When designing mission-critical equipment for aerospace and defence applications, failure is not an option; therefore, extensive testing and simulation using highly reliable automated test equipment (ATE) are required.
Beyond ensuring that the ATE is designed for high performance and to execute tests reliably, it must also support long lifecycles and offer the flexibility and agility needed to meet evolving test requirements. When a component needs to be changed in ATE designed for aerospace and defence system testing, the revalidation process can be cumbersome, so integrators and end users must work with suppliers who plan for long-term production and support.
Here we explore two examples of how switching and simulation products from Pickering Interfaces support the needs of both integrators and companies who need high-performance, high-reliability ATE.
Differentiated solutions
An integrator bidding for the development of a test solution for a key player in the US aerospace and defence industry faces stiff competition from several solutions providers. In this case, often, price will not be the deciding factor. Instead, contractors are highly focused on developing flexible solutions designed to meet their test needs over many years.
For integrators, this requires a solution that is agile enough to meet evolving requirements as well as offering other unique value propositions for the end user.
Recently, Pickering worked with DMC, a long-term integrator partner, to differentiate their test solution and win a contract to build a PXI-based test system for sophisticated ground support equipment. DMC needed to be sure that its suppliers could help them meet the following key requirements under the following conditions: Since longevity and long-term support were critical, the system would use a combination of PXI modules and Ethernet-based communication to an LXI mainframe. Components had to be compatible with these open-standard platforms, and to be supported for 15 to 20+ years. All components had to be designed for reliability since a failure could lead to a signal misfiring or a short circuit, which could cause damage to the expensive test equipment and the system also needed components that supported easy and early detection of faults during run-time operations.
In short, DMC needed a switching solution that consisted of a variety of switches with high signal integrity, ensured test system safety, had the ability to detect faults quickly and provided long-term support.
DMC had worked with Pickering for nearly 15 years, and so was confident they could architect a switching solution that would meet the user’s unique requirements. In addition to its broad range of commercial off-the-shelf (COTS) switches Pickering can also make modifications to its standard products to produce switching solutions that offer the exact functionality required.
After reviewing the switching requirements of this system, it was clear that standard switches would not meet all the switching needs of this test solution. Since there are many risks of a switch not performing exactly as expected, DMC was not willing to take a chance on using a switch that could cause signal integrity issues between the DUT and measurement equipment.
With minimal non-recurring engineering (NRE) costs, Pickering collaborated with DMC to extend its PXI-based switching portfolio, developing switching modules (40-619 series) that met the exact specifications required, providing the ability to directly monitor contact state and detect relay faults in-situ. Pickering also helped DMC enhance the safety and reliability of the test solution with the following products:
l 60-103B-002 LXI Modular Switching Chassis – Pickering added a feature to its standard 60-103B chassis to develop a new modular switching chassis that has an added safety feature to asynchronously force relays open upon a system fault condition.
l 40-792 Series PXI 2MBit/s 75Ω Tributary Daisy-Chain Switch – Pickering modified an existing COTS switch to provide DMC’s preferred topology for switching 75 Ω impedance-matched communication signals.
Pickering also conformally coated all modules to reduce the risk of potentially hazardous situations caused by the environment in which the test system is residing.
As a result of Pickering’s ability to provide semi-custom components carrying the same guarantee of long-term support as its standard COTS products, it was able to help DMC create a differentiated solution compared to competitor offerings.
Beyond product flexibility, Pickering provided DMC with several other advantages. First, this switching solution enabled high channel density, which means this test solution offers a smaller footprint. Additionally, for switching and routing of communication signals, the solution provides superior impedance matching to avoid the possibility of reflections occurring and disrupting signal integrity, resulting in poor test results. Pickering also provides a unique ‘fail-safe mode’ for this solution so that, when an external signal is received by our chassis, it will force all relays to their open state, protecting the test system by disconnecting the DUT from the test equipment in the event of an external fault condition.
Avionics field test systems
For military aircraft in the field, engineers or technicians perform maintenance and make upgrades at regular intervals, as well as on an as-needed basis when there is an issue with an in-service plane. With frequent maintenance, it is not practical to send planes back to a manufacturer or to send service technicians out into the field every time maintenance is required. Instead, field test systems are used so that this maintenance, known as depot maintenance, can be performed in the field.
When trouble-shooting electrical issues with a plane, these test systems are designed to identify the lowest level line-replaceable unit (LRU) that can be swapped to address the issue instead of performing component-level diagnostics.
For one large military plane manufacturer, the depot test system it built was large and expensive; therefore, many end users did not want to purchase it and preferred to contract maintenance and support to another provider. To resolve this issue, the company needed to develop a more flexible, adaptable and smaller system. However, this type of diagnostic field testing must support a wide variety of LRUs with various signal types. For example, the module may be required to switch between a MIL-STD-1553 avionics bus and a 1kW power supply; therefore, a modular switching subsystem that offers the versatility to be custom-configured was necessary.
To meet these requirements, Pickering was approached due to its ability to provide PXI-based modular switching and simulation solutions that provided product support for many years.
During initial discussions, Pickering determined that the customer required purpose-built switch modules that could perform high-density switching, since portability is crucial for field test systems. Pickering was able to facilitate this requirement easily, since the company employs a modular switching approach that inherently supports many different test instruments in a small footprint.
In addition to providing the switching for this test system, the customer also decided it was best to use Pickering’s PXI-based linear variable differential transformers (LVDTs) to measure linear displacement, since the PXI-based simulators could be more easily integrated into the test system that their existing option. These LVDT modules can be used to test the avionics equipment to be sure it is reading the electrical signals from the sensors for potential errors. The LVDT sensor can also be hooked up to an LRU to generate signals to simulate displacement and measure linear displacement to ensure the control system reacts appropriately.
As a result of this new PXI-based test system using Pickering products at its core, this customer can now offer its customers a more competitive, comprehensive, and compact long-term support solution for depot testing.
Long-term product support
When parts in an ATE used for aerospace and defence applications become obsolete, it is a huge undertaking to revalidate the system design for new parts. These companies need a commitment from their suppliers that they will continue to support components even if something reaches its end of life (EOL). An immense amount of time and money is invested by customers in developing their products, test systems, and the corresponding test sequences; therefore, they need help to preserve their test investment by offering a commitment to support components 15-20 years from the date of delivery. Pickering is able to provide functional replacements for obsolete components and can often manufacture older versions of products as special orders for compatibility purposes.
Some companies learn the hard way that they should have put more thought into their switching/relays when test systems quickly fail or become unsupported. In the aerospace and defence industry, however, the lesson is too costly to learn.
Author details: Tom Sarfi, Business Development Manager, Pickering Interfaces
