**Saia Unit 5 Flashcards
Battery/DC power
Provides electric potential
AC power
Provides electric potential
Capacitor
Temporarily stores an electric charge
Ammeter
Measures current
Voltmeter
Measures electric potential
Switch
Controls ON/OFF
Transformer
Increase or decrease voltage
Rheostat
Variable resistor
Diode/rectifier
Electrons flow in only one direction
Ground
A neutral object ready to receive electrons
Rectifier
Converts AC to DC
Imaging system contains 3 systems
Operators console
High voltage-generator/section
X-ray tube
Components of the Operators console function on relatively
Low voltage and amperage for Personnel safety
High voltage generator/section function on relatively
High voltage and amperage making them unsafe to be located near humans
X-ray tube functions on
High voltage and amperage which is Insulated for safety
Resistor
Inhibits electron flow
The operators console allows the radiographer to control
The X-ray tube current (mAs), voltage (KVP), and exposure time
MAs= quantity
Refers to the number of X-rays in the beam
KVP= quality
Refers to the penetrability of the beam
Exposure time =
How long voltage is applied
Current will only flow when voltage is applied
Operators console also includes
AEC selection
Bucky selection
On/off switch
Line compensation
Adjusts the incoming voltage to the precise value that the system is designed to operate on - most operate on 220V however the power companies voltage can vary by as much as 5% thus the need for a compensator to keep voltage at a constant 220V
Auto transformer
Variable ratio transformer which supplies a precise voltage to the filament circuit and to the high voltage circuit.
Once the voltage has passed through the auto transformer
It is no longer susceptible to fluctuations or surges in the line voltage
KVP selector
The secondary side of the autotransformer ,the percentage of available voltage is selected by the technologist, usually in 2 control selectors, a major (steps of 10KV) and minor KV (steps of 1-2KV)
Selected voltage from secondary of auto transformer is delivered to
The high voltage(step up) transformer
High voltage transformer has a fixed ratio of 1000:1, every volt becomes a kilovolt
The filament circuit
High amperage is required for thermionic emission in the filament, it is necessary to step-down the voltage - as voltage decreases amperage increases.
MA selector (part of the filament circuit)
Resistors or a rheostat along the filament circuit which controls the amperage delivered to the filament
Most filaments operate at between
3-6 amps,
As amperage to filament increases thermionic emission increases
MA =
The number of electrons thermionically emitted per second
Exposure timers (5 different types)
Mechanical (wind up timer)
Synchronous (measures voltage pulses -capable of 1/120 of a second)
MAS (delivers a selected mAs w/o setting the “S”)
Electric (modern - capable of 1/1000 of a second)
AEC (automatic exposure control)
High voltage generator
Increases voltage to kilovolts, increases amperage for thermionic emission, converts AC to DC
A high voltage generator consists of 3 main parts
High voltage transformer - step up
Filament transformer - step down
Rectifier - converts AC to DC
The high voltage transformer
Reconfigures wattage from primary to secondary, wattage remains constant between primary and secondary sides of the transformer
The more turns on a transformer
The stronger the magnet, the stronger the magnet the higher the voltage
Watt
The unit of electrical power
- volts x amps = watts
The primary side of the transformer
Is the side of the transformer that is initially supplied with current
The secondary side of the transformer
The side of the transformer in which current is induced to flow
Transformers can change voltage and/or amperage between primary and secondary sides of the transformer but…
Wattage remains constant between primary and secondary sides of the transformer
Step up transformer
Voltage is increased from primary to secondary sides
Step down transformer
Voltage is decreased from primary to secondary
Transformer “stepping”
How voltage is affected from primary to secondary sides of a transformer
High voltage transformer
Step up transformer
2 iron cores, operates by mutual induction
Fixed ratio - approximately 1000:1
Primary side initially supplied w/volts and amps
Secondary side induced kilovolts and milliamps
Filament transformer
Step down transformer
2 iron cores, operates by mutual induction
Fixed ratio - approximately 1:3
Primary side initially supplied with volts and amps
Secondary side induced volts and amps
If grid ratio is greater than 1
Step up transformer
If grid ratio is less than 1
Step down transformer
Voltage rectification
Converting AC to DC
Why convert from AC to DC
Transformers only work on AC
X-ray tube is most efficient on DC
Solid state diode/rectifier
Uses material which is semi conductive
Current is conducted through a diode only in one direction, opposed in the other
Cathode is uniquely designed to emit electrons
But not receive
Anode is uniquely designed to receive electrons but
But not to emit
Filament current
Amperage delivered to filament for thermionic emission
Tube current
Electrons traveling from cathode to anode (mAs)
The higher the current voltage, the greater the
Amplitude of the wave
During the positive cycle of the unrectified waveform
Anode is energized with positive charge
Cathode is energized with negative charge
Electrons flow from cathode to anode
During the negative cycle of the unrectified waveform
Anode is energized with negative charge
Cathode is energized with positive charge
Electrons cannot flow from cathode to anode
Half wave rectification is accomplished with
2 diodes which only allow the positive cycle of AC waveform to be conducted through the circuit.
1/120 second of dead time between pulses
Full wave rectification is accomplished with
4 diodes for each phase of power, two diodes block the negative pulse, two redirect it so that it is traveling the same direction as the positive pulse
Cycles per second is measures in
Hertz
Each cycle has a positive and negative and positive pulse
(2pulses), 120 pulses per second
Have wave rectification
60 pulses per second, only the positive pulse of AC waveform used to make xray, 100% voltage ripple
Full wave rectification
120 pulses per second, both the positive and negative pulses used to make xray, 100% voltage ripple
3 phase power
3 independent voltage waveforms working together in phase for mor efficient way to use voltage. Each voltage waveform has 120 pulses per second
3 phase 6 pulse -
360 pulses per second. 13% ripple
3 phase 12 pulse -
720 pulses per second, 4% ripple
High frequency generator
Modern system of powering an xray system, more efficient usage of available voltage.
Creates “square” waveforms of extremely high frequency creating high efficient power.
Only 1% ripple - less mAs required, lower patient exposure.
Voltage ripple
How far the voltage waveform falls from its peak