SELF INDUCTION

DURING AC FLOW, MAGNETIC FIELD IS NOT CONSTANT. AN

OPPOSING ACTION WITHIN THE COIL IS PRODUCED

SELF INDUCTION

• INDUCED VOLTAGE IN AC CIRCUIT WILL OPPOSE THE SOURCE VOLTAGE

• IF THE SOURCE OF EMF INCREASES, THE INDUCED COIL VOLTAGE WILL OPPOSE IT AND ATTEMPT TO REDUCE IT.

• IF THE SOURCE OF EMF DECREASES, THE INDUCED COIL VOLTAGE WILL ATTEMPT TO INCREASE IT.

• LINE VOLTAGE COMPENSATOR WHICH TAPS OFF OF THE AUTOTRANSFORMER IN THE X-RAY CIRCUIT

MUTUAL INDUCTION

• IT IS NOT NECESSARY TO PHYSICALLY MOVE A MAGNET TO PRODUCE A CURRENT FLOW

• THE INTENSITY OF THE MAGNETIC FIELD, IF IT CHANGES, WILL PRODUCE A CURRENT FLOW

• HOW DOES THIS WORK?

• Placing an electromagnetic near the coil and alternating the current through the electromagnet.

• Therefore, mutual induction can only be generated with AC.

TRANSFORMERS

• Transform potential and current energies to higher or lower intensities using electromagnetism.

• Operate only on AC current

• Transformers change the magnitude of current and the voltage in AC circuit

• Step-up transformer

• Step down transformer

TYPES OF TRANSFORMERS

• CLOSED CORE• “SQUARE

DOUGHNUT OF MAGNETIC MATERIAL

Autotransformer

• Single iron core with only one winding

• Acts as both primary and secondary

• Works on self induction

• Used for line voltage compensator by stepping up voltage or stepping down voltage as needed

• Not suitable as a high voltage transformer

SHELL TYPE TRANSFORMER

• “TRAPS” MORE MAGNETIC FIELD LINES IN PRIMARY WINDOW

• MORE EFFICIENT

• USED IN X-RAY EQUIPMENT

ELECTROMAGNETISM AS IT APPLYS TO X-RAY UNITS

• AUTOTRANSFORMER=SELF INDUCTION (BASED ON LENZ’S LAW)

• LINE VOLTAGE COMPENSATOR IS TAPPED OFF OF THE AUTOTRANSFORMER

• KVP MAJOR AND MINOR ARE TAPPED OFF OF AUTOTRANSFORMER

• Step up transformer: converts Voltage to Kilovoltage

• Step down transformer: reduces voltage but increases current to supply to the filament (x-ray filaments need between 3-6 amps to heat up and “burn off” number of electrons for the mA station selected)

RECTIFICATIONSOUNDS NASTY!

Rectifiers

• Changes AC to DC

• X-ray units require AC current for transformers

• X-ray Tubes need DC current

RECTIFIERS

• Electronic device (diodes)

• Located between secondary side of step-up transformer and x-ray tube

• Vacuum-tube Type

• Solid State Diodes

X-ray unit

• Line Voltage Compensator

• Autotransformer (increases voltage 100-400)

• Adjusts and reads voltage

• Has a # of connections located along its length

High voltage generator

• High voltage transformer

• converts low voltage into kVp needed for production of x-rays

• Filament transformer

• Rectifiers

TRANSFORMER LOSSES OR INEFFICIENCY

• Resistance : current and copper wire

• hysteresis: alternating reversal of magnetic field

• eddy current: (Lenz’s law) currents that oppose the changing magnetic field causes loss in efficiency (page 102-103)