Hio

1. X-RAY GENERATORS
PRESENTOR: DR.PREETHI

2. INTRODUCTION
 AN XRAY GENERATOR IS A DEVICE THAT SUPPLIES ELECTRIC POWER TO THE XRAY
TUBE
NEED FOR ELECTRICAL ENERGY IN A XRAY TUBE???
 TO BOIL ELECTRONS FROM THE FILAMENT
 ACCELERATE ELECTRONS FROM CATHODE TO ANODE
 XRAY GENERATOPS ALSO HAVE A TIMER MECHANISM TO REGULATE THE LENGTH
OF XRAY EXPOSURE

3. PARTS OF A GENERATOR
CONTROL PANEL OR
CONSOLE
TRANSFORMER
ASSEMBLY
-SELECT APPROPRIATE kVp, mA,
EXPOSURE TIME
-HAS METERS
TWO EXPOSURE BUTTONS
-READIES FOR EXPOSURE BY
HEATING FILAMENT AND ROTATING
ANODE
-STARTS EXPOSURE
LOW VOLTAGE
TRANSFORMERS-
FILAMENT
CIRCUIT
HIGH VOLTAGE
TRANSFORMERS
AND RECTIFIERS-
SUPPLIES THE
XRAY TUBE
GROUND METAL BOX
FILLED WITH OIL

6. TRANSFORMERS
 A TRANSFORMER IS A DEVICE THAT INCREASES OR DECREASES THE VOLTAGE IN
A CIRCUIT
 THE XRAY GENERATOR RECEIVES 115 OR 230V, 60Hz AC
 FILAMENT HEATING REQUIRES A POTENTIAL DIFFERENCE OF APPROX. 10V
 ELECTRON ACCELERATION REQUIRES A POTENTIAL DIFFERENCE VARYING
BETWEEN 40,000V AND 1.50,000V
 TRANSFORMERS ARE USED TO CHANGE THE POTENTIAL DIFFERENCE OF
INCOMING ELECTRIC ENERGY TO APPROPRIATE LEVEL

7.  A TRANSFORMER CONSISTS OF TWO WIRE COILS WRAPPED AROUND A CLOSED
CORE
 THE CORE MAY BE A SIMPLE RECTANGLE WITH THE WINDINGS WOUND AROUND
OPPOSITE SIDES OF THE RECTANGLE
 THE CIRCUIT CONTAINING THE FIRST COIL (WHICH IS CONNECTED TO THE
AVAILABLE ELECTRIC ENERGY) IS CALLED THE PRIMARY CIRCUIT
 THE CIRCUIT CONTAINING THE SECOND COIL(FROM WHICH COMES THE MODIFY
ELECTRIC ENERGY) IS CALLED THE SECONDARY CIRCUIT

9.  THE CORE OF THE TRANSFORMER IS LAMINATED
 IT IS MADE UP OF THIN SHEETS OF SPECIAL IRON ALLOY
SEPARATED FROM EACH OTHER BY THIN INSULATIONG
LAYERS
 THIS LAYERS CLAMPED TOGETHER TIGHTLY
 PURPOSE: REDUCE EDDY CURRENTS WHICH IS WASTE
POWER AND APPEAR AS HEAT IN THE TRANSFORMER
CORE

10.  WHEN CURRENT FLOWS THROUGH THE PRIMARY COIL, IT CREATES A MAGNETIC
FIELD WITHIN THE CORE, AND THIS MAGNETIC FIELD INDUCES A CURRENT IN
THE SECONDAFRY COIL
 CURRENT ONLY FLOWS IN THE SECONDARY CIRCUIT WHEN THE MAGNETIC
FIELD IS INCREASING OR DECREASING
 NO SECONDARY CURRENT FLOWS WHILE THE MAGNETIC FIELD IN THE CORE IS
IN A STEADY STATE
 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

12. CORE
 THE TRANSFORMER CORES ARE ALWAYS DESIGNED SO THAT THEY FORM A
CLOSED CIRCUIT
THREE THYPES OF CORE:
 CORE TYPE
 SHELL TYPE
 CROSS TYPE OR H TYPE

14. LAWS OF TRANSFORMERS
 THE VOLTAGE IN THE TWO CIRCUITS IS PROPORTIONAL TO THE NUMBER OF TURNS IN
THE TWO COILS

15. STEP UP TRANSFORMER
 A TRANSFORMER WITH MORE TURNS IN THE SECONDARY COIL THAN THE
PRIMARY COIL INCREASES THE VOLTAGE OF THE SECONDARY CIRCUIT IS CALLED
A STEP UP TRANSFORMER

16. STEP DOWN TRANSFORMER
 A TRANSFORMER WITH FEWER TURNS IN THE SECONDARY COIL THAN THE
PRIMARY COIL DECREASES THE VOLTAGE OF THE SECONDARY CIRCUIT IS CALLED
A STEP DOWN TRANSFORMER

17.  THE SECOND LAW IS SIMPLY A RESTATEMENT OF LAW OF CONSERVATRION OF
ENERGY
 A TRNASFORMER CANNOT CREATE ENERGY
 AN INCREASE IN THE VOLTAGE MUST BE ACCOMPANIED BY A CORRESPONDING
DECREASE IN CURRENT
 THE PRODUCT OF VOLTAGE AND CURRENT IN THE TWO CIRCUITS MUST BE
EQUAL

18.  𝑉𝑃 𝐼𝑃 = 𝑉𝑆 𝐼𝑆
 𝑉𝑃 = voltage in the primary coil
 𝐼𝑃 = current in the primary coil
 𝑉𝑆 = voltage in the secondary coil
 𝐼𝑆 = current in the secondary coil

19. POWER
 THE PRODUCT OF VOLTAGE AND CURRENT IS POWER
 IF THE POTENTIAL DIFFERENCE IN VOLTS AND CURRENT IN AMPERES, THEN
POWER WILL BE IN WATTS
 W=V×I
 POWER IS SAME ON BOTH HIGH VOLTAGE AND LOW VOLTAGE SIDES OF THE
TRANSFORMER

20. AUTOTRANSFORMERS
 The voltage supplied to the x-ray room connects to the x- ray generator
through an autotransformer in most cases
 Functions :
 Provides voltage for x-ray tube filament circuit
 Provides voltage for the primary coil of the high voltage transformer
 Provides a convenient location for kVp meter that indicates the voltage to be
applied across the x-ray tube

21.  An autotransformer consists of a single winding wound on a laminated closed
core
 The autotransformer works on the principle of self induction
 An alternating current applied between the input points will induce a flow of
magnetic flux around the core
 This magnetic flux will link with all the turns forming the coil , inducing voltage
into each turns of winding

23.  Example
 If 230V are applied between points
A and B connect to 115 turns of the
autotransformer winding the volts
per turn will be 2
 By suitable selection if taps one
may select the number of turns to
supply the necessary voltage to the
other components of the x-ray
generator

24. FILAMENT CIRCUIT
 The filament circuit regulates current flow through the filament of the x-ray tube
 The filament is a coiled tungsten wire that emits electrons when it is heated by
this current flow
 Not much power is needed to heat this filament to the necessary high
temperature

25.  A current flow of 3 to 5 A with an applied voltage of about 10 V are typical values
 This current merely heats the filament does not represent the current across the
x-ray tubes
 The power to heat the x-ray filament is provided by small stepdown transformer
called filament transformer
 The filament is connected directly to the second winding of this transformer

27.  The primary winding of filament transformer obtain its voltage by tapping of an
appropriate number of turns from the autotransformer
 This voltage will be around 100 to 220 V across the primary winding
 To reduce this to the desired 10 V range , the primary coil in the stepdown
transformer in the filaments circuit has appropriately 10 to 20 times as many
turns of wire as the secondary coil

28.  The secondary winding of filament transformer has only a very small voltage
across it and is connected to the filament of x-ray tube
 The x-ray tube of course has very high voltage across it
 This makes it necessary to provide high voltage insulation between the secondary
and primary windings of the filament transformer
 The filament transformer is usually placed in the same oil field grounded metal
tank as the high voltage transformer

29.  Precise control of filament heating is critical, because of a small variation in the
filament current resulting in large variation in x-ray tube current
 The x-ray tube current is produced by the flow of electrons from their point of
origin(filament) to anode(target) of x-ray tube

30.  The x-ray filament current may be controlled by altering the voltage to the
primary of the stepdown transformer by addition of resistors connected in a
series in the circuit leading from the autotransformer
 If the resistance is increased more voltage must be used to push current through
the resistance, making less voltage available to the filament transformer primary

31. HIGH VOLTAGE CIRCUIT
 The circuit has 2 transformers , an autotransformer and a step up transformer
 The auto transformer is actually kVp selector and is located in control panel
 The voltage across the primary coil of stepup transformer can be varied by
selecting the appropriate number of turns in the autotransformer
 The kVp can be adjusted in steps from approximately 40 to 150 kVp

33.  The stepup transformer is sometimes called high voltage transformer
 It has many more turns in the secondary coil than the primary coil and it
increases the voltage by a factor of approximately 600
 The potential difference across the secondary coil may be as high as 1,50,000 V
 So it is immersed in oil in the transformer assembly for maximum insulation

34.  Two meters are incorporated in to the high voltage circuit, one to measure kVp
and the other to measure mA
 The meters themselves are located under control panel
 They indicate potential across the x-ray tube and the actual current flowing
through the tube during x-ray exposure
 The voltmeter measures the difference in electrical potential between two points
 Electrons moving through the difference in potential constitute an electric current

35.  In a closed circuit the same number of electrons flows through all points
 An ammeter counts the number of electrons flowing past a point per unit time
and can be placed in the circuit wherever it is most convenient
 The ratio of voltage across the primary and secondary coils in a transformer is
propotional to the number of turns in two coils

36.  kVp meter can be placed in the circuit between the autotransformer and step up
transformer
 The voltage which energizes the kVp meter is the voltage from autotransformer
that will be applied to the primary windings of high voltage transformer when
exposure begins
 Because the kVp meter records the selected kVp before the actual exposure
begins is usually term the prereading peak kilovolt meter

37.  The voltage in this circuit is relatively small and the meter can be located on
control panel with minimum of insulation and without serious risk of electrical
shock
 The connections for the mA meter must be in the secondary coil of the high
voltage transformer to record current flow accurately
 The mA meter is in a circuit with a potential difference of up to 150 kilo kVp to
minimize the risk of electric shock

38.  The connections are made at the point at which the transformer is grounded,
which is the center of coil with a voltage across the coil of 150kVp, the potential
on one side is +75 kVp and on other side -75 kVp
 The center of coil is at zero potential
 If the meter is connected at this point, it may be placed on a control panel
without risk of shock to the operator

39. RECTIFICATION
 CHANGES ALTERNATING CURRENT OUTPUT OF
HIGH VOLTAGE TRANSFORMER TO DIRECT
CURRENT
 ALLOWS CURRENT FLOW IN ONE DIRECTION
ONLY
 XRAY TUBE IS A RECTIFIER BECAUSE CURRENT
WILL NOT FLOW FROM ANODE TO CATHODE

40. P AND N TYPE SEMICONDUCTOR
 THE HEART OF A RECTIFIER IS A SEMI CONDUCTOR- CRYSTALLINE SILICON
 SILICON HAS 4 VALENCE ELECTRONS

41. -THE DEVICE FORMED BY P-
N JUNCTION IS CALLED
DIODE.
-SOLID STATE RECTIFIERS
ARE DIODES
-FORWARD BIAS
-REVERSE BIAS

42. HALF WAVE RECTIFICATION
 THE CURRENT FLOW IS BLOCKED IN THE INVERSE HALF OF THE CYCLE
 BY DOING SO XRAY TUBE CONVERTS AC TO DC
 BECAUSE ONLY HALF OF THE ELECTRICAL WAVE IS USED TO PRODUCE XRAYS IT
IS CALLED HALF WAVE RECTIFICATION
 ADVANTAGE: PROTECT THE XRAY TUBE FROM THE FULL POTENTIAL OF THE
INVERSE CYCLE

43. +
-

44. FULL WAVE RECTIFICATION
 BOTH HALVES OF THE ALTERNATING VOLTAGE ARE USED TO PRODUCE XRAYS
 SO THE XRAY OUTPUT PER UNIT TIME IS TWICE AS LARGE AS IT IS WITH HALF
WAVE RECTIFICATION
 FOUR DIODES USED
 120 PULSES/SECOND
 EXPOSURE TIME HALF OF HALFWAVE CIRCUIT

46. SINGLE PHASE GENERATORS

47. THREE PHASE GENERATORS
 COMMERCIAL ELECTRIC POWER IS DELIVERED IN THREE PHASE AC
 PHASE 120 DEGREE APART
 Produces nearly constant potential
 more efficient than single phase
 shorter exposures

48. THREE-PHASE TRANFORMERS
 A three-phase transformer is used to convert the low voltage AC to high voltage
AC. It has three sets of primary and secondary windings. These windings are
connected in one of the two configurations, namely, delta and wye (star).
Generally, the primary windings are of delta configuration and the secondary is
connected with wye configuration.
 SIX PULSE, SIX RECTIFIER
 SIX PULSE, TWELVE RECTIFIER
 TWELVE PULSE

52. RIPPLE FACTOR
 VARIATION IN THE VOLTAGE ACROSS THE XRAY
TUBE EXPRESSED AS A PERCENTAGE OF THE
MAXIMUM VALUE

53. MEDIUM FREQUENCY GENERATORS
 USES THE PRINCIPLE OF HIGH FREQUENCY CURRENT TO PRODUCE AN ALMOST
CONSTANT POTENTIAL VOLTAGE TO THE XRAY TUBE WITH A TRANSFORMER OF
SMALL SIZE
 PRINCIPLE: IN A T6RANSFORMER, THE VOLTAGE INDUCED IN THE SECONDARY
COIL IS PROPORTIONAL TO THE RATE OF CHANGE OF CURRENT IN THE PRIMARY
COIL

55. THANK YOU