U.S. patent number 3,746,862 [Application Number 05/093,913] was granted by the patent office on 1973-07-17 for protective circuit for x-ray tube and method of operation.
This patent grant is currently assigned to Picker Corporation. Invention is credited to Daniel F. Lombardo, Walter E. Splain.
United States Patent |
3,746,862 |
Lombardo , et al. |
July 17, 1973 |
PROTECTIVE CIRCUIT FOR X-RAY TUBE AND METHOD OF OPERATION
Abstract
A protective circuit and method of operation for interrupting a
signal which is applied to an X-ray tube when the signal attains a
value which exceeds a maximum rating for the tube. The protective
circuit includes a signal generating circuit for developing a limit
signal which varies in value with respect to time in accordance
with a maximum tube rating signal, a programming circuit for
developing a program signal having a value representative of a
preselected signal to be applied to the X-ray tube, and a
comparator circuit for developing an interrupt signal if the
program signal exceeds the value of the limit signal.
Inventors: |
Lombardo; Daniel F. (Cleveland,
OH), Splain; Walter E. (Woodbridge, OH) |
Assignee: |
Picker Corporation (Cleveland,
OH)
|
Family
ID: |
22241693 |
Appl.
No.: |
05/093,913 |
Filed: |
November 30, 1970 |
Current U.S.
Class: |
378/98;
378/118 |
Current CPC
Class: |
H05G
1/54 (20130101) |
Current International
Class: |
H05G
1/54 (20060101); H05G 1/00 (20060101); H05g
001/26 () |
Field of
Search: |
;250/93,103,95 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Lawrence; James W.
Assistant Examiner: Church; C. E.
Claims
Having thus described my invention, I claim:
1. In an X-ray apparatus a protective circuit for limiting the
value of a signal applied to an X-ray tube and comprising:
signal generating means for generating a limit signal which varies
in value as a function of elapsed exposure time in accordance with
the value of a maximum tube rating signal;
programming circuit means for developing a program signal having a
value representative of the value of a preselected signal to be
applied to said X-ray tube;
comparator means for monitoring the limit and program signals for
developing an output signal when the value of a said limit signal
attains a predetermined value with respect to the value of a said
program signal; and,
actuatable circuit means coupled to a said comparator circuit means
for, upon receipt of a said output signal, interrupting a signal
which is applied to said X-ray tube.
2. An apparatus as defined in claim 1 wherein said programming
means includes variable circuit means for altering the value of a
said program signal in accordance with the value of the voltage to
be applied to said X-ray tube.
3. An apparatus as defined in claim 1 wherein said signal
generating means includes circuit means for generating a said limit
signal which decreases in value with respect to time in accordance
with the value of a decreasing maximum power rating with respect to
exposure time of said X-ray tube.
4. An apparatus as defined in claim 3 wherein said signal
generating circuit means includes variable control means for
varying the rate at which a said limit signal decreases with
respect to time.
5. An apparatus as defined in claim 4 wherein said programming
means includes variable circuit means for altering the value of a
said program signal in accordance with the value of the voltage to
be applied to said X-ray tube.
6. An apparatus as defined in claim 4 wherein said programming
means includes variable circuit means for altering the value of a
said program signal in accordance with the value of the current to
be applied to said X-ray tube.
7. An apparatus as defined in claim 4 wherein said programming
means includes first variable circuit means for altering the value
of a said program signal in accordance with the value of the
voltage to be applied to said X-ray tube; and,
second variable means for altering the value of a said program
signal in accordance with the value of the current to be applied to
said X-ray tube.
8. An apparatus as defined in claim 1 wherein said signal
generating means includes circuit means for generating a said limit
signal which decreases in value with respect to time and which
varies in the rate of decrease in value with respect to time.
9. An apparatus as defined in claim 8 wherein said programming
means includes first variable circuit means for altering the value
of a said program signal in accordance with the value of the
voltage to be applied to said X-ray tube; and,
second variable means for altering the value of a said program
signal in accordance with the value of the current to be applied to
said X-ray tube.
10. An apparatus as defined in claim 1 wherein said signal
generating means includes circuit means for generating a said limit
signal which decreases in amplitude by a predetermined amount for N
intervals of time where N is equal or greater than five.
11. An apparatus as defined in claim 1 wherein said signal
generating means includes circuit means for generating a said limit
signal having a plurality of timed portions each being of a
different amplitude.
12. An apparatus as defined in claim 11 wherein said programming
means includes variable circuit means for altering the value of a
said program signal in accordance with the value of the current to
be applied to said X-ray tube.
13. An apparatus as defined in claim 11 wherein said programming
means includes first variable circuit means for altering the value
of a said program signal in accordance with the value of the
voltage to be applied to said X-ray tube; and,
second variable means for altering the value of a said program
signal in accordance with the value of the current to be applied to
said X-ray tube.
14. An apparatus as defined in claim 1 wherein said signal
generating means includes a plurality of circuit means each for
generating a said limit signal which varies in value with respect
to time in accordance with one of a plurality of different
predetermined tube rating signals;
actuatable switch means for selectively developing a pattern of
control signals representative of a desired one of said plurality
of predetermined tube rating signals; and,
second actuatable circuit means coupled to said actuatable switch
means for, upon receipt of a pattern of control signals, actuating
a signal generating circuit means corresponding to said received
pattern of control signals to thereby generate a said limit signal
which varies in accordance with a selected one of said plurality of
predetermined tube rating signals.
15. An apparatus as defined in claim 14 wherein said programming
means includes variable circuit means for altering the value of a
said program signal in accordance with the value of the current to
be applied to said X-ray tube.
16. An apparatus as defined in claim 14 wherein said programming
means includes first variable circuit means for altering the value
of a said program signal in accordance with the value of the
voltage to be applied to said X-ray tube; and,
second variable means for altering the value of a said program
signal in accordance with the value of the current to be applied to
said X-ray tube.
17. An apparatus as defined in claim 1 wherein said signal
generating means includes a timer means for developing a plurality
of patterns of signals each representative of the elapsed time;
a plurality of circuit means each for generating a limit signal
which varies in accordance with one of a plurality of predetermined
time functions; and,
second actuatable circuit means coupled to said timer means for,
upon receipt of one of a said plurality of patterns of signals,
actuating a signal generating circuit means corresponding to a said
received pattern of signals to thereby generate a limit signal
which varies in accordance with a selected one of said plurality of
time functions.
18. An apparatus as defined in claim 17 wherein said programming
means includes variable circuit means for altering the value of a
said program signal in accordance with the value of the current to
be applied to said X-ray tube.
19. An apparatus as defined in claim 18 wherein said programming
means includes first variable circuit means for altering the value
of a said program signal in accordance with the value of the
voltage to be applied to said X-ray tube; and,
second variable means for altering the value of a said program
signal in accordance with the value of the current to be applied to
said X-ray tube.
20. A control system for indicating that the input power which is
applied to an X-ray tube has exceeded a level defined by a maximum
tube power rating which varies in value with respect to time and
comprising;
tube limit signal generating means for developing a limit signal
which varies in value as a function of elapsed exposure time in
accordance with variations in a said maximum power rating of the
tube with respect to time;
variable programming circuit means for developing a program signal
having a value representative of the value of voltage and current
signals applied to said X-ray tube;
comparator means for monitoring the limit and program signals for
developing an output signal when the value of a said limit signal
attains a predetermined value with respect to the value of a said
program signal; and
indicator circuit means coupled to a said comparator circuit means
for, upon receipt of a said output signal, developing an output
indication that the tube input power has exceeded the maximum power
rating.
21. An apparatus as defined in claim 20 wherein said variable
program circuit means includes first variable circuit means for
developing a first signal having a value representative of the
value of a voltage potential to be applied to said X-ray tube;
second variable circuit means for developing a second signal having
a value representative of the value of a current to be applied to
said X-ray tube; and,
resolving circuit means coupled to said first and second circuit
means for developing a said program signal having a value
representative of the values of said voltage potential and said
current to be applied to said X-ray tube.
22. An apparatus as defined in claim 20 wherein said variable
program circuit means includes first variable circuit means for
developing a first signal having a value representative of the
value of a current to be applied to said X-ray tube;
second variable circuit means for developing a second signal having
a value representative of the value of a current to be applied to
said X-ray tube; and,
resolving circuit means coupled to said first and second circuit
means for developing a said program signal having a value
representative of the values of said current to be applied to said
X-ray tube.
23. An apparatus as defined in claim 20 wherein said tube limit
signal generating means includes timer means for developing a
plurality of patterns of control signals each representative of the
elapsed exposure time;
a plurality of signal generating circuits each for developing a
limit signal which decreases in value at a different predetermined
rate;
actuator circuit means coupled to said timer means for, upon
receipt of said plurality of predetermined patterns of signals,
actuating a corresponding one of said plurality of signal
generating circuits to thereby develop a limit signal which
decreases in value at a corresponding predetermined rate.
24. An apparatus as defined in claim 23 wherein said timer means
includes time accumulator means for developing a plurality of
patterns of signals each of which take the form of binary coded
decimal signals; and matrix circuit means for converting said
binary coded decimal signals to a plurality of patterns of signals
each of which takes the form of analog signals.
25. In an X-ray apparatus a protective circuit for indicating that
the value of a signal applied to an X-ray tube has reached a
time-varying maximum tube limit rating and comprising:
an X-ray tube;
a voltage supply source coupled to said X-ray tube for applying an
operating signal to said X-ray tube;
means for varying the value of a said operating signal applied to
said X-ray tube;
waveform generating means for developing a limit signal having a
value which decreases as a predetermined function with respect to
elapsed exposure time for a preselected period of time;
monitor circuit means for developing a signal having a value
representative of a said operating signal applied to said X-ray
tube;
comparator means coupled to said waveform generating means and said
circuit means for developing an output signal when the value of the
limit signal decreases to a predetermined level relative to the
monitor signal; and,
indicator circuit means coupled to said comparator circuit means
for, upon receipt of a said output signal, developing an output
indication that the operating signal has reached a maximum limit
value.
26. An apparatus as defined in claim 25 wherein said waveform
generating means includes circuit means for generating a said limit
signal which decreases in value with respect to time and which
varies in the rate of decrease in value with respect to time.
27. An apparatus as defined in claim 25 wherein said waveform
generating means includes a plurality of circuit means each for
generating a said limit signal which varies in value with respect
to time in accordance with one of a plurality of different
predetermined tube rating signals;
actuatable switch means for selectively developing a pattern of
control signals representative of a desired one of said plurality
of predetermined tube rating signals; and,
second actuatable circuit means coupled to said actuatable switch
means for, upon receipt of a pattern of control signals, actuating
a signal generating circuit means corresponding to said received
pattern of control signals to thereby generate a said limit signal
which varies in accordance with a selected one of said plurality of
predetermined tube rating signals.
28. In an X-ray apparatus a protective circuit for monitoring the
value of a signal applied to an X-ray tube from exceeding a
time-varying maximum tube limit rating and comprising:
signal generating means for generating a limit signal which
decreases in value as a predetermined, non-linear function with
respect to elapsed exposure time in accordance with the value of a
time-varying maximum tube rating;
programming circuit means for developing a program signal having a
value representative of the value of a preselected signal applied
to a said X-ray tube;
comparator means for monitoring the limit and program signals for
developing an output signal when the value of a said limit signal
decreases to a predetermined value relative to the value of a said
program signal; and,
indicator circuit means coupled to said comparator circuit means
for, upon receipt of a said output signal, developing an output
indication that the operating signal has reached a maximum limit
value.
29. An apparatus as defined in claim 28 wherein said signal
generating means includes a timer means for developing a plurality
of patterns of signals each representative of the elapsed time;
a plurality of circuit means each for generating a limit signal
which varies in accordance with one of a plurality of predetermined
time functions; and,
second actuatable circuit means coupled to said timer means for,
upon receipt of one of a said plurality of patterns of signals,
actuating a signal generating circuit means corresponding to a said
received pattern of signals to thereby generate a limit signal
which varies in accordance with a selected one of said plurality of
time functions.
30. An apparatus as defined in claim 28 wherein said signal
generating means includes a plurality of circuit means each for
generating a said limit signal which varies in value with respect
to time in accordance with one of a plurality of different
predetermined tube rating signals;
actuatable switch means for selectively developing a pattern of
control signals representative of a desired one of said plurality
of predetermined tube rating signals; and,
second actuatable circuit means coupled to said actuatable switch
means for, upon receipt of a pattern of control signals, actuating
a signal generating circuit means corresponding to said received
pattern of control signals to thereby generate a said limit signal
which varies in accordance with a selected one of said plurality of
predetermined tube rating signals.
31. A method of protecting an X-ray tube in an X-ray apparatus
comprising the steps of:
generating a limit signal which decreases in value with respect to
elapsed exposure time in accordance with a decrease in the value of
the amplitude with respect to exposure time of a maximum signal
which may be applied to the X-ray tube;
developing a program signal having a value representative of the
value of a preselected signal to be applied to said X-ray tube;
comparing the values of the limit signal and program signal;
developing an output signal if the value of said program signal
exceeds the value of said limit signal; and,
interrupting a signal applied to said X-ray tube in response to the
receipt of an output signal.
Description
CROSS REFERENCES TO RELATED PATENT APPLICATIONS AND PATENTS
U.S. Patent application Ser. No. 743,421, to Walter E. Splain,
entitled "X-Ray Tube Kilovoltage Control System", filed July 9,
1968, and assigned to the same assignee as the present
invention.
U.S. Pat. No. 3,284,631 to Walter E. Splain, entitled "Device for
Determining the Current-Time Output of an X-Ray Tube", issued on
Nov. 8, 1966, and assigned to the same assignee as the present
invention.
U.S. Pat. No. 3,502,877 to Walter E. Splain, entitled
"Grid-Controlled X-Ray Tube Control System", issued Mar. 24, 1970
and assigned to the same assignee as the present invention.
U.S. Pat. No. 3,521,067, to Walter E. Splain, entitled "X-Ray Tube
Current Stabilization", issued July 21, 1970 and assigned to the
same assignee as the present invention.
BACKGROUND OF THE INVENTION
This invention pertains to the art of electrical circuits for
limiting the value of a signal applied to an electronic device, and
more particularly, to a protection circuit for interrupting a
signal which is applied to an X-ray tube if the value of the signal
exceeds a predetermined value.
In the operation of X-ray equipment, a very high voltage potential
signal, for example 125 kilovolts, is applied to the anode of the
X-ray tube. When operated at this voltage potential, a current of
250 milliamperes may flow through the X-ray tube. The resultant
input power applied to the tube will then be in excess of 30,000
watts. While this input power level may be maintained for a
relatively short time duration exposure, i.e., on the order of 0.05
seconds, a longer exposure time will result in permanent damage to
the X-ray tube.
X-ray tube protection circuits for use in most radiographic modes
of operation have heretofore included circuitry for monitoring the
value of the voltage potential signal which is applied to the X-ray
tube, and if this signal exceeds a predetermined constant level,
the signal is removed from the tube. These protective circuits have
been satisfactory to a large extent; however, these circuits do not
take into account the fact that the maximum input power which may
be applied to an X-ray tube decreases as the elapsed exposure time
increases.
Also, in the operation of X-ray equipment, the high potential
signal applied to the anode of the tube is adjusted to vary the
intensity of X-rays which are produced by the tube. With different
X-ray procedures, i.e., high speed, low speed, large focal spot,
small focal spot, overtable operation and undertable operation,
there are different requirements as to X-ray intensity and exposure
time.
In certain X-ray procedures it is desirable to apply a very high
intensity level of X-rays for an extremely short period of time.
With the above-described tube protection circuits, it was not
possible to apply a signal to the tube having a value great enough
to produce the desired X-ray intensity level because the protection
circuit would remove the signal from the tube since the signal
exceeded the predetermined level.
Also, if the exposure time of the tube is increased beyond a given
period of time, the tube will be permanently damaged, even when
operated at a conservative potential level, in view of the fact
that the maximum input power which may be applied to an X-ray tube
decreases rapidly with respect to time. This type of tube damage
will occur in the phototimed mode of operation if an X-ray
technician merely inadvertently leaves a lead apron on the X-ray
table at a position in the path of the X-rays so as to prevent the
phototiming circuit from deenergizing the X-ray tube.
It has been found to be highly desirable to compare the value of
the signal applied to the X-ray tube not merely with a constant
tube limit signal, but to instead compare the value of the signal
applied to the X-ray tube to a limit signal which varies in value
in accordance with a limiting parameter of the X-ray tube, such as
the maximum input power which may be applied to the tube.
SUMMARY OF THE INVENTION
The present invention is directed toward a protective circuit and
method of operation for interrupting the operation of an X-ray tube
whenever a signal applied to the tube exceeds a maximum
time-varying rating for the tube, thereby overcoming the noted
disadvantages, and others, of such previous systems.
In accordance with one aspect of the present invention, there is
provided in an X-ray apparatus a protective circuit for limiting
the value of a signal applied to an X-ray tube. The protective
circuit includes a signal generating circuit for generating a limit
signal which varies in value with respect to time in accordance
with the value of a maximum tube rating signal, a programming
circuit for developing a program signal having a value
representative of the value of a preselected signal to be applied
to the X-ray tube, and a comparator circuit for monitoring the
limit and program signals for developing an output signal whenever
the value of the limit signal attains a predetermined value with
respect to the value of the program signal.
In accordance with another aspect of the present invention, the
signal generating circuit includes a circuit for generating a limit
signal which decreases in value with respect to time in accordance
with the value of a decreasing maximum power rating with respect to
exposure time of the X-ray tube.
In accordance with another aspect of the present invention, the
signal generating circuit includes a variable control for varying
the rate at which the limit signal decreases with respect to
time.
In accordance with another aspect of the present invention, the
signal generating circuit includes a circuit for generating a limit
signal which decreases in amplitude by a predetermined amount at
each interval for N intervals of time where N is equal to or
greater than five.
In accordance with still another aspect of the present invention,
the signal generating circuit includes a circuit for generating a
limit signal having a plurality of timed portions each being of a
different amplitude.
In accordance with another aspect of the present invention, the
signal generating circuit includes an actuatable switching circuit
for selectively developing a pattern of control signals
representative of a desired one of a plurality of predetermined
tube rating signals, and a second actuatable circuit coupled to the
actuatable switching circuit for, upon receipt of a pattern of
control signals, actuating the signal generating circuit
corresponding to the received pattern of control signals to thereby
generate a limit signal which varies in accordance with a selected
one of the plurality of predetermined tube rating signals.
In accordance with still another aspect of the present invention,
the programming circuit includes a variable circuit for altering
the value of the programmed signal in accordance with the value of
a voltage to be applied to the X-ray tube.
In accordance with still another aspect of the present invention,
the programming circuit includes a variable circuit for altering
the value of the program signal in accordance with the value of a
current and/or a voltage to be applied to the X-ray tube.
In accordance with another aspect of the present invention, there
is provided a method of protecting an X-ray tube in an X-ray
apparatus. The method includes the steps of generating a limit
signal which decreases in value with respect to time in accordance
with a decrease in the value of the amplitude with respect to
exposure time of a maximum signal which may be applied to the X-ray
tube, developing a program signal having a value representative of
the value of a preselected signal to be applied to the X-ray tube,
and comparing the values of the limit signal and the program signal
and developing an output signal if the value of the program signal
exceeds the value of the limit signal.
In accordance with another aspect of the present invention, the
method includes the step of interrupting the signal applied to the
X-ray tube in response to the receipt of an output signal.
It is therefore an object of the present invention to provide a
protective circuit for an X-ray tube for interrupting the operation
of the X-ray tube when the signal applied to the tube exceeds a
maximum rating for the tube.
Another object of the present invention is to provide a protective
circuit for an X-ray tube which monitors the value of a signal to
be applied to the tube and also monitors a time-varying signal
representative of a maximum rating for the tube.
Another object of the present invention is to provide in an X-ray
system a control circuit for interrupting the signal which is
applied to an X-ray tube whenever the value of that signal exceeds
the value of a maximum input power rating for the tube.
A further object of the present invention is to provide a
protective circuit for interrupting the operation of an X-ray tube
whenever the input power applied to the tube exceeds a
predetermined time-varying maximum power rating for the tube.
A further object of the present invention is to provide a
protective circuit for developing an output indication whenever the
value of a signal applied to the X-ray tube exceeds the value of a
maximum rating for the tube.
Another object of the present invention is to provide a method of
operation of a protective circuit for interrupting a signal applied
to an X-ray tube whenever that signal attains a value in excess of
a maximum rating for the tube.
These and other objects and advantages of the invention will become
apparent from the following description of the preferred embodiment
of the invention as read in conjunction with the accompanying
drawings and in which:
BRIEF DESCRIPTION OF DRAWINGS
FIG. 1 is an electrical block diagram illustrating in basic form
the X-ray tube protective system of the present invention;
FIGS. 2 through 5 are electrical schematic diagrams illustrating in
more detail the circuitry of the protective system shown in FIG. 1;
and,
FIG. 6 is a graphical representation of a typical curve
representative of the maximum input power to be applied to an X-ray
tube as a function of exposure time.
DESCRIPTION OF A PREFERRED EMBODIMENT
FIG. 1 illustrates an X-ray tube protective system 10 which is
generally comprised of circuitry for developing a tube limit
signal, circuitry for developing another signal having a value
representative of the signal to be applied to the X-ray tube, and a
comparator circuit 12 for developing an interrupt signal whenever
the X-ray tube representative signal exceeds the value of the tube
limit signal.
More particularly, the tube limit signal generating circuitry
includes a tube limit decoding circuit 14 for developing a pattern
of signals representative of the desired mode of operation, i.e.,
large focal spot, small focal spot, single speed, triple speed,
overtable operation, and undertable operation. The pattern of
signals developed by the tube limit decoding circuit 14 is applied
to a tube limit adjustment circuit 16, which is in turn coupled to
a tube limit curve generator 18. Also, a time accumulator circuit
20 having a plurality of output circuits for developing a pattern
of binary coded decimal signals representative of elapsed time is
coupled to a time decoding matrix circuit 22. The decoding matrix
circuit 22 is in turn coupled to the tube limit curve generator
18.
Thus, the tube limit curve generator 18 generates a signal which
varies in value with respect to time in accordance with the value
of a maximum tube power rating. This signal is applied to one of
the input terminals of the comparator circuit 12.
The circuitry for developing a signal having a value representative
of the signal to be applied to the X-ray tube generally includes a
first variable resistor arrangement VR-1 in which the resistance
may be varied in accordance with the selected voltage potential to
be applied to the X-ray tube, and a second variable resistance
arrangement VR-2 in which the resistance may be varied in
accordance with the value of the current to be applied to the X-ray
tube. The resistive arrangements VR-1, VR-2 are connected in series
between a positive 20 volt voltage potential source and a negative
20 volt voltage potential source. The junction point between the
resistance arrangement VR-1 and the resistance arrangement VR-2 is
connected directly to the other input terminal of the comparator
circuit 12.
The output terminal of the comparator circuit 12 is connected
through an amplifier 24 including a feedback path 26 to the input
terminal of an inverter 28. The output terminal of the inverter 28
is connected to one of the input terminals of a NAND gate 30. The
other input terminal of the NAND gate 30 is connected to circuitry
for developing a signal representative of an exposure, and the
output terminal of the NAND gate 30 is connected to the X-ray tube
supply source. Thus, when a signal is developed by the comparator
circuit 12 indicative of a tube overload condition, an output
signal is developed by the NAND gate 30 to interrupt the X-ray tube
supply source thereby removing the high potential signal from the
X-ray tube.
The output terminal of the NAND gate 30 is also coupled through an
inverter 32 to one terminal of a monitoring lamp L-1. The other
terminal of lamp L-1 is connected directly to a positive 28 volt
supply source. Thus, the monitoring lamp L-1 is energized whenever
an interrupt signal is applied to the X-ray tube supply source.
The output terminal of the tube limit generator 18 is connected
through a resistor R1 to the positive 20 volt supply source in
order to maintain this terminal at a fixed operating potential
prior to the current drain applied to this terminal by the tube
limit curve generator 18 as the tube limit signal is developed.
Also, a backup time drive signal is applied to the time decoding
matrix circuit 22 by a conductor AA which is coupled to the output
terminal of an amplifier 34. The input terminal of the amplifier 34
is connected through a resistor R2 to the positive 20 volt supply
source.
Reference is now made to FIG. 2 which illustrates in more detail
the comparator circuit 12, the amplifier and feedback circuits 24,
26, the inverter circuits 28, 32, the NAND gate 30, and the
amplifier 34, as well as the resistance arrangements VR-1, VR-2.
More particularly, the resistance arrangement VR-1 generally
comprises a plurality of resistors R3, R4, R5, R6 each having one
terminal connected to a common junction point T1. The other
terminals of the resistors R3, R4, R5, R6 are respectively
connected to one of the terminals of a plurality of single-pole,
single-throw switches S3, S4, S5, S6. The other terminals of the
switches S3, S4, S5, S6 are connected in common to the positive 20
volt supply source.
Similarly, the resistance arrangement VR-2 includes a plurality of
resistors R7, R8. R9, R10 each having one terminal connected in
common to a junction point T2. The other terminals of the resistors
R7, R8, R9, R10 are respectively connected to one of the terminals
of a corresponding number of single-pole, single-throw switches S7,
S8, S9, S10. The other terminals of the switches S7, S8, S9, S10
are connected in common to the negative 20 volt supply source.
The junction point T1 of the resistance arrangement VR-1 is
connected directly to the base of a PNP transistor Q1 in the
comparator circuit 12. The base of the transistor Q1 is also
connected directly to the collector of an NPN transistor Q2, and
through a capacitor C1 to an output terminal AE.
The collector of transistor Q1 is connected through a resistor R3
to an output terminal AD, and is also connected directly to the
base of a transistor Q3 in the amplifier and feedback circuits 24,
26. The emitter of transistor Q1 is connected to the cathode of a
diode D1 having its anode connected in common with the anode of a
diode D2. The cathode of the diode D2 is connected directly to the
emitter of a PNP transistor Q4
The collector of transistor Q4 is connected directly to an output
terminal AC, and the base of this transistor is connected through
the resistor R1 to the positive 20 volt supply source and is also
connected directly to the output terminal AE. The commonly
connected anodes of the diodes D1, D2 are connected to the
collector of a PNP transistor Q5 having its base connected through
a resistor R4 to the positive 28 volt supply source. The base of
the transistor Q5 is connected to the anode of a Zener diode Z1
having its cathode connected directly to the positive 28 volt
supply source. Also, the base of transistor Q5 is connected through
a resistor R5 to the output terminal AC.
The emitter of the transistor Q2 is connected directly to the
junction point T2 of the resistance arrangement VR-2 and the base
of this transistor is connected directly to the common contact of a
single-pole, double-throw relay 36. The normally-closed contact of
the relay 36 is connected through a resistor R6 to the positive 20
volt supply source and the normally-open contact of the relay 36 is
connected through a resistor R7 to the positive 20 volt supply
source. Also connected to the normally-open contact of the relay 36
is the cathode of a Zener diode Z2 having its anode connected
directly to the negative 20 volt supply source. Similarly, the
cathode of a Zener diode Z3 is connected to the normally-closed
contact of relay 36 and its anode is connected directly to the
negative 20 volt supply source. One terminal of the relay coil 38
of the relay 36 is connected through a resistor R8 to the positive
20 volt supply source and the other terminal is connected to a
common junction point T3. Also, a diode D3, polarized as shown in
FIG. 2, is connected across the terminals of the coil 38 of relay
36.
The common junction point T3 is connected through a diode D4,
polarized as shown in FIG. 2, to an output terminal AB. The output
terminal is also connected through a single-pole, single-throw
switch UTL-1 to ground. The switch UTL-1, upon being closed,
actuates circuitry in the tube limiting decoding circuit 14 for
undertable and large focal spot operation.
The junction point T3 is also connected through a diode D5,
polarized as shown in FIG. 2, and a single-pole, single-throw
switch UTS-1 to ground. The switch UTS-1, upon being closed,
actuates circuitry in the tube limit decoding circuit 14 for
undertable and small focal spot operation.
The collector of transistor Q3 in the amplifier and feedback
circuits 24, 26 is connected through a resistor R9 to the base of a
PNP transistor Q6, and the emitter of transistor Q3 is connected
directly to ground. The base of transistor Q3 is also connected
through a resistor R10 to the collector of the transistor Q6.
The emitter of transistor Q6 is connected directly to the positive
20 volt supply source, the base of this transistor is connected
through a resistor R11 to the positive 20 volt supply source, and
the collector of this transistor is connected through a resistor
R12 to ground. Also, the collector of transistor Q6 is connected
through a resistor R13 to the base of an NPN transistor Q7 having
its emitter connected directly to ground. The collector of the
transistor Q7 is connected through a diode D6, polarized as shown
in FIG. 2, to a junction point T4 in the inverter 28.
The junction point T4 in the inverter 28 is connected through a
resistor R14 to the positive 20 volt supply source and through a
resistor R15 to the base of an NPN transistor Q8. The collector of
the transistor Q8 is connected through a resistor R16 to the
positive 20 volt supply source, the emitter of this transistor is
connected directly to ground, and the base of this transistor is
also connected through a resistor R17 to the output terminal AD.
Finally, the collector of the transistor Q8 provides a common
junction point T5 which is connected to the collector of an NPN
transistor Q9 in the NAND gate 30 and to the cathode of a diode D7
in the inverter 32.
The anode of the diode D7 is connected through a resistor R18 to
the base of an NPN transistor Q10 having its emitter connected
directly to ground and its collector connected to one terminal of
the monitor lamp L-1. The other terminal of the lamp L-1 is
connected directly to the positive 28 volt supply source. The base
of transistor Q10 is also connected through a resistor R19 to the
output terminal AD, and the anode of the diode D7 is also connected
through a resistor R20 to the positive 20 volt supply source.
The base of the transistor Q9 in the NAND gate 30 is connected
through a resistor R22 to the output terminal AD and is also
connected through a pair of series-connected resistors R23, R24 to
the positive 20 volt supply source. The junction point between the
series-connected resistors R23, R24 is connected to the anode of a
diode D8 having its cathode connected to circuitry within the X-ray
apparatus for developing an exposure signal. The base of transistor
Q9 is connected directly to ground and the collector of this
transistor is also connected to the X-ray tube supply source and to
the anode of a diode D9. The cathode of diode D9 is connected
directly to ground. In addition, the output terminal AD is
connected directly to a negative 8 volt supply source.
The cathode of diode D9 is connected to an NPN transistor Q10 in
the amplifier circuit 34. The base of this transistor is connected
through the resistor R2 to the positive 20 volt supply source, the
collector of this transistor is connected directly to the positive
20 volt supply source, and the emitter of this transistor is
connected to an output terminal AA. Finally, a resistor R25 is
connected between the output terminal AA of the amplifier circuit
34 and ground.
Reference is now made to FIG. 3 which illustrates in more detail
the circuitry within the time decoding matrix circuit 22 and the
circuit connections between the matrix circuit 22 and the timer
accumulator circuit 20. More particularly, the timer accumulator
circuit 20, upon being actuated, generates a pattern of binary
coded decimal signals representative of the elapsed time. In other
words, once an exposure cycle is commenced, the timer accumulator
circuit 20 begins a counting sequence with the pattern of binary
signals applied to the output terminals being changed at
preselected intervals of time. The pattern of signals which appears
on the output terminals of the timer accumulator circuit 20 for
each time interval is set forth in Table I below.
The output terminals of the timer accumulator circuit 20 are
connected to the input terminals DA through DQ of the time decoding
matrix circuit 22. As illustrated in FIG. 3, the decoding matrix
circuit 22 generally comprises a digital-to-analog matrix for
actuating selected ones of the nine NPN transistors Q11 through
Q19.
More particularly, the input terminal BA of the decoding matrix
circuit 22 is connected to the cathode of a diode D10 having its
anode connected to a junction point T5. Seven diodes D11 through
D17 have their anodes connected to the junction point T5 and their
cathodes respectively connected to the input terminals BC, BE, BG,
BI, BK, BM, BO. The junction point T5 is connected to the cathode
of a Zener diode Z11 and is also connected through a resistor R26
to the output terminal AA.
Similarly, the input terminal BB of matrix circuit 22 is connected
to the cathode of a diode D18 having its anode connected to a
junction point T6. The junction point T6 is connected to the
cathodes of seven diodes D19 through D25 having their anodes
respectively connected to input terminals BC, BE, BG, BI, BK, BM,
BO. The junction point T6 is connected to the cathode of a Zener
diode Z10 and is also connected through a resistor R27 to the
terminal AA.
In a like manner, the input terminal BD of matrix circuit 22 is
connected to the cathode of a diode 26 having its anode connected
to a junction point T7. The junction point T7 is in turn connected
to the anodes of six diodes D27 through D32 having their cathodes
respectively connected to the input terminals BE, BG, BI, BK, BM,
BO. Also, the junction point T7 is connected directly to the
cathode of a Zener diode D9 and through a resistor R28 to the
terminal AA.
The input terminal BF is connected to the cathode of a diode D33
having its anode connected to a junction point T8, which is in turn
connected to the cathode of a Zener diode Z8. The junction point T8
is also connected to the anode of five diodes D34 through D38
having their cathodes respectively connected to the input terminals
BG, BI, BK, BM, BO. In addition, the junction point T8 is connected
through a resistor R29 to the terminal AA.
Similarly, the input terminal BH is connected to the cathode of a
diode D39 having its anode connected to a junction point T9 which
is in turn connected to the cathode of a Zener diode Z7. The
junction point T9 is also connected to the anode of four diodes D40
through D43 having their cathodes respectively connected to the
terminals BI, BK, BM, BO. In addition, the junction point T9 is
connected through a resistor R30 to the common terminal AA.
In a like manner, the input terminal BJ is connected to the cathode
of a diode D44 having its anode connected to a junction point T10
which is in turn connected to the cathode of a Zener diode Z6. The
junction point T10 is connected to the anode of three diodes D45,
D46, D47, and is also connected through a resistor R31 to the
common terminal AA. The cathodes of diodes D45, D46, D47 are
respectively connected to the input terminals BK, BM, BO.
The input terminal BL of the matrix circuit 22 is connected to the
cathode of a diode D48 having its anode connected to the cathode of
a Zener diode Z5 and to the anodes of a pair of diodes D49, D50.
The cathodes of diodes D49, D50, are respectively connected to the
input terminals BM, BO. In addition, the anode of diode B48 is
connected through a resistor R32 to the common terminal AA.
The input terminals BM, BO are respectively connected to the
cathodes of a pair of diodes D51, D52 having their anodes connected
in common to the cathode of a Zener diode Z4. The anodes of the
diodes D51, D52 are connected through a resistor R33 to the common
terminal AA.
Finally, the common terminal AA is connected through a resistor R34
to the anodes of eight diodes D53 through D60 having their cathodes
respectively connected to the input terminals BQ, BN, BL, BJ, BH,
BF, bd, BB. The anodes of these diodes are also connected to the
cathode of a Zener diode Z12.
The anodes of the Zener diodes Z4, Z5, Z6, Z7, Z8, Z9, Z10, Z11,
Z12 are respectively connected to the base terminals of transistors
Q19, Q18, Q17, Q16, Q15, Q14, Q13, Q12, Q11. In addition, the base
terminals of these transistors are respectively connected through
the resistors R35 through R43 to a negative 8 volt supply source.
The emitters of the transistors Q11 through Q19 are connected
directly to the negative 8 volt supply source. The collectors of
transistors Q11 through Q14 are respectively connected through
resistors R44 through R47 to a common terminal T11 which provides
an output terminal AH. Similarly, the collectors of transistor Q15,
Q16, Q17, are respectively connected through resistors R48, R49,
R50 to a common terminal T12 which provides an output terminal AG.
Finally, the collectors of transistors Q18, Q19 are respectively
connected through resistors R51, R52 to a common terminal T13 which
provides an output terminal AF.
Reference is now made to FIG. 4 which illustrates in more detail
the circuitry of the time limit adjustment circuit 16 and the time
limit curve generator 18. More particularly, the time limit
adjustment circuit 16 includes eight input terminals AL, AM, AN,
AO, AS, AT, AW, AY which are each connected to the stationary
contacts of a set of four potentiometers.
Thus, input terminal AO is connected to the commonlyconnected
stationary contact of a set of four potentiometers P1, P2, P3, P4;
the input terminal AN is connected to the stationary contact of a
set of potentiometers P5, P6, P7, P8; the input terminal AM is
connected to the stationary contacts of a set of four
potentiometers P9, P10, P11, P12; and the input terminal AL is
connected to the commonly-connected stationary contacts of a set of
four potentiometers P13, P14, P15, P16.
Similarly, the input terminal AF is connected to the
commonly-connected stationary contact of a set of four
potentiometers P17, P18, P19, P20; the input terminal AT is
connected to the commonly-connected stationary contact of a set of
four potentiometers P21, P22, P23, P24; the input terminal AW is
connected to the commonly-connected stationary contact of a set of
four potentiometers P25, P26, P27, P28; and the input terminal AY
is connected to the commonly-connected stationary contact of a set
of four potentiometers P29, P30, P31, P32. The other stationary
contacts of the potentiometers P1, P2, P3, P4 are respectively
connected to the other stationary contacts of the pontentiometers
P17, P18, P19, P20. Similarly, the other stationary contacts of the
potentiometers P5, P6, P7, P8 are respectively connected to the
other stationary contacts of the potentiometers P21, P22, P23, P24.
In a like manner, the other stationary contacts of the
potentiometers P9, P10, P11, P12 are respectively connected to the
other stationary contacts of the potentiometers P25, P26, P27, P28.
Finally, the other stationary contacts of the potentiometers P13,
P14, P15, P16 are respectively connected to the other stationary
contacts of the potentiometers P29, P30, P31, P32.
The movable contacts of the potentiometers P1 through P32 are
respectively connected to the anodes of a corresponding member of
diodes D61 through D92. Also, the cathodes of the diodes D61
through D76 are respectively connected to the cathode of the diodes
D77 through D92.
As illustrated, the tube limit curve generator 18 includes four NPN
transistors Q20, Q21, Q22, Q23 having their collectors connected in
common to an output terminal AE. The base terminal of transistor
Q20 is connected through a resistor R53 to the negative 8 volt
supply source and is also connected to the cathodes of diodes D61,
D65, D69, D73. Similarly, the base of transistor Q21 is connected
through a resistor R54 to the negative 8 volt supply source and is
also connected to the cathodes of the diodes D62, D66, D70, D74. In
a like manner, the base of transistor Q22 is connected through a
resistor R55 to the negative 8 volt supply source and is also
connected to the cathodes of the diodes D63, D67, D71, D75.
Finally, the base of transistor Q3 is connected through a resistor
R56 to the negative 8 volt supply source and is also connected to
the cathodes of the diodes D64, D68, D72, D76.
The negative 8 volt supply source is coupled directly to all of the
junction points between the series connected potentiometers P1
through P32. The emitters of the transistors Q20, Q21, Q22, provide
the output terminals AH, AG, AF, respectively, of the time limit
curve generator 18.
Reference is now made to FIG. 5 which illustrates in more detail
the tube limit decoding circuit 14. This circuit generally
comprises four mode of operation switches, i.e., an overtable
switch, OT-1, and overtable low speed switch OTL-1, an undertable
low speed switch UTL-2, and a high and low speed switch HSS-1.
These switches are connected through appropriate relays in order to
cause the tube limit curve generator 18 to generate a maximum tube
input power curve appropriate to the mode of operation.
More particularly, the switches OT-1, OTL-1 are single-pole,
single-throw switches with each switch having one terminal
connected directly to ground. The other terminal of the switch OT-1
is connected through a diode D93 polarized as shown in FIG. 5 to
one of the terminals of a coil 39 of a relay 40. The other terminal
of the coil 39 is connected directly to the positive 28 volt supply
source and a diode D94, polarized as shown in FIG. 5, is coupled
across the terminals of the relay coil 39.
The other terminal of switch OTL-1 is connected through a diode
D95, polarized as shown in FIG. 5, to one of the terminals of a
coil 42 of a relay 44. The other terminal of coil 42 is connected
directly to the positive 28 volt supply source. A diode D96
polarized as shown in FIG. 5, is coupled across the terminals of
the relay coil 42.
The other terminal of the switch UTL-2 is connected through a diode
D97, polarized as shown in FIG. 5, to the same terminal of relay
coil 42 which is connected to diode D95.
The relay contacts of relay 40 take the form of double-pole,
double-throw contacts 46, 48. The common contact of the sets of
contacts 46, 48 are respectively connected to a pair of terminals
of the high and low speed switch HSS-1. The switch HSS-1 takes the
form of a double-pole, double-throw switch. The other contacts of
the switch HSS-1 are connected directly to ground.
The relay contacts of relay 44 take the form of four sets of
single-pole, double-throw contacts 50, 52, 54, 56. The common
terminal of contact set 50 is connected directly to the
normally-closed terminal of contact 46 of relay 40, the common
terminal of contact set 52 is connected directly to the
normally-closed terminal of contact 48 of relay 40, the common
terminal of contact set 54 is connected to the normally-open
terminal of contact 46 of relay 40, and the common terminal of
contact set 56 is connected to the normally-open terminal of
contact 48 of relay 40.
As illustrated, the normally-open terminals of contact sets 50, 52,
54, 56 provide the output terminals AL, AM, AN, AO, respectively,
of the tube limit decoding circuit 14. Similarly, the
normally-closed terminals of the contact sets 50, 52, 54, 56
provide the output terminals AS, AT, AW, AX of the decoding circuit
14.
Reference is now made to FIG. 6 which is a graphical representation
of a typical maximum input tube power curve PC having the
time-varying limit curve which is generated by the tube limit curve
generator 18 superimposed thereon. More particularly, the maximum
input tube power curve TC represents the maximum voltage times
current (KV .times. MA) as a function of exposure time which may be
applied to the X-ray tube without damaging the X-ray tube. This
curve which may be obtained from the tube manufacturer, will vary
according to the mode of operation, i.e., high speed, low speed,
overtable, etc.
The limit curve AC which is generated by the tube limit curve
generator 18 generally takes the form of a decreasing staircase
type signal which may be adjusted in amplitude for each time
interval to closely approximate the value over each time interval
of the maximum input tube power curve PC. In other words, the
intervals of time, T1, T2, T3, T4 are predetermined fixed intervals
of time of equal time duration, and the voltage, i.e., V1, V2, V3,
V4, generated by the tube limit curve generator 18 for each
interval of time may be adjusted to satisfy the approximation of
the input tube power curve TC.
OPERATION OF THE PROTECTIVE CIRCUIT
Prior to the actual operation of the X-ray tube protection circuit,
the potentiometers P1 through P32 are adjusted so that the eight
sets of curves which are generated by the tube limit curve limit
generator 18 closely approximate the maximum input tube power
curves recommended by the tube manufacturer. The eight curves
generally represent different combinations of: types of tubes, size
of focal spot, and anode rotation. In other words, there are eight
possible combinations of these parameters which require a different
maximum input tube power curve. As discussed before, the maximum
input tube power curve PC as illustrated in FIG. 6 is a typical
curve for input power versus exposure time; however, it is to be
appreciated that eight different curves each having different
amplitudes with respect to exposure times would be required for the
eight possible modes of operation.
Thus, in order to generate a signal for overtable, large focal
spot, triple-speed operation, the four potentiometers P1, P2, P3,
P4, are adjusted to set the voltage amplitude of the curve for the
regions RE-1, RE-2, RE-3, RE-4 respectively. Similarly, in another
mode of operation, i.e., in the overtable, large focal spot,
single-speed operation, the potentiometers P5, P6, P7, P8 would be
adjusted to obtain the desired signal amplitudes over the exposure
regions RE-1, RE-2, RE-3, RE-4, respectively.
Accordingly, the potentiometers P1 through P32 correspond to the
following modes of operation:
Mode of Operation Potentiometers Overtable, large focal spot,
triple-speed P1, P2, P3, P4 Overtable, large focal spot,
single-speed P5, P6, P7, P8 Undertable, large focal spot,
triple-speed P9, P10, P11, P12 Undertable, large focal spot,
single-speed P13, P14, 15, P16 Overtable, small focal spot,
triple-speed P17, P18, P19, P20 Overtable, small focal spot,
single-speed P21, P22, P23, P24 Undertable, small focal spot,
triple-speed P25, P26, P27, P28 Undertable, small focal spot,
single-speed P29, P30, P31, P32
upon commencement of an exposure cycle, the timer accumulator
circuit 20 begins a counting cycle in binary-coded-decimal logic
which is applied to the time decoding matrix circuit 22. The diode
matrix in the decoding matrix circuit 22 performs the function of
converting the binary-coded-decimal logic signals to analog signals
which are then applied to the transistors Q11 through Q19 to
actuate these transistors to either forward or reverse biased
states. The patterns of binary signals, and the states of the
transistors Q11 through Q19 are set forth in Table I below:
TABLE I
Time Transistor Bits from Time Accumulator -- 20 Range Turned on
__________________________________________________________________________
8 16 32 64 128 256 512 1024
__________________________________________________________________________
0 0 0 0 0 0 0 0- 2.77ms Q11 1 1 1 1 1 1 1 0 2.77- 22ms Q12 1 1 1 1
1 1 0 22ms- 44ms Q13 0 1 1 1 1 1 0 44ms- 88ms Q14 0 0 1 1 1 1 0
88ms- 176ms Q15 0 0 0 1 1 1 0 176ms- 352ms Q16 0 0 0 0 1 1 0 352ms-
704ms Q17 0 0 0 0 0 1 0 0.704ms- 1.4sec. Q18 0 0 0 0 0 0 1 1.4sec-
2.8sec. Q19
__________________________________________________________________________
upon the actuation of each of the transistors Q11 through Q19, a
different resistance value of a corresponding resistor R44 through
R52 is coupled into the circuit to thereby cause the generated
limit signal AC to decrease in value with elapsed exposure time.
Thus, as the transistors Q11 through Q19 are sequentially forward
biased, the resistors R44 through R52 are sequentially coupled into
the circuit to thereby cause the limit curve AC to take the form of
a decreasing stairstep type function with respect to time.
With reference to FIG. 5, the switches OT-1, UTL-1, UTL-2, HSS-1,
and their associated relays 40, 44, provide circuitry for switching
the desired set of four potentiometers of the potentiometers P1
through P32 into the circuit. In other words, upon closure of the
switch OTL-1, assuming the switch HSS-1 is in the position as
indicated, the overtable, large focal spot, triple-speed
potentiometers P1 through P4 are placed into the circuit to
generate a limit curve AC representative of the maximum input tube
power which may be applied to the X-ray tube when operated in that
mode of operation.
The output current I2 from the tube limit curve generator 18 is
applied across the resistor R1 to develop a voltage V2 which is
proportional to the maximum allowed input power at the particular
time interval of the exposure time. This voltage signal is applied
to one of the input terminals of the comparator circuit 12.
When the X-ray tube supply source is set by the X-ray technician
for a desired voltage potential and current signal to be applied to
the X-ray tube, the resistive arrangements VR-1, VR-2 are
simultaneously set to develop a signal V1 representative of the
voltage potential (KV) and current (MA) to be applied to the X-ray
tube during an actual exposure. The voltage signal V1 is applied to
the other input terminal of the comparator circuit 12.
Thus, if the voltage V1 remains less than the voltage V2, the
signal developed by the comparator circuit remains at a binary 0
thereby causing the X-ray tube supply source to continue to supply
a voltage potential signal to the X-ray tube.
If the signal V1 representative of the value of the signal which is
applied to the X-ray tube exceeds the value of the time-varying
signal V2, the signal developed by the comparator circuit 12
changes to a binary 1 signal which is applied through the amplifier
24, inverter 28, NAND gate 30 to thereby interrupt the voltage
signal which is applied to the X-ray tube by the tube supply
source.
Accordingly, as long as the value of the programmed signal V1
remains less than the value of the tube limit signal V2, the
exposure will continue until it is terminated by either a
phototimer or a preset timer. If the value of the programmed signal
V1 exceeds the value of the limit signal V2, the exposure is
immediately terminated. Also, the monitoring lamp L-1
simultaneously provides a visual indication that the exposure has
been terminated.
Although the invention has been shown in connection with a
preferred embodiment, it will be readily apparent to those skilled
in the art that various changes in form and arrangement of parts
may be made to suit requirements without departing from the spirit
and scope of the invention as defined by the appended claims.
* * * * *