X-Ray Generators IS DESCRIBED IN DETAIL IN THIS PPT. CONTENT TAKEN FROM MULTIPLE BOOKS AND JOURNALS.

1. X-RAY GENERATOR,
TRANSFORMER, EXPOSURE
TIMER & SWITCH
Mr. Rohit Bansal
Assistant Professor
(Radiophysics)

2. X-RAY GENERATOR
An X-ray generator is a device that produces X-rays.
Together with an X-ray detector, it is commonly used
in a variety of applications including medicine, X-ray
fluorescence, electronic assembly inspection, and
measurement of material thickness in manufacturing
operations. In medical applications, X-ray generators
are used by radiographers to acquire x-ray images of
the internal structures.

3. Components
 An X-ray generator generally contains an X-ray tube to produce the X-
rays. Possibly, radioisotopes can also be used to generate X-rays.
 An X-ray tube is a simple vacuum tube that contains a cathode, which
directs a stream of electrons into a vacuum, and an anode, which collects
the electrons and is made of tungsten to evacuate the heat generated by
the collision. When the electrons collide with the target, about 1% of the
resulting energy is emitted as X-rays, with the remaining 99% released as
heat. Due to the high energy of the electrons that reach relativistic speeds
the target is usually made of tungsten even if other material can be used
particularly in XRF applications.
 An X-ray generator also needs to contain a cooling system to cool the
anode; many X-ray generators use water or oil recirculating systems

4.  Our X ray tube requires electrical energy for two primary purpose:
1. To boil the electrons from the filament.
2. To accelerate these electrons from cathode to Anode.

5. TRANSFORMER
Introduction
 Transformer is a static device.
 It transfers AC electrical power from one circuit to the another circuit
without physical contact and without changing its frequency and phase,
but the voltage can be increased or decreased. The transformer consist of
two circuits, namely the primary circuit and the secondary circuit. Both
circuits coils are wound around an iron core. When current flows through
the primary circuit, a magnetic field is generated, which induces a current
to flow in the secondary circuit.
 It works on the Michal Faradays law of Electromagnetic Mutual Induction.

7. Principle
It works on the principle of Electromagnetic Mutual Induction.
Electromagnetic Mutual Induction:
 When the current is provided to the Primary Winding it behaves as
electromagnet due to this the EMF is induced in the Secondary winding as
it comes in the area having magnetic field lines due to primary Winding.
Vs = Ns.dΦ/dt
Where Vs = Secondary Winding Voltage
Ns = Secondary Winding Turns .

8.  The core of a transformer is laminated
 It is made up of thin sheets of special iron alloy separated from each other by thin
insulating layers
 This layers clamped tightly together
 The purpose of lamination is to reduce eddy currents which is waste power and appear
as heat in the transformer core

9.  When current flows through the primary coil, it creates a magnetic field
within the core, and this magnetic field induces a current in the secondary
coil
 Current only flows through the primary coil , It creates a magnetic field
induces a current in the secondary coil i.e. either increasing or decreasing

10.  In the primary circuit is connected to a battery and the secondary circuit to
a voltmeter
 No secondary current flows while the magnetic field in the core is in a
steady state
 When the switch in the primary circuit is closed, the battery drives current
through the primary coil ,which creates magnetic in the iron core
 As magnetic field increases, it induces a current through the secondary
coil
 Thus current builds up a potential difference between the two ends of the
coil, the voltmeter needles swings to one side

11.  As soon as the magnetic field stabilizes ,the potential across the
secondary coil drops to zero and remains there until the switch in primary
coil is opened
 When the switch is opened ,the magnetic field induces a potential
difference across the secondary coil
 The polarity of the potential is reversed ,and the voltmeter needle moves
in the opposite direction

12.  The important fact to remembers that a current only flows in the secondary
circuit when the magnetic field is increasing or decreasing
 Alternating current is used for a transformer because it is produced by a
potential difference (voltage) that changes continuously in magnitude and
periodically in polarity
 Current flows in one direction while the voltage is positive and in opposite
direction while the voltage is negative

13.  The most important characteristic of alternating current is that its voltage
changes continuously so it produces a continuously changing magnetic
field
 Therefore an alternating current in the primary coil of a transformer
produces an alternating current in the secondary coil

14. Transformer Law
Transformer Law of Voltage: The ratio of incoming voltage and outgoing voltage is
proportional to the number of turns on the both the primary and secondary coils.
Vp/Vs=Np/Ns
V= Voltage, N= Number of Turns, p= Primary coil, s= Secondary Coil.
Transformer Law of Current: The change in current is inversely proportional to the ratio of
the number of turns in primary coil to the number of turns in this secondary coil.
Is/Ip=Np/Ns
I= Current, N= Number of Turns, p= Primary coil, s= Secondary Coil.
Turn Ratio: The ratio of the number of turns in the secondary coil and the number of turns in
the primary coil.
Ns:Np
If the number of turns in the secondary coil is greater than the primary circuit, the voltage is
increased.

16. Basis of construction
 Core type transformer: Its core has two limbs .The windings are wounded
on two limbs of the core material.
 Shell type transformer: Its core has three limbs and two windows. Both
the windings are wounded on the central limb.
 Spiral core transformer: The core constructed is similar to wheels of
spokes. The windings are wounded these spokes like structure

19. Basis of Windings
 Step up Transformer: A transformer in which the secondary voltage is
greater than the primary voltage is called a Step-up Transformer. In this
type of Transformer the number of turns in the secondary coil is greater
than the primary coil. The voltage coming from the Autotransformer passes
through the step-up Transformer, where it is significantly increased.
Np < Ns

20.  Step down Transformer: A transformer in which the secondary voltage is lower than the
primary voltage is called a Step-down Transformer. In this Step-down Transformer,0 the
number of turns in the secondary coil are lesser than in the primary coil. The filament
circuit consists of a Step-down Transformer to reduce the voltage from 220V to 10V. It
controls the heating of the filament. If the voltage of the filament is too high, the filament
may burn, thus reducing the voltage, and the current flow through a Step-down
Transformer before reaching the filament.
Np > Ns

21.  Isolation Transformer/ Autotransformer: A Transformer has only one winding. The
winding act as both the primary and secondary coils of the transformer. The
autotransformer regulates the voltage which is supplied to the step-up Transformer.
The autotransformer has a kVp selection switch, from which the required to voltage
can be selected.
Np = Ns

22. Advantages:
Less costly
Better regulation
Low losses as compared to ordinary two winding transformer of the same rating.
Disadvantages:
An autotransformer does not provide electrical isolation between its windings.
The secondary winding is not insulated from the primary winding.
Used only in the limited places where a slight variation of the output voltage from input
voltage is required

23. Basis of coolant
 Oil filled self cooling: Oil filled self cooled type uses small and medium-sized distribution
transformers. The assembled windings and core of such transformers are mounted in a
welded, oil-tight steel tanks provided with a steel cover.. The oil helps in transferring the
heat from the core and the windings to the case from where it is radiated out to the
surroundings.
 Oil filled water cooled: This type is used for much more economic construction of large
transformers. The cooling coil is mounted near the surface of the oil, through which cold
water keeps circulating. This water carries the heat from the device.
 Air Blast: This type is used for transformers that use voltages below 25,000 volts. The
transformer is used at houses

24. Applications
1. Transmitting electrical energy over long distances through wires.
2. Transformers with several secondary's are used in television and radio
receivers where several different voltages are required.
3. Used as voltage regulator
4. Used almost everywhere in day to day life.

25. Rectifiers
A Rectifier is a device that converts an oscillating two-directional alternating
current (AC) into a single-directional direct current (DC)
The following two types of rectifier circuit can be used:
I. Half wave rectifier
II. Full wave rectifier

26. Half wave Rectifier
 The process of removing one-half the input signal to establish a dc level is called half-
wave rectification.
 In Half wave rectification, the rectifier conducts current during positive half cycle of input
ac signal only.
 Negative half cycle is suppressed or clipped.

27.  AC voltage across secondary terminals AB changes its polarity after each
half cycle.
 During negative half cycle terminal A is negative so diode reversed biased
and conduct no current.so current flows through diode during positive half
cycle only.
 In this way current flow through load in one direction

28. Disadvantage of Half wave rectifier:
 Since, power is delivered only during one half of the cycle of the input alternating
voltage, therefore, its power output and rectification frequency is low.
 Transformer utilization factor is also low.
 The DC output power produced from the half wave rectifier is not satisfactory to make a
general power supply

29. Full-Wave Rectifier
 In Full wave rectification current flow through the load in same direction for both half
cycle of input ac.
 This can be achieved with two diodes working alternatively.
 For one half cycle one diode supplies current to load and for next half cycle another
diode works.

30.  Output frequency of FWR:
 Output frequency of FWR is equal to double of input frequency.
 This means when input ac completes one cycle, rectified wave completes two cycles
Fout = 2 Fin

31. Full Wave Bridge Rectifier
 Consists of 4 diodes instead of 2
 During first half cycle D1 and D3 are conducting while D2 and D4 are in the “off”
state.
 During 2nd half cycle D2 and D4 are conducting while D1 and D3 are in the “off”
state.

32. Filament Circuit
 Cathode is heated by current from the low voltage supply.
 Output is controlled by MA selector.
 Increasing MA= More Heating Current to Cathode= Increased
temperature= Increased thermionic emission.
 Two level of heating of Cathode:
1. Standby heating
2. During Exposure heating

33. Single-Phase Generator
 A single-phase generator is a system of production, distribution and
consumption of electrical energy formed by a single alternating
current or phase and therefore all the voltage varies in the same way.
 The single-phase distribution of electricity is usually used when the
loads are mainly lighting and heating, and for small electric motors. A
single-phase supply connected to an AC electric motor will not
produce a rotating magnetic field, so single-phase motors need
additional circuits for startup and are unusual for power ratings above
10 kW.

34. Three-Phase Generator
 A three-phase system is a system of production, distribution and
consumption of electrical energy formed by three alternating single-phase
currents of equal frequency and amplitude, which have a phase difference
between them of 120 ° electrical, and are given in a determined order.
Each of the single-phase currents forming the system is designated by the
name of phase.

35. Exposure timer
 Control the duration of x ray exposure.
 Terminates after the preset time have elapsed or the when the receptor
have received a specific level of exposure.
 Operator control switches and timers turns radiation ON and OFF.
Types:
1. Manual Timers
2. Electronic Timer
3. Automatic Exposure control.

36.  Manual Timer: is shut off after machine effectively counts in an
synchronous motor.
 Electronic Timer: Based upon the time it fully takes to fully charge the
capacitor. When capacitor limit is reached the electricity allows to run off
from it . It is accurate and produce the exposure time as short as 1 ms.
 Automatic Exposure Control ( AEC) or Phototimer : AEC measures the
actual amount of radiation exposure incident on IR and terminates the x
ray production when required amount is obtained. •

37. Switch
 The function of the switching section is to connect the high voltage (kVp)
to the X-ray tube during the exposure and to disconnect this supply from
the tube at the end of the exposure.
 Such switching commonly occurs between the autotransformer and the
high-tension transformer, where it is known as primary switching, or
between the high-tension transformer and the X-ray tube, where it is
known as secondary switching.

38. Primary Switching: All modem X-ray units make use of solid-state switching.
This type of switching has the advantage that there are no moving parts,
overcoming the problems experienced with earlier mechanical system.
Secondary Switching: Solid-state devices such as SCRs cannot withstand the
very high voltages present in the high-tension circuit, therefore high-tension
valves must be used. In the past, special triode valves were used; modern
generators make use of a grid-controlled X-ray tube.

39. Diode
 A diode is a two-terminal electronic component that conducts electricity primarily in
one direction. It has high resistance on one end and low resistance on the other
end.
 Diodes are used to protect circuits by limiting the voltage and to also transform AC
into DC.

40. Thank you