principle of radiography chapter 5
incoming line current
all xray equipment operates from an incoming line of 210-220 volt
the main x ray circuit
must boost the voltage to the range necessary to produce x rays and to permit the radiographer to adjust the amperage, voltage and length of exposure.
the main switch
are usually enclosed in an electrical power box
the exposure switch
is simple connection that permit current to flow through the circuit. also activates the rotating anode of the x ray tube. The anode must be turning at a sufficiently high speed to avoid melting of the target by the high kilovoltage exposure.
to aviod possibility of error
all xray unit that utilize rotating anode have circuitry that prevent an exposure until the anode is turning at the corret speed.
what type od power does an xray generator supply?
AC electrical power
How can a changing magnetic field produce a current?
by motion between a magnetic and a coil
what type of coil does a single phase generator use?
a single coil (solenoid)
what are single phase generator characterized by?
a production of a single wave that is sinusoidal varying voltage and circuit
what happen to the induce current as the voltage fluctuates through each cycle in a single phase generator?
is also fluctuates
when are xray produced in a single phase generator?
only during the positive half of the rotation. nothing is produced during the negative half
at what frequency is AC generated in a single phase generator?
60 cycles/sec. or 60 Hz
what is the ripple of the waveform of a single phase generator?
what is the least efficient way to produce x ray?
single phase generator
what is the average energy for a single phase generator
how does half wave single-phase generator operate?
it suppresses the negative half of the cycle to where it doesn't go below the 0 line, but nothing is being produced
half wave single-phase
60 Hz per second
how much cycle is available of x ray production on a HALF WAVE single-phase generator?
only one half of the cycle is available for x ray production
when are x ray produced for the full wave single phase generator?
produce xray during both half of the AC cycle
Full wave single phase
-It convert the negative wave to positive
-60 Hz per 120's second
Use pulsating DC current
what can you do with a full wave single phase generator that you can't do with a half wave?
use a higher mA and KVp and shorter exposure time
what do 3 phase generator produce?
full wave rectification the voltage never drop to zero
three- phase, six pulse
-13-25% ripple (it means that the voltage in the xray tube never falls below
75-87% of the KVP setting on the console).
-use AC current
-35% higher average photon energy
what % more of x ray can be produced with a 3 phase generator vs. a single phase full wave generator?
12-16% more xray
what is better for a 3 phase generator vs. a single generator
require less mAs that the single phase , high rating for mA and KVp ( can set technique higher) and exposure time are a short as 1 msec. to has more efficient x ray production
what is the disadvantage of three phase generator vs. a single phase generator
contrast is less with the 3 phase generator because of the increase of KVp
how does 3 phase 6 pulse generator produce its pulse per cycle?
produce 3 pulse every half cycle which is 6 pulse/ Hz, 360 /second. one pulse every 1/360 sec. getting faster and faster that the single phase
3 phase 12 pulse generator
-use current supply in AC
what is the newest development generator?
high frequency generator
what does the high frequency generator use for voltage?
voltage with frequency higher that 60 AC cycle
what does the high frequency generator ripple?
what are the advantage of high frequency generator?
-less than 2% voltage ripple
-greater mR/MAs output
-shorter exposure time (less chance of motion)
-lower patient dose (25% less)
-longer tube life
what are falling load generator designed to produce?
designed to produce exposure in shorter posible time by setting the x ray tube begging at the highest mA setting and then allowing to fall during exposure ( without exceeding the heat loading capacity of the tube)
what were falling load generators development primary for?
primary for use with AEC device (where there are not predetermined exposure time)
What do falling load generator provide as far as mA and time?
the highest mA setting at the shortest time posible
what cause the shortened tube life in the falling load generator?
use high mA and KV
the unit of power is watt : V x A =W formula applies to 3 phase generator
formula for single phase generator
V x A x 0.7 = W
high frequency generator
use AC and DC power convert to change the incoming line voltage frequency from 60 Hz to the 6,000 Hz range. Work with a range of 500 to 25.000 Hz
how does a capacitor discharged mobil unit work?
feed standard incoming line voltage to primary coil of high voltage transformer ; voltage across electrodo drop during exposure
what is use to start and stop exposure for a capacitor discharge mobile unit
a grid controlled tube is usually used to act as a switch to start and stop exposure
automatic exposure control (AEC)
provide correct exposure regardless of patient size, control the time of the exposure.
components: 3 ion chambers placed between the patient and the imagen receptor.
it turn off the x ray bean when the proper exposure is reached
an autotransformer function as a
KVp and mAs selector
variation between maximina and minimum voltage
means how low the wave go
the only radiation of any clinical values is:
the only radiation of any clinical values is:
-The radiation that is absorbed in the detector
-is able to converted to a radiographic imagen for interpretation
where is the exposure switch located?
primary side of the step up transformer
where is the mA meter located?
in the secondary side of the step up transformer
what is the typical amperage and voltage sent to the filament circuit?
the transformer that has a single winding that acts as both the primary and secondary winding is called?
a transformer with more turns in its primary winding that in the secondary would be expect to ?
decrease the voltage an increase the A Amperage ( step down transformer)
which of the following circumstance would cause the backup timer to activate during the operation of an AEC unit?
a tabletop exam is being performer with the chest board select
special unit 150 KVp
capacitor discharge unit
provide an rms voltage significantly lower that the peak voltage
battery operated movie unit
batteries supply nonpulsating direct current to a rotary converter, which provides current similar to 3 phase even greater frequency. compared to capacitor discharge machine this unit have the obvious advantage of 3 phase exposure constantly, higher rms voltage and no leakage.
falling load generator
must be used with AECs. it begin exposure at the highest possible mA and then allowing to fall during exposure. it can short the X-ray tube life considerable.it leave the kvp under radiographer control.
do not control any factor except time `
is how height the wave go