In class today our physics teacher was demonstrating how ionic fluids move when a high voltage exists between them. A USB microscope was placed above the test rig, and the image was projected onto the virtual board. He used a 500V-5kV supply, limited to 60µA. The demonstration was interesting, but more interesting was what happened when he turned the supply voltage up: the image on the board began to flicker, then broke up completely and eventually "no signal" popped up. It also caused the USB microscope to reset.

I'm thinking it was interference, but how could a high voltage but low current supply cause such problems for the projector?

I think it might be related to my digital clock having difficulties (resetting, alarm going off randomly, time skipping several seconds at a time) when it is within about 10 cm of my plasma ball, because both use high voltages.

Any ideas?

  • \$\begingroup\$ AC or DC inverter? \$\endgroup\$ – smashtastic Nov 3 '10 at 18:48
  • \$\begingroup\$ I'm not sure. It plugs into the mains. When you turn up the voltage it whines very loudly. I'm thinking it's probably a flyback transformer with a variable oscillator for adjusting the voltage. \$\endgroup\$ – Thomas O Nov 3 '10 at 18:51
  • \$\begingroup\$ Your digital clock uses high voltages? Is it a Nixie clock by any chance? :) \$\endgroup\$ – Kevin Vermeer Nov 4 '10 at 0:26
  • \$\begingroup\$ My digital clock does not use high voltages, it operates off two AA's. I should clarify, the plasma ball uses high voltages, as does the EHT. \$\endgroup\$ – Thomas O Nov 4 '10 at 7:58

Its not a result of the high voltage but rather a by product of how that high voltage is generated. Very high frequency switching is used, such devices often emit a ton of RF around 25Mhz depending on the design. This is what throws off the USB scope and other digital electronics.

As for the whining your heard, plasma can actually transfer energy to the air very effectively. If fact you can even build a tweeter from plasma generation.

Incidently be careful with that stuff, ionizing the air into plasma generates a fair amount of ozone which isn't good for the lungs.

  • \$\begingroup\$ The EHT was a good five feet away from the projector, so it's pretty amazing it can cause problems that far away. It's possible noise got into the video cable though. \$\endgroup\$ – Thomas O Nov 3 '10 at 19:04
  • \$\begingroup\$ I've seen that plasma tweeter before. It looks pretty cool. \$\endgroup\$ – Thomas O Nov 3 '10 at 19:06
  • \$\begingroup\$ I'm not sure what it looked like, but if its of the 2 electrode type with a 'beam' of plasma flowing between the tips (like the tweeter) then both electrodes and the stream of plasma are acting a pretty good sized antenna with no shielding at all. \$\endgroup\$ – Mark Nov 3 '10 at 19:10
  • \$\begingroup\$ No it was just an EHT power supply, like any normal supply but it produces 5kV. It wasn't a plasma generator. \$\endgroup\$ – Thomas O Nov 3 '10 at 19:13
  • \$\begingroup\$ well a "plasma generator" is nothing but a high voltage supply, all you do is place the probes close enough, and set the voltage high enough, to arc through the air and ionize it. You can tweak it with tip metallurgy but thats the basics. Additionally ionic liquids produce plasma at the liquid-air boundary when setup with a high voltage. From your description the ionic liquid was directly under the microscope, so the leads from the EHT had to be right under the microscope also, the probes/plasma/liquid was radiating the interference, which was quite close to the USB scope. \$\endgroup\$ – Mark Nov 3 '10 at 19:32

Most likely partial HV discharges (corona) - these have an extremely fast risetime (sub nS) and therefore have a very wide spectral content. The high voltage also means the instantaneous current can be extremely high, so it gets everywhere.

  • \$\begingroup\$ classic electromagnetic interference (EMI) \$\endgroup\$ – JustJeff Nov 4 '10 at 1:20

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