physics chapter 4 part 2 Flashcards
Parts of the secondary circuit
Secondary side of step up transformer, the milliamperage meter, a rectifier bank, and the X-ray tube
Parts of the primary circuit
Consists if the main power switch(connected to incoming power supply), circuit breakers, the auto transformer, the timer circuit, and the primary side of the step up transformer
Parts of the filament circuit
Rheostat, step down transformer and the filaments
Know what causes the pulsation in a single phase circuit
The alternating change in voltage from zero to maximum potential 120 times each second in a full wave rectified circuit
Know how a 3 phase circuit or 3 phase power works
Six pulse circuit requires 6 rectifies to produce six usable pulses per cycle, 12 pulse circuit requires 12 rectifies to produce 12 useable pulses per cycle
What does the 3 phase provide?
More efficient xray production
Know what the end result will be for 3 phase
Wave form which never reaches zero, thereby providing an increased voltage
Why circuit breakers are included within a circuit
To protect against short circuits and electric shock
What are auto transformers
An adjustable transformer controlled by the kilovoltage peak selector on the operating console
How does the radiographer control the autotransformer
When radiographer selects a kVp setting
What does the autotransformer operates under?
Principle of self induction
Why is an autotransformer sometimes balled kVp selector
Because of its function
What’s an autotransformers primary purpose
To provide a voltage that will bE increased by the step up transformer to produce the kilovoltage selected at the operating console
What does the step up transformer in the primary circuit change?
◾️increase voltage from autotansformer to kVp necessary for xray production
◾️alternating current from low voltage to high voltage
What is the step up transformer in the primary circuit a dividing line of?
Between the primary and secondary circuits
Where the 2 parts of the step up transformer in the primary circuit are located?
◾️primary coil ➡️ primary circuit
◾️secondary coil➡️secondary circuit
How does the step up transformer differ from the autotansformer
This transformer is not adjustable and increase the voltage from the autotransformer by a fixed amount
Why is the exposure timer located in the primary circuit?
It’s easier to control (turn in or off) a low voltage than a very high one
First variation of timer and explain it
Synchronous timer➡️ based on a synchronous meter
Second variation of timer and explain it
Electronic timer➡️ very sophisticated and accurate timer that is most widely used today based on the time it takes to charge a capacitor.
Third variation of timer and explain it
mAs timer- variation of electronic timer, but it monitors the current passing through the X-ray tube and terminates the exposure when the desired mAs is reached. Located in the secondary circuit.
Know how the aec works differently than an exposure timer
Uses the patient body part of interest as the variable in determining when to terminate exposure. AEC uses a device called the ionization chamber.
What AEC controls
Only the quantity of radiation reaching the IR and therefore has no effect on other image characteristics such as contrast
Know what secondary circuit begins with
The rest of the step up transformer
Know what the milliampere meter is
A device placed in the secondary circuit that monitors X-ray tube current
Know where and why the tube is grounded
To prevent electrical shock ➡️ secondary circuit
What rectifiers are
Convert AC ➡️ DC allows current to flow from anode ➡️ cathode and electrons from cathode to anode. Made of two semi-conducting crystals
Which rectifiers are commonly used today
Solid state rectifier
How we get the best use of rectifiers
Arranged in pairs so that the AC cycle has an open “path” from each direction
Know the type of current needed for transformer
AC
What current must supply X-ray tube
DC
Know how the current flows inside X-ray tube
Anode ➡️ cathode
Know what the symbol means and stands for
Solid state rectifiers/diode
Current flow is with the direction of the arrow and electron flow is against the arrow
Define half-wave rectification
When only two rectifiers are used and only one half of the AC cycle flows through the xray and the other half is suppressed
Define full-wave rectification
When four rectifiers are used and both halves of the AC are used.
•By using four rectifiers & arranging them in specific way, both halves of the AC are used
•Resulting waveform is illustrated
•In effect, we “invert” the negative half of the cycle, thereby making use of the entire cycle
Define ripple
Measures the amount of variation between maximum and minimum voltage
Know what filament circuit begins with
Rheostat
Define milliampere parameter
(Tube current) it reflects the rate of flow of electrons passing through the X-ray tube during exposure
Be able to describe what happens when you adjust milliamperage on operating console
You are adjusting the rheostat and the amount of resistance in the filament circuit and ultimately the amount of current applied to the filament in the X-ray tube.
Know the relationship between milliamperage and resistance
⚫️inverse
Higher milliamperage lower the resistance
Know the goal of the filament circuit
Literally boil electrons out of the filament wire
What would happen in the filament circuit if the current gets too high
The tiny wire will be damaged or destroyed
What’s the role of the rheostat in the filament circuit
Controls filament temperature and the rate at which electrons are boiled off of the filament
What’s the role of the timer in the filament circuit
Determines the duration of this process
What’s the role of the step down transformer In the filament circuit
Used in the filament circuit to increase the current by reducing the voltage that is applied to the filament
Know the purpose if the filament circuit
To control the degree to duration that the filament is heated, which in turn controls the number of electrons boiled off that will ultimately become the tube current
Know how the filaments are represented in the console
Large focal spot and small focal spot
