5 Flashcards

. Filament circuit

The step-down transformer is located in the filament circuit. In order to increase the current necessary for the desired level of thermionic emission in the filament, there needs to be a decrease the voltage. This is done with a step-down transformer. Remember, when there is a decrease in voltage there is an increase of current.

D. The secondary side of the step-up transformer, the rectification system, and the x-ray tube

The x-ray circuit is three separate circuits combined: the primary circuit, the secondary circuit, and the filament circuit. The secondary circuit contains the secondary side of the step-up transformer, the rectification system, and the x-ray tube.

. 5:1

The transformer ratio is found by dividing the wire turns of the secondary side by the wire turns of the primary side. In this example, there would be 5 turns on the secondary side to every 1 turn on the primary side.

A. True

This is true. The falling between zero and 100% causes there to be a short gap between x-ray photon production. This short gap means that a larger mAs must be used in order to produce a diagnostic x-ray beam.

C. Circuit breaker

The circuit breaker, located on the primary side of the x-ray circuit, will stop incoming voltage by “breaking” the circuit. This protects the entire circuit from being damaged in the event the x-ray machine attempts to draw too much power.

A. Converting low voltage into kilo-voltage

In order to make an x-ray exposure, the x-ray tube requires voltage in the levels of kilo-volts. This is achieved by converting the low voltage that is delivered by the autotransformer into high voltage using a step-up transformer. The step-up transformer uses a process called mutual induction to convert low voltage into high voltage.

B. Diode

Diodes are the main component within rectifiers. Diodes work by allowing current to flow in only one direction.

The term, "half-wave rectification" describes the removal of the negative oscillating wave that is present in alternating current (AC).

D. Lowering voltage and raising current

The step-down transformer that is located in the filament circuit is responsible for lowering voltage and increasing the current that is delivered to the tungsten filament.

C. Measures low voltage and reads in kilo-voltage

It is low voltage that is produced on the primary side of the x-ray circuit. This low voltage, produced by the autotransformer, is read by the kVp meter and translated into kilo-voltage.

B. 400 Volts

Secondary voltage (100) x Primary turns (200) = 20,000

Secondary turns (50) x Primary voltage (x) = 50x

50x = 20,000

A. Secondary side of the step-up transformer

There are more windings on secondary side of the step-up transformer. This is what allows low voltage to be converted into kilo-voltage through the process of mutual induction. A step-up transformer has more turns of wire on the secondary side and a step-down transformer has more turns of wire on the primary side. Remember, the autotransformer only has one coil and adjusts levels of voltage through the process of self induction

B. Direct Current (DC)

Direct current is the only type of electricity that can be used in the production of x-ray photons. The use of alternating current would cause the x-ray tube current to flow in the wrong direction (anode to cathode not cathode to anode).

B. Less voltage

Voltage is reduced when there are less wire windings on the primary side as compared to the secondary side.

B. Allowing current to only flow in one direction

The rectification system is responsible for converting AC into DC. It uses electronic diodes that only allow the current to flow in one direction. Using a combination of four of these diodes allows for the complete rectification of both, the positive and negative, wave forms of AC before it reaches the x-ray tube. Transformers are responsible for the level adjustments of voltage and current.

. Core

The largest portion of the transformer is the core. The core is typically composed of iron and is where the tightly wound wire located.

A. Primary coil

In a step-down transformer, there are more turns on the PRIMARY side than on the secondary side. The decrease in wire turns on the secondary side acts to reduce the voltage delivered to the filament circuit. A decrease in voltage works to increase the mA to the filament.

B. Indirect relationship

Remember that due to the law of conservation, when voltage drops current increases, and when voltage increases current drops. The product of voltage and current will always equal total power. This means that the relationship between voltage and current is indirect.

A. Cathode to anode

In order to prevent tube damage and for the x-ray tube to function properly, the current that flows inside the x-ray tube must only flow from cathode to anode. The rectification system in the x-ray circuit is what makes this possible. It converts the AC that is delivered by the step-up transformer into DC before the current is delivered to the tube.

C. The autotransformer

Voltage to the filament circuit is sent from the autotransformer to the rheostat and then delivered to the step-down transformer. The step-down transformer is what lowers voltage and increases the current delivered to the tungsten filament at the cathode.

D. Mutual induction

Mutual induction uses two coils of wire placed next to each other. A primary coil and a secondary coil. If the secondary coil has more windings than the primary coil, this is called a step-up transformer because it increases voltage. If the secondary coil has fewer windings than the primary coil, this is called a step-down transformer because it decreases voltage.

A. True

This is true since the transformers within the circuit only operate with alternating current (mutual induction).

C. Convert AC to DC

The role of rectification within the x-ray circuit is to convert alternating current (AC) to direct current (DC).

C. 4%

A three phase, twelve pulse generator produces a 4% voltage ripple since the oscillating wave only falls 4% below 100% total energy

• D. On the primary side of the step-down transformer The rheostat is a variable resistor that is highly precise. It is used to adjust levels of voltage coming from the autotransformer, once the technologist has made an mA selection. The rheostat controls the amount of voltage that is sent to the primary side of the step-down transformer.

A. Step-up

Since the turn ratio is not a whole number, you can infer that the primary side has more wire turns than the secondary side. 10 turns secondary side divided by 20 turns primary side = 0.5:1 ratio

B. mA

The current that flows from cathode to anode inside the x-ray tube is measured in mA and the current that flows to the filament is measured in A. Remember, as voltage goes up, the current goes down. The massive increase of voltage that occurs on the secondary side of the step-up transformer leads to the current that travels across the tube to be dropped to the levels of mA.

. AC

Transformer, which use the process of mutual induction, will only operate with a changing electric current (AC). If the primary side of an electric transformer receives DC, it will induce no current in the secondary side. The electronic diodes that make up the rectification system are what converts the AC coming from the secondary side of the step-up transformer into DC before it reaches the x-ray tube.

A. High voltage for the secondary side of the circuit

In order to produce the voltage necessary to make a radiographic exposure, we need to convert the low voltage supplied by the autotransformer into levels of kilo-voltage. This is done by using a step-up transformer located on the secondary side of the x-ray circuit. This process is referred to as mutual induction.

B. Filament current

Filament current is what determines the temperature of the tungsten filament. The more current that is delivered from the step-down transformer, the higher the temperature of the tungsten filament. The higher the temperature of the filament, the more electrons are burned off and are available for the production of x-rays once potential difference (kVp) has been applied to the tube.

• B. Increases Decreasing the voltage ripple increases image quality since low voltage ripples produce a more consistent x-ray beam.

B. Decrease receptor exposure

Generator with 100% voltage ripple are the least efficient at producing x-ray photons due to the wave form having to oscillate between 100% and 0%.

C. Thermionic emission

Thermionic emission is the process of burning off electrons from the tungsten filament located at the cathode. The level of mA is determined by the number of electrons burned off, but does not refer to the process of thermionic emission.

A. Self induction

kVp is selected using an autotransformer, a single coil of wire wrapped around an iron core. Connections are made along different points on the wire in order to increase or decrease voltage to desired levels. This process is referred to as self induction because there is only one coil.

C. AC into DC

The tube current, or current flowing from cathode to anode, must only do just that. If current was to alternate between the cathode and anode, the results would be harmful to the tube and would impede the production of x-ray photons. The rectification system is comprised of diodes that only allow the flow of current in one direction. These diodes converts the AC that is coming from the step-up transformer into the DC that is sent to the x-ray tube.

C. 100%

With full-wave rectification, the wave must fall to the zero line before reaching 100%. This 100% decrease in current causes the circuit to produce an 100% voltage ripple.

B. Low voltage produced through self induction

The autotransformer supplies the x-ray circuit with what is considered low voltage. It is both, safer and easier, to control and change voltage at lower levels than higher levels. This is done with a single coil using a process called self induction. Voltage is then increased to the level of kilo-voltage when it crosses from the primary side of the circuit to the secondary side using a step-up transformer and a process called mutual inductio

B. Located on the primary side of the x ray circuit

The primary side of the x-ray circuit controls the delivery of voltage to the step-up transformer and that is why the exposure timer is located on the primary side. It’s an electronic device whose job is to “make” or “break” the voltage that travels across the x-ray tube.

B. Actual focal spot

Electrons that are produced by thermionic emission at the cathode interact with the anode at the actual focal spot.

B. False

This is false. A diode can only be placed in one direction since diodes allows current to pass in only one direction

B. False

This is false, A transformer must have alternating current (AC) in order for mutual induction to occur.

B. Less wire windings on the primary side

A "step-up" transformer will have a greater amount of wire windings on the secondary side compared to that of the primary side.

Between the secondary side of the step-up transformer and the x-ray tube

Remember, before the current coming from the secondary side of the step-up transformer can be delivered to the x-ray tube, it needs to be rectified. The rectification system converts AC into DC using diodes that only allow the flow of current in one direction.

. A single core of wire wrapped around an iron core

The autotransformer is a single coil of wire with an iron core that has a number of connections along its length. Depending on which connections are chosen, the autotransformer will step-up or step-down the voltage sent to the step-up transformer.

C. Voltage

The transformers role within the x-ray circuit is to either increase or decrease voltage.

A. Primary circuit, secondary circuit, and the filament circuit

The x-ray circuit is comprised of three separate circuits: the primary circuit, the secondary circuit and the filament circuit.

C. 2 and 3

When there is a decrease voltage in the filament circuit, there is an increase in current. Higher levels of current will result in a tungsten filament that reaches a higher temperature. This will cause more electrons to be burned off through thermionic emission. Both, b and c are correct.