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)
RECTIFICATION
SOUNDS 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 99-100)