Transcript Physics 3 - NYCC SP-01

Chapter 3
The Generation of
X-Rays:
The X-Ray Machine
The X-ray Machine
The x-ray machine is divided into three separate
circuits, each having a specific function but
collectively having one goal - the production of
a controlled x-ray beam.
 The three circuits are:
 Primary or tube filament regulating circuit
 Secondary or tube kilovoltage regulating circuit
 Timing circuit

Transformers
A transformer is an electrical device with no
moving parts & operates on the principle of
mutual induction that transmits current
from one circuit (primary circuit) to another
(secondary circuit) that are not electrically
or physically connected.
 The two are magnetically connected in that
they are both wound around the same iron
core.

Transformers
Transformers are made up of four parts:
Primary coil
Secondary coil
Core
Insulation
 In transmitting the current from the primary
circuit to the secondary circuit, alterations
are made in the voltage & amperage.

Transformers
This is due to the conservation of energy. A
transformer that raises the voltage is a step-up
transformer; one that lowers voltage is a stepdown transformer.
 The determining factor in whether a
transformer is step-up or step-down & to
what extent it performs either of these tasks is
the relative number of windings in the
primary & secondary coils.

Transformers
 If
there are more primary windings
than secondary it is a step-down
transformer, conversely if the
number of secondary windings is
greater than the number of primary
windings it is a step-up
transformer.
Transformers
Recall
that when voltage goes up,
the amperage goes down.
Therefore a step down transformer
will have increased amperage
coming out.
We can decrease both the
amperage & the voltage by using
resisters.
Transformers
 The
amount of voltage increase or
decrease when using transformers
can be calculated using the
following relationship (which does
not account for transformer loss):
Applied voltage = # of primary windings
Delivered volts # of secondary windings
Transformers

For example, if a transformer has 10 times as
many primary windings as secondary (step-down)
& 110 volts are applied to it. What is the delivered
voltage?
Applied voltage = # of primary windings
Delivered volts # of secondary windings
110 = 10
X
1
10X = 110
X= 11 Volts
Transformers
 According
to the Law of Conservation
of Energy, energy can neither be
created or destroyed but can be
changed to different forms.
 The unit of electrical energy is the
watt, which is the product of voltage
times amps.
 Volts X Amps = Watts
Transformers
Or substituting:
Volts X Amps(primary) = Volts X Amps(secondary)
 We can therefore see that an increase in voltage
will mean a corresponding decrease in amperage.
 A transformer delivering 500 times the applied
voltage will deliver 1/500th of the applied
amperage

Autotransformers
A variable or autotransformer is a
transformer with a single core. It allows us
to fine tune the amount of amperage &
voltage. Current is supplied to this coil from
an incoming line & the voltage for each turn
of the coil is calculated as:
 Applied Voltage = Voltage Per Turn
# of Turns

Autotransformers
For Example, if an autotransformer has 100
turns in the coil and 100 volts were applied.
What would be the voltage for each turn?
Applied Voltage = Voltage Per Turn
# of Turns
100 = 1
100

Autotransformers
 This
is the fine tuner and on a whole, will
be increasing voltage for x-ray
production.
PRIMARY or TUBE
REGULATING CIRCUIT
 This
functions to accomplish the first
essential for the generation of x-rays:
The source of electrons (thermionic
emission or the boiling off of
electrons).
The Primary or Tube Filament
Regulating Circuit
The parts of the circuit are:
Incoming voltage supply - 110 or 220 volts.
Choke coil voltage regulator (variable resister)
- it decreases both voltage & amperage.
Voltmeter or Ammeter.
Filament or Step-down transformer - lowers
the line current to 3-10 volts & 3-5 amps.
Cathode filament of the tube

The Secondary or Tube
Kilovoltage regulating Circuit
 This
functions to accomplish the second
& third essentials for the generation of
x-rays:
The means of accelerating the electrons
Stopping them with great impact
The Secondary or Tube
Kilovoltage regulating Circuit
The parts of this circuit are:
Incoming voltage Supply-110 or 220 volts
Autotransformer - step-up
Peak kilovoltage meter
Power or step-up transformer to increase incoming
voltage to 30 to 120 kV
Rectification system-converting from AC to DC current
X-ray tube
Milliammeter - measuring the # of e- passing from the
cathode to anode

The Timing Circuit
This functions to control the predetermined
time that the high voltage is applied to the
tube, therefore controlling the time that xrays will be produced.
 It is attached to the secondary circuit.
 The timing circuit is completely
independent from the primary & secondary
circuits.
