Author Topic: Second of two dental x-ray generators  (Read 958 times)

Offline klugesmith

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Second of two dental x-ray generators
« on: May 05, 2020, 07:24:56 AM »
From that same dental office, a few hours after Covid lockdown began, I picked up a second x-ray generator. We figured it was permitted under the rules about electrical construction and health care facilities.
This one is bigger & fancier; supposed to go up to 100 kVp and 15 mA. Five wires between control box and the head. Registered with the state bureau of radiation safety and taxation.


This venerable GE product line has a set of slip rings to allow 360 degree rotation of joint between head and manipulator.
The wires run in ordinary flexible line cords, one 2-wire and one 3-wire. So old that the inner insulation is hard and cracked in many places, at both ends of the cords.


After pulling out the 5-brushes board, I was unable to disengage the slip ring shaft from its bushings. Anybody know how that works? Hidden screws? Press fits? Ended up taking down the awkward combination of head and manipulator still joined (minding the strong springs inside manipulator).

Anybody know the wire connections? Gnd and mA are obvious. The other three slip rings, P1 and A1 and X, are connected with low resistance inside the head - I guess primary windings of separate HV and filament transformers.  We can see the inside of a similar unit in this video by Glasslinger:
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Yesterday I put the brushes board back in place and restored all the wires, but am having trouble with continuity at the slip ring interface. Anybody got any hints?  It would be real handy if the slip ring joint can be separated, then just use five narrow hose clamps to make the electrical connections.  Thanks!

Offline johnf

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Offline klugesmith

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Re: Second of two dental x-ray generators
« Reply #2 on: May 10, 2020, 06:22:49 AM »
Got it working, but failed to separate the slip ring shaft connection.

Step 1: Disassembled the joint immediately above the place where slip ring allows infinite rotation.
That one step makes it much easier to move the apparatus without help.


Step 2. scrubbed the slip rings and brushes with steel wool, and got them nice and clean.  Soldered new wires to the brushes board and put that back in place.   After checking everything with an ohmeter, re-connected the control box and got success.

No radiographs, or even glow on a fluorescent screen, just ionization measured with quartz fiber "pen" dosimeter.
First zap, set for 1/2 second at 50 kV peak, moved the line upscale by 100 mR (almost 1 milligray/millisievert).

With the x-ray beam cone covered with lead bibs (from same dental office), I measured the HV current directly by putting a meter in series with the mA monitor wire.  The direction of current was from control box into the x-ray head.  Who wants to figure out which XRT secondary (cathode or anode) the wire is connected to?


Please remember that these intentional radiators can emit ionizing rays at a dangerous rate.   For this machine, even more hundreds of roentgens/hour than the "first" generator.  Top scale on radiation meters intended for nuclear reactor meltdowns and nuclear wars.   Like taking the lid off a 1000 curie (37 TBq) radioisotope source emitting low energy gamma rays.
« Last Edit: May 10, 2020, 06:28:34 AM by klugesmith »

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Re: Second of two dental x-ray generators
« Reply #2 on: May 10, 2020, 06:22:49 AM »

 


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