Grenadier's big thread of RÃ¶ntgen related shenanigans / Electromagnetic Radiation / Forums

Forums

4hv.org :: Forums :: Electromagnetic Radiation

« Previous topic | Next topic »

Grenadier's big thread of RÃ¶ntgen related shenanigans

first previous 15 16 17 18 next last

Move Thread

LAN_403

Adam Munich

Sat Mar 19 2011, 09:49PM

Registered Member #2893 Joined: Tue Jun 01 2010, 09:25PM
Location: Cali-forn. i. a.
Posts: 2242

Alright, I fixed the HV feedthrough problem, yet the CW *still* leaks. This time it's oil seeping out of the lid, and I can't get it sealed...

I'm thinking about taking all the caps and diodes off the PCB and point to point wiring the CW so it's nice and "skinny". Then I can put it in a PVC tube or something, because this container just does not want to keep oil inside, and I can't glue it because its polyethylene.

Conundrum

Sat Mar 19 2011, 11:14PM

Registered Member #96 Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4061

superglue and baking soda on the outside, sand down the edges and coat with superglue accelerant to provide a keying point?

Just a thought.

-A

Adam Munich

Mon Mar 21 2011, 02:24AM

Registered Member #2893 Joined: Tue Jun 01 2010, 09:25PM
Location: Cali-forn. i. a.
Posts: 2242

I gave up with the tupperware. Instead I opted for PVC pipe.

To fit the cw in there I needed to shrink it (no pcb).

After that I got some PVC pipe and fittings to make the case, then I made some feedthroughs with brass bolts and sealing washers, then I slid the CW in there and superglued it in place.

I am leaving the current limiting resistor in, mainly because if I left it out I'd probably do something stupid and blow all the diodes. Those carbon comp resistors are indestructible.

Here is the completed CW. The threaded fitting is held on with pvc cement, while the end cap is just going to be slid on and hot glued (to allow for modification).

The flyback needed its own container, so i found some tupperware that doesn't leak.

And then I proceeded to put the FBT in there. I ran out of hardware though and so it sits on my floor until tomorrow.

Here is the tube shield I made today.

And here is everything so far. There is still some room for the heater batteries and rheostat, so yay.

Also, it is going to take more than 22V to make 75kV, so I'm going to need both a 6s lipo and a 1 or 2s lipo to put in series.

Adam Munich

Tue Mar 22 2011, 02:03AM

Registered Member #2893 Joined: Tue Jun 01 2010, 09:25PM
Location: Cali-forn. i. a.
Posts: 2242

Today's progress.

The Hot glue seal leaked on the CW, so I removed that and just dripped PVC cement on the seam. That will both seal it and allow for removal if need be.

I then covered the CW with electrical tape because I was bored.

After that I finished the flyback's container. The FBT is held in place by its primary winding, and it seems to be staying put.

I then connected everything up

for a test. The entire circuit puts out 75 to 80kV at 31V in. I'm not sure why, when it used to do the same at only 22V in some weeks ago. I presume that this is because there are corona losses from the external wiring, but I'm not going to bother fighting it. 31V is just a 6s and a 3s lipo in series.

I'm probably going to buy a 3000mAh lipos, they should provide me with 30 1 minute exposures which is more than plenty. I'm not buying the lipos until I get the linear regulator done, and that is on this week's to-do list.

Some sparking next to an m&m at full power. It hurts my ears. EDIT 4got the video

As for the tube, I got the feedthroughs made, now I need to figure out how to insulate the HV feedthrough from the lead container. I'm thinking a PVC tube and loads of hot glue.

As for the tube I've been playing with the heater, and it definitely doesn't need many volts to get hot. Here is a "hotness chart"

I have prepared just by looking at the light. I'm going to limit it at 2V which should give me 2.5 or so mA of anode current.

Some heater pics
@1.5V

@2V

And after all of these modifications there is no more leaking :D

Freitsu

Tue Mar 22 2011, 10:19AM

Registered Member #3147 Joined: Sun Aug 29 2010, 10:53AM
Location: Finland
Posts: 56

Nice to see the progress on your project Grenadier!

You'll be taking radiographs in notime...

OT: did you get those tubes?

Proud Mary

Tue Mar 22 2011, 05:16PM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

I have no anode heating and cooling curves for dental tubes to look at, but would be concerned that a one minute exposure as you mention above could well exceed the heat capacity of the anode, and so cause irreversible damage. General purpose dental X-ray tubes are designed with exposures of less than one second in mind.

Heat capacity is exceeded when the rate of heat input to the anode exceeds the rate at which it can be dissipated, and is one of the key parameters of any X-ray tube.

Running the tube at reduced anode current - as you suggest - may perhaps be sufficient to keep the tube from overheating in long exposures, but you should investigate the anode heating and cooling cycle before committing to anything that might ruin it.

James

Tue Mar 22 2011, 06:04PM

Registered Member #3610 Joined: Thu Jan 13 2011, 03:29AM
Location: Seattle, WA
Posts: 506

There's a heating chart in the Kodak 2200 manual linked in here

This is for a Trophy TRX708 dental tube which is among the smallest I'm aware of. Max filament voltage is around 4.6V in most dental tubes, which ought to give you somewhere between 7-10 mA. If you run it at a low current like 2-3 mA the heat load on the anode will be substantially lower and the filament will last a lot longer at low temperature as well. At full output it will glow brightly like a normal tungsten light bulb.

Adam Munich

Tue Mar 22 2011, 07:28PM

Registered Member #2893 Joined: Tue Jun 01 2010, 09:25PM
Location: Cali-forn. i. a.
Posts: 2242

Here is the tube data proud mary

The anode heat storage capacity is 7kJ

Proud Mary

Tue Mar 22 2011, 08:10PM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

Grenadier wrote ...

Here is the tube data proud mary

The anode heat storage capacity is 7kJ

Brilliant! Hangzhou Wandong Electron Co have made things easy by giving the maximum continuous power - 110W.

This would mean a maximum current of 1.47mA from a 75kV constant voltage supply. I'd say go with a bit less, because it's always best to be on
the conservative side where expensive parts are concerned.

With 75kV/1.25mA you will be getting somewhere between 25 - 30 Gy/hr at 30cm from the anode across the whole beam cone.

Adam Munich

Tue Mar 22 2011, 09:43PM

Registered Member #2893 Joined: Tue Jun 01 2010, 09:25PM
Location: Cali-forn. i. a.
Posts: 2242

Well the CW is certainly capable of making 1.5mA, and 30Gy/hr is certainly enough x-radiation for me. The tube will also be under oil to help suck away some heat.

I need to figure out how to mount the tube in that tupperware w/o using any glue. Maybe some sort of foamboard contraption could do that.

first previous 15 16 17 18 next last

Moderator(s): Chris Russell, Noelle, Alex, Tesladownunder, Dave Marshall, Dave Billington, Bjørn, Steve Conner, Wolfram, Kizmo, Mads Barnkob