduce both the cost and space. The application required a great number of crosspoint switches, and LXI solutions are much more effective at implementing these large matrix systems because of the lack of mechanical restrictions when compared to modular solutions.
With no LXI solution on the market, our company developed a standard product for this type of application. A 2U box with three density options of 100x2, 200x2, and 300x2, each with two poles, was produced. The entire system was contained in 6U of rack space. It could be implemented using three 2U LXI devices to construct an 800x2 two-pole matrix with simple and cost-effective interdevice cabling to link the products. This solution was 30% less expensive than the alternatives and occupied just one-third of the space of alternative approaches.
As you plan your next test system or assess the requirements for an existing systems upgrade, look at LXI where it makes sense. Don’t discount other platforms either, and don’t be nervous about mixing them. Your hardware and software vendors should support all of the platforms relevant to their business.
About the Authors
David Owen is the business development manager for Pickering Interfaces. Over the last 25 years, he has held key engineering, product management, and strategic marketing positions with Marconi Instruments, then IFR (now part of Aeroflex). Mr. Owen was the named innovator of more than 10 patents in the field of RF signal generation and analysis and has written many application and technical support notes for signal generation and signal switching and management. e-mail: firstname.lastname@example.org
Bob Stasonis is the Americas/Asia sales and marketing director for Pickering Interfaces. In the last 30 years, he has held technical, sales, and marketing positions with Pickering Interfaces, Teradyne, GenRad, and Schlumberger. Mr. Stasonis is on the board of directors and past president of the PXI Systems Alliance, board member for the LXI Consortium, and the vice president of marketing for the American Society of Test Engineers. e-mail: email@example.com
Tags: ATE LXI/PXI/VXI