The Basic X-ray Circuit (Ch 6 Part 2)

The power for x-ray generation comes from the incoming line current or main power, which comes in the form of what two things?

1. Single-Phase power

2. Three-phase power (multiphase power)

What is the incoming line current in the U.S for alternating current?

60 Hz

How many volts does the incoming line of current carry?

200-240 volts

What does nearly all x-ray equipment operate on?

210-220 volts

Single-phase power could be presented as:

1. Incoming line: alternating current (AC) or negative side

2. Incoming line: direct current (DC) or full-wave rectified

What is this image showing?

How single phase-power could be presented

During single-phase, the tube will drop to zero how many times a second using an incoming line of 60 Hz?

120 times

_____ x-rays are produced when the tube drops to zero

No

Three-phase power (multiphase) could be presented as:

1. Three-phase incoming line: alternating current (AC)

2. Three-phase incoming line: direct current (DC) or full-wave rectified

What is this image showing?

Three-phase power

What phase is the machines preferred power?

Three phase

Every time the machines power begins to drop it is boosted back up by what?

The next incoming wave of power

During three phase the voltage _____ reaches 0, however voltage ripple occurs

Never

What are the two circuits in an x-ray unit?

1. Main, tube, or high voltage circuit

2. Filament or low voltage circuit

What is the main purpose of the main, tube, or high voltage circuit?

To provide the tube with potential difference (kVp) and produce x-rays

The main, tube, or high voltage circuit modifies the incoming power so that the radiographer can control what three things?

1. Voltage (kVp)

2. Amperage (mA)

3. Exposure time (seconds)

What all makes up the main, tube, or high voltage circuit?

• Main switch

• Circuit breakers

• Exposure switch

Main switch

Turns the power on and off

Circuit breakers

Prevents overload (fire)

Exposure switch

A remote controlled device to allow the flow of electrons through the circuit (begins exposure)

The exposure switch activates the rotating of the ______

Anode

What are the two steps to the exposure switch?

1. Pressing the exposure switch halfway starts the anode rotating

2. Pressing the exposure switch all the way takes the exposure

What is the purpose of the filament or low voltage circuit?

It provides the filament with modified power in order for thermionic emission to occur. Basically the purpose is to heat up the filament

The filament or low voltage circuit modified the incoming line power to produce __________ from the filament wire

Thermionic emission

The filament or low voltage circuits incoming voltage is stepped down from?

6 to 12 volts

The filament or low voltage circuits amperage (current) is modified to?

3 to 5 amperes

The filament or low voltage circuit’s amperage will provide enough current to _____ electrons at the filament to produce the milliamperes necessary across the tube

Boil off

The filament or low voltage circuit supply is draw directly from the _____ supply

Main circuits

When you set the mA station (100,200,400 etc) you are actually adjusting the number of _______ flowing through the filament or low voltage circuit

Amps

What is the amperage in the filament or low voltage circuit adjusted with?

A variable resistor known as a rheostat

What is the rheostat referred to as?

The mA selector

Once the technique is set and the exposure begins with the filament or low voltage circuit, the current is sent to the ______ to be modified before it reaches the filament

Step down transformer

When designing an x-ray room, the control console must be placed in a manner that is impossible for the operator to be?

Exposed

An exception to the rule above is in mobile radiography where the cord must be ______long minimally

6 feet

A radiographer will stand on the ______ side of the main circuit

Primary, low-voltage

What are the 3 types of exposure timers?

1. Electronic timer

2. mAs timer

3. Automatic Exposure Control (AEC)

The electronic timer is the most complicated and expensive, but the most ______ timer

Accurate

The electronic timer operates by charging a ________ which then terminates the exposure

Silicon-controlled rectifier (SCR)

The electronic timer is accurate to ________ millisecond

1 (0.001 second)

What is the most common timer used under modern radiographic/x-ray equipment

Electronic timer

The mAs timer is used in ________ units

Capacitor discharge

The mAs timer monitors the product of mA and time to give the _____ desired

mAs

When using the _______ timer, the tech sets the mAs and it decides what mA and time to use

mAs

What is automatic exposure control (AEC) also known as?

Automatically exposure devices (AED)

What are automatic exposure controls programmed to do?

Automatically terminate the exposure when a predetermined exposure has been reached

AEC’s only control the ______ while the mA and kVp still must

be set by the radiographer though

Exposure time

What are the two types of AEC’s?

1. Phototimer or photomultiplier

2. Ionization chamber

The phototimer is an older device that used a ______ to

regulate the exposure

Thyratron

The phototimer is placed _____________ meaning that x-rays will pass through the patient, tabletop, and cassette to strike a photo (light) emitting

screen

Under the patient and the cassette

The phototimer’s light energy is changed into electrons by a _______

Photomultiplier tube

When the phototimer’s number of electrons reaches a preset value, the exposure is _______; however this is problem because the photomultiplier is located behind the cassette, making these readings inaccurate

Terminated

The phototimer or photomultiplier is _____ used today

Rarely

Where are ionization chambers placed?

Between the patient and the cassette

When using an ionization chamber, the x-rays ionize the ______in the chamber and the liberate electrons which will cause a current (electrical charge) that travels along a wire to a timer in the circuit

Gas/air

Ionization chambers must be thin (5 mm) and _______

Radiolucent

Where are ionization chambers located?

In front of the cassette

When the ionization chambers predetermined amount of current is produced, the exposure is _______

Terminated

What makes up the vast majority of AEC’s today?

Ionization chambers which are commonly used due to their efficiency and accuracy in measuring exposure

The ________ of an AEC is the length of time necessary

for the AEC to respond to the radiation and for the generator to terminate

the exposure

Minimum reaction time

Phototimers have a minimum reaction time of _________

0.05 seconds (1/20th of a second)

Ionization chambers have a minimum reaction time of _________

0.001 seconds (1 millisecond)

The AEC’s _______ will terminate the exposure at a specific time

even if the AEC does not read the predetermined exposure

Backup time

Who sets the AEC’s backup time?

Technologist

The AEC’s backup time should _______ be set when using an AEC

Always

The AEC’s backup time _________ exceed the tube limit

Cannot

The AEC’s backup time should be set to ______% of the anticipated manual

mAs

150%

What would you set the back-up mAs at if your anticipated technique was 75 kVp @ 50 mAs?

You figure this out by doing 50 × 1.5 = 75 mAs

TH U.S Public Law 90-602 states that generators must terminate the exposure at _______ mAs for above 50 kVp

600 mAs

The U.S Public Law 90-602 sates the generators must terminate the exposure at ______ mAs for exposure below 50 kVp

2000 mAs

What is the falling load generator is specifically designed for what?

Three phase or high frequency generators

A falling load generator’s exposure begins with a _____ amperage and then will fall

during the exposure

High

What are the two disadvantages of using the falling load generator?

1) The operator will not know what mA the machine will select and must rely on the mAs timer to terminate the exposure

2) They shorten tube life due to a higher mA setting being used, so the filament will wear out quicker

Where are all of the technologist-operated controls located?

On the low voltage side of the main circuit to minimize hazard of electrical shock

The main/tube/high voltage circuit and filament/low voltage circuit combine at

the ________ to complete the basic x-ray circuit

Control console

What does the control console consist of?

• Line monitor = monitors electricity coming in

• Line compensator = keeps constant source of power

• Rotor/Exposure Switch

• mA Selector (Rheostat)

• Time Selector

• kVp Selector (Autotransformer)

What is 1 pointing to?

Main breaker

What is 2 pointing to?

Exposure switch

What is 3 pointing to?

Autotransformer

What is 4 pointing to?

Timer circuit

What is 5 pointing to?

High-voltage step-up transformer

What is 6 pointing to?

Four-diode rectification circuit

What is 7 pointing to?

Filament circuit variable resistance

What is 8 pointing to?

Filament step-down transformer

What is 9 pointing to?

X-ray tube

What is 10 pointing to?

Rotor stator

Where is the autotransformer located in the circuit?

Between incoming line and exposure switch

Where is the variable resistor located in the circuit?

In the filament circuit between incoming line and step-down transformer

Where is the timer circuit located in the circuit?

Between exposure switch and step-up transformer

Where is the stator located in the circuit?

Separate circuit from stator of anode motor

Where is the switch located in the circuit?

Between autotransformer and timer circuit

Step-up transformer

Used to increase kVp level for x-ray production

Ground

Helps prevent you from being electrocuted

mA meter

Measures current

Rectification bridge

Changes AC to DC

Step-down transformer

Used in filament circuit to increase current flow to the cathode

Focal spot selector

Large or small focal spot determines which wire will be heated

What are the 4 types of generators?

1. Single Phase (A)

2. three-Phase, Six-Pulse (3ø, 6P)

3. Three-Phase, Twelve- Pulse (3ø, 12P)

4. High frequency (HF)

A single phase generator has a full-wave rectified current that produces 2 pulses per cycle or _____ pulses per second

120

The voltage drops to ______ twice per cycle for a single phase generator

Zero

A single phase generator has a _____% voltage ripple

100