X-Ray Generator (first part of Exam 3 Concepts)

Will add transformers later

X-Ray Tube (Contains + Function)

Contains: thermionic vacuum diode

• cathode

• anode

Function: converts electrical energy into electromagnetic energy

Conditions to Produce X-Ray Photons

1. source of electrons (large amount)

2. high PD

3. vacuum

kVp

Kilovoltage Peak

• beam: energy level (penetrability) of the X-ray beam

• sets PD (voltage) between anode & cathode

mAs

Milliamperage per Second

• beam: # of photons produced & length of exposure

• sets the amount of current (or e^-) per second during exposure

• mA x exposure time (s)

X-Ray Circuits

1. Filament Circuit - determines filament current (mA setting)

   1. current that heats filament

   2. measured in Amps (low voltage & high amperage)

      1. 6-12 V & 3-5 A

2. Tube Circuit - determines the tube current during the exposure

   1. passes between 2 electrodes & produces x-rays

   2. measured in mA (high voltage & low amperage)

      1. 50-120 kV & 0.1.0.5 A

• e^- produced by filament are driven across the gap by the voltage applied to the cathode & anode

• a small change in filament current produces a large change in tube current

Generator Divisions

Sections

1. low voltage (primary side)

2. high voltage (secondary side)

3. tube

Circuits

1. tube circuit (high voltage to tube)

2. filament circuit (high amperage, low voltage to filament)

Primary Side (Low Voltage)

• adjusts incoming voltage to the technical factors we choose

  • tube circuit - adjust kVp

  • filament circuit - adjust mAs

• Components

  • autotransformer

  • rheostat

  • kVp meter

  • timing circuit

Main Switch

2-Stage Switch

1. current to induction motor & filament

2. closes tube circuit & begins exposure

Autotransformer & kVp Selectors

variable transformer (single coil); adjusts incoming supplied voltage to the desired voltage for the X-ray tube (also operates using self-induction)

• kV selector - taps on secondary side of the autotransformer

  • kV major - adjusts in units of 10

  • kV minor - adjusts in units of 1

kVp Meter

voltmeter that prereads the kVp going to step-up transformer (to be applied to the tube) & ensures correct voltage reaches it

• wired in parallel

• if there are voltage fluctuations, autotransmitter is adjusted (V not kV here)

• lets you know if something is wrong

Timing Circuit

responsible for terminating the exposure

Rheostat

variable resistor (mA selector); adjusts incoming current to the desired amperage to be sent to the step-down transformer (filament)

• 3-5 amps & 6-12 volts

Focal Spot Selector

determines which filament receives current

• dual focus tube

  

Step-Up (High Tension) Transformer

increases voltage (from autotransformer) to tube as it leaves from primary to secondary coil

Secondary Side (high voltage) (distinction)

• primary vs. secondary distinction made at step-up, high tension transformer

• primary side - incoming volts adjusted by autotransformer

• secondary side - high voltage to be sent to the tube

Step Down (filament) Transformer

sends increased amperage to filament for thermionic emission

mA Meter

measures tube current

• wired in series on secondary side of high tension (step-up) transformer

mAs Meter (not in diagram) - needed for short exposure times less than 100 ms because ammeter will not measure it accurately

Rectification Circuit

converts AC → DC

• enhances heating capacity of X-ray tube, permitting larger exposures

• DC ensures electrical current flows in one direction (cathode → anode)

X-Ray Tube (+ Components)

utilizes high voltage to accelerate electrons toward the target and produce x-rays

1. filament - thermionic emission (boiling off of electrons when metal is heated)

2. cathode - negative diode to create high PD

3. anode - positive diode to create high PD