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Re: [TCML] Dentist x ray trans question

Hi Forrest,

If the unit was manufactured after 1979, it will not contain any PCB's. And, some manufacturers, most notably GE, never used PCB's in ANY of their X-ray machines. You can test a small sample of the oil - does it smell/look like mineral oil and does it readily burn an oil-soaked piece of paper? To know for sure, use a PCB testing kit. See:

Dental X-ray machines typically drive the X-ray tube from a 60 - 100 kVpeak source at 7 - 15 mA. This is NOT the continuous duty current rating of your transformer - it cannot take this load continuously. The short on-time and thermal mass prevents winding overheating in normal X-ray supply usage. The X-ray energy (in keV) of an X-ray system is the peak output voltage, so the RMS voltage of your dental X-ray transformer will be in the range of about 40 - 70 kVRMS.

Most modern single-phase X-ray transformers use two identical HV windings with a common grounded center tap, similar to the construction of larger NST's. In larger X-ray systems, an ammeter is placed in series with the two ends of the low-voltage side of the HV windings to measure output current. Dental transformers usually tie these together and connect these to the transformer's grounded core. Unlike NST's, X-ray transformers are not safely current limited, so an external inductive ballast should be used in series with the primary to prevent overheating the secondary windings prolonged heavy loading.

Unless you have suitable high voltage rectifiers and resistors, or 50kV high voltage divider, there is no way to safely measure the output of your transformer at full voltage. To estimate its output, you can drive the transformer from a LV source, such as a filament transformer powered from a variac, while measuring the output from ONE of the HV windings to center-tap ground. The ratio of the output versus input voltage will give you an estimate of the turns ratio (N) for one half of the transformer. Your transformer's HV end-end output will then be about 120*N*2 volts RMS, and Vpeak will be about 1.414 times this.

Got any pictures of the system and transformer? These would help us provide additional information, especially if yours is an older system. The oldest Ritter systems are almost 100 years old. I do not know if all older single-phase systems consistently used a pair of center-tapped HV windings.

Hope this helped - good luck and _PLAY SAFELY_. These units are potentially deadly... (NPI)

Bert Hickman
Stoneridge Engineering, LLC
Alternative email: berthickman1@xxxxxxxxx
World's source for "Captured Lightning" Lichtenberg Figure sculptures,
magnetically "shrunken" coins, and scarce/out of print technical books

Buds mohrstamping mail wrote:
Hi all,  Got a dental x ray transformer given to me this past
weekend.  Mfg’d by Ritter Dental MFG co. inc.   Rochester NY.  Does
anyone know anything about this unit?  PCB’s maybe!?  voltage?  Unit
only has primary tap info on it.  Any help would be appreciated.
Forrest Mohrman Engineer bud@xxxxxxxxxxxxxxxx || 440.647.4316

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