Chapter 3 The Generation of X-Rays: The X-Ray Machine

The X-ray Machine n The x-ray machine is divided into three separate circuits, each having a specific function but collectively having one goal - the production of a controlled x-ray beam. n The three circuits are: 4 Primary or tube filament regulating circuit 4 Secondary or tube kilovoltage regulating circuit 4 Timing circuit

Transformers n A transformer is an electrical device with no moving parts & operates on the principle of mutual induction that transmits current from one circuit (primary circuit) to another (secondary circuit) that are not electrically or physically connected. n The two are magnetically connected in that they are both wound around the same iron core.

Transformers n Transformers are made up of four parts: ¶Primary coil ·Secondary coil ¸Core ¹Insulation n In transmitting the current from the primary circuit to the secondary circuit, alterations are made in the voltage & amperage.

Transformers n This is due to the conservation of energy. A transformer that raises the voltage is a step-up transformer; one that lowers voltage is a step- down transformer. n The determining factor in whether a transformer is step-up or step-down & to what extent it performs either of these tasks is the relative number of windings in the primary & secondary coils.

Transformers n If there are more primary windings than secondary it is a step-down transformer, conversely if the number of secondary windings is greater than the number of primary windings it is a step-up transformer.

Transformers \ Recall that when voltage goes up, the amperage goes down. Therefore a step down transformer will have increased amperage coming out. \ We can decrease both the amperage & the voltage by using resisters.

Transformers n The amount of voltage increase or decrease when using transformers can be calculated using the following relationship (which does not account for transformer loss): Applied voltage = # of primary windings Delivered volts # of secondary windings

Transformers n For example, if a transformer has 10 times as many primary windings as secondary (step-down) & 110 volts are applied to it. What is the delivered voltage? Applied voltage = # of primary windings Delivered volts # of secondary windings 110 = 10 X 1 10X = 110 X= 11 Volts

Transformers n According to the Law of Conservation of Energy, energy can neither be created or destroyed but can be changed to different forms. n The unit of electrical energy is the watt, which is the product of voltage times amps. n Volts X Amps = Watts

Transformers n Or substituting: Volts X Amps(primary) = Volts X Amps(secondary) n We can therefore see that an increase in voltage will mean a corresponding decrease in amperage. n A transformer delivering 500 times the applied voltage will deliver 1/500 th of the applied amperage

Autotransformers n A variable or autotransformer is a transformer with a single core. It allows us to fine tune the amount of amperage & voltage. Current is supplied to this coil from an incoming line & the voltage for each turn of the coil is calculated as: n Applied Voltage = Voltage Per Turn # of Turns

Autotransformers n For Example, if an autotransformer has 100 turns in the coil and 100 volts were applied. What would be the voltage for each turn? /Applied Voltage = Voltage Per Turn # of Turns /100 = 1 100

Autotransformers n This is the fine tuner and on a whole, will be increasing voltage for x-ray production.

PRIMARY or TUBE REGULATING CIRCUIT n This functions to accomplish the first essential for the generation of x-rays: èThe source of electrons (thermionic emission or the boiling off of electrons).

The Primary or Tube Filament Regulating Circuit n The parts of the circuit are: ÀIncoming voltage supply or 220 volts. ÁChoke coil voltage regulator (variable resister) - it decreases both voltage & amperage. ÂVoltmeter or Ammeter. ÃFilament or Step-down transformer - lowers the line current to 3-10 volts & 3-5 amps. ÄCathode filament of the tube

The Secondary or Tube Kilovoltage regulating Circuit n This functions to accomplish the second & third essentials for the generation of x-rays: èThe means of accelerating the electrons èStopping them with great impact

The Secondary or Tube Kilovoltage regulating Circuit n The parts of this circuit are: ÊIncoming voltage Supply-110 or 220 volts ËAutotransformer - step-up ÌPeak kilovoltage meter ÍPower or step-up transformer to increase incoming voltage to 30 to 120 kV ÎRectification system-converting from AC to DC current ÏX-ray tube ÐMilliammeter - measuring the # of e - passing from the cathode to anode

The Timing Circuit n This functions to control the predetermined time that the high voltage is applied to the tube, therefore controlling the time that x- rays will be produced. n It is attached to the secondary circuit. n The timing circuit is completely independent from the primary & secondary circuits.