SELF INDUCTION

1
SELF INDUCTION

• DURING AC FLOW, MAGNETIC FIELD IS NOT CONSTANT.
  AN OPPOSING ACTION WITHIN THE COIL IS PRODUCED

2
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

3
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?

4

• Placing an electromagnetic near the coil and
  alternating the current through the
  electromagnet.
• Therefore, mutual induction can only be generated
  with AC.

5
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

6
TYPES OF TRANSFORMERS

• CLOSED CORE
• SQUARE DOUGHNUT OF MAGNETIC MATERIAL

7
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

8
SHELL TYPE TRANSFORMER

• TRAPS MORE MAGNETIC FIELD LINES IN PRIMARY
  WINDOW
• MORE EFFICIENT
• USED IN X-RAY EQUIPMENT

9
ELECTROMAGNETISM AS IT APPLYS TO X-RAY UNITS

• AUTOTRANSFORMERSELF INDUCTION (BASED ON LENZS
  LAW)
• LINE VOLTAGE COMPENSATOR IS TAPPED OFF OF THE
  AUTOTRANSFORMER
• KVP MAJOR AND MINOR ARE TAPPED OFF OF
  AUTOTRANSFORMER

10

• 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)

11
RECTIFICATIONSOUNDS NASTY!
12
Rectifiers

• Changes AC to DC
• X-ray units require AC current for transformers
• X-ray Tubes need DC current

13
RECTIFIERS

• Electronic device (diodes)
• Located between secondary side of step-up
  transformer and x-ray tube
• Vacuum-tube Type
• Solid State Diodes

14
X-ray unit

• Line Voltage Compensator
• Autotransformer (increases voltage 100-400)
• Adjusts and reads voltage
• Has a of connections located along its length

15
High voltage generator

• High voltage transformer
• converts low voltage into kVp needed for
  production of x-rays
• Filament transformer
• Rectifiers

16
TRANSFORMER LOSSES OR INEFFICIENCY

• Resistance current and copper wire
• hysteresis alternating reversal of magnetic
  field
• eddy current (Lenzs law) currents that oppose
  the changing magnetic field causes loss in
  efficiency (page 102-103)