11-02-2020

AC and DC X-RAY Generators

CONVENTIONAL AC GENERATORS 

The mains alternating current (50 Hz) is applied to a circuit (basically a step-up transformer) which elevates it from 230V to 70.000V (70kV).

The high voltage (still at 50Hz) is applied to a rectifier circuit which:

- Eliminates the negative portion of the waves (half wave rectifier), or

- Converts the negative half-waves into positive (full wave rectifier)

- The portion of wave useful for image formation is limited to the “crest”

- All the rest doesn’t produce film blackening, but it is noxious for the patient


HIGH FREQUENCY AND DC GENERATORS

- The HF generator employs a specific circuitry (INVERTER) which generates a waveform of much higher frequency than the mains

- Typical operating frequency of an HF generator is in the order of several tens of kilohertz (kHz)

- A specific circuits “flattens” the crests of the waves to further increase the amount of useful radiation

- Such almost flat waveform is called “constant potential”, or DC


COMPARISON OF WAVEFORM



DC GENERATOR

If the ripple is smaller than 4%, the IEC standards allow to give the generator the “constant potential” or DC attribute.



HF TECHNOLOGY ADVANTAGES

- Tubehead more compact and lighter, because the high voltage transformer is smaller

- Patient dose reduced by 25%, because the “soft” X-ray portion is reduced

- kV value can be lower (60 kV instead of 70) because the entire waveform is “useful” to produce image

- Complete line voltage fluctuation insensibility

- Exposure times shorter


AC and DC X-RAY Generators

CONVENTIONAL AC GENERATORS  The mains alternating current (50 Hz) is applied to a circuit (basically a step-up transformer) which elevates it from 230V to 70.000V (70kV). The high voltage (still at 50Hz) is applied to a rectifier circuit w...

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