[time-nuts] 4046 variations (was EPE GPS....)

Bob Paddock bob.paddock at gmail.com
Sun Sep 27 21:51:48 UTC 2009

> The part might look "wrong" without this information. One case was a 3.15A fuse in >series with a 27R resistor at the 28V supply input. The fuse can never blow (no the >aircraft didn't have 115V 400Hz supplies).
> The reason was a pater exercise to obtain intrinsic safety approval without formal >testing. The rules said a specific type of fuse must be used at the input, the minimum >rating of that approved type of fuse was 3.15A!

I've been down a similar road.  We designed a low power radio remote control to
run some Coal Mining equipment.  The regulatory bureaucrats in the UK
Coal Mining
industry for intrinsic safety told us we *had* to use a particular
power diode, don't
recall the number any more, or they would not approve our product.  That diode
leaked more current that our product took while transmitting!  If we
wanted to use
any modern diode, they would let us do that if we paid them nearly a hundred
grand to "get it tested and approved", and listed by them as an
approved component.  So
we used their diode and put up with the constant complaints about
short battery life. :-(


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