Part 2 | The Enjoyment of Deployment - Automated Test Best Practices
As mentioned in Part 1 of this blog series, printed circuit boards (PCBs) are getting more complex every year. The testing goals of most industries seem to be faster, more intelligence, smaller footprint, and of course, less cost. That last one is one of the more vexing problems of the test engineering department. If the product costs less, there is less money for testing, and by inference, less test time as production volumes soar. This is the “fun” part. Let’s explore what this means.
Now if you happen to work in an industry where the product you are testing has safety liability and in many cases wartime issues, automated testing is far more important than perhaps what the accountants and production managers thought was adequate. Let me elaborate.
Say you are a test engineering manager in the automotive industry. If you are testing active safety features like anti-lock brakes (ABS) or a collision avoidance system (CAS), and because of inadequate testing, a vehicle crashes and takes lives and property, then the lawyers get involved as lawsuits against the manufacturer cost time and millions of dollars. Can you see why your test strategy must be comprehensive enough and fast enough to provide the most accurate test at the lowest cost?
Now let’s up the ante a bit. You work in the defense industry… for a manufacturer who won the contract at the lowest cost. If your test strategy is not accurate enough, that missile or smart bomb may not achieve its mission. So, who wins the war?
Now I am not faulting accounting or production here. They all have jobs to do. My point is that in a safety or defense application, the value of communication to define and justify the most reliable test required – the second C word of this series – is key.
Your team must understand:
- How much test is needed
- How testing cost affects the sale price
- Which resources are embedded in the PCB
- How much time you have to test each component
- The time to market for your product
- The timeline to get your test systems ready
- The expected volume of products to be tested over the product life cycle is
Let’s look at each of these testing best practices.
- How much test is enough? A company I used to work for used the acronym JET – Just Enough Test. Engineering should be able to point out the most critical features that must be verified at the final test. Again, communication is crucial at the test system design phase. How to test the functions and what instrumentation is needed?
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- Again, the decisions here are a balancing act – What is the cost of testing? How much does it affect the sale price per product? What are the liability issues of failure (e.g., Active Safety, military weapons) and in some cases, the company's reputation in the market?
- What self-test resources are embedded in the PCB? As PCBs get more complex, more intelligence is often added to verify functionality through self-test. If this is so, how do you enable self-test? How much functionality is covered? Is it faster to verify these functions through self-test or using the test system’s facilities?
- How much time do I have to get ready? From the moment you get the initial test specification, when will the first PCB appear at my test station? Knowing that info up front lends a certain urgency to your plans.
- What is the expected volume of products over the product life cycle? In this case, you may need to communicate with your test equipment vendors. This is probably your biggest long-term strategy. The volume of product tested and the expected number of operations and measurements made help determine the type of instrumentation, switching subsystem, test fixturing, and so on.
- For example, if each test cycle uses a multiplexer 100 times and the relays are rated for 10,000,000 cycles, you can test approximately 100,000 PCBs before the multiplexer may fail. So, work with your test equipment vendors to select the right products to ensure that your test systems remain reliable. In the case of switching, this could mean selecting a more robust multiplexer, or ensuring that the vendor has adequate diagnostic tools, and you create a maintenance schedule to guarantee maximum test system up time.
- Is there a need to allow for expansion in the future of this test system? Are there other products in the pipeline that could be tested on this system with little or no expansion? This is probably the most critical in defense. After all, their manufacturing strategy is usually a medium volume throughput, medium to high mix of products. Your test system might serve testing multiple units under test (UUTs) in production, but your test system design might be deployed to depot repair sites, where multiple test programs are the norm.
- Expansion could mean extra PXI slots or added PXI/LXI modular chassis, free space for other instruments and extra connections on any mass interconnect to address new instruments in the future.
- Don’t forget the limitations of your test budget. If engineering or sales want to prepare for future test programs, ask for the money now!
The correct choice of platform is crucial if future flexibility and scalability of your automated test system may be required, and industry-standard architectures will provide optimum longevity and reliability due to their continual maintenance by dedicated consortiums and the breadth of support among leading test & measurement vendors. The following video will provide more guidance on choosing the most effective test platform for your applications, with an emphasis on switching systems - the foundation of most test systems.
Check out our video "Automated Switch System Platforms Explained"