transformers used in the x rays production circuit.pptx

in radiotherapy the use of x rays are plays a dominant role . in the production of x-rays , the transformers plays a major role in the production circuit. Different types of transformers and their working principles are discussed briefly in this presentation

1. GOOD MORNING

2. TOPICS Filament and high voltage transformers High voltage circuits Half and Full wave rectifiers

3. TRANSFORMERS Transformer is a device used to change the input AC voltage. The voltage may be increased or decreased . It works upon the principle of self and mutual inductance. The transformer basically consists of two coils, namely, primary and secondary. The input in given to the primary coil and the output is taken from the secondary coil.

4. TYPES OF TRANSFORMERS There are two types of transformers, we know Step-up transformers Step-down transformers In addition to these there is a another transformer called auto transformer.

5. FILAMENT TRANSFORMER [STEP-DOWN] What is the need? For x ray production , the process of thermionic emission has to be done , for that we have to heat the tungsten filament. 10v with current (3-6A ) is enough to heat the filament. But we have the supply voltage of 230v. So we reduce the voltage by using step down transformer. The function of the step-down transformer is to convert high voltage from the primary coil into low voltage in the secondary coil. The number of turns in the primary coil is grater than the number of coil in the secondary coil. =   is the no. of turns in the secondary coil is the no. of turns in the primary coil  

6. HIGH VOLTAGE TRANSFORMER [STEP-UP] The number of turns in the primary coil is lesser than the number of coil in the secondary coil. The function of the step-up transformer is to convert low voltage from the primary coil into high voltage in the secondary coil. =   Here is grater than ,so the factor is greater than 1 , and the output voltage will be greater than the given input voltage.   What is the need? In x ray tube the electron has to be accelerated in the high speed , for that the supply voltage of 220v is not enough. It needs a potential difference ranges (40kv to 150kv). It was done by the step-up transformer . If the line voltage is 220 V at 60 cycles/s, the peak voltage will be , because the line voltage is normally expressed as the root mean square value. Thus, if this voltage is stepped up by an x-ray transformer of turn ratio 500:1, the resultant peak voltage applied to the x-ray tube will be 500*220* = 155.6kV  

7. AUTO TRANSFORMER The autotransformer consists of a single winding wound on a laminated iron core and it is working on the principle of self induction. The primary voltage is applied across two of the terminals, and the secondary voltage taken from two terminals, almost always having one terminal in common with the primary voltage. The primary and secondary circuits, therefore, have a number of windings turns in common

8. if 230 V are applied between points A and B , which involves 115 turns of the autotransformer winding, then the volts per turn (230 ÷ 115) will be 2. By a suitable selection of taps, one may select the number of turns to supply the necessary voltage to the other components. A selection of 55 turns will provide voltage of 110 V, while a selection of 160 turns provide 320 V. Thus, an autotransformer can function as a step-up or step-down transformer

9. CIRCUIT DIAGRAM OF X-RAY UNIT

10. HIGH VOLTAGE CIRCUIT COMPONENTS: Step up transformer – to supply high voltage to x-ray tube X ray tube Auto transformer – to adjust voltage stepwise Rheostat – to provide desired resistance in the circuit. Milli ammeter Voltmeter Voltage selector switch – for changing the no. of turns in the auto transformer

11. RECTIFIERS A rectifier is an electrical device used to convert alternating current (AC) into direct current (DC) by allowing a current to flow through the device in one direction only. Diodes work like one-way valves within the rectifier to maintain this flow of current. This process is generally known as “rectification.”

12. NEED FOR RECTIFICATION IN X RAY PRODUCTION If alternating voltage is applied directly to the X-ray tube, the anode(target) will emit electrons, whenever it is negative with respect to cathode(filament). These electrons will travel towards the cathode and bombard the filament and destroy the filament. This is called back projection which is avoided by the supply of rectified DC voltage. Thus, rectifiers play an important role in X-ray production.

13. HALF WAVE RECTIFIER In a half wave rectifier, a single diode is used. An alternating voltage is applied to the diode as input. The output is obtained across the resistance R. When the plate is positive, the diode will allow the current to flow. When the plate is negative, the diode will not allow the current. Therefore, the diode will allow the current only during those half cycles when the plate is positive. Hence, the output current is always in one direction.

14. FULL WAVE RECTIFIER In the half wave rectifier, the input voltage is used only in one half of the cycle. The other half of the cycle is not used. Therefore, there is a need for a rectifier, which will use the full cycle of the input. This is possible by having two or more number of diodes

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