Transcript step up transformer

X-RAY CIRCUITY
RT 244 – 2012
Circuitry & Function
Let’s go back to the starting point
Contributions by Mosby, Thompson Publisher, Carlton, Bushberg, and the WWW.
1
The Control Console
• The control console is
device that allows the
technologist to set
technical factors (mAs
& kVp) and to make
an exposure.
• Only a legally
licensed individual is
authorized to
energize the console.
2
Operating Console has meters
to measure
• kVp, mA, & exposure time
• Modern units only display mAs
• Units with ACE’s will have a separate
meter for mAs
3
Control Panel
• All the electric circuits connecting the meters
and controls are at low voltage to minimize the
possibility of shock.
4
Technique
selection
• The process begins at the control panel such as the one
shown.
• The technologist selects a technique which will specify the
kVp, mA, exposure time, and focal spot .
• When the exposure switch is depressed, manipulation of
electricity to produce x-rays begins.
• It is necessary to follow the sequence of events in two parts.
• the voltage through to the x-ray tube,
• then go back and follow the voltage and current through to
the filament.
Control Panel Circuit Elements
POWER SUPPLY
–
–
2a.
60 Hz AC 120 to 480 V
Panel Power On/Off
AUTOTRANSFORMER
1. line compensation
1a.
2a.
a. line meter
b. primary side adjustments
2. kVp selection
a. secondary side
adjustments
variable turns ratio
1b.
3.
3. filament circuit power
6
Operating Console Controls:
• Line Compensation
• Quantity = # of x-rays
– Milliroentges (mR) or (mR/mAs)
• Quality = the pentrability
– Kilovolts peak (kVp) or HVL
7
Electric Circuits
• Modifying electric flow and controlling
electricity results in an electric circuit.
8
How the current
gets to the TUBE
9
Generator+ Tranformers
(where the power comes from)
10
Circuitry:
Source: Carlton & Adler (1996). Principles of radiographic imaging: An art and a science. (96-99).
• MAIN CIRCUIT
 Modifies incoming current
to produce x-rays
 Boosts voltage to range
necessary produce
x-rays.
 Modifies incoming line
power to produce
thermionic emission from
the filament wire.
FILAMENT CIRCUIT
• Filament circuit adjusts to
mA ratings (50, 100, 200,
etc.).
• After mA selection,
current sent to step down
transformer to modify
amps that reach filament
on x-ray tube
11
3 Divisions of Circuit Board
• PRIMARY
(CONTROL PANEL)
yellow
• SECONDARY
(HIGH VOLTAGE)
blue
• FILAMENT
(LOW CURRENT)
purple
12
13
X-Ray Machine Circuit
14
Functional Position
Control Console
Transformers
Tube
16
17
Complete Single-Phase Rectifier Circuit
high voltage,
low current
Bushberg, et al., The Essential Physics
of Medical Imaging, 2nd ed., p. 126.
© UW and Brent K. Stewart PhD, DABMP
18
18
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
MAINBREAKER
AUTOTRANSFORMER – KVP - Meter
EXPOSURE SWITCH
TIMER CIRCUIT
HIGH VOLTAGE STEP UP TRANSFORMER
RECTIFIER - Ma Meter
FILAMENT CIRCUIT VARIABLE SELECTPR
FILAMENT STEP DOWN TRANSFORMER
X-RAY TUBE
ROTOR / STATOR
19
20
21
high voltage,
low current
Bushberg, et al., The Essential Physics
of Medical Imaging, 2nd ed., p. 126.
© UW and Brent K. Stewart PhD, DABMP
22
22
23
Name the parts
of the Circuit board # A
1.
2.
3.
4.
5.
6.
7.
8.
TIMER
KVP METER
MA OR AMMETER
RECTIFIER
MA SELECTOR
LINE COMPENSATOR
INCOMING POWER
MAIN BREAKER –
2 - 110 VOLTS LINES
9.AUTOTRANSFORMER
10. STEP DOWN TRANS
11. FOCAL SPOT
SELECTOR
12. STEP UP
TRANSFORMER
13. MINOR KVP SELECTOR
14. MAJOR KVP
SELECTOR
15. X-RAY TUBE
24
Important Parts
Of The Circuit Board TO ID
•
•
•
•
•
•
•
•
•
•
•
1
2
3
4
No #
5
6
7
8
9
10
Incoming Line Voltage
Autotransformer
KVP Selector
Timer
Ma Selector
Primary Side (Low Voltage)
Secondary Side (High Voltage)
X-ray Tube
Rectifier
STEP – Up Transformer
STEP – Down Transformer
25
5
6
4
8
#1
7
3
9
mA
selector
10
2
26
See Circuitry Review handout and chart for numbers
• Wavelength is the
distance from the peak of
one wave to the peak of
the next wave.
• Frequency refers to the
number of waves that go
by a specific point in one
second. Remember that
electromagnetic energy
waves all travel at the
same speed—the speed
of light
• Measured in
• Hertz or angstrom
27
Current from the outlet
28
Line Compensation
• Most imaging systems are designed to operate
on 220 V. (some 110 V or 440 V)
• However power from the wall is not always
accurate continuously
29
Line Compensation
• Wired to the autotransformer is the line
compensator
• Designed to maintain the accurate voltage
required for consistent production of highquality images
• Today’s line compensators are automatic and
are not displayed on the control panel
30
Line Compensator
31
TRANSFORMERS
(Step Up or Step Down)
• Increases the VOLTAGE going to
the ANODE side of the tube OR
• 110 volts to 110,000 volts
• Decreases the CURRENT going to
the CATHODE side of the tube
• 5 Amps to 50 milliamps
32
Transformers
• Autotransformer
• Step Up
• Step Down
AUTOTRANSFORMER
34
AUTOTRANSFORMER
• RAISES OR LOWERS THE
VOLTAGE
• KVP TAPS LOCATED
• 220 VOLTS INCOMING
CONVERTED FROM
100 T0 300 VOLTS
• VOLTMETER LOCATED OFF OF
AUTOTRANSFORMER
35
Autotransformer – Self Induction
• There is only one wire – but
works like when there are 2
wires =
• The windings are used as
the primary and secondary
coils
• The induced voltage varies
on where the outside wires
are connected (KVP Taps)
36
Autotransformer
• The power for the x-ray imaging system is
delivered first to the autotransformer
• The autotransformer works on the
principle of electromagnetic induction
• It has one winding and one core
• There are a number of connections along
its length
37
Autotransformer
• A’s = primary
connections &
power into the
transformer
• Other connections
allow for variations
of voltages
38
Autotransformer
• Is designed to step up voltage to about
twice the input voltage value
• The increase in voltage is directly related
to the number of turns
• Operates on SELF INDUCTION
39
kVp selection
40
Filaments
Operate at currents of 3 to 6 amperes (A)
• Current comes from
Autotransformer
• Controls the Ma
selection
• Focal Spot Selector
Switch located here
41
• Nearly all x-ray equipment operates from
an incoming line of ____?
• The filament circuit in an x-ray tube
operates at about what 10 volts of current
42
X-ray tube current
or Filament circuit
• A separate circuit crossing from cathode to
anode
• Measured in milliampers (mA)
• What determines how many x-rays are
created?
43
X-ray tube current or Filament
circuit
• # of e- is determined by the temperature of
the filament. The hotter the filament the
more e• Are their any limiting factors to thermionic
emission?
44
mA selection
45
FILAMENT CURRENT
• MA METER vs
• AMMETER ??
• MEASURE THE
MA GOING TO
THE XRAY TUBE
46
RHEOSTAT
• VARIABLE REISITOR
• regulate the amount of resistance in a
circuit
• • mA control is found between the
• AMMETER
47
Generator+ Tranformers
(where the power comes from)
48
TRANSFORMER
• is responsible for supplying a
precise voltage to the x-ray
machine.
49
TRANSFORMER FORMULAS
(STEP UP OR DOWN)
•
•
•
•
•
V = voltage
N = # turns
p = primary
s = secondary
I = current
•
Vp = N p
Vs
Ns
•
Vp = I s
Vs
Ip
•
Np = I s
Ns
Ip
50
Transformers

Autotransformer



Step-up or step-down
Variable Turns Ratio
Controls kV by varying
V sent to HVT
• HV
–
–
–
–
Step-up
Fixed TR > 1 (500 to 1000)
VS > VP
 V to kV
• Filament
–
–
–
–
Step-down
Fixed TR < 1
IS > IP (VS<VP)
I in filament to cause eemission
51
Transformer Efficiency
• By design
–
–
–
–
Shell – most
Closed core
Open core
Air core
• Ideal – no loss
• Reality best = ~95%
induction
• Loss due to
– Cu resistance
•  wire diameter
– Eddy currents
• Laminate core
– Hysteresis
•  core mag. perm.
52
TRANSFORMERS
(Step Up or Step Down)
• Increases the VOLTAGE
going to the ANODE side of
the tube OR
• 110 volts to 110,000 volts
• Decreases the CURRENT
going to the CATHODE side
of the tube
• 5 Amps to 50 milliamps
53
TRANSFORMERS
• STEP UP OR DOWN
• OPEN CORE, CLOSED
CORE OR SHELL TYPE
• ABOUT 95% EFFICIENT
• AUTOTRASFORMER = _____
induction
• Functions to provide
___________
• Both types require AC for
operation
54
INDUCTION
• MUTUAL INDUCTION is the?
• SELF INDUCTION is the
• A transformer must have ________to
produce an electric or magnetic current
?
55
MUTUAL INDUCTION
(STEP UP & DOWN TRANSFORMERS)
56
AC
• Amplitude and polarity of the current vary
with time
• AC – sinusoidal wave
• AC varies amplitude and periodic reversal
of polarity
57
STEP UP TRANSFORMER
58
Electricity
• Is more efficiently tansported over long
distances at low currents ahd high voltage
in order to avoid large power losses
59
Faraday’s law
Regulate the strength of the induced current
• Strength of the Magnet
• Speed of the motion
• Angle of the magnet
• Number of turns on the conduction coil
60
ELECTROMAGNETIC
INDUCTION
3 WAYS TO CREATE MOTION BETWEEN
LINES OF FORCE AND A CONDUCTOR
• Move the conductor through mag field
• Move magnetic lines of force
• Vary the magnetic flux
61
62
FUSES
• PREVENT SHOCK FROM A SHORT
CIRCUIT –
• THE HIGHER CURRENT WILL MELT
THE FUSE – STOPPING THE FLOW
OF ELECTRICITY
• CIRCUIT BREAKERS HAVE
REPLACED FUSES - POWER TOO
HIGH IT WILL CUT OFF – not damage
appliance
63
Question?
What is directly proportional to
the number of x-rays reaching
the IR?
64
How do you convert
msec to sec?
1000ms = 1 sec
100ms = 0.1 sec
10 ms = 0.01 sec
65
mAs Timers
• Monitors the product of mA and exposure
time
• Terminates the exposure when the desired
mAs value is reached
• Located on the secondary side of the highvoltage transformer since actual tube
current must be monitored
66
mAs Timers
• Designed to proved the highest mA for the
shortest exposure
• What is the name of this type of imaging
system generator? Hint: most modern and
most common
67
TIMER SWITCH
• Timer switch
ends exposure
• Timer – length of
exposure set at
control panel
68
Exposure Timers
• The timer circuit is separate from the other
main circuits of the imaging system
• It is a mechanical or electronic device whose
action is to “make” and “break” the high
voltage across the x-ray tube
• This is done on the primary side of the high
voltage transformer.
69
5 types of timing circuits
• 2 most common:
• Electronic Timer
– Computer controlled
– allow a wide range of time intervals
– are accurate to intervals as small as 1 ms
– can be used for rapid serial exposures
70
AEC Control
• AEC measure the quantity of radiation
reaching the IR
• Automatically terminates when the IR has
received enough radiation for desired OD
• Two types are common
71
EXPOSURE & TIMER SWITCH
EXPOSURE SWITCH – BEGINS THE EXPOSURE
Timer switch ends exposure
(unless exposure button is let go prior to end of exposure because of
dead man switch)
 Timer circuit controls number of photons produced.
TYPES:
• MECHANICAL – NO LONGER USED
•
spring wounded, and not very accurate.
• Synchronous timers: synchronous motor w/60 revolutions/second;
min. exposure time is 1/60 sec, and timer in multipulse
• (i.e., 1/30,1/20).
• AEC - TIMERS: monitors time and mA and terminates exposure
when desired mAs is attained. Designed to provide the highest safe
tube current for the shortest time.
• mA METER OR AMMETER
IS located on secondary side of high voltage section.
72
EXPOSURE
SWITCH
TIMER
73
Back up time for AEC
• P 116 Bushong (8th ed)
• Back-up time should be set (electronic
timer to 1.5 the expected exposure)
• Usually set automatically
• Exposure timer as short a 1 ms
• *Reg Rev Q: Manual reset timer = 6 sec (?)
74
APR
• Anatomically Programmed Radiography
(Ch 20)
– Radiologic Technologist selects on the
console a picture of a written description
of the anatomic part to be imaged and
the patient body habitus
– A computer selects the appropriate kVp
and mAs.
75
APR
76
Generator+ Tranformers
(where the power comes from)
77
generator
A generator is a device that converts
mechanical energy into electrical energy
78
X-ray Generator
cathode
anode
F
• Transformers
– HV (step-up)
– Filament (step down)
• Rectification
• Connection to tube
diodes
HV
79
generators
•An AC generator produces a
current that is expressed
mathematically as a
sinusoidal wave ~
• Function to change mechanical energy in
to electrical energy
• Electrical current flowing through a
conductor in one direction is _______
• A battery is a source of direct current
80
GENERATOR
• THAT CREATE AN ALTERNATING
CURRENT ARE CALLED:
• AN ALTERNATOR –
• CONVERT MECHANICAL ENERGY INTO
ELECTRICITY
81
• WHAT MEASURES ELECTRIC
POTIENTAL = VOLT
• CURRENT = AMP
• ELECTRIC CIRCUIT IS THE
PATHWAY FOR ELECTRIC CURRENT
82
High-Voltage Generator
• Responsible for increasing the output
voltage from the autotransformer to the
kVp necessary for x-ray production
• 3 parts: High-voltage transformer, filament
transformer and rectifiers
83
High voltage transformer
• Or step up transformer
• Connected to the Major and Minor kVp
selector
• Increases the volts from the
autotransformer to kilovolts
84
Step Up Transformer
85
Voltage Rectification
• Converts AC to DC current
• During the negative cycle current can only
flow from anode to cathode
• E- must travel cathode to anode – DC
current keeps e- traveling in the correct
direction, cathode to anode
• Attracted to the positive anode
86
Voltage Rectification
87
X-Ray Tube Circuit
88
Rectifier tube failure
2 types
• A diode electron tube
• A vacuum tube
• If one rectifier were malfunctioning the inverted
voltage would not be rectified - therefore the
resulting mAs would be ½ that expected
89
Filament transformer
• Or step down
transformer
• Reduces the
current to the
filament
90
High-Voltage Generation –
converts 110 volts
of AC to kilovolts of DC
• The generator is a FIXED component of
the imaging system, not under the control
of the technologist
• Three basic types: single phase, three
phase, and high frequency
• The generator affects the quality and
quantity of photons produced
91
Single Phase Power
= Pulsating X-ray beam
What are the 2 types?
92
Half-Wave Rectification – photons
are produced & emitted only during
positive cycle
• 100% voltage ripple - quality is the same
as full-wave rectification but quantity is half
93
Full-Wave Rectification – same as
half-wave except there is no dead
time
• Half the exposure time is needed for fullwave than half-wave
94
Three-Phase Power : 6 pulse or 12
pulse
• Results in higher quality and quantity
photons
95
96
High-Frequency: nearly constant
positive voltage
• Less than 1% ripple
• Modern X-ray machines have Highfrequency falling-load generator
– Automatically adjusts to the highest mA at the
shortest exposure time possible
97
High Frequency
98
Voltage Ripple
• Single-phase power has 100% ripple
– Voltage varies from zero to the maximum
value
• Three-phase power has 14% ripple
– Voltage never falls below 86% of the
maximum
• Three-phase, 12 pulse has 4% ripple
– Voltage never falls below 96% of the
99
Voltage Ripple
• High-frequency power has 1% ripple
– Voltage to the tube never falls below 99%
• What does this mean for x-ray photon?
100
Voltage generators (power
supply)
101
102
VOLTAGE RIPPLE
Ripple effect differences
103
? What is missing?
104
• A three-phase generator operates on
three single phase currents, each one
out of phase by _____ degrees
105
Review Handouts
•Circuit Board
•Symbols
•Function
106
107
108
Questions on imaging systems?
109