THEORY OF OPERATION

The theory of operation of the IFD has its roots in concepts normally associated with biological systems.

As biological systems age, they undergo changes that negatively affect their functional status.  In other words they degrade with age.  Electronic systems are similar in that their environment (temperature cycles, humidity, oxidation, pollution, vibration and other mechanical stresses, etc.) also negatively affects their functionality.  The reliability of the electromechanical components, such as wires, crimps, connectors, contacts, circuit breakers, solder joints, relays, etc, is compromised in a series of mysterious intermittent type failures that tend to worsen over time. These anomalous operational failures can range in magnitude from inconvenient or mission failures to critical safety risks and often to preventable accidents.  

In continuing with the biological analogy, the IFD employs artificial neural networks both in its hardware and software.   Their use is best described with an example of the human brain and its function of monitoring the nervous system.  

When you put your shoes on, you don’t want to be told every second of the day that your shoe is on, because all you really care about is when the situation changes.  We only want to know when the laces become untied, a pebble gets inside or when some other change from the steady state occurs.  In accomplishing this task, the brain is functioning using what has been called parallel distributed processing.  This processing is accomplished biologically using what is termed as neural systems or neural networks.  The human neural system is listening to all sensors (nerves) in all parts of the body continuously.  It is not using some on-off sampling technique which would require far too much processing time, but rather is conducting more efficient continuous, analog monitoring of all points all of the time.  However, it is only interested in change or differential information.

The continuous and distributed nature of the analog sensing is very important because any change that occurs could come randomly from any point and at any time.  It is important to note that a random event is an event, which by its very nature can occur somewhere in time from the start point to infinity, but the important point is that you don’t know when, where or at what severity it is going to happen.  This is why the scanning, sampling or interval related testing or measurement function as is currently employed in virtually all other digital-based test equipment CANNOT reliably detect these types of random intermittent failures.

At its roots, the IFD’s neural-analog hardware network closely mimics this parallel-distributed processing of the human brain to detect random intermittence.  Rather than spending the bulk of a technology’s time taking and processing serial measurements of mostly “good” readings (which you don’t need), the IFD efficiently concentrates on detecting brief, low-level changes or upsets in impedance.  Because it’s parallel, it does it on all the connected lines at the same time.  The resulting increase in probabilities to accurately detect and isolate an intermittent event is staggering!  In fact it’s some three million to one times more probable on just a single test line.  Multiply this amount times the number of lines to be tested and you quickly see the significant advantages of neural-analog technology for this type of problem.

The type of random failure event which derives from the electronic aging processes that we are interested in detecting and evaluating are circuit inter-connectivity type failures.  The process that begins the search for these intermittent type events usually comes from a system or operator who has experienced some sort or electronics failure during the operation of the system or equipment.  When an attempt is made to reproduce these failures on the ground (aircraft) or in the shop or test lab, a common result is an inability to detect and/or duplicate the previously observed failure.

At the root of this No Fault Found (NFF) problem is the aging process itself, causing connectivity elements to degrade wherein they become intermittent rather than completely open or sometimes shorted.  Due to the inherent on-off action of digital testers as well as the defect itself being of an on-off nature, these random, in time and place, failure “events”, do not synch-up well with the normally unsynchronized digital-testing window.  Small micro-breaks, which are most likely to occur during functional operation and/or testing, are often of a one-shot nature, and are simply not detected at test time with traditional digital testing techniques.  These micro-break intermittencies are important to detect because during operation in a stressful environment, they can just as easily open or short sufficiently as to cause system failures.  If this NFF phenomenon is allowed to progress unchecked, it starts a tedious chain of events resulting in even further degradation and mistrust of the associated electronics systems as even perfectly good units are targeted as possible defective units.   The IFD was designed to break this diagnostic circle of guesswork by testing for aging type defects on a continuous basis using analog rather than digital means, and by taking advantage of neural’s, all points-all-the-time sensing technology.