US4402086A — Safety device for extra-high voltage generator, p…

Claim 1

Independent Claim 388 words

In an extra-high voltage generator connected to an X-ray tube for polarizing the electrodes of said X-ray tube into direct current voltages incorporating at least one vacuum tube with control grids inserted by its anode-cathode path between at least one of the positive and/or negative poles of at least one source of said voltage and one of the electrodes of the X-ray tube, the control grid of each vacuum tube being energized by means of a voltage control loop incorporating a square-wave nominal value signal generator supplying a first nominal value signal whose duration corresponds to the exposure time and whose amplitude is a predetermined and regulatable fraction of the desired polarization voltage of the X-ray tube, an analog comparator circuit for comparing said first nominal value signal with a constant fraction of the voltage applied to one of the electrodes of the X-ray tube relative to earth and supplying an error voltage, an amplitude modulator amplifying the wave supplied by an oscillator as a function of said error signal, an amplitude demodulator coupled to said amplitude modulator in an insulating manner by means of a transformer and for the duration of said first nominal value signal supplying a demodulated direct voltage to a control circuit polarizing the grid of the vacuum tube with respect to its cathode; a safety device comprising at least one measuring resistor inserted between the other positive and/or negative terminal of the at least one source and earth and supplying between its terminals a voltage drop proportional to the current in the X-ray tube; a high-speed electronic switching having a threshold receiving said voltage drop and which controls its closure when it exceeds a predetermined threshold value corresponding to exceeding the nominal current in the tube by a predetermined quantity; means for controlling the temporary inhibition of the transmission of the modulated wave to the demodulator in such a way as to bring about the cut-off of the vacuum tubes by the initial polarization of its grid in the absence of demodulated voltage, the disappearance of current in the series-connected vacuum tubes and the X-ray tube leading to the automatic re-opening of the switch and the rapid re-application of the polarization voltage of the X-ray tube, when the variation between the successive exceedings of said threshold is greater than a predetermined time interval.

Claim 2

Dependent Claim 388 words

In an extra-high voltage generator connected to an X-ray tube for polarizing the electrodes of said X-ray tube into direct current voltages incorporating at least one vacuum tube with control grids inserted by its anode-cathode path between at least one of the positive and/or negative poles of at least one source of said voltage and one of the electrodes of the X-ray tube, the control grid of each vacuum tube being energized by means of a voltage control loop incorporating a square-wave nominal value signal generator supplying a first nominal value signal whose duration corresponds to the exposure time and whose amplitude is a predetermined and regulatable fraction of the desired polarization voltage of the X-ray tube, an analog comparator circuit for comparing said first nominal value signal with a constant fraction of the voltage applied to one of the electrodes of the X-ray tube relative to earth and supplying an error voltage, an amplitude modulator amplifying the wave supplied by an oscillator as a function of said error signal, an amplitude demodulator coupled to said amplitude modulator in an insulating manner by means of a transformer and for the duration of said first nominal value signal supplying a demodulated direct voltage to a control circuit polarizing the grid of the vacuum tube with respect to its cathode; a safety device comprising at least one measuring resistor inserted between the other positive and/or negative terminal of the at least one source and earth and supplying between its terminals a voltage drop proportional to the current in the X-ray tube; a high-speed electronic switching having a threshold receiving said voltage drop and which controls its closure when it exceeds a predetermined threshold value corresponding to exceeding the nominal current in the tube by a predetermined quantity; means for controlling the temporary inhibition of the transmission of the modulated wave to the demodulator in such a way as to bring about the cut-off of the vacuum tubes by the initial polarization of its grid in the absence of demodulated voltage, the disappearance of current in the series-connected vacuum tubes and the X-ray tube leading to the automatic re-opening of the switch and the rapid re-application of the polarization voltage of the X-ray tube, when the variation between the successive exceedings of said threshold is greater than a predetermined time interval.

Claim 3

Dependent Claim 48 words

A safety device according to claim 1, wherein said electronic switch is coupled to one of the inputs of the at least one modulator comprising at least one active element in such a way as to polarize the latter beyond its cut-out during the closing of the switch.

Claim 4

Dependent Claim 153 words

A safety device according to claim 2, wherein said switch comprises a first high voltage npn switching transistor, whose emitter is connected to the terminal of said measuring resistor which is at a negative potential compared with earth when traversed by the current of the X-ray tube, the other terminal of the resistor being connected to earth, the base of the transistor being coupled to said other terminal via a coupling circuit comprising a resistor connected in series with a connection constituted by another resistor and a capacitor in parallel, so as to rapidly saturate the same as a result of rises and block the same as a result of voltage drops at the terminals of the measuring resistor, and wherein in its saturated state the collector of the transistor is coupled to the control electrode of the modulator in such a way that a voltage blocking its output current is applied thereto.

Claim 5

Dependent Claim 267 words

A safety device according to claim 3, wherein said high voltage generator further comprises two extra-high voltage sources connected in series, the first souce being connected by its positive pole to the anode of a first tetrode, whose cathode is connected to the anode of the X-ray tube, and wherein a second tetrode has its anode connected to the cathode of the X-ray tube and the other positive/negative poles are joined together by means of a first and second measuring resistor of equal values and in series, whose junction is connected to earth, the control grids of the two tetrodes being in each case energized by a separate control loop in which the amplitude of said first nominal value signal is respectively compared in absolute value with equal fractions of the anode or cathode voltages of the X-ray tube relative to earth to generate error signals, modulating means for modulating a first and second pentode which modulate respectively said control grids and wherein the emitter of said transistor is connected at the junction of the second measuring resistor with the positive pole of the second source, the coupling circuit supplying its base being connected to the center of a resistive voltage divider connected between the respective junctions of said first and second measuring resistor with the two sources, and in which the collector of the transistor is respectively connected in parallel with the two control grids of the pentodes by two circuits formed in each case by a resistor and a diode in series, for applying thereto negative polarization voltages beyond the cut-off of their anode current.

Claim 6

Dependent Claim 182 words

A safety device according to claim 1, which also comprises an integrating circuit energized by the voltage drop at the terminals of said first and second measuring resistors; a bistable latch-type multivibrator, whose output normally supplies a low state and whose switchover by the transition of said output to the high state is obtained by exceeding a predetermined voltage threshold at the output of the integrating circuit, which supplies the control input of the multivibrator; the output of said multivibrator energizing the base of a second npn switching transistor, whose emitter is connected to earth and whose collector is directly connected to the nominal value input and connected via a resistor to the output of the generator supplying the nominal value signal, in such a way that the saturation of said second transistor, controlled by the high state of the output of said multivibrator, inhibits the application of said first nominal value signal to an analog comparator circuit including a pair of differential amplifiers, up to the resetting to the initial state of the multivibrator by means of a second time signal.

Claim 7

Dependent Claim 130 words

A safety device according to claim 5, wherein the nominal value generator of the high voltage generator supplies a second positive square-wave signal of constant amplitude and of duration equal to that of the exposure time and in which the multivibrator is provided with a supplementary switching transistor controlling the resetting of multivibrator by short-circuiting by means of its collector-emitter path when it is saturated, the base-emitter junction of the saturated transistor of the multivibrator, so as to block the same, the supplementary transistor being supplied at its base by means of a differentiating circuit receiving the second square-wave signal with the polarity necessary for the unblocking thereof, so as to control for each exposure start the resetting of the multivibrator, as well as the blocking of the other transistor.

Claim 8

Dependent Claim 181 words

A safety device according to claims 5 or 6, wherein the output of the multivibrator is connected to the anode of a first diode, whose cathode is connected to one of the terminals of a first resistor and in which the other terminal of the first resistor is connected to the collector of said second transistor by means of a capacitor at its emitter by means of a second resistor and a second diode conducting in the opposite direction from its base-emitter junction mounted in parallel and to the base of said second transistor by means of a third diode conducting in the same direction as its base-emitter junction, in such a way that the voltage drop caused at the terminals of the second resistor by the charging current of the capacitor due to the nominal value voltage rise polarizes said second transistor, so that it conducts with a current decreasing with time in the same way as the charging current of the capacitor, so as to constitute a so-called "MILLER" integrator for the positive transition of the nominal value signal.

Claim 9

Dependent Claim 137 words

A safety device according to claim 7, further comprising an inverter stage incorporating a third npn transistor, mounted in a common emitter configuration, which is connected to earth and whose collector is connected by means of a resistor to a positive supply terminal, the third transistor receiving at its base the second positive square-wave signal so as to be saturated throughout the exposure time and blocked outside said time, in which the collector of the third transistor is connected to the anode of a third diode, whose cathode is connected to the base of said second transistor by means of a third resistor, so as to polarize it in such a way that its conduction at the end of each exposure period makes it possible to discharge the capacitor across said third resistor at its collector-emitter path.

Annuity Stage	Window Opens	Payment Deadline	Surcharge Period Until	Estimated Fee	Status
3.5 Years (Year 4)	1986-08-29	1987-02-28	1987-08-30	$2000.00	Window Closed / Lapsed
7.5 Years (Year 8)	1990-08-29	1991-02-28	1991-08-30	$3760.00	Window Closed / Lapsed
11.5 Years (Year 12)	1994-08-29	1995-02-28	1995-08-30	$7700.00	Window Closed / Lapsed

Safety device for extra-high voltage generator, particularly an X-ray generator

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