Huntron - Dealing with Signature Differences Using a Huntron Tracker

Our thanks to Huntron for allowing us to reprint the following article.

One of the most often asked questions that Tracker users ask is "when is a different signature considered a fault? - Simply put, "what makes a bad signature?" To answer these questions, we must explore what causes signatures to be different.

First, the definition of a different signature when referring to Trackers is any signature that appears different from the signature we are using for comparison (e.g. A channel versus B channel signature comparison). In the case of computer-controlled Trackers, the comparison signature is the "Stored" signature saved on the computer's hard drive. When the "test" signature deviates from the "Stored" signature by a user set amount (tolerance), the program flags that particular pin as being different. The key word here is "different" since "different" does not necessarily mean "bad."

Different signatures can be caused by anything that affects the physical makeup of the circuit. Variations in the manufacturing process by IC makers, noisy and oscillating signatures, capacitors charging, board revision levels, board mounted potentiometers, jumpers, and switches, problems during PCB manufacturing, and faulty components can all cause a Tracker system to flag a signature as different. The question arises when trying to interpret which of these causes is generating the "different" signature. Interpreting signatures comes with practice, but we will make some suggestions here to assist the user with deciding what makes a signature "bad" rather than just "different"...

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