X-ray tube current ..

[Alphatronique]

Hi

have simple question ...

in X-ray tube and x-ray machine it specify like 70Kv  0.1ma

ok 70Kv Right that easy  but how it limit to 0.1ma ? 
since tube internal resistance was fix  if limit current, the voltage will drop so it no longer 70Kv ?

or i miss the point and the current draw was limited by tube internal resistance
but i remember see unit whit adjustable current

my idea was use ebay china dental  x-ray source  whit a Suniray CCD X-ray imager
for use it as DIY x-ray machine for QFN/ BGA inspection  O0  but need 1ma current and E-bay dental stuff was 0.1ma

Best regard

[mikeselectricstuff]

You set the voltage constant, then adjust the filament current to get the required beam current.

Another issue is whether a dental tube has a small enough spot size to be useful for inspection. Beam current is less of an issue as you can adjust exposure time as required, though at some point you will have thermal issues as dental tubes aren't designed for long exposures, so will rely mostly on the thermal mass of the oil to keep temperatures sensible.

I'd suggest taking some samples along to a friendly dentist to try before going any further.

[Alphatronique]

Hi

great so filament voltage play whit tube internal resistance

i have on hand already the most expensive part the project ,the CCD/imager

but lack right now of source and since x-ray was bit dangerous i prefer but already made unit
and the china dental unit look good and no to expensive ;-) and probably bit more safe that rectifier tube whit flyback

unfortunately i normally not friend whit dentist 

i see some nice picture of raspberry-pi take whit dental equipment , so must doable
http://www.raspberrypi.org/wp-content/uploads/2013/03/final_zpsb98e0379.jpg

[mikeselectricstuff]

Hi

great so filament voltage play whit tube internal resistance

i have on hand already the most expensive part the project ,the CCD/imager

but lack right now of source and since x-ray was bit dangerous i prefer but already made unit
and the china dental unit look good and no to expensive ;-) and probably bit more safe that rectifier tube whit flyback

Some Chinese dental units have been shown to be very unsafe -
http://www.bbc.co.uk/news/health-20579318
 there are plenty of used old Wester units around, so may be a safer bet

i see some nice picture of raspberry-pi take whit dental equipment , so must doable
http://www.raspberrypi.org/wp-content/uploads/2013/03/final_zpsb98e0379.jpg

Nice, but may not be good enough for inspection.

[Alphatronique]

Hi


umm it exactly same machine i look   lol   
honestly was afraid that a true dentist use that sort of thing on live patient

but my plan was to put it on shield box made of some layer of drywall and point source to the concrete floor
and of course never let it connected to power source , i not trust DIY solution but still not trust china version to

i agree that to not resolution that a true machine for BGA but ,may see that it QFN have lot of void on thermal pad
but honestly i not think that it will helpfully ,but customer ask for got it BGA x-ray image even if cannot interpret it
on my side i knot that solde was right since process was stick controlled  buy it ask request it  so ..

[mikeselectricstuff]

Hi

but my plan was to put it on shield box made of some layer of drywall and point source to the concrete floor

..er lead, not drywall...
Although X-rays are mostly very directional, you do get some scatter, and you don't know if the sides of the tube are well enough shielded.

Also, with a cheap Chinese unit, chances are the PSU and cooling are marginal, so probably won't like running at any serious duty cycle.

[Alphatronique]

Hi

i read at many place  that for dentist office it require 1" of dry wall for effective shielding

not like lead since i already suffer lead poisoning in the past  ,and may expensive to buy/ship/dispose later

i see that i now have lead-free apron so may  put a one/few in sandwich interleaved in the drywall sheet
and will of course make cation for interleave joint to for avoid weak spot

but thank allot Mike for all the reply ;-)

p.s. just got a idea i have lot of SN100C  Tin bar for my wave solder   ,was easy to cast in sheet and Sn atomic weight was half the Pb  so 3-5 mm of tin may got good result if put directly around x-ray head   and material was in stock  ;-)

[Psi]

I have a circuit diagram of a rapiscan xray generator driver board somewhere if it would help.

[richard.cs]

i read at many place  that for dentist office it require 1" of dry wall for effective shielding

not like lead since i already suffer lead poisoning in the past  ,and may expensive to buy/ship/dispose later

Lead sheet is safe to work with with only basic precautions and can be nicely formed into shape. Wash your hands after working with it or wear gloves, nothing more is required to prevent lead poisoning. Sheet steel cut and welded into a box would also work well. Drywall will work in sufficient thicknesses, but without knowing how much attenuation you need it's impossible to say how much shielding (of any type) is required.

[Fraser]

One sggestion.....look for a used mail scanner and avoid all the issues that you are facing. They are heavy, but well designed. A modern Todd unit sold in the UK for around $300 not so long ago. Far safer than playing with a cheap dental source. Modern mail scanners are better than the old fluoroscope versions and you can achieve magnification by positioning of the object within the inspection chamber.

Having worked with X-Ray as part of my job, I have great respect for it, and the safety aspects of its use. Open X-Ray is very usefull but users should be 'badged' to check exposure levels over time. You may get away with uncontrolled use but remember .... there is no SAFE dose of X-Ray's above background     All exposure should be avoided where possible.

[mikeselectricstuff]

Another issue is that in some countries, open X-ray sources will be subject to licensing and regulation.
I have a mail scanner, and have got some fairly good images using an SLR and x-ray screen inside the cabinet, but I think the tube spot size is a bit too big.

[amyk]

Any lead for shielding will be far less hazardous than the x-rays themselves...

[Alphatronique]

Hi

nor sure a mail scanner have resolution for that (point source)   ,the intra oral CCD sensor i use have
933 X 606 pixel  whit 0.03mm pixel size  (31.1 x 20.2 mm 15Lp/mm )  that horribly expensive sensor
but fortunately patient  shew cable ,so time to time some end up on E-bay for low cost ;-) just need to fix the cable
 
MFG claim very low exposure dose need  see some were that it need 5 mrad  ,some manufacturer claim
it even no need shielding whit used whit the "right" source

so think will wait to find a good source ,and try to put hand on 3mm lead sheet even if i really not like play whit it

also please note that i not intend to scan all BGA/QFN  only do first and last one in a batch 
so this made maximum  that 10  exposure / week

Best regard

[Alphatronique]

Hi

a small follow-up ,got on ebay a old "minXray 210"  portable x-ray generator for good price

unfortunately unit not working and was very unsafe  ,brain of machine logic was a 555 in monostable ;-)
but chip was die and shoot x-ray as long you keep finger on trigger button !!!  (not what to be last patient on that)
and i also found 2 broke wire in the sealed head that contain HV transformer and tube
one wire was current resistor tap to ammeter and second one was one of the transformer tap

so fix back the broke wire and the replace the 555 chip ,but still noting, unit draw lot of current but not blow fuse
made quick math and it may normal 63Kv @ 12ma = ~ 800W  ,but transformer humm  and vibrate allot

and Dental  CCD still not trig and my old geiger counter to so i assume it not generate  X-RAY ,even if i treat it as it work

next week-en will re-open sealed case and make in deep test on HV transformer for try to see what wrong
my idea was feed it @1V rms 60 HZ and make sure have 630volt at output
not have clue yet for test filament (tube was inside another tube and pain to access ..

p.s.  tube seem to not draw current even if ammeter wire was fix  ,i validate the panel meter and it accurate and work
in transformer it have 1K resistor in serie whit GND side and current meter plug on it , since meter internal resistance was low
i assume the 1K was here only as safety if ammeter become open , i test panel meter whit current source @10ma and it show 10ma

Best regard

[Alphatronique]

Hi

ok after investigation HV transformer was bad and ARC to Core

that explain the oil color to .. and current draw by the transformer

so i not sure if will put all if the trash ,or will try to rewind the HV coil

[SeanB]

How many turns inside that crepe paper?

[Alphatronique]

Hi

it have 2 layer of paper  ,then each layer of coil was separate by kind of Mylar/paper (kind-off)
whit a generous 1/4 inch  extent on both side of the coil for avoid have winding to close to core

and not sow on image but be-then coil and core it have think plastic sheet but it have arc under

but think picture was better that my bad English ;-)

[SeanB]

Oil got water in it first, then it arced over. That was one well wound unit.

[Alphatronique]

HI

HV part was well sealed and  air tight  , my theories was shipping damage

was poorly packaged ,and box arrive round like a balloon ,and have bend external casing  made on 1/8 aluminium plate

and inside sealed  of the transformer 2 wire have broke , since HV coil was "floating"  over the primary winging
it may have hit the core and puncture the Kraft paper ,then at first power up here it ark and self destroy

will try today to unwind it and repair it but not easy since it all oil impregnated  ,and now oil was carbon filled
so will need to replace it and flush it couple of time for remove much as carbon as possible

[Alphatronique]

Hi

ok forgot it that go to trash , first and last layer use bigger wire but internal of winging use thin hair wire

not possible to unwind it after was warped and resin filled

on picture i put a 30 Ga wire warp  wire for size comparison

 i also confirm that it not a moisture issue ,part of my 10 year job as sub contractor fo GE was made
transformer monitoring system ,and i remember that still have some of the moist sensor we used on it sensor/dryer 
so the reading ppm was in normal range ;-)

seem that this x-ray project will go back on a tablet  for undetermined time

[SeanB]

Shock damage, so it needs to be rewound for sure with that amount of cooking through the layers. I bought an oil moisture measuring system on auction a few years ago, just for the nice case it was in. Still have the insides, and the carbide powder in oil is still good. I did try it a few times on oil, it showed up water at low levels, not surprising here in humid Durban.

[Alphatronique]

Hi

if my memory was good oil may got ~50ppm  over it it saturated and water go strait to bottom of the tank


so anway think i will come back to my first idea that start that tread ,buy a dangerous and unsafe china unit

tear it down and post image here of how it build (seem no one have made it yet)
then rebuild it whit proper safe way ,probably  try to fit it on my old minXray casing and lead coffin 
,and resue the old collimator

other option was try to buy another commercial safe unit but shipping and import cost make it quickly expensice
and may still end as not functional  ..

so at least china junk will polychlorinated biphenyls (PCBs) safe oil  and it tear down may informative for other

and i read many paper wrote on it and seem that most issue come from shielding of tube that expose operator finger
to way over safe FDA dose for case  leaking  and bad collator that exposes patient whole head instead
and finally and the most biggest issue for me was HV regulation of power supply that out of tolerance
speciafied 63Kv but was actually 43kV i assume here it use voltage trippler and cap was to low value
and under load voltage drop .. ?

Best regard