| Electronics > Beginners |
| KV/µA source, how do you measure the output? |
| << < (3/4) > >> |
| Dundarave:
--- Quote from: Leuven on June 29, 2019, 05:53:16 am ---It's a catch 22 though, I don't have access to another system. --- End quote --- If you measure a solid difference in power flow between when the powder coat is flowing and when it is not, you really wouldn’t need a comparison system: what else could account for the power usage except charge flow via the powder? Then you just use your values measured today as your baseline for the future. |
| Ian.M:
That seems troublesome to build. Only the 10x 1G resistors need to be in oil or potted. It would probably be a lot more convenient to get axial resistors and assemble them into a thick walled Perspex tube that can be used as the EHT probe and fill it with melted petroleum jelly. Perspex is OK up to 90°C for short-term use, so you can use a hair-drier or hot air gun on low to keep the jelly melted while you tap out all air bubbles. Why petroleum jelly, not oil? Well its a decent dielectric, and if the seals aren't perfect it wont leak so readily as oil if you can keep it below its melting point, yet its still very easy to clean off the resistors if you ever need to do any maintenance. The tube ends could be plugged with neutral cure silicone sealant, but my preference would be brass plugs with double O ring seals. Although screening the 10G resistor assembly is desirable it severely increases the dielectric stress on the perspex tube, and you would need 100KV insulation over the screen at the 'hot' end. Also the effect of the distributed capacitance to ground from the resistor chain to the screen would be to over-voltage the first few resistors during fast transients e.g if the EHT source sparks to the probe or to ground. Direct readout on a DMM on a 2V range should be possible - its input impedance will be high compared to the 100K lower resistor in the divider. Put a good quality 0.1uF capacitor across the 100K resistor to swamp the stray capacitance across the resistors in the divider chain. Use a NE2 neon bulb in parallel to protect the DMM if the 10G resistor chain breaks down or flashes over Caution: if the ground lead comes off, it will blow the DMM. |
| Leuven:
I think the easiest and cheapest way is still the voltage divider. How does this sound: 50 x 36MΩ resistors + one 470KΩ, all rated for 3.5kV. I can get them cheap - about £15 all in. Current flow 50µA across the resistors, accuracy well within 5%. |
| Ian.M:
It depends on the length of the resistors as 50 in a row is going to be unreasonably long. If you need 20mm each including joints that's a 1m long EHT probe! Folding or zig-zagging the resistor chain makes it a *LOT* harder to manage the stray capacitances and stress on the insulation. Personally I'd expect anything over 60cm long to be pretty unwieldy to use. Fewer, higher value, higher voltage resistors would be preferable. Of course you could put the resistor chain in an oil bath separate from the probe, but then you'll need >>100KV rated flexible EHT cable and there's a much greater risk to operator safety. |
| joeqsmith:
Dang, that's an expensive repair bill. I assume the end goal is to save money. Do you think that the output degrades and you could have it serviced before a major failure happens? Or maybe know when to order a new part before it totally fails? IMO, it seems like you would just keep a spare part on hand (assuming it's for a business) to avoid down time or maybe find a more reliable gun. |
| Navigation |
| Message Index |
| Next page |
| Previous page |