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The MANUFACTURER'S DATASHEETS I read specifically call out a small (10 ohm for example) series resistor to mitigate the tantalum's known inability to handle surges. Tek followed these guidelines.
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The OTHER problems tantalums have with a short lifetime and a catastrophic failure mechanism, that we now know so well, probably did not become fully understood until years later after it was too late. That was not something Tek would become aware of until it was too late. When tantalums first became available they had some great advantages. From an engineering perspective their size makes it possible to squeeze more functionality into a smaller space. Their cost makes them economically attractive and lowers instrument costs. What would you have done when presented with this new technology? Dennis -----Original Message-----
From: Chuck Harris [mailto:cfharris@...] Sent: Wednesday, October 10, 2012 5:20 AM I suspect that tek engineers didn't put the resistors and inductors before the tantalum capacitors to protect from surges, but rather to act as an input resistor to a simple RC filter.... the network was there because they wanted to clean up the power going to subassemblies. The fact that the small resistors and inductors acted as surge current limiters, and fuses was just a happy side benefit. Tek engineers used the tantalums just like everyone else did during that era, as small sized large value storage capacitors that had good HF characteristics. It wasn't until much later that the capacitor manufacturers started seeing surge related failures, and began to provide warnings about limiting surge currents. They never told you to limit working voltage to 1/2 the capacitor's rated voltage... that is something that NASA learned as it tried to qualify tantalums for space use. NASA learned about the voltage issues because one of their standard ways of qualifying parts was to run them at 2x their rated voltage, which in the case of a tantalum was a disaster. Even if the part survived the testing, it was damaged and set to fail under normal operation. -Chuck Harris Miroslav Pokorni wrote: Hello Dennis, |
