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GENERATORS
- 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
- 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