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Registered Member #2893
Joined: Tue Jun 01 2010, 09:25PM
Location: Cali-forn. i. a.
Posts: 2242
Here's the new schematic. (i forgot to put in the second reed relay but you get the picture). It should keep the bulb warm, and there will be no voltage spike.
As for a lead apron, i'm going to make one out of lead flashing and a cooking apron. Even though it's not necessary, as i'll be 250-400' away and the rays will be in the 4mm lead box; i'd feel safer in one. Mainly i won't need more than 45kVp though.
Too bad i can't use a resistor. That would've been easier. However, the light bub becomes more resistive as the transformer tries to draw more current, where as a power resistor does not. I'll start with a 60w lightbub, and if that's not enough i'll go to 75, then 100. Still, any better way?
BTW; does anyone have a schematic for an ss-white marksman?
Registered Member #33
Joined: Sat Feb 04 2006, 01:31PM
Location: Norway
Posts: 971
One possible caveat that I see is that the relay needs to stand off half of the maximum tube voltage between the coil part and the switch part. The battery and filament current rheostat will also be floating at this voltage. DO NOT consider grounding the cathode of the tube unless you've connected it to the center tap of the transformer. If you ground the output of one side of the transformer, the core will float at half of the tube voltage, and the insulation between the core and primary will break down. It is a good idea to ground the core of the transformer in any case.
Do you want a schematic of the control unit or of the x-ray head? If it's the latter, the schematic I posted earlier is going to be quite close.
Registered Member #2893
Joined: Tue Jun 01 2010, 09:25PM
Location: Cali-forn. i. a.
Posts: 2242
Anders M. wrote ...
One possible caveat that I see is that the relay needs to stand off half of the maximum tube voltage between the coil part and the switch part. The battery and filament current rheostat will also be floating at this voltage. DO NOT consider grounding the cathode of the tube unless you've connected it to the center tap of the transformer. If you ground the output of one side of the transformer, the core will float at half of the tube voltage, and the insulation between the core and primary will break down. It is a good idea to ground the core of the transformer in any case.
Do you want a schematic of the control unit or of the x-ray head? If it's the latter, the schematic I posted earlier is going to be quite close.
Anders M.
No, i planned to leave the tube floating, the transformer grounded to the big lead box grounded to a water pipe or something. When adjusting the filament voltage, the mains switch will be disengaged. The relay isn't going to be useless, because it is only switching a net voltage of 3.7V. However i'm worried about backflow into the arduino though, which is why i have one relay controlling another. besides, if anything goes wrong i can always kill the mains.
Registered Member #33
Joined: Sat Feb 04 2006, 01:31PM
Location: Norway
Posts: 971
There is still a problem. The cathode side of the X-ray tube is connected to one end of the HV-transformer, so its potential is half of the tube voltage above ground. This means that the switch part of the filament relay is also at this voltage. The arduino and the relay control and all that stuff should be at around ground potential, which means that the coil of the relay is at ground potential, and the switch part is at several tens of kilovolts. Unless the relay is a special high-isolation-voltage one, it will arc over for sure. Are you with me?
Unfortunately I don't have the schematics for any control units, but I do have a few patent numbers describing how they do the current control with a simple feedback system to control the filament transformer, if you're interested.
Registered Member #2099
Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1714
I'm also planning an x-ray system with battery-powered filament (one of these years). Filament on/off control will either be opto-isolated (with a fiber!) or use a mechanical switch actuated by a "remote" solenoid. This: would be overkill.
Registered Member #2893
Joined: Tue Jun 01 2010, 09:25PM
Location: Cali-forn. i. a.
Posts: 2242
Anders M. wrote ...
There is still a problem. The cathode side of the X-ray tube is connected to one end of the HV-transformer, so its potential is half of the tube voltage above ground. This means that the switch part of the filament relay is also at this voltage. The arduino and the relay control and all that stuff should be at around ground potential, which means that the coil of the relay is at ground potential, and the switch part is at several tens of kilovolts. Unless the relay is a special high-isolation-voltage one, it will arc over for sure. Are you with me?
Unfortunately I don't have the schematics for any control units, but I do have a few patent numbers describing how they do the current control with a simple feedback system to control the filament transformer, if you're interested.
Anders M.
I thought about that, and the relay will be controlled by a battery separate from the arduino. (which is why the reed relay is in there) I really don't know of a better way to isolate then that. Even if the transformer arcs through the relay, it'll just hit the 12v gel-cell. There really shouldn't be any damage. I could even put the relay under oil, but that will slow down it's switching ability dramatically. I could even put a second reed relay to further isolate the system.
And sure, i'm interested.
Klugesmith wrote ...
I'm also planning an x-ray system with battery-powered filament (one of these years). Filament on/off control will either be opto-isolated (with a fiber!) or use a mechanical switch actuated by a "remote" solenoid. This: would be overkill.
Hmm, if the relay fails i'll definitely try the solenoid idea.
Just got the variac today. I like it. It lowers the output voltage nicely. It only lowers the current by 200ma at the low end. [this means 200ua on the secondary]
This is perfect. At 45kvp it should toss out 500ua heater full power. At 75(90?)kVp it should only supply 800ua.
Since more rays will be absorbed by the phosphor screen at 45 than 75(90?), less radiation is needed. Id rather have longer exposure times than short ones. This gives me more photographic control.
Anyway... i'm broke. Anyone know where i can get a lead apron free? If any of you have one, or lead sheet, i'd be willing to trade something. How about a prototype 741 ic? Or a cdv-700 geiger probe?
[Mod edit: merged triple post, use the edit button if you want to add info to a post]
Registered Member #33
Joined: Sat Feb 04 2006, 01:31PM
Location: Norway
Posts: 971
Grenadier wrote ...
Anders M. wrote ...
There is still a problem. The cathode side of the X-ray tube is connected to one end of the HV-transformer, so its potential is half of the tube voltage above ground. This means that the switch part of the filament relay is also at this voltage. The arduino and the relay control and all that stuff should be at around ground potential, which means that the coil of the relay is at ground potential, and the switch part is at several tens of kilovolts. Unless the relay is a special high-isolation-voltage one, it will arc over for sure. Are you with me?
Unfortunately I don't have the schematics for any control units, but I do have a few patent numbers describing how they do the current control with a simple feedback system to control the filament transformer, if you're interested.
Anders M.
I thought about that, and the relay will be controlled by a battery separate from the arduino. (which is why the reed relay is in there) I really don't know of a better way to isolate then that. Even if the transformer arcs through the relay, it'll just hit the 12v gel-cell. There really shouldn't be any damage. I could even put the relay under oil, but that will slow down it's switching ability dramatically. I could even put a second reed relay to further isolate the system.
And sure, i'm interested.
The relay will still have to be controlled by the arduino, and the part between the relay and the arduino will have to stand off the full half of the tube voltage. Personally I would use a fiber optic receiver and a logic level MOSFET to switch the filament. Getting enough isolation otherwise is not particularly easy.
The patent I was talking about is US patent number 3527947, it can be viewed directly here . I don't think it's particularly useful in your case, but it gives some insight into how it's usually done, and it's a very easy way to get the tube to run at a preset current.
Registered Member #2893
Joined: Tue Jun 01 2010, 09:25PM
Location: Cali-forn. i. a.
Posts: 2242
wrote ...
The relay will still have to be controlled by the arduino, and the part between the relay and the arduino will have to stand off the full half of the tube voltage. Personally I would use a fiber optic receiver and a logic level MOSFET to switch the filament. Getting enough isolation otherwise is not particularly easy.
The patent I was talking about is US patent number 3527947, it can be viewed directly here . I don't think it's particularly useful in your case, but it gives some insight into how it's usually done, and it's a very easy way to get the tube to run at a preset current.
Anders M.
Well, I'm hoping that the relay controlled by a reed relay under oil will be enough. It should, since canola oil is an excellent insulator. The oil won't affect the reed's function, being a sealed argon bubble and all, but it will insulate the switch from the solenoid.
I could always build a solenoid switch though. I might try that, and if it's reliable, i may use it. What should i use for contacts? I was thinking a light spring, like the ones in a pen.
Registered Member #2893
Joined: Tue Jun 01 2010, 09:25PM
Location: Cali-forn. i. a.
Posts: 2242
Well, i built a heatsink. It's just two heat pipes crudely soldered to a piece of copper pipe that slides over the anode bar. I'm not sure if i'm going to use it though. What i've been thinking about is putting a 12v computer fan under the oil too. Just to circulate it. It won't run fast, but it'll keep the oil floating. The last thing i want is boiling oil around the anode bar and cold oil everywhere else.
Also, does polarity matter when connecting the heater. I forgot which wire went to the hv. There's an electrostatic lens around the filament, and i'm positive if it's connected to a wire; and if it is which one.
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Grenadier's big thread of Röntgen related shenanigans
