I Fart In Your General Direction!

I was hastily interrupted at work today by an announcement from a co-worker that "there was a problem with grounding on SPRED." (It's the diagnostic I'm most responsible for on PEGASUS.) It turns out that today was spent ferreting out ground loops in our experiment.

The idea's that we have one giant experimental electrical grounding point (the same thing as the third prong in home electrical sockets). With big honking currents going through, say, our vacuum vessel, we'd like discharges to ground to go through the vacuum vessel straight to that single ground and not (for example) through a circuitous route through our expensive diagnostic equipment. This means that we have several ground paths: through the vessel; instrumentation; our data acquisition room; and the building itself. Each path should stay separated from the others. Essentially, we can't have electrical contact between two grounding paths -- which can be a huge difficulty to find should there be a problem! (Think two signal cables brushing against the machine -- then multiply by ~5000. That's just the cables.)

Enter the loopbuster. When clipped onto our 'main' ground point, this handy homemade gadget dumps a strong, modulated current to ground. Should a ground loop exist, the current will also seek its way through to the place where the unwanted contact is taking place. We probe for where the current is going with a wand that has an antenna at the tip; near the presence of the modulated current, it will render the current modulation into audio. While this is very cool in and of itself, even cooler is the message that is being broadcast: "I fart in your general direction!"

There's something to be said for being able to make your own gadgets -- and exploit programmable EEPROM's. :)