At 02:31 AM 5/31/2013, alan.b.pearce@stfc.ac.uk wrote: > > I do something very similar for an apparatus that hangs beneath > > helicopters: > >Do tell what it is for ... > >Is the sealing just so they can spray gun wash it? Its the controller for a drop carousel for seismic crews. There is a=20 large carousel that has up to 16 electrically-releasable hooks. The=20 hooks are holding large, heavy bags filled with whatever the seismic=20 crew needs at each particular test location. The carousel hangs below the helicopter at the end of a 30 or 40 foot=20 cable. There is also a 3-conductor cable strapped to the tether -=20 the lines are Gnd, Drop, Reset. Its a *really* simple circuit but has an extreme amount of ESD=20 protection for both the input lines as well as the solenoid output=20 lines. Its in the enclosure that we chose because its replacing a=20 mechanical stepper relay that simply wasn't sufficiently reliable -=20 that's all the space that we were allowed to have. I would have=20 preferred to use the rectangular fiberglass enclosures that we=20 normally use but the available space was a cylinder, so that's what we used= .. The customer tells me that they get miniature lightning bolts from=20 the carousel to ground if they hover too low. But we've never had an=20 ESD-related failure - Transzorbs are *wonderful* devices. It needed to be waterproof, both because they fly while its raining=20 as well as the high-pressure spray wash. The top of the carousel is=20 completely open to the elements and everything gets soaking wet. All of the metal that is exposed is either tin-plated brass or=20 tin-plated copper. No corrosion issues so far. dwayne --=20 Dwayne Reid Trinity Electronics Systems Ltd Edmonton, AB, CANADA (780) 489-3199 voice (780) 487-6397 fax www.trinity-electronics.com Custom Electronics Design and Manufacturing --=20 http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .