Building a REAL MANS microwave

[Stray Electron]

As for 'pressurized gas', there's the pics below. These are of a unit from a test set for a military fighter plane combat radar. It's basically just a pressure regulator and doesn't say what the gas actually is, apart from the cryptic "GX2" (or GN2") label on the pipe connector from the gas source. More interesting for the show of how low volume military test gear was constructed. The wires are all teflon insulated. Not because they needed to be, but because _everything_ in the associated gear used that wire.

   We used Sulfur Hexafluoride for pressurizing the "waveguide" in multi-mega watt search RADARs.  IIRC it was only pressurized to about 7 PSIG. All of the insulators and spacers used in and around it were pure Teflon.  We called the conductors "waveguide" but it was actually a rigid, round, coax and bolted together in sections.

   Teflon insulated wire has been pretty much standard in all military electronics and military support equipment for the last 30 years or more since the conductor is usually silver plated copper.

[German_EE]

I may have told this story before so if I have then sorry for the dupe.

I was once called as a technical witness in a court case. The owner of a Chinese Takeaway had two microwave ovens that were used to heat up the cartons of food before handing them to the customer but he got tired of opening the door, putting the food in, closing the door and then starting the microwave.

So...............

He removed the doors and defeated the safety switches so that the microwave ovens could run continuously. Finding that the ovens did not work so well (they were no longer a cavity) he put an aluminum panel on the front with a slot just big enough for a hand holding a carton. Everything worked well until he found that all of his family that worked there had trouble moving their fingers.

Two people lost all of the fingers on their right hand and a third person managed to have two fingers saved. He took the microwave oven manufacturer to court because the instructions did not tell him that removing the door and fitting an aluminum plate in its place was a bad idea. He lost.

[rs20]

He removed the doors and defeated the safety switches so that the microwave ovens could run continuously. Finding that the ovens did not work so well (they were no longer a cavity) he put an aluminum panel on the front with a slot just big enough for a hand holding a carton. Everything worked well until he found that all of his family that worked there had trouble moving their fingers.

Two people lost all of the fingers on their right hand and a third person managed to have two fingers saved. He took the microwave oven manufacturer to court because the instructions did not tell him that removing the door and fitting an aluminum plate in its place was a bad idea. He lost.

I'm curious to know the medical side of this -- what exactly happened to the fingers? Was it heat, or radiation? Cell death due to heat, or DNA damage? Or not cell death at all? (IIRC, microwaves don't have enough energy to enact ionization).

[DenzilPenberthy]

YEah, the microwave radiation is non ionising so it would just have a thermal effect on the hands. However, it would heat the finger tissue pretty evenly all the way through so by the time your hand is hot enough to activate the 'ow that's hot' nerves in your skin, the whole of your finger is probably cooked. Full thickness tissue burns = they chop your fingers off in the hospital

[SeanB]

As for 'pressurized gas', there's the pics below. These are of a unit from a test set for a military fighter plane combat radar. It's basically just a pressure regulator and doesn't say what the gas actually is, apart from the cryptic "GX2" (or GN2") label on the pipe connector from the gas source. More interesting for the show of how low volume military test gear was constructed. The wires are all teflon insulated. Not because they needed to be, but because _everything_ in the associated gear used that wire.

GN2 is dry gaseous nitrogen, typically obtained from a high pressure cylinder, commonly used for aircraft tyre inflation, and for purging of internal pitot static plumbing during maintenance. The cylinders are typically refilled ( at least in the military) by a dedicated support unit, where they have the air liquifier plant to compress and dry the air and then compress in a high pressure compressor series to get it to first drop out the water vapour, then the CO2 , then finally the O2, leaving behind the N2 and traces of other rare gases ( He, Ar, Kr, Ne Ra ) which is finally condensed into the liquid gas by evaporation. This then is stored in large Dewars, and as needed used to fill cryotanks or fed to an evaporator to generate high pressure gas for filling cylinders.

Aircraft test gear often uses the same instrumentation as the actual aircraft uses, along with the same fittings, plumbing and wiring, so as to have common connectors. There you find them using internally a circular bayonet connector for a connector, despite it being a connector costing $100 or more, in an application where it never will be disconnected, just because the same connector is used on the airframe and it has enough terminals ( or at least enough, I have seen a 200 pin connector used with 5 wires in it) to handle the loom. the ground pitot static set used the same piping internally as the helicopter, which made ordering a replacement tube difficult, I eventually replaced a serviceable one on the airframe to get the used pipe, as it was considered expendable. Did not just use the airframe number but replaced the pipe, important to have the parts match the paperwork, though there was the hanger queen which at one time did have 5 3 axis gyro units in it, while there was wiring and mounting there for only 2. That one lost a lot of parts for AOG use, I took almost all the hydraulic system ( or at least the instrumentation part I dealt with) out as spares. That helicopter actually flew again..... The other hanger queen was at one point 3 broomsticks holding wiring looms, a serial number plate and 2 rows of racking with assorted hardware and panels.