Making the Case for Modular Test Systems - From NPI to EoL

Author : Bob Stasonis, Pickering Interfaces

05 June 2023

When building automated functional test systems - at whatever phase in the product lifecycle - engineers today recognise the benefits of a modular approach. Using a flexible and modular test platform, such as PCI eXtensions for Instrumentation (PXI), allows engineers to more effectively create scalable test systems.

Automated testing demands change over time. In the new product introduction (NPI) phase, engineers verify design requirements. In the mass production phase, end-of-line (EoL) test systems validate the product. Furthermore, as products evolve or become obsolete, test systems are modified, or equipment reused in forthcoming projects. 

By understanding the key issues at each specific phase, organisations can make better informed decisions. Taking a modular approach to system development means that they can accelerate development and mitigate risk across the entire product lifecycle. 

What are modular test systems? 
Modular test systems usually consist of computer-controlled chassis housing multiple instrumentation and switching modules, interconnected to form a completely automated solution. PXI has become the most adopted modular hardware platform for electronic test and measurement applications. 

Why is PXI ideal for modular test systems? 
Introduced back in 1997, PXI is an industry-standard chassis-based architecture that defines how instruments, computers and other devices can be interconnected using a common bus (either PCI or PCI Express). A rugged, high-performance platform, PXI is well suited to scenarios where tight timing and synchronisation between modules are required. It offers a comprehensive range of module types from test vendors and can be easily expanded with additional chassis and racks. 

Phase 1 - Designing test systems for NPI
In the initial stages of an NPI, engineers need to quickly, efficiently and iteratively test products to verify design requirements. This can be best accomplished by taking into consideration the following: 

• Conducting tests early in the design phase, when the focus isn’t always on how difficult the product may be to test. Bringing test engineers into discussions sooner means they can advise on how to incorporate testability into product designs. Considering potential product enhancements and new designs helps ensure the test system arrangement offers the necessary flexibility and scalability to handle these future requirements. Modular test equipment is inherently flexible, allowing engineers to quickly adapt the test system to design changes without having to completely alter it. 
• Cost and availability are important, particularly beyond the verification testing needed in product development. High-volume production testing can mean repeat purchasing of expensive or scarce equipment - thereby contributing to budgets being exceeded or deadline overruns. 

Designing test systems early in the NPI process, based on industry-standard modular architectures, can boost project success rates. Modular test systems are reconfigurable, meaning they can adapt to changing needs as products are being defined. 

Platforms like PXI don’t tie organisations to specific vendors - enabling the mixing and matching of constituent test elements based on which prove to be most optimal. Similarly, modular systems don’t limit organisations to specific programming interfaces, allowing engineers to use their preferred platform and tools. 

Phase 2 - Moving from NPI to high-volume testing 
When products move from the validation testing required for NPI to the EoL production testing of finished products, engineers are no longer identifying design issues. Instead, they’re checking for component or manufacturing faults. NPI test systems can be ramped up to production testing if they are designed with the following in mind: 

• Footprint, cost and equipment availability are vital for production test systems. In the NPI phase, engineers are working with a full test bench, upon which there is adequate space for equipment. On the production floor, however, space is certain to be limited. Equipment cost and availability also have implications for production testers - where organisations may need one tester for NPI, they’ll often need multiple sets for production. 
• For high-volume production, it’s essential to optimise the productivity of all test processes by minimising the setup and test execution time of each test station. The device-under-test (DUT) must be able to quickly and reliably connect/disconnect from each stage, so time isn’t wasted between units as they move through the test system. This requires reliable interfacing, such as mass interconnects, where connections are made simultaneously via reliable, high-usage connectors in a standard streamlined interface. 
• Test systems must be reliable and quick to repair should faults develop, in order to minimise any adverse impact on production. Also, because production testers are often handed off for operation by technicians in completely different locations, they must be well-documented and easy to operate. Testers may also need to integrate with factory management systems. 

Based on CompactPCI, PXI offers all the reliability benefits of the PCI architecture (including industry adoption and COTS technology), while also adding a rugged mechanical form factor. An industry consortium defines hardware, electrical, software, power and cooling specifications. The modular architecture employed means that if a module fails, it can be easily checked, then swapped or repaired, without affecting the operation of other modules in the system. And with PXI’s standard form factor, chassis are easy to integrate with mass interconnect systems. 

Modularity helps maximise throughput too. For example, PXI instrumentation and switching modules are integrated into chassis with built-in high-speed timing and synchronisation, while standard embedded or remote controllers can easily be upgraded as faster models become available. The PXI standard supports the latest PXI Express format, delivering higher bandwidth for faster data transfers. Platforms like PXI also enable parallel testing on multiple DUTs, since instrumentation can be readily duplicated, further speeding test operations. 

Modular systems also provide better value than fixed functionality instruments, since they offer greater flexibility, scalability and reliability, while still being relatively easy and inexpensive to develop and maintain. Industry-wide vendor support of PXI provides competition that results in best-in-class performance and pricing, plus long-term availability. 

Phase 3 - Evolving test systems as products change 
As products evolve, it’s inevitable that test systems will need to be modified or components will require replacement. The considerations outlined below help set production test systems up for long-term success throughout the entire product lifecycle: 

• Every duplicated test system should produce the same results, so quality and consistency of performance across multiple systems will be mandated. Interconnection can become a failure point, as DUTs are mechanically connected and disconnected. Other points of error may include faulty instrumentation, unreliable or mismatched signal paths impacting signal integrity, or operator mistakes. Regular maintenance checks, knowledge of expected component life and high-quality documentation will all help with mitigating these risks. 
• When test systems move from NPI into production, they must be easy to use, debug and adapt to design changes. Industry-standard test hardware and software will provide familiarity, scalability and flexibility - thus leading to a streamlining of tester deployments. 
• Reliable test equipment vendors and system integrators offer consistent, documented products and tools. Engineers depend heavily on these providers for ongoing support of products and obsolescence management, along with timely software updates to enhance systems. 

Modular systems offer improved scalability compared to fixed systems, since it’s easier to add or remove modules to increase or decrease capacity. This scalability is critical as test requirements change over time (for instance, as new products are added to manufacturing lines). Typically, PXI vendors offer families of instruments and switching modules, so engineers can seamlessly add more I/O connections. Reusable equipment allows test set-ups for new products to be quickly assembled with minimal design effort. 

The PXI Systems Alliance (PXISA) governs the PXI standard - continuing to upgrade its hardware and software specifications, and thereby reducing the risk of obsolescence and protecting original equipment investments. 

Supporting design and test engineers across the entire product lifecycle 
From initial design through to the production phase, test is critical across all aspects of the product lifecycle. Modular automated test systems, built on industry-standard platforms like PXI, deliver the flexibility and scalability needed by organisations to accelerate development and mitigate risks. 

Pickering Interfaces helps customers move test equipment from product design and validation through to full-scale production. Knowing that such shifts may require changes in test strategy and involve new stakeholders - it works across these groups to ensure organisations maximise their investments. To facilitate replication of test systems, the company can create custom bill-of-materials (BoM) for subassemblies and custom part numbers for complete systems. 

With a portfolio of thousands of off-the-shelf PXI modules, the ability to modify products to meet specific system needs, plus decades of relevant experience, Pickering provides a clear path to successful system implementation. It acts as a long-term test system support partner, assisting customers with tackling the obsolescence issues they face. Additionally, the company has board-level membership of the PXISA industry consortium, actively contributing to the governance and maintaining of the PXI standard. 

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