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46 The PCB Magazine • July 2016 ered above. Now, there are two modes to the flying probe that should be discussed, as there can be some confusion. The flying probe tester operates in two distinctive modes—direct and indirect. With direct testing the flying probe provides a full resistive test on every board. This includes continuity and discontinuity (with- in the adjacency window). Test time can be very easily calculated, as every board will take the same amount of time to test. All nets are screened against the continuity and discontinu- ity thresholds. With indirect testing, also known as indirect testing by signature comparison, the method changes. With this method the first board goes through what is called a capacitive or discharge gather. These values are stored as a temporary master. The board then receives a direct test to validate the board against the design require- ments. When the board completes and passes, the capacitive values are committed as the dis- charge or capacitive master. Now here is the big difference between indirect and direct: The sec- ond board receives the same capacitive or dis- charge gather, but once that test is complete, those values are compared to the master. ONLY those readings that are outside the capacitive master threshold are retested in direct or resis- tive mode. If the values of the second tested board are all within tolerance to the capacitive master the board will pass with no resistive re- testing whatsoever. In this test method is how the flying probes develop their speed of test. There is quite a gambit of tools in the T&M world to provide validation to your PCB. I know I have only touched on some highlights of all the test and measurement requirements in the field. There are other tests and tools necessary. My goal was to highlight some major specifics in the T&M theatre so the next time when you are wondering what some tests are all about and how they work you will have some background information to help. PCB Todd Kolmodin is the vice presi- dent of quality for Gardien Services USA, and an expert in electrical test and reliability issues. To read past columns, or to contact Kolmodin, click here. It started when NASA an- swered a call for a tool to detect dangerous gases and chemicals with a smartphone. The result be- came a smartphone-linked device that can do just about anything someone can build a sensor for. When the Department of Homeland Security (DHS) put out its request in 2007, NASA Ames Research Center scientist Jing Li already had a sensor that reacted to various gases and compounds—she'd been working on it for space applications, like evaluat- ing atmospheres on other planets. Li needed a way for the device to "sniff" the air for samples and a system that would allow it to interface with a smartphone. Li's team settled on a small fan to gather the air samples, and ap- proached George Yu of Genel Systems Inc., who was able to deliver the cell phone interface system. Building on the system he de- veloped with NASA, Yu created his NODE platform—a cylinder not much bigger than a thumb that can transmit data from sen- sors to a smartphone or other smart device or store it to be up- loaded to any computer. Unlike the sensor devel- oped for DHS, NODE operates independently of the cell phone and transmits the data it gathers using Bluetooth wireless technology. "Using a common platform for multiple sensor modules, you save a lot of money," Yu says. The product line went on the market in 2012, and by summer of 2014 it was already in its sec- ond generation, NODE+, which Yu says is faster, uses less power, is more durable. Turn Your Smartphone into Any Kind of Sensor TEST & MEASUREMENT: THE CASE FOR VALIDATION