Month: November 2020

The primay power source in my home made X-Ray machine is an high-voltage high-frequency transformer. This transformer is drived by a Mazilli ZVS circuit and it’s capable to output 6kV from 12V. It’s input circuit uses a center tapped coil drived in balanced way by two mosfets of the ZVS, with input voltage feeded into the center tap. This gives balanced sinusoidal waveform on it’s output. Sin wave helps the “slow” high voltage diodes of the HV multiplier chain to turn ON and OFF correctly minimizing RFI generation.

Transformer characteristcs:

• Nominal allowable output 4.5-7.5kV @ 10mA from 10-15V@ 8A
• 50kHz working frequency
• Completly encased in epoxy
• ZVS drive. Primary winding is a center tapped coil
• ETD54 N87 ferrite core ungapped and #B66396W1022T1 Epcos coil former
• Primary winding 4+4 turns of 2.5mm2 wire
• Secondary HV winding 1400 turns 0.2mm dia CuEn

The realization of such kind of transformer presents many challenging problems to be solved. First one is insulation. I’m using standard ETD54 horizontal plastic coil former.

This requires an 8mm clearance/creepage free space between every single layer of the secondary high voltage winding and the side walls.

The insulation between ferrite core and first layer is insufficent because Epcos coil former is not rated for 6kV. I’ve fixed it wrapping a first insulation layer of 4 turns of 0.2mm thick PTFE tape. Each layer is made winding side by side 100 turns of the enameled wire. In total I’ve 14 layers with 0.4mm thick layers of PTFE between each coil winding layer.

The primary is periferic and very far from inner core. The need of a massive insulation between secondary and primary resulted in 3mm total thickness of PTFE tape. I’ve feared that positioning it near the core coud let me not enought space for the primary into the coil former. Winding the primary on external side of the coil former gives me some clearance even I exceed the coil former sides height. The HV output terminals are soldered to silicon insulated HV cable rated 10kV and the whole transfrmer is encased into epoxy. This prevents any kind of corona effect induced disasters like arcing, fire and smoke and gives to the whole trafo a mechanical rigidity and protection. I’ve made a custom cardboard mould for this.

The top of the transformer is separate from the bottom of the cardboard mould by a couple of insulating paper risers of 10mm diameter to let the epoxy to fill every side of the transformer with sufficent thickness

Hello! I’ve tested this “Dentalfilm ECO30” and “Ergonomix” with my improvised X-Ray machine.

Them are self developing film for X-Ray imaging of dental implants etc. Them are relatively small like 35x24mm but are also extremly sensible, sharp and easy to use. A secure way to get some decent results from your X-Ray improvided machine. The small size results ideal for imaging of IC’s and insects. I’ve no insects but I’m full of IC’s so…

 

 

 

Finally I’ve made it! Yes, I’ve built an X-Ray machine for non destructive inspection of circuits and objects.

The level of radiation generated by this device is sufficent to induce cancer or radiation illness, please don’t build and don’t operate such device. There is also another risk: it requires very high voltage to be operated. It generates very high and potentially lethal voltages.

How it’s made this demostrative prototype of X-Ray machine?

Look at my device. From the left to the right you can see:

1. HV generator, ZVS type, drives a TV type flyback transformer. It’s not used in flyback mode because ZVS outputs a pure sinewave so it’s just working  as standard high frequency transformer. It’s output it’s around 15kV with 16V drive voltage. The ZVS diver starting voltage is 7V so, changing the voltage into the range 7-32V I can select output voltage. The whole assembly is enclosed into an electrical juncton box and insulated with silicon gel.
2. SHV 6 stage voltage multiplier. This part it’s made with a 6 stage voltage multiplier enclosed in epoxy. It takes the 15kV input and multiply it x6 to the output. It’s maximum output voltage with 16V input to the ZVS is 90kV. I’ve operated it to 120kV maximum without any troubles for diodes and It’s scarry!
3. X-Ray tube. This unit is a generic replacement for medical use. It’s a surplus tube from Ukraine and was made during soviet era. The big copper disk on the bottom is the anode. The two black wires on the top are the filament wires. You have to connect one of the two leads to the multiplier GND in order to provide a return path to the catode for the electrons that will circulate into the tube during operation.

How to generate X-Rays?

Basicly you just need to properly feed an X-ray generator tube. What it needs to be happy and hot? A proper high voltage for the anode and enought current flowing into it’s filament to heat the catode.

The heated catode generates a cloud of electrons around it that are accellerated to the anode by HV. When they reach the anode, the hit force is enought to convert some of them into X-Rays.

The ZVS driver, the HV flyback, capacitors and diodes used for the high voltage multiplier where bought from highvoltageshop.com

You can see a similar schematic of the ZVS sold by them:

The high voltage multiplier is made stacking 6 Cockcroft-Walton voltage doubler circuits.

Some more pictures of the multiplier and the X-Ray tube:

 

Using an X-Ray image intensifier screen positioned after the item to be inspected, you can take pictures of the shadows left where X-Rays cannot pass the object or are attenuated. Higher density appares as higher density shadows on the improvised “fluoroscopy” screen. You can get a proper X-Ray intensifier by scrapping an X-Ray medical cassette. Medical X-Ray casettes have glued on  inner sides this kinds of screens. Them are sold on eBay with specified emission color and sensibility like blue or green fluorescence emission ORTHO 100 or 400.Look at the pictures below.

 

Carefully regulating high voltage and filament current, you can generate X-Rays into a broad range of energy so you can “trim” them to acomplish the needed job. For metallic objects you’ll need higher voltages, for insects you’ll need much lower voltages… you have to experiment. I stronly recomand the use of a CCTV circuit to see what appares into the fluoroscopy screen from a protected remote location like a different room. You can use a standard analog BW CCTV camera and a cheap LCD screen that accept AV input. It’s usually a yellow RCA female connector on the screen back or side. Use a remote control of the HV generator. You can leave filament turned ON but stay away protected by at least a concrete wall during operation.

This is how looks an X-Ray intensifier screen that have blue characteristic. It’s a very fine grain screen. You can notice that the subject it’s a BDEG scintillation probe. The NaI(Tl) crystal on bottom it’s very dark because of it’s high density. The 1mm alluminium enclosure is clearly visible but it still permit to see the glass photomultiplier tube. Look how much free space there is between photo katode and first dynode! The glass body of the PMT is very evident. You can see also on the lower end of the image the yellow light emitted by the filament of the X-Ray tube. To protect the X-Ray intensifier for this light I’ve glued on it’s back a black cardboard pannel but… some light leaked!